ORGANIC SUBSTANCE ANALYSIS
(outdated organizational analysis), qualities. and quantities. determination of the composition of the org. in-in and establishment of their structure.
When determining qualities. composition of org. they use a variety of methods based on chemistry. p-tions, accompanied by the formation of products with characteristic properties (color, smell, melting temperatures, etc.), and on physical measurements. and physical-chemical (chromatographic, spectral, etc.) characteristics of the identified compounds.
With quantities, analysis of org. the quantity of the reagent entering the distribution with the determined org is established. conn., or measure diff. physical and physical-chemical characteristics associated with the number of compounds being determined.
O.v. A. includes elemental analysis, structural-group (including functional and stereospecific), molecular analysis, phase analysis And structural analysis.
Historically, methods for elemental analysis of org. were the first to be developed. in-in (A. Lavoisier, late 18th century), based on their oxidation and gravimetric, titrimetric. or gasometric determination of the formed simple compounds. individual elements. First elemental methods microchemical analysis(microanalysis) was developed by F. Pregl in the beginning. 20th century From the 2nd half. 20th century For elemental analysis, automatic methods are widely used. analyzers based on combustion of the analyzed sample org. in-va and gas chromato-graphic. separation and determination of combustion products. The analyzer is equipped with a computer and automatic sample introduction system.
Isotope analysis of org. the purpose is to determine the content of individual isotopes in them, as well as to determine the ratio of the same org. compounds containing different or combinations thereof. For this purpose, mass spectrometry or multiple gas-liquid chromatography is most often used (for example, when separating ordinary and deuterated forms of methane or benzene). Naib. chromatography-mass spectrometry is effective.
Most functional analysis methods are based on interaction. individual functions group org. conn. with suitable reagents. Such districts can be selective or limitedly selective, that is, they are characteristic, respectively. only for one or several. functional groups.
Most often, solutions associated with the formation or disappearance of substances, bases, oxidizing agents, reducing agents, water, gases, and, less commonly, sediments and colored substances are used. The resulting compounds and bases determine acid-base titration in aquatic or non-aqueous environments. In a non-aqueous environment, separate potentiometric titration of compounds and bases of different strengths when present together.
In the case of oxidation-reduction. solutions, the speed of which is low, back titration is usually used, i.e., the excess of the reagent is titrated. On the formation or absorption of water in the districts of the org. conn. based on the definition of plural. functional groups using Fischer's reagent(see also Aquametry).
Methods based on flows, which are accompanied by the release or absorption of gas, are rarely used, since measuring volume or pressure usually requires bulky equipment.
Gravimetric measurements are based on the formation of sediments. methods for determining a small number of functions. groups. Slightly soluble compounds used in these cases are, as a rule, metallic. carbonic and sulfonic acids, salts org. bases, complex connections. (including chelate ones).
Formation of colored compounds. often quite specific and allows you to selectively determine the function. photometric groups methods. Solutions have become widespread (especially in microanalysis), leading to the formation of fluorescent compounds, since the sensitivity of determining the function. The group in this case is quite large.
A special type of functional. analysis consider methods based on preliminary. interaction of the substance being determined with reagents and determination of the resulting product. For example, aromatic after nitration can be determined polarographically, and the relationship between the amino group and naphthalene sulfonyl chloride can be determined fluorometrically.
Below are examples of the most. frequently used functional methods. analysis.
The determination of active hydrogen in alcohols, amines, amides, carbonic and sulfonic compounds, mercaptans and sulfonamides is based on their interactions. with Grignard reagents (usually methyl magnesium iodide; see Cerevitin method)or with LiAlH 4 and measuring the volume of methane or hydrogen released, respectively. Active in acetylene and its homologues is determined by the solution with salts Ag(I), Hg(I) or Cu(I) with the last, titrimetric. determination of the separated ones.
Connections with unsaturated carbon-carbon bonds are most often brominated, iodinated or hydrogenated. In the first two cases, unreacted Br 2 or I 2 is determined iodometrically, and during hydrogenation the volume of absorbed H 2 is measured. The number of double bonds can be determined by the addition of mercury salts to the last. titration of the released substance.
When determining hydroxyl groups, they most often use acetic, phthalic or pyromellitic anhydride, the excess of which is titrated. You can use acid chlorides. Hydroxy groups in phenols are usually titrated with base solutions in a non-aqueous medium. Phenols are easily brominated and combined with diazonium salts, therefore they are titrated with solutions of Br 2 or diazonium salts, or a bromide-bromate mixture is added to the solution under study, the excess is determined iodometrically (see also Falin's reaction).
Carbohydrates can be determined by oxidation with sodium periodate and subsequent. titration of excess oxidizing agent or formed compounds. Numerous have been developed. variations of this method (see, for example, Malaprada reaction).
To determine org. peroxy compounds (including peroxy acids) most often use their interaction. with KI and subsequent titration of the released I 2 with Na 2 S 2 O 3 solution.
The analysis of alkoxy compounds consists of interaction. of the analyzed substance with hydroiodic acid to form alkyl iodides (see. Zeisel method). The latter are determined by different methods - gravimetrically (in the form of AgI) or titrimetrically (acid-base titration). Carbon compounds can be determined similarly. To identify C 1 -C 4 -alkoxy groups, the resulting alkyl iodides are converted into quaternary ammonium compounds, which are analyzed by thin-layer or paper chromatography.
The definition of epoxy groups is based on their reaction with hydrogen chloride to form chlorohydrins; upon completion of the solution, the excess HCl is titrated with alkali solution.
For the determination of carbonyl compounds. (aldehydes and ketones) max. oximation is often used, i.e. their conversion into interaction. with hydroxylamine hydrochloride; The HCl released as a result of the reaction is titrated with an alkali solution (the end point of the titration is set using an indicator or potentiometrically). There are a large number of modifications of this method. Aldehydes can also be determined by the solution with Na bisulfite followed by. acid-base titration. Less commonly used are aldehydes with Ag + ions, reaction with hydrazines and the formation of Schiff bases.
Quinones are reduced with Ti(III) chloride or V(II) sulfate; the excess of the reducing agent is determined titrimetrically. Quinones can also be determined iodometrically.
To determine carbon compounds and their salts, max. Acid-base titration is often used in non-aqueous media.
A large number of methods have been developed for the analysis of carbon derivatives. Anhydrides after their hydrolysis to a solution are titrated with alkali solutions. In the case of analyzing a mixture of an acid and its anhydride, the sum of both substances is determined by acid-base titration, and then the anhydride is mixed with morpholine or aniline and the released acids are titrated. In the latter case, you can also determine the excess base by titration with HCl solution. Acid halides or their mixtures with compounds are determined in the same way. In this case, instead of solutions with amines, interactions are often used. acid halide with alcohol and last. separate titration of free carbonic acid and the released halogen-rich acid with alkali solution.
The determination of carbon esters is based on their hydrolysis with an alkali solution, the excess is titrated with a solution. Small amounts of esters are usually determined spectrophotometrically in the form of Fe(III) salts of hydroxamic acids formed during interaction. esters with hydroxylamine.
To determine nitrogen-containing org. a large number of methods have been proposed. Compounds capable of reduction (nitro-, nitroso-, ) are determined titanium- or vanadatometrically: an excess solution of Ti(III) or V(II) salt is added and the unreacted reducing agent is titrated with a solution of Fe(III) salt.
Titration of ramie solution (usually HClO 4) in a non-aqueous medium is widely used in determination. This method often allows you to separately determine org. and non-org. bases in mixtures, as well as org. bases of varying strength when present together. Amines can be determined, like hydroxy derivatives, by the ratio of their acylation. To determine primary aromatics. amines are often titrated with solution in an acidic medium, accompanied by the formation of a diazo compound. A similar titration of secondary amines leads to their N-nitrosation and is also used in the analysis. During microanalysis of primary aromatics. amines, the resulting diazo compounds are usually combined with the corresponding azo components and the resulting dye is determined spectrophotometrically. In the case of analyzing mixtures of primary, secondary and tertiary amines, titration with HClO 4 solution is most often used in a non-aqueous medium of the initial mixture (all amines are titrated), the mixture after acetylation with acetic anhydride (only tertiary amines are titrated) and the mixture after treatment with acetylacetone or salicylic aldehyde ( the sum of secondary and tertiary amines is titrated).
To determine aryldiazonium salts with a solution of the analyzed substance, titrate weighed portions of the azo component (3-methyl-1-phenyl-5-pyrazolone, m-phenylenediamine, etc.) or add a solution of the azo component to the analyzed solution, the excess to The swarm is titrated with NaNO 2 solution in an acidic environment. In the case of the analysis of diazo compounds, it is also possible to use gasometry. analysis based on the decomposition of the studied compound. with the release of N 2, the volume of which is measured. Sometimes, as in the case of the analysis of amines, diazo compounds are determined by the combination with the last. spectrophotometric rich. determination of the resulting dye.
Hydrazines are usually titrated iodometrically. In the case of thiols, interaction can also be used. them with silver salts or acid-base titration. Org. sulfides are oxidized with a bromide-bromate mixture, the excess is determined titrimetrically.
Widespread for quality. and quantities. functional Selective and fairly sensitive methods of IR spectroscopy and NMR have also been analyzed.
The emergence of stereospecific analysis of org. in-in the 2nd half. 20th century associated with the development of chromatographic methods. To separate enantiomers, most often a preliminary reaction is carried out between the analyzed substances and optically active reagents to form diastereomers, which are then separated by gas-liquid or high-performance liquid chromatography on columns with optically active stationary phases.
Molecular analysis of org. in-in founded ch. arr. on the use of chromatography and others. spectral methods, which make it possible to establish the structure of the org. connections.
Phase analysis, which allows qualitative and quantitative analysis of crystalline materials. org forms connection, carried out using radiography And electronography. X-ray, structural analysis allows you to set the structural structure of the org with high accuracy. v-va, determine the lengths of bonds between atoms and the angles between bonds.
The analysis methods listed above are based on the direct determination of the analyzed substances or derivatives obtained from them. In O. v. A. Indirect methods are also often used. So, for example, carbon compounds can be isolated from the analyzed mixture in the form of sparingly soluble silver or other salts and then using the atomic absorption method. spectroscopy or X-ray fluorescence analysis to determine the amount of the corresponding metal; Based on the results of such an analysis, the content of carbon dioxide can be calculated. In liquid chromatography, the use of indirect detection of the separated substances is effective, in which an active component is added to the mobile phase, forming easily detectable compounds with the separation products or with the substances being chromatographed.
