The classification of amines is diverse and is determined by what feature of the structure is taken as the basis.
Depending on the number of organic groups associated with the nitrogen atom, there are:
primary amines - one organic group at the nitrogen RNH 2
secondary amines - two organic groups at the nitrogen R 2 NH, organic groups can be different R "R" NH
tertiary amines - three organic groups at nitrogen R 3 N or R "R" R "" N
According to the type of organic group associated with nitrogen, aliphatic CH 3 - N6H 5 - N are distinguished
According to the number of amino groups in the molecule, amines are divided into monoamines CH 3 - NH 2, diamines H 2 N (CH 2) 2 NH 2, triamines, etc.
Amine nomenclature.
the word “amine” is added to the name of the organic groups associated with nitrogen, while the groups are mentioned in alphabetical order, for example, CH 3 NHC 3 H 7 - methylpropylamine, CH 3 N (C 6 H 5) 2 - methyldiphenylamine. The rules also allow the name to be composed based on a hydrocarbon in which the amino group is considered as a substituent. In this case, its position is indicated using a numerical index: C 5 H 3 C 4 H 2 C 3 H (NH 2) C 2 H 2 C 1 H 3 - 3-aminopentane (the upper numerical indices in blue indicate the numbering order of C atoms) . For some amines, trivial (simplified) names have been preserved: C 6 H 5 NH 2 - aniline (the name according to the rules of nomenclature is phenylamine).
In some cases, established names are used, which are distorted correct names: H 2 NCH 2 CH 2 OH - monoethanolamine (correctly - 2-aminoethanol); (OHCH 2 CH 2) 2 NH - diethanolamine, the correct name is bis (2-hydroxyethyl) amine. Trivial, distorted and systematic (composed according to the rules of nomenclature) names quite often coexist in chemistry.
Physical properties of amines.
The first representatives of the amine series - methylamine CH 3 NH 2, dimethylamine (CH 3) 2 NH, trimethylamine (CH 3) 3 N and ethylamine C 2 H 5 NH 2 - are gaseous at room temperature, then with an increase in the number of atoms in R amines become liquids , and with an increase in the chain length R to 10 C atoms - crystalline substances. The solubility of amines in water decreases as the chain length R increases and as the number of organic groups associated with nitrogen increases (transition to secondary and tertiary amines). The smell of amines resembles the smell of ammonia, higher (with large R) amines are practically odorless.
Chemical properties of amines.
The distinctive ability of amines is to add neutral molecules (for example, hydrogen halides HHal, with the formation of organoammonium salts, similar to ammonium salts in inorganic chemistry. For the formation of a new bond, nitrogen provides an unshared electron pair, acting as a donor. The H + proton involved in the formation of the bond (from hydrogen halide) plays the role of an acceptor (receiver), such a bond is called a donor-acceptor bond (Fig. 1). Emerging covalent bond N–H is completely equivalent to the N–H bonds present in the amine.
Tertiary amines also add HCl, but when the resulting salt is heated in an acid solution, it decomposes, while R is split off from the N atom:
(C 2 H 5) 3 N+ HCl ® [(C 2 H 5) 3 N H]Cl
[(C 2 H 5) 3 N H]Cl ® (C 2 H 5) 2 N H + C 2 H 5 Cl
When comparing these two reactions, it can be seen that the C 2 H 5 group and H, as it were, change places, as a result, a secondary is formed from the tertiary amine.
Dissolving in water, amines capture a proton in the same way, as a result, OH ions appear in the solution, which corresponds to the formation of an alkaline environment, which can be detected using conventional indicators.
C 2 H 5 N H 2 + H 2 O ® + + OH -
With the formation of a donor-acceptor bond, amines can add not only HCl, but also haloalkyls RCl, and a new N–R bond is formed, which is also equivalent to the existing ones. If we take a tertiary amine as the initial one, then we get a tetraalkylammonium salt (four R groups on one N atom):
(C 2 H 5) 3 N+ C 2 H 5 I ® [(C 2 H 5) 4 N]I
These salts, dissolving in water and some organic solvents, dissociate (decompose), forming ions:
[(C 2 H 5) 4 N]I ® [(C 2 H 5) 4 N] + + I –
Such solutions, like all solutions containing ions, conduct electricity. In tetraalkylammonium salts, the halogen can be replaced by an HO group:
[(CH 3) 4 N]Cl + AgOH ® [(CH 3) 4 N]OH + AgCl
The resulting tetramethylammonium hydroxide is a strong base, similar in properties to alkalis.