The methods of analysis and the equipment used depend on the specific task of O. v. a.: determination of the main ingredient of the mixture, org. or non-org. impurities in org. wow, org. impurities in inorganic in-ve or analysis of a complex multi-component mixture of in-in.
Methods O. century. A. widely used in the development of industrial technology. produced by org. products and in the production process itself for the development of methods for analyzing raw materials, auxiliary. in-in, in-between. products at different stages of production, to control production. process, finished products, wastewater and gas emissions, to identify impurities in intermediate and final products, and to develop analytes. techniques that ensure the necessary kinetic. research. In all cases, it is necessary to choose the optimal one. options for analysis methods and their combinations in accordance with the requirements for speed, reproducibility, accuracy, etc.
When developing an analyte. parts of normative and technical. documentation for raw materials, auxiliary. materials and finished products first of all establish the minimum necessary and sufficient number of analytes. indicators. Such indicators include melting point, pH, basic content. substances in the product, which are determined by a direct method (usually titrimetrically using potentiometry) or indirectly, by subtracting from the mass of the entire product the mass of impurities determined by chromatography. (most often), electrochemical. or spectrophotometric. methods. When using the function analysis to determine the main items usually choose a method that involves determining this item by function. group formed at the last stage of its receipt. If necessary, when the analyzed substance is obtained by multi-stage synthesis, it is determined according to different functions. groups. Analyst. the methods chosen for the analysis of raw materials and finished products must have Ch. arr. good reproducibility and accuracy.
Analytical methods used in production control must be rapid and continuous (for example, redox metry, pH metry, ). The basis of methods for monitoring production processes is org. in-in often lies the definition of a vanishing function. group, i.e., a group undergoing transformation at a given stage of production, which makes it possible to accurately record the end of the corresponding stage. In this case, thin-layer, gas-liquid, high-performance liquid chromatography, spectrophotometry, and electrochemical are widely used. methods, flow-injection. analysis.
For analysis there will be intervals. titrimetry is most often used for manufactured products, and for reaction analysis. mixtures-complex chromatographic. and spectral methods, including gas chromatography-mass spectrometry, a combination of gas chromatography with Fourier transform infrared spectroscopy.
The analysis of environmental objects has acquired great importance. When developing appropriate methods for analyzing basic the requirements for them are high sensitivity and correct identification of the substances being determined. These requirements are met by gas chromatography-mass spectrometry using two or more stationary phases.
In clinical analysis (analysis of blood, urine, tissues and other objects for the content of drugs, metabolites, steroids, amino acids, etc.) important is not only the sensitivity, accuracy and rapidity of the analysis, but also the reproducibility of its results. When the latter requirement is critical, gas chromatography-mass spectrometry under standard conditions, as well as high-throughput flow injection, are used. analysis and a variety of enzyme methods with high selectivity.
Lit.: Guben Weil, Methods of organic chemistry, vol. 2, Methods of analysis, trans. with him. 4th ed., M.. 1963; Cheronis N. D., Ma T. S., Micro- and semi-micro methods of organic functional analysis, trans. from English, M., 1973; Siggia S.. Hannah J. G., Quantitative organic analysis by functional groups, trans. from English, M.; 1983. B. I. Kolokolov.
Chemical encyclopedia. - M.: Soviet Encyclopedia. Ed. I. L. Knunyants. 1988 .
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The study of organic matter begins with its isolation and purification.
1. Precipitation
Precipitation– separation of one of the compounds of a gas or liquid mixture of substances into a precipitate, crystalline or amorphous. The method is based on changing the solvation conditions. The effect of solvation can be greatly reduced and the solid substance can be isolated in its pure form using several methods.
One of them is that the final (often called target) product is converted into a salt-like compound (simple or complex salt), if only it is capable of acid-base interaction or complex formation. For example, amines can be converted to substituted ammonium salts:
(CH 3) 2 NH + HCl -> [(CH 3) 2 NH 2 ] + Cl – ,
and carboxylic, sulfonic, phosphonic and other acids - into salts by the action of corresponding alkalis:
CH 3 COOH + NaOH -> CH 3 COO – Na + + H 2 O;
2CH 3 SO 2 OH + Ba(OH) 2 -> Ba 2+ (CH 3 SO 2 O) 2 – + H 2 O;
CH 3 P(OH) 2 O + 2AgOH -> Ag(CH 3 PO 3) 2– + 2H 2 O.
Salts as ionic compounds dissolve only in polar solvents (H 2 O, ROH, RCOOH, etc.). The better such solvents enter into donor-acceptor interactions with the cations and anions of the salt, the greater the energy released during solvation, and the higher solubility. In non-polar solvents, such as hydrocarbons, petroleum ether (light gasoline), CHCl 3, CCl 4, etc., salts do not dissolve and crystallize (salt out) when these or similar solvents are added to a solution of salt-like compounds. The corresponding bases or acids can be easily isolated from salts in pure form.
Aldehydes and ketones of non-aromatic nature, adding sodium hydrosulfite, crystallize from aqueous solutions in the form of slightly soluble compounds.
For example, acetone (CH 3) 2 CO from aqueous solutions crystallizes with sodium hydrosulfite NaHSO 3 in the form of a slightly soluble hydrosulfite derivative:
Aldehydes easily condense with hydroxylamine, releasing a water molecule:
The products formed in this process are called oximes They are liquids or solids. Oximes have a weakly acidic character, manifested in the fact that the hydrogen of the hydroxyl group can be replaced by a metal, and at the same time - a weakly basic character, since oximes combine with acids, forming salts such as ammonium salts.
When boiled with dilute acids, hydrolysis occurs, releasing the aldehyde and forming a hydroxylamine salt:
Thus, hydroxylamine is an important reagent that makes it possible to isolate aldehydes in the form of oximes from mixtures with other substances with which hydroxylamine does not react. Oximes can also be used to purify aldehydes.
Like hydroxylamine, hydrazine H 2 N–NH 2 reacts with aldehydes; but since there are two NH 2 groups in the hydrazine molecule, it can react with two aldehyde molecules. As a result, phenylhydrazine C 6 H 5 –NH–NH 2 is usually used, i.e. the product of replacing one hydrogen atom in a hydrazine molecule with a phenyl group C 6 H 5:
The reaction products of aldehydes with phenylhydrazine are called phenylhydrazones.Phenylhydrazones are liquid and solid and crystallize well. When boiled with dilute acids, like oximes, they undergo hydrolysis, as a result of which free aldehyde and phenylhydrazine salt are formed:
Thus, phenylhydrazine, like hydroxylamine, can serve to isolate and purify aldehydes.
Sometimes another hydrazine derivative is used for this purpose, in which the hydrogen atom is replaced not by a phenyl group, but by an H 2 N–CO group. This hydrazine derivative is called semicarbazide NH 2 –NH–CO–NH 2. The condensation products of aldehydes with semicarbazide are called semicarbazones:
Ketones also readily condense with hydroxylamine to form ketoximes:
With phenylhydrazine, ketones give phenylhydrazones:
and with semicarbazide - semicarbazones:
Therefore, hydroxylamine, phenylhydrazine and semicarbazide are used for isolating ketones from mixtures and for their purification to the same extent as for isolating and purifying aldehydes. It is, of course, impossible to separate aldehydes from ketones in this way.
Alkynes with a terminal triple bond react with an ammonia solution of Ag 2 O and are released in the form of silver alkinides, for example:
2(OH) – + HC=CH -> Ag–C=C–Ag + 4NH 3 + 2H 2 O.
The starting aldehydes, ketones, and alkynes can be easily isolated from poorly soluble substitution products in their pure form.
2. Crystallization
Crystallization methods separation of mixtures and deep purification of substances are based on the difference in the composition of the phases formed during partial crystallization of the melt, solution, and gas phase. An important characteristic of these methods is the equilibrium, or thermodynamic, separation coefficient, equal to the ratio of the concentrations of the components in the equilibrium phases - solid and liquid (or gas):
Where x And y– mole fractions of the component in the solid and liquid (or gas) phases, respectively. If x<< 1, т.е. разделяемый компонент является примесью, k 0 = x / y. In real conditions, equilibrium is usually not achieved; the degree of separation during single crystallization is called the effective separation coefficient k, which is always less k 0 .
There are several crystallization methods.
When separating mixtures using the method directional crystallization the container with the initial solution slowly moves from the heating zone to the cooling zone. Crystallization occurs at the boundary of the zones, the front of which moves at the speed of movement of the container.
It is used to separate components with similar properties. zone melting ingots cleaned of impurities in an elongated container moving slowly along one or more heaters. A section of the ingot in the heating zone melts and crystallizes again at the exit from it. This method provides a high degree of purification, but is low-productive, therefore it is used mainly for cleaning semiconductor materials (Ge, Si, etc.).
Counterflow column crystallization is produced in a column, in the upper part of which there is a cooling zone where crystals are formed, and in the lower part there is a heating zone where the crystals melt. The crystals in the column move under the influence of gravity or using, for example, a screw in the direction opposite to the movement of the liquid. Method characterized by high productivity and high yield of purified products. It is used in the production of pure naphthalene, benzoic acid, caprolactam, fatty acid fractions, etc.
To separate mixtures, dry and purify substances in a solid-gas system, they are used sublimation (sublimation) And desublimation.
Sublimation is characterized by a large difference in equilibrium conditions for different substances, which makes it possible to separate multicomponent systems, in particular, when obtaining substances of high purity.
3. Extraction
Extraction- a separation method based on the selective extraction of one or more components of the analyzed mixture using organic solvents - extractants. As a rule, extraction is understood as the process of distributing a dissolved substance between two immiscible liquid phases, although in general one of the phases may be solid (extraction from solids) or gaseous. Therefore, a more accurate name for the method is liquid-liquid extraction, or simply liquid-liquid extraction Usually in analytical chemistry the extraction of substances from an aqueous solution using organic solvents is used.
The distribution of substance X between the aqueous and organic phases under equilibrium conditions obeys the distribution equilibrium law. The constant of this equilibrium, expressed as the ratio between the concentrations of substances in two phases:
K= [X] org / [X] aq,
at a given temperature there is a constant value that depends only on the nature of the substance and both solvents. This value is called distribution constant It can be approximately estimated by the ratio of the solubility of the substance in each of the solvents.
The phase into which the extracted component has passed after liquid extraction is called extract; phase depleted of this component - raffinate.