Primary and secondary amines interact with nitrous acid HON=O, but they react in various ways. Primary alcohols are formed from primary amines:
C 2 H 5 N H 2 + H N O 2 ® C 2 H 5 OH + N 2+H2O
Unlike primary amines, secondary amines form yellow, sparingly soluble nitrosamines with nitrous acid, compounds containing the >N–N = O moiety:
(C 2 H 5) 2 N H+H N O 2 ® (C 2 H 5) 2 N N\u003d O + H 2 O
Tertiary amines do not react with nitrous acid at ordinary temperature, thus, nitrous acid is a reagent that makes it possible to distinguish between primary, secondary and tertiary amines.
When amines are condensed with carboxylic acids, acid amides are formed - compounds with the -C (O) N fragment
The condensation of amines with aldehydes and ketones leads to the formation of the so-called Schiff bases, compounds containing the -N=C2 moiety.
The interaction of primary amines with phosgene Cl 2 C=O gives compounds with the –N=C=O group, called isocyanates (Fig. 2D, obtaining a compound with two isocyanate groups).
Among aromatic amines, aniline (phenylamine) C 6 H 5 NH 2 is the most famous. In terms of properties, it is close to aliphatic amines, but its basicity is less pronounced - in aqueous solutions it does not form an alkaline environment. Like aliphatic amines, it can form ammonium salts with strong mineral acids [C 6 H 5 NH 3] + Cl -. When aniline reacts with nitrous acid (in the presence of HCl), a diazo compound containing the R–N=N moiety is formed; it is obtained in the form of an ionic salt called the diazonium salt (Fig. 3A). Thus, the interaction with nitrous acid is not the same as in the case of aliphatic amines. The benzene nucleus in aniline has reactivity, characteristic of aromatic compounds ( cm. AROMATICITY), upon halogenation, hydrogen atoms in ortho- and pair-positions to the amino group are substituted, resulting in chloranilines with various degrees of substitution (Fig. 3B). The action of sulfuric acid leads to sulfonation in pair-position to the amino group, the so-called sulfanilic acid is formed (Fig. 3B).
Getting amines.
When ammonia reacts with haloalkyls, such as RCl, a mixture of primary, secondary and tertiary amines is formed. The resulting by-product HCl adds to the amines to form an ammonium salt, but with an excess of ammonia, the salt decomposes, which allows the process to be carried out up to the formation of quaternary ammonium salts (Fig. 4A). Unlike aliphatic haloalkyls, aryl halides, for example, C 6 H 5 Cl, react with ammonia with great difficulty; synthesis is possible only with catalysts containing copper. In industry, aliphatic amines are obtained by the catalytic interaction of alcohols with NH3 at 300–500°C and a pressure of 1–20 MPa, resulting in a mixture of primary, secondary, and tertiary amines (Fig. 4B).
The reaction of aldehydes and ketones with the ammonium salt of formic acid HCOONH4 gives rise to primary amines (Fig. 4C), while the reaction of aldehydes and ketones with primary amines (in the presence of formic acid HCOOH) leads to secondary amines (Fig. 4D).
Nitro compounds (containing the -NO 2 group) form primary amines upon reduction. This method, proposed by N.N. Zinin, is little used for aliphatic compounds, but is important for obtaining aromatic amines and formed the basis industrial production aniline (Fig. 4e).
As separate compounds, amines are used little, for example, polyethylenepolyamine [-C 2 H 4 NH-] is used in everyday life n(trade name PEPA) as a hardener for epoxy resins. The main use of amines is as intermediates in the preparation of various organic matter. The leading role belongs to aniline, on the basis of which a wide range of aniline dyes is produced, and the color "specialization" is laid already at the stage of obtaining the aniline itself. Ultrapure aniline without homologues is called in the industry "aniline for blue" (meaning the color of the future dye). "Aniline for red" must contain, in addition to aniline, a mixture ortho- and pair-toluidine (CH 3 C 6 H 4 NH 2).