In industry, the most common is countercurrent multi-stage extraction. The required number of separation stages is usually 5–10, and for difficult-to-separate compounds – up to 50–60. The process includes a number of standard and special operations. The first includes the extraction itself, washing the extract (to reduce the content in impurities and removal of mechanically entrapped source solution) and re-extraction, i.e. reverse transfer of the extracted compound into the aqueous phase for the purpose of its further processing in an aqueous solution or repeated extraction purification. Special operations are associated, for example, with a change in the oxidation state of the separated components.
Single-stage liquid-liquid extraction, effective only at very high distribution constants K, are used primarily for analytical purposes.
Liquid extraction devices – extractors– can be with continuous (columns) or stepped (mixers-settlers) phase contact.
Since during extraction it is necessary to intensively mix two immiscible liquids, the following types of columns are mainly used: pulsating (with reciprocating movement of the liquid), vibrating (with a vibrating package of plates), rotary-disk (with a package of disks rotating on a common shaft), etc. d.
Each stage of the mixer-settler has a mixing and settling chamber. Mixing can be mechanical (mixers) or pulsating; multi-stage is achieved by connecting the required number of sections into a cascade. Sections can be assembled in a common housing (box extractors). Mixer-settlers have an advantage over columns in processes with a small number of stages or with very large flows of liquids. Centrifugal devices are promising for processing large flows.
The advantages of liquid-liquid extraction are low energy costs (there are no phase transitions requiring external energy supply); possibility of obtaining highly pure substances; possibility of complete automation of the process.
Liquid-liquid extraction is used, for example, to isolate light aromatic hydrocarbons from petroleum feedstocks.
Extraction of a substance with a solvent from the solid phase often used in organic chemistry to extract natural compounds from biological objects: chlorophyll from green leaves, caffeine from coffee or tea mass, alkaloids from plant materials, etc.
4. Distillation and rectification
Distillation and rectification are the most important methods for separating and purifying liquid mixtures, based on the difference in the composition of the liquid and the vapor formed from it.
The distribution of mixture components between liquid and vapor is determined by the value of relative volatility α:
αik= (yi/ xi) : (yk / xk),
Where xi And xk,yi And yk– mole fractions of components i And k respectively, in a liquid and the vapor formed from it.
For a solution consisting of two components,
Where x And y– mole fractions of the volatile component in liquid and vapor, respectively.
Distillation(distillation) is carried out by partial evaporation of the liquid and subsequent condensation of steam. As a result of distillation, the distilled fraction is distillate– is enriched with a more volatile (low-boiling) component, and the non-distilled liquid – VAT residue– less volatile (high-boiling). Distillation is called simple if one fraction is distilled from the initial mixture, and fractional (fractional) if several fractions are distilled. If it is necessary to reduce the temperature of the process, distillation is used with water vapor or an inert gas bubbling through a layer of liquid.
There are conventional and molecular distillation. Conventional distillation are carried out at such pressures when the free path of molecules is many times less than the distance between the surfaces of liquid evaporation and vapor condensation. Molecular distillation carried out at very low pressure (10 –3 – 10 –4 mm Hg), when the distance between the surfaces of liquid evaporation and vapor condensation is commensurate with the free path of the molecules.
Conventional distillation is used to purify liquids from low-volatile impurities and to separate mixtures of components that differ significantly in relative volatility. Molecular distillation is used to separate and purify mixtures of low-volatile and thermally unstable substances, for example, when isolating vitamins from fish oil and vegetable oils.
If the relative volatility α is low (low-boiling components), then the separation of mixtures is carried out by rectification. Rectification– separation of liquid mixtures into practically pure components or fractions that differ in boiling points. For rectification, column devices are usually used, in which part of the condensate (reflux) is returned for irrigation to the upper part of the column. In this case, repeated contact is carried out between the flows of the liquid and vapor phases. The driving force of rectification is the difference between the actual and equilibrium concentrations of the components in the vapor phase, corresponding to given composition of the liquid phase. The vapor-liquid system strives to achieve an equilibrium state, as a result of which the vapor, upon contact with the liquid, is enriched with highly volatile (low-boiling) components, and the liquid - with low-volatile (high-boiling) components. Since the liquid and steam move towards each other (countercurrent), with sufficient at the height of the column in its upper part, an almost pure, highly volatile component can be obtained.
Rectification can be carried out at atmospheric or elevated pressure, as well as under vacuum conditions. At reduced pressure, the boiling point decreases and the relative volatility of the components increases, which reduces the height of the distillation column and allows the separation of mixtures of thermally unstable substances.
By design, distillation apparatuses are divided into packed, disc-shaped And rotary film.
Rectification is widely used in industry for the production of gasoline, kerosene (oil rectification), oxygen and nitrogen (low-temperature air rectification), and for the isolation and deep purification of individual substances (ethanol, benzene, etc.).
Since organic substances are generally thermally unstable, for their deep purification, as a rule, packed distillation columns operating in a vacuum. Sometimes, to obtain especially pure organic substances, rotary film columns are used, which have a very low hydraulic resistance and a short residence time of the product in them. As a rule, rectification in this case is carried out in a vacuum.
Rectification is widely used in laboratory practice for deep purification of substances. Note that distillation and rectification serve at the same time to determine the boiling point of the substance under study, and, therefore, make it possible to verify the degree of purity of the latter (constancy of the boiling point). For this purpose they use also special devices - ebulliometers.
5.Chromatography
Chromatography is a method of separation, analysis and physico-chemical study of substances. It is based on the difference in the speed of movement of the concentration zones of the components under study, which move in the flow of the mobile phase (eluent) along the stationary layer, and the compounds under study are distributed between both phases.
All the various methods of chromatography, which were started by M.S. Tsvet in 1903, are based on adsorption from the gas or liquid phase on a solid or liquid interface.
In organic chemistry, the following types of chromatography are widely used for the separation, purification and identification of substances: column (adsorption); paper (distribution), thin-layer (on a special plate), gas, liquid and gas-liquid.
In these types of chromatography, two phases come into contact - one stationary, adsorbing and desorbing the substance being determined, and the other mobile, acting as a carrier of this substance.
Typically, the stationary phase is a sorbent with a developed surface; mobile phase – gas (gas chromatography) or liquid (liquid chromatography).The flow of the mobile phase is filtered through the sorbent layer or moves along this layer.B gas-liquid chromatography The mobile phase is a gas, and the stationary phase is a liquid, usually deposited on a solid carrier.
Gel permeation chromatography is a variant of liquid chromatography, where the stationary phase is a gel. (The method allows the separation of high molecular weight compounds and biopolymers over a wide range of molecular weights.) The difference in the equilibrium or kinetic distribution of components between the mobile and stationary phases is a necessary condition for their chromatographic separation.
Depending on the purpose of the chromatographic process, analytical and preparative chromatography are distinguished. Analytical is intended to determine the qualitative and quantitative composition of the mixture under study.
Chromatography is usually carried out using special instruments - chromatographs, the main parts of which are a chromatographic column and a detector. At the moment of sample introduction, the analyzed mixture is located at the beginning of the chromatographic column. Under the influence of the flow of the mobile phase, the components of the mixture begin to move along the column at different speeds, and well-sorbed components move along the sorbent layer more slowly. Detector at the outlet from the column automatically continuously determines the concentrations of separated compounds in the mobile phase. The detector signal is usually recorded by a recorder. The resulting diagram is called chromatogram.
Preparative chromatography includes the development and application of chromatographic methods and equipment to obtain highly pure substances containing no more than 0.1% impurities.
A feature of preparative chromatography is the use of chromatographic columns with a large internal diameter and special devices for isolating and collecting components. In laboratories, 0.1–10 grams of a substance are isolated on columns with a diameter of 8–15 mm; in semi-industrial installations with columns with a diameter of 10–20 cm, several kilograms. Unique industrial devices with columns with a diameter of 0.5 m have been created to produce several tons of the substance annually.
Substance losses in preparative columns are small, which allows the widespread use of preparative chromatography for the separation of small quantities of complex synthetic and natural mixtures. Preparative gas chromatography used to produce highly pure hydrocarbons, alcohols, carboxylic acids and other organic compounds, including chlorine-containing ones; liquid– for the production of drugs, polymers with a narrow molecular weight distribution, amino acids, proteins, etc.
Some studies claim that the cost of high-purity products obtained chromatographically is lower than those purified by distillation. Therefore, it is advisable to use chromatography for the fine purification of substances previously separated by rectification.
2.Elemental qualitative analysis
Qualitative elemental analysis is a set of methods that make it possible to determine what elements an organic compound consists of. To determine the elemental composition, an organic substance is first converted into inorganic compounds by oxidation or mineralization (alloying with alkali metals), which are then examined by conventional analytical methods.
The enormous achievement of A.L. Lavoisier as an analytical chemist was the creation elemental analysis of organic substances(the so-called CH analysis). By this time, numerous methods for gravimetric analysis of inorganic substances (metals, minerals, etc.) already existed, but they were not yet able to analyze organic substances in this way. Analytical chemistry of that time was clearly “limping on one leg”; Unfortunately, the relative lag in the analysis of organic compounds and especially the lag in the theory of such analysis is felt even today.
Having taken up the problems of organic analysis, A.L. Lavoisier, first of all, showed that all organic substances contain oxygen and hydrogen, many contain nitrogen, and some contain sulfur, phosphorus or other elements. Now it was necessary to create universal methods quantitative determination of these elements, primarily methods for the precise determination of carbon and hydrogen. To achieve this goal, A. L. Lavoisier proposed burning samples of the substance under study and determining the amount of carbon dioxide released (Fig. 1). In doing so, he was based on two of his observations: 1) carbon dioxide is formed during the combustion of any organic substance; 2) the starting substances do not contain carbon dioxide; it is formed from the carbon that is part of any organic substance. The first objects of analysis were highly volatile organic substances - individual compounds such as ethanol.
Rice. 1. The first device of A. L. Lavoisier for the analysis of organic
substances by combustion method
To ensure the purity of the experiment, the high temperature was provided not by any fuel, but by solar rays focused on the sample by a huge lens. The sample was burned in a hermetically sealed installation (under a glass bell) in a known amount of oxygen, the released carbon dioxide was absorbed and weighed. The mass of water was determined indirect method.
For the elemental analysis of low-volatile compounds, A. L. Lavoisier later proposed more complex methods. In these methods, one of the sources of oxygen necessary for sample oxidation was metal oxides with which the burnt sample was mixed in advance (for example, lead(IV) oxide). This approach was later used in many methods of elemental analysis of organic substances, and usually gave good results. However, the methods of CH analysis according to Lavoisier were too time-consuming, and also did not allow the hydrogen content to be determined accurately enough: direct weighing of the resulting water was not carried out.