Aliphatic diamines are the initial compounds for the production of polyamides, for example, nylon (Fig. 2), which is widely used for the manufacture of fibers, polymer films, as well as components and parts in mechanical engineering (polyamide gears).
Polyurethanes are obtained from aliphatic diisocyanates (Fig. 2), which have a complex of technically important properties: high strength combined with elasticity and very high abrasion resistance (polyurethane shoe soles), as well as good adhesion to a wide range of materials (polyurethane adhesives). They are widely used in foamed form (polyurethane foams).
Based on sulfanilic acid (Fig. 3), anti-inflammatory drugs sulfonamides are synthesized.
Diazonium salts (Fig. 2) are used in photosensitive materials for blueprinting, which makes it possible to obtain an image bypassing the usual silver halide photograph ( cm. LIGHT COPYING).
Mikhail Levitsky
Amines are organic derivatives of ammonia containing the amino group NH 2 and an organic radical. In general, the formula of an amine is the formula of ammonia in which the hydrogen atoms are replaced by a hydrocarbon radical.
Classification
- According to how many hydrogen atoms in ammonia are replaced by a radical, primary amines (one atom), secondary, tertiary are distinguished. Radicals can be the same or different types.
- An amine may contain more than one amino group, but several. According to this characteristic, they are divided into mono, di-, tri-, ... polyamines.
- According to the type of radicals associated with the nitrogen atom, there are aliphatic (not containing cyclic chains), aromatic (containing a cycle, the most famous is aniline with a benzene ring), mixed (fat-aromatic, containing cyclic and non-cyclic radicals).
Properties
Depending on the length of the chain of atoms in the organic radical, amines can be gaseous (tri-, di-, methylamine, ethylamine), liquid or solid substances. The longer the chain, the harder the substance. The simplest amines are water soluble, but as you move to more complex compounds, the water solubility decreases.
Gaseous and liquid amines are substances with a pronounced smell of ammonia. Solids are practically odorless.
Amines show up in chemical reactions strong basic properties, as a result of interaction with inorganic acids alkylammonium salts are obtained. The reaction with nitrous acid is qualitative for this class of compounds. In the case of the primary amine, alcohol and gaseous nitrogen are obtained, with the secondary, an insoluble yellow precipitate with a pronounced smell of nitrosodimethylamine; with the tertiary reaction does not go.
They react with oxygen (burn in air), halogens, carboxylic acids and their derivatives, aldehydes, ketones.
Almost all amines, with rare exceptions, are poisonous. So, the most famous representative of the class, aniline, easily penetrates the skin, oxidizes hemoglobin, depresses the central nervous system, disrupts metabolism, which can even lead to death. Toxic to humans and couples.
Signs of poisoning:
- shortness of breath
- cyanosis of the nose, lips, fingertips,
- rapid breathing and increased heartbeat, loss of consciousness.
First aid:
- wash off the chemical reagent with cotton wool and alcohol,
- provide access to clean air,
- call an ambulance.
Application
— As a hardener for epoxy resins.
— As a catalyst in the chemical industry and metallurgy.
- Raw materials for the production of polyamide artificial fibers, such as nylon.
— For the manufacture of polyurethanes, polyurethane foams, polyurethane adhesives.
- The initial product for the production of aniline - the basis for aniline dyes.
- For the production of medicines.
— For the manufacture of phenol-formaldehyde resins.
- For the synthesis of repellents, fungicides, insecticides, pesticides, mineral fertilizers, rubber vulcanization accelerators, anti-corrosion reagents, buffer solutions.
— As an additive to motor oils and fuels, dry fuel.
— To obtain light-sensitive materials.
- Urotropin is used as a food additive, as well as an ingredient in cosmetics.
In our online store you can buy reagents belonging to the class of amines.
methylamine
Primary aliphatic amine. It is in demand as a raw material for the production of medicines, dyes, pesticides.
diethylamine
secondary amine. It is used as an initial product in the production of pesticides, drugs (for example, novocaine), dyes, repellents, additives to fuel and motor oils. Reagents are made from it for corrosion protection, for beneficiation of ores, curing of epoxy resins, and acceleration of vulcanization processes.
Triethylamine
Tertiary amine. It is used in the chemical industry as a catalyst in the production of rubber, 
epoxy resins, polyurethane foams. In metallurgy, it is a hardening catalyst in non-firing processes. Raw material in the organic synthesis of medicines, mineral fertilizers, weed control agents, paints.
1-butylamine
Tert-butylamine, a compound in which a tert-butyl organic group is bonded to nitrogen. The substance is used in the synthesis of rubber vulcanization enhancers, drugs, dyes, tannins, weed and insect control preparations.
Urotropin (Hexamine)
polycyclic amine. A substance in demand in the economy. Used as a food additive, drug and drug component, ingredient in cosmetics, buffer solutions for analytical chemistry; as a dry fuel, polymer resin hardener, in the synthesis of phenol-formaldehyde resins, fungicides, explosives, corrosion protection agents.
Amines entered our lives quite unexpectedly. Until recently, these were poisonous substances, a collision with which could lead to death. And now, after a century and a half, we are actively using synthetic fibers, fabrics, building materials, dyes, which are based on amines. No, they did not become safer, people were simply able to "tame" them and subdue them, deriving certain benefits for themselves. About which one, and we'll talk further.
Definition
For the qualitative and quantitative determination of aniline in solutions or compounds, a reaction with is used at the end of which a white precipitate in the form of 2,4,6-tribromaniline falls on the bottom of the test tube.
Amines in nature
Amines are found in nature everywhere in the form of vitamins, hormones, metabolic intermediates, they are also found in animals and plants. In addition, when living organisms rot, medium amines are also obtained, which, in a liquid state, spread an unpleasant smell of herring brine. The "cadaveric poison" widely described in the literature appeared precisely due to the specific ambergris of amines.
For a long time, the substances we are considering were confused with ammonia due to a similar smell. But in the mid-nineteenth century, the French chemist Wurtz was able to synthesize methylamine and ethylamine and prove that they release hydrocarbons when burned. This was the fundamental difference between the mentioned compounds and ammonia.
Obtaining amines in industrial conditions
Since the nitrogen atom in amines is in lowest degree oxidation, then the reduction of nitrogen-containing compounds is the simplest and most affordable way to obtain them. It is he who is widely used in industrial practice because of its cheapness.
The first method is the reduction of nitro compounds. The reaction during which aniline is formed is named by the scientist Zinin and was carried out for the first time in the middle of the nineteenth century. The second method is to reduce amides with lithium aluminum hydride. Primary amines can also be reduced from nitriles. The third option is alkylation reactions, that is, the introduction of alkyl groups into ammonia molecules.
Application of amines
By themselves, in the form of pure substances, amines are used little. One rare example is polyethylenepolyamine (PEPA), which makes epoxy resin easier to cure in the home. Basically a primary, tertiary or secondary amine is an intermediate in the production of various organics. The most popular is aniline. It is the basis of a large palette of aniline dyes. The color that will turn out at the end depends directly on the selected raw material. Pure aniline gives Blue colour, and the mixture of aniline, ortho- and para-toluidine will be red.
Aliphatic amines are needed to obtain polyamides such as nylon and others. They are used in mechanical engineering, as well as in the production of ropes, fabrics and films. In addition, aliphatic diisocyanates are used in the manufacture of polyurethanes. Due to their exceptional properties (lightness, strength, elasticity and the ability to attach to any surface), they are in demand in construction (mounting foam, glue) and in the shoe industry (anti-slip soles).
Medicine is another area where amines are used. Chemistry helps to synthesize antibiotics of the sulfonamide group from them, which are successfully used as second-line drugs, that is, reserve ones. In case bacteria develop resistance to essential drugs.