The CH analysis method was improved in 1814 by the great Swedish chemist Jens Jakob Berzelius. Now the sample was burned not under a glass bell, but in a horizontal tube heated from the outside, through which air or oxygen was passed. Salts were added to the sample, facilitating the combustion process. The released water absorbed solid calcium chloride and weighed. The French researcher J. Dumas supplemented this technique with the volumetric determination of released nitrogen (CHN analysis). The Lavoisier-Berzelius technique was once again improved by J. Liebig, who achieved quantitative and selective absorption of carbon dioxide in a ball absorber he invented (Fig. 2.).
Rice. 2. Yu. Liebig's apparatus for burning organic substances
This made it possible to sharply reduce the complexity and labor intensity of CH analysis, and most importantly, to increase its accuracy. Thus, Yu. Liebig, half a century after A.L. Lavoisier, completed the development of gravimetric analysis of organic substances, begun by the great French scientist. Applying his methods, Yu. By the 1840s, Liebig had figured out the exact composition of many organic compounds (for example, alkaloids) and proved (together with F. Wöhler) the existence of isomers. These techniques remained virtually unchanged for many years, their accuracy and versatility ensured the rapid development of organic chemistry in the second half of the 19th century. Further improvements in the field of elemental analysis of organic substances (microanalysis) appeared only at the beginning of the 20th century. The corresponding research of F. Pregl was awarded the Nobel Prize (1923).
It is interesting that both A.L. Lavoisier and J. Liebig sought to confirm the results of a quantitative analysis of any individual substance by counter-synthesis of the same substance, paying attention to the quantitative ratios of the reagents during the synthesis. A.L. Lavoisier noted that chemistry generally has two ways to determine the composition of a substance: synthesis and analysis, and one should not consider oneself satisfied until one succeeds in using both of these methods for testing. This remark is especially important for researchers of complex organic substances. Their reliable identification and identification of the structure of compounds today, as in the time of Lavoisier, require the correct combination of analytical and synthetic methods.
Detection of carbon and hydrogen.
The method is based on the oxidation reaction of organic matter with copper (II) oxide powder.
As a result of oxidation, the carbon included in the analyzed substance forms carbon (IV) oxide, and hydrogen forms water. Carbon is determined qualitatively by the formation of a white precipitate of barium carbonate upon interaction of carbon (IV) oxide with barite water. Hydrogen is detected by the formation of crystalline hydrate Cu8O4-5H20, blue in color.
Execution method.
Copper (II) oxide powder is placed in test tube 1 (Fig. 2.1) at a height of 10 mm, an equal amount of organic matter is added and mixed thoroughly. A small lump of cotton wool is placed in the upper part of test tube 1, onto which a thin layer of white powder without aqueous copper (II) sulfate is poured. Test tube 1 is closed with a stopper with a gas outlet tube 2 so that one end of it almost touches the cotton wool, and the other is immersed in test tube 3 with 1 ml of barite water. Carefully heat in the burner flame first the upper layer of the mixture of the substance with copper (II) oxide, then the lower
Rice. 3 Discovery of carbon and hydrogen
In the presence of carbon, turbidity of barite water is observed due to the formation of barium carbonate precipitate. After a precipitate appears, test tube 3 is removed, and test tube 1 is continued to be heated until water vapor reaches aqueous copper (II) sulfate. In the presence of water, a change in the color of copper (II) sulfate crystals is observed due to the formation of crystalline hydrate CuSO4*5H2O
Halogen detection. Beilyitein's test.
The method for detecting chlorine, bromine and iodine atoms in organic compounds is based on the ability of copper (II) oxide to decompose halogen-containing organic compounds at high temperatures to form copper (II) halides.
The analyzed sample is applied to the end of a pre-calcined copper wire and heated in a non-luminous burner flame. If there are halogens in the sample, the resulting copper (II) halides are reduced to copper (I) halides, which, when evaporated, color the flame blue-green (CuC1, CuBr) or green (OD) color. Organofluorine compounds do not color the flame of copper (I) fluoride is non-volatile. The reaction is non-selective due to the fact that nitriles, urea, thiourea, individual pyridine derivatives, carboxylic acids, acetylacetone, etc. interfere with the determination. If available alkali and alkaline earth metals, the flame is viewed through a blue filter.
Nitrogen detection, sulfur and halogens. "Lassaigne's Test"
The method is based on the fusion of organic matter with sodium metal. When fused, nitrogen turns into sodium cyanide, sulfur into sodium sulfide, chlorine, bromine, iodine into the corresponding sodium halides.
Fusion technique.
A. Solids.
Several grains of the test substance (5-10 mg) are placed in a dry (attention!) refractory test tube and a small piece (the size of a grain of rice) of sodium metal is added. The mixture is carefully heated in a burner flame, uniformly heating the test tube, until a homogeneous alloy is formed. It is necessary to ensure that the sodium melts with the substance. When fused, the substance decomposes. Fusion is often accompanied by a small flash of sodium and blackening of the contents of the test tube from the resulting carbon particles. The test tube is cooled to room temperature and 5-6 drops of ethyl alcohol are added to eliminate residual sodium metal. After making sure that the remaining sodium has reacted (the hissing stops when a drop of alcohol is added), 1-1.5 ml of water is poured into the test tube and the solution is heated to a boil. The water-alcohol solution is filtered and used to detect sulfur, nitrogen and halogens.
B. Liquid substances.
A refractory test tube is vertically fixed on an asbestos mesh. Metallic sodium is placed in the test tube and heated until it melts. When sodium vapor appears, the test substance is introduced dropwise. Heating is intensified after the substance is charred. After the contents of the test tube are cooled to room temperature, it is subjected to the above analysis.
B. Highly volatile and sublimating substances.
The mixture of sodium and the test substance is covered with a layer of soda lime about 1 cm thick and then subjected to the above analysis.
Nitrogen detection. Nitrogen is qualitatively detected by the formation of Prussian blue (blue color).
Method of determination. Place 5 drops of the filtrate obtained after fusing the substance with sodium into a test tube, and add 1 drop of an alcohol solution of phenolphthalein. The appearance of a crimson-red color indicates an alkaline environment (if the color does not appear, add 1-2 drops of a 5% aqueous solution of sodium hydroxide to the test tube). Subsequently, add 1-2 drops of a 10% aqueous solution of iron (II) sulfate , usually containing an admixture of iron (III) sulfate, a dirty green precipitate is formed. Using a pipette, apply 1 drop of cloudy liquid from a test tube onto a piece of filter paper. As soon as the drop is absorbed by the paper, 1 drop of a 5% solution of hydrochloric acid is applied to it. If available nitrogen, a blue spot of Prussian blue appears.
Detection of sulfur.
Sulfur is qualitatively detected by the formation of a dark brown precipitate of lead (II) sulfide, as well as a red-violet complex with a solution of sodium nitroprusside.
Method of determination. The opposite corners of a piece of filter paper measuring 3x3 cm are moistened with the filtrate obtained by fusing the substance with metallic sodium (Fig. 4).
Rice. 4. Carrying out a seu test on a square piece of paper.
A drop of a 1% solution of lead (II) acetate is applied to one of the wet spots, retreating 3-4 mm from its border.
A dark brown color appears at the contact boundary due to the formation of lead (II) sulfide.
A drop of sodium nitroprusside solution is applied to the border of another spot. At the border of the “leaks” an intense red-violet color appears, gradually changing color.
Detection of sulfur and nitrogen when present together.
In a number of organic compounds containing nitrogen and sulfur, the discovery of nitrogen is hindered by the presence of sulfur. In this case, a slightly modified method for determining nitrogen and sulfur is used, based on the fact that when an aqueous solution containing sodium sulfide and sodium cyanide is applied to filter paper, the latter is distributed along the periphery of the wet spot. This technique requires certain operating skills, which makes its application difficult.
Method of determination. Apply the filtrate drop by drop into the center of a 3x3 cm filter paper until a colorless wet spot with a diameter of about 2 cm is formed.
Rice. 5. Detection of sulfur and nitrogen in the joint presence. 1 - a drop of a solution of iron (II) sulfate; 2 - a drop of a solution of lead acetate; 3 - drop of sodium nitroprusside solution
1 drop of a 5% solution of iron (II) sulfate is applied to the center of the spot (Fig. 5). After the drop is absorbed, 1 drop of a 5% solution of hydrochloric acid is applied to the center. In the presence of nitrogen, a blue Prussian blue spot appears. Then, 1 drop of a 1% solution of lead (II) acetate is applied along the periphery of the wet spot, and 1 drop of sodium nitroprusside solution is applied on the opposite side of the spot. If sulfur is present, in the first case, a dark brown spot will appear at the place of contact of the “leaks”, in the second case, a spot of red-violet color. The reaction equations are given above.
Fluoride ion is detected by the discoloration or yellow discoloration of alizarine zirconium indicator paper after acidification of the Lassaigne sample with acetic acid.
Detection of halogens using silver nitrate. Halogens are detected in the form of halide ions by the formation of flocculent precipitates of silver halides of various colors: silver chloride is a white precipitate that darkens in the light; silver bromide - pale yellow; silver iodide is an intense yellow precipitate.
Method of determination. To 5-6 drops of the filtrate obtained after fusing the organic substance with sodium, add 2-3 drops of diluted nitric acid. If the substance contains sulfur and nitrogen, the solution is boiled for 1-2 minutes to remove hydrogen sulfide and hydrocyanic acid, which interfere with the determination of halogens Then add 1-2 drops of 1% solution of silver nitrate. The appearance of a white precipitate indicates the presence of chlorine, pale yellow - bromine, yellow - iodine.
If it is necessary to clarify whether bromine or iodine is present, the following reactions must be carried out:
1. To 3-5 drops of the filtrate obtained after fusing the substance with sodium, add 1-2 drops of dilute sulfuric acid, 1 drop of a 5% solution of sodium nitrite or a 1% solution of iron (III) chloride and 1 ml of chloroform.
When shaken in the presence of iodine, the chloroform layer turns purple.
2. To 3-5 drops of the filtrate obtained after fusing the substance with sodium, add 2-3 drops of diluted hydrochloric acid, 1-2 drops of a 5% solution of chloramine and 1 ml of chloroform.
In the presence of bromine, the chloroform layer turns yellow-brown.
B. Discovery of halogens using Stepanov’s method. It is based on the transformation of a covalently bonded halogen in an organic compound into an ionic state by the action of sodium metal in an alcohol solution.
Detection of phosphorus. One method for detecting phosphorus is based on the oxidation of organic matter with magnesium oxide. Organically bound phosphorus is converted into phosphate ion, which is then detected by reaction with molybdenum liquid.