Harmful effects on the human body
It is known that amines are very toxic substances. Any interaction with them can cause harm to health: inhalation of vapors, contact with open skin or ingestion of compounds into the body. Death occurs from a lack of oxygen, since amines (in particular, aniline) bind to blood hemoglobin and prevent it from capturing oxygen molecules. Alarming symptoms are shortness of breath, blue nasolabial triangle and fingertips, tachypnea (rapid breathing), tachycardia, loss of consciousness.
In case of contact with these substances on bare areas of the body, it is necessary to quickly remove them with cotton wool previously moistened with alcohol. This must be done as carefully as possible so as not to increase the area of \u200b\u200bcontamination. If symptoms of poisoning appear, you should definitely consult a doctor.
Aliphatic amines are a poison for the nervous and cardiovascular systems. They can cause depression of liver function, its degeneration and even oncological diseases of the bladder.
Chemical properties of amines.
Since amines, being derivatives of ammonia, have a structure similar to it (i.e., they have an unshared pair of electrons in the nitrogen atom), they exhibit properties similar to it. Those. amines, like ammonia, are bases, since the nitrogen atom can provide an electron pair to form a bond with electron-deficient particles according to the donor-acceptor mechanism (corresponding to the definition of Lewis basicity).
I. Properties of amines as bases (proton acceptors)
1. Aqueous solutions of aliphatic amines show an alkaline reaction, because when they interact with water, alkylammonium hydroxides are formed, similar to ammonium hydroxide:
CH 3 NH 2 + H 2 O CH 3 NH 3 + + OH -
Aniline practically does not react with water.
Aqueous solutions are alkaline in nature:
The bond of a proton with an amine, as with ammonia, is formed according to the donor-acceptor mechanism due to the lone electron pair of the nitrogen atom.
Aliphatic amines are stronger bases than ammonia, because alkyl radicals increase the electron density on the nitrogen atom due to + I-effect. For this reason, the electron pair of the nitrogen atom is held less firmly and interacts more easily with the proton.
2. Interacting with acids, amines form salts:
C 6 H 5 NH 2 + HCl → (C 6 H 5 NH 3) Cl
phenylammonium chloride
2CH 3 NH 2 + H 2 SO 4 → (CH 3 NH 3) 2 SO 4
methyl ammonium sulfate
Amine salts - solids, highly soluble in water and poorly soluble in non-polar liquids. When reacting with alkalis, free amines are released:
Aromatic amines are weaker bases than ammonia, since the lone electron pair of the nitrogen atom shifts towards the benzene ring, conjugating with the π-electrons of the aromatic nucleus, which reduces the electron density on the nitrogen atom (-M effect). On the contrary, the alkyl group is a good electron density donor (+I-effect).
or 
A decrease in the electron density on the nitrogen atom leads to a decrease in the ability to split off protons from weak acids. Therefore, aniline interacts only with strong acids(HCl, H 2 SO 4), and its aqueous solution does not turn litmus blue.
The nitrogen atom in amine molecules has an unshared pair of electrons, which can participate in the formation of a bond by the donor-acceptor mechanism.
aniline ammonia primary amine secondary amine tertiary amine
the electron density on the nitrogen atom increases.
Due to the presence of a lone pair of electrons in the molecules, amines, like ammonia, exhibit basic properties.
aniline ammonia primary amine secondary amine
the basic properties are enhanced, due to the influence of the type and number of radicals.
C6H5NH2< NH 3 < RNH 2 < R 2 NH < R 3 N (в газовой фазе)
II. Amine oxidation
Amines, especially aromatic ones, are easily oxidized in air. Unlike ammonia, they are capable of being ignited by an open flame. Aromatic amines spontaneously oxidize in air. Thus, aniline quickly turns brown in air due to oxidation.