Method of determination. Several grains of the substance (5-10 mg) are mixed with double the amount of magnesium oxide and ashed in a porcelain crucible, first with moderate and then with strong heating. After cooling, the ash is dissolved in concentrated nitric acid, 0.5 ml of the resulting solution is transferred to a test tube, added 0.5 ml of molybdenum liquid and heat.
The appearance of a yellow precipitate of ammonium phosphomolybdate indicates the presence of phosphorus in the organic matter
3. Qualitative analysis by functional groups
Based on selective reactions of functional groups (See presentation on the topic).
In this case, selective reactions of precipitation, complexation, decomposition with the release of characteristic reaction products, and others are used. Examples of such reactions are presented in the presentation.
What is interesting is that it is possible to use the formation of organic compounds, known as organic analytical reagents, for group detection and identification. For example, dimethylglyoxime analogs interact with nickel and palladium, and nitroso-naphthols and nitrosophenols with cobalt, iron and palladium. These reactions can be used for detection and identification (See presentation on topic).
4. Identification.
Determination of the degree of purity of organic substances
The most common method for determining the purity of a substance is to measure boiling point during distillation and rectification, most often used for the purification of organic substances. To do this, the liquid is placed in a distillation flask (a round-bottomed flask with an outlet tube soldered to the neck), which is closed with a stopper with a thermometer inserted into it and connected to a refrigerator. The thermometer ball should be slightly higher holes in the side tube through which steam comes out. The thermometer ball, being immersed in the steam of a boiling liquid, takes on the temperature of this steam, which can be read on the thermometer scale. If the boiling point of the liquid is above 50 ° C, it is necessary to cover the upper part of the flask with thermal insulation. At the same time, it is necessary to using an aneroid barometer, record the atmospheric pressure and, if necessary, make a correction. If a chemically pure product is distilled, the boiling point remains constant throughout the entire distillation time. If a contaminated substance is distilled, the temperature during distillation rises as more is removed low boiling impurity.
Another commonly used method for determining the purity of a substance is to determine melting point For this purpose, a small amount of the test substance is placed in a capillary tube sealed at one end, which is attached to the thermometer so that the substance is at the same level as the thermometer ball. The thermometer with a tube with the substance attached to it is immersed in some high-boiling liquid, for example glycerin, and slowly heat over low heat, observing the substance and the increase in temperature. If the substance is pure, the moment of melting is easy to notice, because the substance melts sharply and the contents of the tube immediately become transparent. At this moment, the thermometer reading is noted. Contaminated substances usually melt at a lower temperature and over a wide range.
To control the purity of a substance, you can measure density.To determine the density of liquids or solids, they most often use pycnometer The latter, in its simplest form, is a cone equipped with a ground glass stopper with a thin internal capillary, the presence of which helps to more accurately maintain constant volume when filling a pycnometer. The volume of the latter, including the capillary, is found by weighing it with water.
Pycnometric determination of the density of a liquid comes down to simply weighing it in a pycnometer. Knowing the mass and volume, it is easy to find the desired density of the liquid. In the case of a solid substance, first weigh the pycnometer partially filled with it, which gives the mass of the sample taken for research. After this, the pycnometer is supplemented with water (or whatever - another liquid with a known density and not interacting with the substance under study) and weighed again. The difference between both weighings makes it possible to determine the volume of the part of the pycnometer not filled with the substance, and then the volume of the substance taken for research. Knowing the mass and volume, it is easy to find the desired density of the substance.
Very often, to assess the degree of purity of organic matter, they measure refractive index. The refractive index value is usually given for the yellow line in the spectrum of sodium with wavelength D= 589.3 nm (line D).
Typically, the refractive index is determined using refractometer.The advantage of this method for determining the degree of purity of an organic substance is that only a few drops of the test compound are required to measure the refractive index. This manual presents the considered physical properties of the most important organic substances. Note also that the universal method for determining the degree of purity of an organic substance is chromatography This method allows not only to show how pure a given substance is, but also to indicate what specific impurities it contains and in what quantities.
The significant difference in the structure and properties of organic compounds from inorganic ones, the uniformity of the properties of substances of the same class, the complex composition and structure of many organic materials determine the features of the qualitative analysis of organic compounds.
In analytical chemistry of organic compounds, the main tasks are to assign analytes to a certain class of organic compounds, separate mixtures and identify isolated substances.
There are organic elemental analysis designed to detect elements in organic compounds, functional– to detect functional groups and molecular– to detect individual substances by specific properties of molecules or a combination of elemental and functional analysis data and physical constants.
Qualitative elemental analysis
The elements most often found in organic compounds (C, N, O, H, P, S, Cl, I; less commonly, As, Sb, F, various metals) are usually detected using redox reactions. For example, carbon is detected by oxidizing an organic compound with molybdenum trioxide when heated. In the presence of carbon, MoO 3 is reduced to lower molybdenum oxides and forms molybdenum blue (the mixture turns blue).
Qualitative functional analysis
Most reactions for the detection of functional groups are based on oxidation, reduction, complexation, and condensation. For example, unsaturated groups are detected by bromination reaction at the site of double bonds. The bromine solution becomes discolored:
H 2 C = CH 2 + Br 2 → CH 2 Br – CH 2 Br
Phenols are detected by complexation with iron (III) salts. Depending on the type of phenol, complexes of different colors are formed (from blue to red).
Qualitative molecular analysis
When performing qualitative analysis of organic compounds, two types of problems are usually solved:
1. Detection of a known organic compound.
2. Study of an unknown organic compound.
In the first case, knowing the structural formula of an organic compound, qualitative reactions to the functional groups contained in the compound molecule are selected to detect it. For example, phenyl salicylate is the phenyl ester of salicylic acid:
can be detected by functional groups: phenolic hydroxyl, phenyl group, ester group and azo coupling with any diazo compound. The final conclusion about the identity of the analyzed compound to a known substance is made on the basis of qualitative reactions, necessarily involving data on a number of physicochemical constants - melting points, boiling points, absorption spectra, etc. The need to use these data is explained by the fact that the same functional groups can have different organic compounds .
When studying an unknown organic compound, qualitative reactions are carried out on individual elements and the presence of various functional groups in it. Having gained an idea of the set of elements and functional groups, the question of the structure of the compound is decided on the basis quantitative determination of elemental composition and functional groups, molecular weight, UV, IR, NMR mass spectra.
The belonging of organic substances to certain classes is established by functional analysis, their purity by chromatography, their structure by all existing physical and chemical research methods, taking into account the method of preparation, and, if necessary, the results of counter synthesis.
Qualitative elemental analysis makes it possible to determine from which atoms of elements the molecules of organic matter are built; Quantitative elemental analysis establishes the composition of the compound and its simplest formula.
When performing elemental analysis, organic substances are “mineralized”, i.e. decompose in such a way that carbon turns into CO 2, hydrogen into H 2 O, nitrogen into N 2, NH 3 or cyanide - CN - ions, etc. Further determination is carried out using conventional methods of analytical chemistry.
In functional analysis, chemical, physical and physicochemical methods are used.
For qualitative samples of functional groups, reactions are selected in which a color change or phase separation occurs (precipitation, gas evolution). Few reactions are known that are characteristic only of one functional group, and in order to establish which class of compounds a given substance belongs to, several qualitative reactions must be performed.
Laboratory work No. 3 “Qualitative elemental analysis”
Practical part
Experience No. 1. Discovery of carbon and hydrogen by burning the substance with copper oxide (P).
Reagents: copper oxide powder (P), sucrose, anhydrous copper sulfate, lime water.
Equipment: test tubes, stopper with gas outlet tube, cotton wool, dry fuel.
On the day of the experiment, black copper oxide powder (P) is poured into test tube “a” (Fig. 31) to a height of about 10 mm. Add one scoop of sucrose, mix thoroughly, and shake the test tube vigorously.
A small lump of cotton wool is inserted into the upper part of test tube “a” in the form of a stopper (Fig. 3.23.). Pour a thin layer of white powder - anhydrous copper sulfate - onto the cotton wool. Close test tube “a” with a stopper with a gas outlet tube. In this case, the end of the tube should almost rest against the cotton wool with CuSO 4. The lower end of the tube is placed in test tube “b”, about 1-2 ml of lime water is first poured into it. The end of the gas outlet tube should be immersed in lime water.
Fig.3.23. Discovery of carbon and hydrogen
Heat test tube “a” on the burner flame. If the stopper tightly closes the test tube, then after a few seconds gas bubbles will begin to emerge from the gas outlet tube. As soon as the limewater becomes cloudy due to the release of a white precipitate of CaCO3, test tube “b” is removed. Test tube “a” continues to be heated along its entire length to the cotton wool until the water vapor reaches the white powder - dehydrated copper sulfate, located on the cotton swab, and causes it to turn blue due to the formation of crystalline hydrate CuSO 4 5H 2 O. If the piece of cotton wool is too large, then it will absorb the released vapors and blueing may not occur.
Experience No. 2. Discovery of nitrogen by fusing the substance with sodium metal.
Reagents: urea, metallic sodium, ethyl alcohol, alcohol solution of phenolphthalein, solution of ferrous sulfate FeS0 4, 2 N HCl solution.
Equipment: dry fuel, test tubes.
To open nitrogen, 5 - 10 mg of the test substance, for example, a few crystals of urea, are placed in a dry test tube. Add a small piece of sodium metal to the urea.
Heat the mixture carefully in the flame of the burner, bring the test tube in and out of the flame, without heating it constantly! When the urea melts, make sure that it mixes with sodium (for the success of the experiment, it is necessary that the sodium melts with the substance, and not separately from it - not on the wall of the test tube!). In this case, sometimes a small flash is observed. Heat until a homogeneous alloy is obtained.
When the test tube has cooled, add 5 drops of ethyl alcohol to eliminate residual sodium metal, which reacts with alcohol less violently than with water. In this case, sodium alkoxide is formed with the release of hydrogen:
2C 2 H 5 OH + 2Na → 2C 2 H 5 0Na + H 2
After making sure that the remaining sodium has reacted with the alcohol (the hissing from the release of gas bubbles stops), add 5 drops of water to the test tube and heat it over a burner flame until everything dissolves. In this case, sodium cyanide goes into solution, and sodium alcoholate with water forms a caustic alkali:
C 2 H 5 OH + NOH → C 2 H 5 OH + NaOH
Add 1 drop of phenolphthalein alcohol solution to the test tube. The appearance of a crimson-red color indicates that an alkali has formed in the solution. After this, add 1 drop of iron sulfate solution FeS0 4 into the test tube, usually containing an admixture of iron (III) oxide salt Fe 2 (S0 4) 3. In the presence of an alkali, a dirty green precipitate of iron (II) hydroxide is immediately formed mixed with a yellow precipitate of iron (III) hydroxide.
If there is an excess of sodium cyanide in the solution, iron (II) hydroxide forms a complex yellow bloody salt:
Fe(OH) 2 + 2NaCN → Fe(CN) 2 + 2 NaOH
Fe(CN) 2 + 4NaCN → Na 4
Use a pipette to place a drop of liquid from the test tube into the center of the filter paper. As soon as the drop is absorbed, 1 drop of 2 N HCl solution is applied to it. After acidification, the dirty green or yellowish precipitate of iron (II) and (III) hydroxides dissolves and, in the presence of nitrogen, a blue spot of the resulting Prussian blue immediately appears:
Fe(OH) 3 + 3 HCl → FeCl 3 + 3 H 2 O
3 Na 4 + 4FeСl 3 → Fe 4 3 + 12 NaСl
Experience No. 3. Discovery of sulfur by fusing organic matter with metallic sodium.
Reagents: thiourea or sulfanilic acid, sodium metal, ethyl alcohol, lead acetate solution Pb(CH3COO) 2.
Equipment: dry fuel, test tubes.
To discover sulfur, the test substance, such as thiourea or sulfanilic acid, is placed in a dry test tube. It is enough to take just a few crystals of the substance (5 – 10 mg).
A piece of sodium metal (a column about 1 mm long) is added to the substance. The test tube is heated, making sure that the sodium does not melt separately, but together with the substance, otherwise the experiment will fail. The small sodium flash observed is not dangerous (see previous experience). In this case, the organic substance (thiourea) turns into an inorganic compound - sodium sulfide.
When the test tube has cooled, add 5 drops of ethyl alcohol to eliminate the residues of metallic sodium, which with alcohol forms sodium alkoxide C 2 H 5 ONa. After the reaction is completed (the release of hydrogen gas bubbles stops), add 5 drops of water to dissolve the alloy and boil to speed up the dissolution. Sodium sulfide will go into solution along with sodium hydroxide, which, however, does not interfere with the further reaction.
To open sulfur, add a few drops of lead acetate solution Pb(CH3COO) 2. In this case, a dark brown precipitate of lead sulfide precipitates:
Pb(CH 3 COO) 2 .+ Na 2 S → PbS ↓ + 2 CH 3 COONa
This is a qualitative reaction to the divalent sulfur ion S -2.
Experience No. 4. Discovery of chlorine through the action of hydrogen on organic matter.
Reagents: chloroform CHCl 3, ethyl alcohol, sodium metal, concentrated nitric acid HNO 3.
Equipment: dry fuel, test tubes.
Place a drop of chloroform CHСl 3 in test tube I. Add 5 drops of ethyl alcohol and a piece of sodium metal (1 mm long column). The following reaction occurs:
C 2 H 5 OH + Na → C 2 H 5 ONa + H 2
Pay attention to the hydrogen released. It can be lit at the hole of the test tube if you first close this hole with your finger to accumulate hydrogen, and then bring the hole to the burner flame. Hydrogen, at the time of release, splits off chlorine from chloroform and forms hydrogen chloride, which then reacts with the resulting sodium alkoxide.
CHCl 3 + 3H 2 → CH 4 + 3HCl
C 2 H 5 ONa + HCl → C 2 H 5 OH + NaCl
After the evolution of hydrogen stops, 2-3 drops of water are added to dissolve the resulting white precipitate, insoluble in ethyl alcohol. In this case, excess sodium alcoholate reacts with water, forming an alkali:
C 2 H 5 OH + HOH → C 2 H 5 OH + NaOH
In the presence of an alkali, the chlorine ion must not be abstracted, since the addition of a silver nitrate solution immediately produces a brown precipitate of silver oxide, masking the precipitate of silver chloride:
AgNO 3 + 2 NaOH → Ag 2 0 + H 2 0 + 2 NaN0 3
Therefore, first add 2 - 3 drops of concentrated nitric acid HNO 3 (in a fume hood) to the solution to neutralize the alkali, and then 2 drops of 0.1 N AgN0 3 solution. In the presence of chlorine, a white cheesy precipitate of silver chloride immediately forms, insoluble in HNO 3:
NaCl + AgNO 3 → AgCl ↓+ NaNO 3
In no case should you take more than 1 drop of chloroform for the reaction, as this only harms the sensitivity of the reaction. The remainder of unreacted chloroform even before adding silver nitrate gives a strong emulsion with water in the form of a whitish cloudy liquid, which will mask the appearance of white turbidity from silver chloride.
Experience No. 5. Discovery of chlorine by the green color of the flame (Beilstein test).
Reagents: chloroform CHСl 3.
Equipment: dry fuel, copper wire.
Take a copper wire about 10 cm long, bent into a loop at the end and inserted at the other end into a small cork plug. Holding the plug, heat the flame loop of the burner until the extraneous color of the flame disappears (a sign of contamination of the copper loop).
2Cu + O 2 → 2 CuO
The cooled loop, covered with a black coating of copper (II) oxide, is lowered into a test tube, at the bottom of which the test substance, for example chloroform, is placed. The loop moistened with the substance is again brought into the burner flame. The characteristic bright green color of the flame immediately appears due to the formation of a volatile copper compound with chlorine. In addition to chlorides, other halogen-containing organic compounds also give a similar color to the flame.
2CHCl 3 + 5CuO → CuCl 2 +4 CuCl + 2CO 2 + H 2 O
To clean, the wire can be moistened with hydrochloric acid and calcined.
In the report, equations of the corresponding reactions are written and a conclusion is drawn about the presence of the analyzed elements in the substances.
Colloquium questions:
1. What inorganic compounds are carbon-, hydrogen-, nitrogen-, sulfur- and chlorine-containing organic compounds converted into for the qualitative determination of the corresponding elements? Why specifically these inorganic compounds?
2. Why are ethyl alcohol and water added when discovering elements such as nitrogen, sulfur, chlorine?
3. What is the meaning of the Beilstein test?
Laboratory work No. 4 “Functional analysis”
In order to distinguish aromatic hydrocarbons from aliphatic ones, some color reactions can be used, for example the reaction of aromatic hydrocarbons with chloroform in the presence of aluminum chloride. This reaction is accompanied by the formation of colored products. Thus, when benzene reacts with chloroform in the presence of AlCl 3, in addition to the main reaction product - colorless triphenylmethane, a colored triphenylcarbenium salt is also formed:
Painted
This reaction can also be used to detect aromatic halogen derivatives.
Experience. Add 2-3 drops of benzene to 1-2 ml of chloroform, mix thoroughly and tilt the test tube slightly to wet the walls. Add 0.5-0.6 g of anhydrous aluminum chloride so that part of the powder falls on the walls of the test tube. Pay attention to the color of the powder on the wall and the color of the solution. In the reaction with benzene, a red-orange color appears, with biphenyl - purple, with naphthalene - blue, with anthracene - green.
In order to distinguish between primary, secondary and tertiary alcohols, the different mobility of the oxo group is used in the reaction of alcohols with a solution of zinc chloride in concentrated hydrochloric acid:
Tertiary alcohols react with this reagent at a faster rate, giving insoluble haloalkyl; Primary alcohols react only with prolonged heating or standing; secondary alcohols occupy an intermediate position.
Experience. A freshly prepared solution of zinc chloride in hydrochloric acid is poured into three test tubes and cooled. Add 3-4 drops of primary, secondary or tertiary alcohols, respectively, to each test tube, shake vigorously and leave in a glass of water at 25-30 0 C. The onset of the reaction is judged by the turbidity of the solution due to the formation of insoluble haloalkyl. The time of turbidity of the solution in each test tube is noted.
Qualitative reactions of carbonyl compounds are numerous and varied, which is explained by the tendency of carbonyl compounds to enter into various substitution and addition reactions.
Fatty aldehydes reduce divalent copper to monovalent copper. Fehling's reagent is used as a reagent containing Cu 2+ ions. Fehling's reagent is prepared before use by mixing freshly prepared copper (II) hydroxide, formed by the reaction of sodium hydroxide with copper (II) sulfate, and a solution of Rochelle salt. When the solutions are drained, copper(II) hydroxide is formed, which with Rochelle salt produces a complex compound such as copper glycolate:
Aromatic aldehydes do not give this reaction.
Experience. Fehling's reagent is prepared in a test tube by pouring off 1 ml of the original solutions and adding 2 ml of a carbonyl compound. The upper part of the contents of the test tube is heated and the appearance of a yellow or red precipitate of copper (I) oxide is observed.
Practical part
Students are given a set consisting of 6 colorless and transparent liquids, among which there is one representative each of alkanes, aromatic hydrocarbons, alcohols (primary, secondary and tertiary) and aldehydes. The names of representatives are indicated by the teacher.
The student’s task, having previously familiarized himself with the basics of functional analysis presented in the introduction, is to draw up an analysis plan so that upon completion it can be concluded about the location of a particular compound in a numbered test tube.
The report describes the observed phenomena, the ongoing reactions and the course of thinking. They draw a conclusion about the belonging of liquids to one class or another and justify it.
Laboratory work No. 5 “Thin layer chromatography”
Chromatography. One of the simplest and most effective methods for studying the composition of a mixture of organic compounds, as well as establishing the degree of purity, is thin layer chromatography (TLC). The most widely used is the adsorption version of TLC.
The process of chromatographic separation in this embodiment is based on the difference in the relative affinity of the components of the analyzed mixture to the stationary phase (sorbent) and is carried out as a result of the movement of the mobile phase (eluent) under the action of capillary forces along a layer of sorbent deposited on a glass or aluminum plate.
Chromatography is carried out as follows. The start and finish lines are marked on the plate (1-1.5 cm from the edge of the plate). A solution of the mixture to be analyzed is applied to the starting line in the form of small spots using a capillary (no more than 2-3 mm in diameter). The plate is then placed in a closed chamber containing the eluent. An eluent is a solvent or a mixture of solvents in varying proportions. Both special chambers and various chemical vessels are used as chromatographic chambers: desiccators, beakers, Petri dishes (Fig. 3.24.).
a) 
b)
Rice. 3.24. a) Desiccator equipped for thin layer chromatography; b) use of a glass and a Petri dish for thin layer chromatography.
When immersing the bottom of the plate in the eluent, the starting line should be above the solvent level. Rising along the plate from bottom to top, the solvent separates the applied test substances, moving them in the sorbent layer at different speeds depending on the nature and properties of the substance. As a result, the components of the mixture remain at different distances from the starting line. Chromatography is completed when the boundary of the moving eluent reaches the finish line.
The plate is then removed from the chromatography chamber and air dried. Colorless compounds are detected by optical (ultraviolet) or chemical methods. The last method involves treating the chromatogram with reagents that react with the analytes to form colored spots. The most accessible and universal detection method is treatment with iodine vapor. To do this, the chromatogram is placed for several minutes in a desiccator saturated with iodine vapor.
After the spots develop, the mobility coefficient R is calculated f, which is the ratio of the distances from the starting line to the center of the spot to the distance from the starting to finishing lines (Fig. 3.25):
R f=L i /L
L i is the distance from the start line to the center of the spot of substance i (cm), L is the distance from the start line to the finish line (cm).
Fig.3.25. Chromatogram obtained by separating a mixture of three components using thin layer chromatography.
Also, to identify the substances included in the mixture being analyzed, solutions of known substances – “witnesses” – are additionally applied to the starting line. After developing the spots and calculating R f compare the characteristics of the “witness” and the analyzed substance.
Practical part
Experience No. 1. Detection of ascorbic acid (vitamin C) in fruit juices.
Reagents: orange juice (lemon, tangerine, rowan, pomegranate, etc.), eluent (ethanol - hexane 3:1), 1% solution of ascorbic acid.
Equipment
Samples of filtered orange juice (lemon, tangerine, rowan, pomegranate, etc.) and a 1% solution of ascorbic acid are applied to the starting line of the plate so that the distance of the stains from the side edges and between each other is at least 1 cm. When the stains dry, the plate is placed in a glass, onto the bottom of which 2 ml of eluent (ethanol - hexane 3:1) is poured. To prevent the eluent from evaporating from the surface of the plate, cover the glass with a Petri dish. After the eluent reaches the finishing line, remove the plate and dry it in air. To detect compounds, place the plate in a desiccator with iodine vapor. Mark the spots that appear and determine the R value f ascorbic acid.
Experience No. 2. Detection of citric acid in lemon.
Reagents: lemon juice, citric acid solution, eluent (ethanol - hexane 3:1).
Equipment: Petri dishes, beakers, Sorbfil adsorbent, capillaries.
Similar to the previous experiment, samples of lemon juice and citric acid solution (“witness”) are applied to the plate. Chromatography and detection are performed similarly to experiment No. 1. Determine the R value f citric acid.
Experience No. 3. Detection of caffeine in tea and coffee.
Reagents: solutions of tea, coffee and caffeine, eluent ethanol.
Equipment: Petri dishes, beakers, Sorbfil adsorbent, capillaries.
Drops of an aqueous solution of tea, coffee and caffeine (“witness”) are applied to the start line of the plate. The plate is placed in a chromatography system with ethanol as eluent. Caffeine is detected using iodine vapor. Determine the value of R f caffeine
Experience No. 4. Caffeine release and qualitative reaction to it.
Reagents: dry tea, 30% aqueous solution of hydrogen peroxide, concentrated ammonia solution, 10% hydrochloric acid solution.
Equipment: porcelain cup, funnel, cotton wool, asbestos mesh, dry fuel, glass slide.
Caffeine can be obtained from tea leaves. To do this, pour about 0.5 - 1 g of dry tea into a porcelain cup, cover it with a funnel with a cotton swab plugged into the hole and heat it on an asbestos mesh for about 10 minutes. First, water droplets condense on the inside of the funnel, and then caffeine begins to sublimate, white thin crystals of which are deposited on the cold walls of the funnel. The heating is stopped and after the porcelain cup has completely cooled, the caffeine crystals are cleaned from the walls of the funnel and dissolved in 1 ml of water.
To check for the presence of caffeine, 1 drop of the resulting solution is applied to a glass slide, 1 drop of a 30% aqueous solution of hydrogen peroxide and 1 drop of 10% hydrochloric acid are added. The mixture is carefully evaporated to dryness over a dry fuel flame. The glass is cooled and 1 drop of concentrated ammonia solution is added, and then the glass is heated again until the water completely evaporates. The purplish-red color of the stain indicates the presence of caffeine.
The report concludes that the declared components were found in juices, fruits and tea (coffee).
Colloquium questions:
1. What is the TLC method based on?
2. What is the mobility coefficient?
3. What is mobile and stationary phase?
4. Name the methods for developing colorless spots.
“Study of the composition of organic compounds, their purification and determination of physical constants”
1. Ivanov V.G., Geva O.N., Gaverova Yu.G. Workshop on organic chemistry. - M.: Academy, 2000.
2. Artemenko A.I. Workshop on organic chemistry. - M.: Higher School, 2001.
3. Ginzburg O.F. Workshop on organic chemistry. Synthesis and identification of organic compounds. - M.: Higher School, 1989.
3.2. Introductory (small) workshop.
Laboratory work No. 6 “Aliphatic hydrocarbons”
Hydrocarbons are the simplest organic compounds, whose molecules consist only of carbon and hydrogen atoms. Carbohydrates, in the molecules of which carbon atoms are connected to each other in open chains (straight or branched), are called acyclic (aliphatic). From lat. Aliphatic– fat. The first compounds of this class to be studied were fats.
Alicyclic hydrocarbons– cyclic compounds, the molecules of which are built from carbon atoms connected to each other by a σ bond. The main representatives of alicyclic hydrocarbons are cycloalkanes (cycloparaffins) And cycloalkenes (cycloolefins).
Based on the nature of the bond between carbon atoms, hydrocarbons can be saturated (saturated) and unsaturated (unsaturated). Saturated hydrocarbons include alkanes (paraffins), and unsaturated hydrocarbons include alkenes (olefins), alkadienes and alkynes.
In alkanes, carbon atoms are connected to each other by a simple (single) bond, in alkenes - by a double bond, and in alkynes - by a triple bond. Alkadienes are unsaturated compounds whose molecules contain two double bonds.
Saturated hydrocarbons under normal conditions are highly chemically inert. This is explained by the fact that all σ-bonds C-C and C-H are very strong (the energies of these bonds are about 380 kJ/mol). They are generally incapable of addition reactions due to the unsaturation of all bonds of carbon atoms. Alkanes either do not react at all or react extremely slowly with most chemical reagents. Strong oxidizing agents (for example, potassium permanganate) also have no effect on alkanes at room temperature.
At relatively low temperatures, only a small number of reactions occur in which hydrogen atoms are replaced by different atoms or groups - substitution reactions.
Alkenes and alkynes are more reactive due to the presence of a double and triple bond, respectively, which can be considered functional groups. It is natural to expect that reactions of alkenes and alkynes will occur via an unsaturated bond - an addition reaction.
Important representatives of alkanes are methane CH 4 - the main part of natural (up to 95-98%) and associated gases. It is present in significant quantities in processing gases. Methane is used mainly as a cheap fuel (in everyday life and industry). It is colorless and odorless. To detect its leakage in gas pipelines, a small amount of a strong-smelling substance (odorant) is added.
Methane is a valuable raw material for the chemical industry. Acetylene, halogen derivatives, methanol, formaldehyde and other substances are obtained from it. Methane is used to produce synthesis gas(water gas).
Isooctane (2,2,4-trimethylpentane) C 8 H 18 is the main component of high-quality fuel (gasoline) for carburetor internal combustion engines.
The middle members of the homologous series of methane C 7 - C 17 are used as fuel for engines (gasoline, kerosene), and also as solvents. Higher alkanes C 18 – C 44 are raw materials for the production of detergents, lubricating oils, and plasticizers. Higher alkanes include ozokerite(mountain wax), consisting mainly of solid alkanes with a branched chain of carbon atoms, the number of which exceeds 25-30.
Many alkenes are widely used as monomers (starting products) to obtain high molecular weight compounds (polymers).
Acetylene is used for welding and cutting metals, because... When burning in oxygen, acetylene creates a high-temperature flame (3150 0 C). Acetylene is also a valuable product for the chemical industry. Synthetic rubber, acetaldehyde and acetic acid, ethyl alcohol and many other substances are obtained from it.
Practical part
Experience No. 1. Production of methane and its properties.
Reagents: sodium acetate, soda lime, bromine water, potassium permanganate solution.
Equipment: test tube with gas outlet tube, stand, stand leg, burner.
A mixture consisting of one part dehydrated finely ground sodium acetate and two parts soda lime (NaOH and CaO) is placed in a test tube with a gas outlet tube. The total volume of the mixture is 1-2 cm (about 1/3 of the height of the test tube). Fix the test tube in a stand in a horizontal position and heat it in the burner flame.
Methane is ignited at the outlet of the gas outlet tube 2 minutes after gas evolution, i.e. after the explosive mixture evaporates (the mixture is explosive!). Please note that methane burns with a luminous flame.
The released methane is passed through solutions of bromine water and KMnO 4 .
Does the color of solutions change? Why?
Experience No. 2. Bromination of hexane.
Reagents: hexane, bromine water.
Equipment: test tube, glass with ice, burner, pipette.
A) Demonstration experience. Place 3 ml of hexane in two cuvettes and add 4-5 drops of a solution of bromine in carbon tetrachloride and mix. One cuvette is placed under a UV light source, and the other is covered with paper and left under traction. After 3-4 minutes, the cuvettes are compared.
B) Place 1 ml of hexane and a few drops of bromine water into a dry test tube. The contents of the test tube are mixed in the cold. . Heat the contents of the test tube in a water bath until the color disappears. The reaction is accompanied by the release of HBr.
How can HBr release be detected?
Experience No. 3. Obtaining ethylene and studying its properties.
Reagents: ethyl alcohol, sulfuric acid, sand, bromine water, potassium permanganate solution.
Equipment: 50 ml conical flask with gas outlet tube, test tubes, burner.
Place 4-5 ml of a mixture of ethyl alcohol and sulfuric acid (1:5) into a conical flask with a gas outlet tube and add a little “boil” for uniform boiling. Heat the flask with the mixture in the burner flame. The released gas is passed through a solution of bromine water without stopping heating. Note whether the bromine color disappears.
After passing the ethylene through bromine water and a solution of potassium permanganate, the ethylene can be ignited at the end of the gas outlet tube. It burns with a non-luminous flame.
Experience No. 4. Preparation of acetylene and study of its properties.
Reagents: calcium carbide, bromine water, potassium permanganate solution.
Equipment: test tube with gas outlet tube, test tubes.
A piece of calcium carbide is placed in a dry test tube and water is added, the test tube is quickly closed with a stopper with a gas outlet tube, and the released gas is passed successively into test tubes with bromine water and a KMnO 4 solution. How does the color of solutions change?
Light the gas at the end of the outlet tube. Acetylene burns with a smoky flame.
The report contains observations, equations of all reactions performed and the names of the resulting substances. They draw a conclusion about the similarities and differences in the properties of aliphatic hydrocarbons.
Colloquium questions:
1. Propose a radical chain mechanism for the bromination of hexane and an ionic mechanism for the bromination of ethylene.
2. Write the reaction equations for the production of acetylene and the reaction equation for acetylene with an ammonia solution of silver oxide.
3. Give examples of hydrocarbons containing a primary, secondary and tertiary carbon atom. Give them a name.
4. Define isomerism. Draw possible isomers of pentane and give them names.
5. Finding the most important hydrocarbons in nature and their use.
Laboratory work No. 7 “Haloalkanes”
Halogen derivatives of hydrocarbons are organic compounds formed by replacing hydrogen atoms in hydrocarbons with halogen atoms. Accordingly, haloalkanes are derivatives of alkanes in the molecules of which one or more hydrogen atoms are replaced by halogen atoms.
Depending on the number of hydrogen atoms replaced by halogen, mono-, di-, trihalogen derivatives, etc. are distinguished.
For example: CH 3 Cl (chloromethane, methyl chloride), CH 2 Cl 2 (dichloromethane, methylene chloride), CHCl 3 (trichloromethane, chloroform), CCl 4 (carbon tetrachloride, carbon tetrachloride).
Based on the type of carbon atom bonded to the halogen, haloalkanes are classified as primary, secondary, or tertiary.
Just as among hydrocarbons, saturated, unsaturated, cyclic and aromatic halogen derivatives of hydrocarbons are distinguished.
bromoethane 2-bromopropane 2-bromo-2-methylpropane
(ethyl bromide) (isopropyl bromide) ( rubs-butyl bromide)
primary secondary tertiary
haloalkane haloalkane haloalkane
chlorocyclobutane bromocyclohexane bromobenzene
Lower alkyl halides are gaseous substances, middle alkyl halides are liquids, and higher alkyl halides are solids. Haloalkyls are almost insoluble in water. The lower members of the series have a characteristic odor.
The chemical properties of halogen derivatives are determined mainly by the halogen atom bonded to the radical. Halogen derivatives undergo substitution and elimination reactions. The presence of a multiple bond leads to an increase in reactivity.
Reactions with nucleophiles are the most common transformations of haloalkanes.
Practical part
Experience No. 1. Preparation of 2-bromopropane (isopropyl bromide).
Reagents: isopropyl alcohol, concentrated sulfuric acid, potassium bromide.
Equipment: test tubes with a gas outlet tube, ice, stands, cups, tiles.
1.5-2 ml of isopropyl alcohol and 2 ml of concentrated sulfuric acid are poured into a test tube with a gas outlet tube. The mixture is cooled and 1-2 ml of water is added. Continuing cooling, pour 1.5 g of potassium bromide into the test tube. Having connected the gas outlet tube, strengthen the test tube obliquely in the leg of the tripod. The end of the outlet tube is immersed in another receiver tube containing 1 ml of water and placed in a glass with water and ice. The reaction mixture is carefully heated to a boil until no more oily drops flow into the receiver and sink to the bottom. In case of strong foaming of the reaction mass, heating is interrupted for a short time. At the end of the reaction, 2-bromopropane is separated from water using a separating funnel, collecting it in a dry test tube or flat-bottomed flask. To dry the 2-bromopropane, add a few pieces of calcium chloride. The resulting product is used for the next experiment.
Experience No. 2. Elimination of halogen from alkyl halides under the action of alkalis.
Reagents: 2-bromopropane (experiment No. 1), sodium hydroxide solution, nitric acid, 1% silver nitrate solution.
Equipment: Separating funnel, test tubes, ice.
The 2-bromopropane obtained in experiment No. 1 is washed in a separating funnel with distilled water. The water is drained, and 2-bromopropane is poured into a test tube, into which 1-2 ml of sodium hydroxide solution is then added. The mixture is heated until it begins to boil, cooled in an ice bath. Under these conditions, alkaline hydrolysis of alkyl halides occurs to form sodium halide. Next, to detect the halogen ion, a small part of the mixture is acidified with nitric acid and a few drops of a 1% silver nitrate solution are added. What's happening?
Experience No. 3. Properties of chloroform (trichloromethane).
Reagents: chloroform, 10% sodium hydroxide solution, iodine solution in potassium iodide, 1% silver nitrate solution, 10% ammonia solution, 20% nitric acid solution;
Equipment: test tubes, reflux condensers, 100 ml glasses, ice.
3.1. 1 ml of chloroform and 1 ml of water are poured into a test tube. Close the test tube with a stopper and shake vigorously. After some time, two layers form, since chloroform is practically insoluble in water. Explain where the organic solvent layer is located, and where the water is and why? And why doesn’t chloroform dissolve in water?
3.2. 1 ml of chloroform is poured into a test tube and a few drops of a solution of iodine in potassium iodide are added. The mixture is shaken vigorously. After some time, the bottom layer becomes pink. Chloroform dissolves iodine well; when shaken, iodine passes from the aqueous layer into chloroform, turning it pink.
3.3. Alkaline hydrolysis of chloroform. 1 ml of chloroform and 3 ml of 10% sodium hydroxide solution are poured into a test tube. The test tube is sealed with a reflux stopper. The mixture is carefully heated until it begins to boil, then cooled in an ice bath. Under these conditions, alkaline hydrolysis of chloroform occurs with the formation of sodium chloride and sodium salt of formic acid:
Methods for analyzing organic medicinal substances differ from methods for analyzing inorganic medicinal substances and have their own characteristics. Unlike inorganic compounds, most organic compounds are not electrolytes, so ionic reactions are not applicable to them. The exceptions are: organic acids and their salts (a):
and mineral acids that dissociate into ions (b):
While reactions between inorganic compounds, for the most part, proceed instantaneously due to the exchange between ions, reactions of organic substances, as a rule, proceed slowly and can often be stopped at the formation of intermediate products, i.e., a whole series of transformations between the starting materials can be observed and the end result. At the same time, all organic compounds are more or less unstable at high temperatures; when heated strongly, they burn completely.
In order to establish whether a given substance belongs to organic compounds. It is necessary, first of all, to discover the presence of carbon in it. Sometimes this does not present any difficulties, since many organic substances become carbonized when calcined, that is, they turn into coal, and thereby confirm the presence of carbon. But in a number of cases, organic substances do not become carbonized when ignited. For example, if you heat alcohol, it can evaporate, and if it catches fire, it burns without a trace. Therefore, the most reliable way to open carbon in an organic compound is to burn this compound with some kind of oxidizing agent.
The composition of a molecule of an organic substance can include, in addition to carbon and hydrogen, other inorganic elements, often halogens - Cl. Vg, F, I
As can be seen from the above formulas, the halogen in the molecules of bromoisal, diiodotyrosine and fluorothane is bonded directly to carbon (covalent bond). Such compounds do not dissociate into ions and therefore it is impossible to determine the halogen in the molecule by the usual analytical reactions (for example, with a solution of silver nitrate).
In this case, to confirm the presence of a halogen in the molecule, it must be converted into an ionogenic state. For this purpose, organic matter must first be destroyed. This process is called mineralization, which is carried out in various ways: combustion, oxidation, heating with hydroxides, fusion with alkali metals, etc. As a result of mineralization, simple inorganic substances are formed in the form of hydrohalic acids or their salts (halides), which dissociate and can be discovered by the usual analytical reactions of the ionic type .
Among the products of mineralization of organic matter, CO 2 and H 2 O are required, which serve as an indicator of the organic nature of the substance.
In the analysis of organic medicinal substances, the determination of relevant physical and chemical indicators, which can serve not only for identification, but also to confirm the purity of medicinal substances, is of great importance.
For example, for solid substances one of the characteristic indicators is the melting point, for liquid substances - the boiling point, density, and refractive index.
These indicators are quite definite only for pure substances. .
If a medicinal substance contains one or another impurity, the melting point of solid substances decreases, and the boiling point of liquid substances increases during distillation.
The refractive index, being a constant value for a pure substance, can deviate greatly in the presence of impurities. However, determining these indicators for organic medicinal substances is not enough. They give only an approximate preliminary idea of the purity of the drug substance. For the reliability of the analysis, it is necessary to carry out a chemical analysis along with the determination of physical and chemical indicators.
A characteristic feature of organic medicinal substances is the presence in their molecules of so-called functional groups, i.e., reactive atoms or groups of atoms determined by chemical reactions.
Functional groups determine the approach to the analysis of organic medicinal substances, since they determine the properties of substances, determine the nature of identification reactions and methods for the quantitative determination of a particular medicinal substance. Knowing the detection reactions of individual functional groups, you can consciously approach the analysis of any medicinal substance of organic nature that is complex in structure.
There are a lot of functional groups (about 100) and the molecules of most medicinal substances are polyfunctional in nature, that is, they simultaneously contain several functional groups in the molecule.
Test questions for consolidation:
1. What is the main difference between medicinal substances of organic nature and medicinal substances of inorganic nature?
2. What is the main feature of the analysis of organic drugs in contrast to inorganic ones?
3. What physical and chemical indicators are used to authenticate organic medicinal products?
Mandatory:
1. Glushchenko N.N., Pletneva T.V., Popkov V.A. Pharmaceutical chemistry. M.: Academy, 2004.- 384 p. With. 151-154
2. State Pharmacopoeia of the Russian Federation / Publishing house “Scientific Center for Expertise of Medicinal Products”, 2008.-704 pp.: ill.
Additional:
1. State Pharmacopoeia 11th edition, issue. 1-M: Medicine, 1987. - 336 p.
2. State Pharmacopoeia 11th edition, issue. 2-M: Medicine, 1989. - 400 p.
3. Belikov V. G. Pharmaceutical chemistry. – 3rd ed., M., MEDpress-inform-2009. 616 pp.: ill.
Electronic resources:
1. Pharmaceutical library [Electronic resource].
URL:http://pharmchemlib.ucoz.ru/load/farmacevticheskaja_biblioteka/farmacevticheskaja_tekhnologija/9
2. Pharmaceutical abstracts - Pharmaceutical educational portal [Electronic resource]. URL: http://pharm-eferatiki.ru/pharmtechnology/
3. Computer support of the lecture. Disk 1CD-RW.