4CH 3 NH 2 + 9O 2 → 4CO 2 + 10H 2 O + 2N 2
4C 6 H 5 NH 2 + 31O 2 → 24CO 2 + 14H 2 O + 2N 2
III. Interaction with nitrous acid
Nitrous acid HNO 2 is an unstable compound. Therefore, it is used only at the moment of selection. HNO 2 is formed, like all weak acids, by the action of a strong acid on its salt (nitrite):
KNO 2 + HCl → HNO 2 + KCl
or NO 2 - + H + → HNO 2
The structure of the reaction products with nitrous acid depends on the nature of the amine. Therefore, this reaction is used to distinguish between primary, secondary and tertiary amines.
Primary aliphatic amines with HNO 2 form alcohols:
R-NH 2 + HNO 2 → R-OH + N 2 + H 2 O
- Of great importance is the diazotization reaction of primary aromatic amines under the action of nitrous acid, obtained by the reaction of sodium nitrite with hydrochloric acid. And then phenol is formed:
Secondary amines (aliphatic and aromatic) under the action of HNO 2 are converted into N-nitroso derivatives (substances with a characteristic odor):
R 2 NH + H-O-N=O → R 2 N-N=O + H 2 O
alkylnitrosamine
· The reaction with tertiary amines leads to the formation of unstable salts and is of no practical importance.
IV. Special properties:
1. Formation of complex compounds with transition metals:
2. Addition of alkyl halides Amines add haloalkanes to form a salt:
By treating the resulting salt with alkali, you can get a free amine:
V. Aromatic electrophilic substitution in aromatic amines (reaction of aniline with bromine water or with nitric acid):
In aromatic amines, the amino group facilitates substitution in the ortho and para positions of the benzene ring. Therefore, aniline halogenation occurs rapidly even in the absence of catalysts, and three hydrogen atoms of the benzene ring are replaced at once, and a white precipitate of 2,4,6-tribromaniline precipitates:
This reaction with bromine water is used as a qualitative reaction for aniline.
In these reactions (bromination and nitration) predominantly formed ortho- and pair-derivatives.
4. Methods for obtaining amines.
1. Hoffmann reaction. One of the first methods for obtaining primary amines is the alkylation of ammonia with alkyl halides:
This is not the best method, since the result is a mixture of amines of all degrees of substitution:
etc. Not only alkyl halides, but also alcohols can act as alkylating agents. To do this, a mixture of ammonia and alcohol is passed over aluminum oxide at high temperature.
2. Zinin's reaction- a convenient way to obtain aromatic amines in the reduction of aromatic nitro compounds. The following are used as reducing agents: H 2 (on a catalyst). Sometimes hydrogen is generated directly at the moment of the reaction, for which metals (zinc, iron) are treated with dilute acid.
2HCl + Fe (shavings) → FeCl 2 + 2H
C 6 H 5 NO 2 + 6 [H] C 6 H 5 NH 2 + 2H 2 O.
In industry, this reaction proceeds by heating nitrobenzene with water vapor in the presence of iron. In the laboratory, hydrogen "at the moment of isolation" is formed by the reaction of zinc with alkali or iron with hydrochloric acid. In the latter case, anilinium chloride is formed.
3. Recovery of nitriles. Use LiAlH 4:
4. Enzymatic decarboxylation of amino acids:
5. The use of amines.
Amines are used in the pharmaceutical industry and organic synthesis (CH 3 NH 2, (CH 3) 2 NH, (C 2 H 5) 2 NH, etc.); in the production of nylon (NH 2 - (CH 2) 6 -NH 2 - hexamethylenediamine); as a raw material for the production of dyes and plastics (aniline), as well as pesticides.
List of sources used:
- O.S. Gabrielyan and others. Chemistry. Grade 10. Profile level: textbook for educational institutions; Bustard, Moscow, 2005;
- "Tutor in Chemistry" edited by A. S. Egorov; "Phoenix", Rostov-on-Don, 2006;
- G. E. Rudzitis, F. G. Feldman. Chemistry 10 cells. M., Education, 2001;
- https://www.calc.ru/Aminy-Svoystva-Aminov.html
- http://www.yaklass.ru/materiali?mode=lsntheme&themeid=144
- http://www.chemel.ru/2008-05-24-19-21-00/2008-06-01-16-50-05/193-2008-06-30-20-47-29.html
- http://cnit.ssau.ru/organics/chem5/n232.htm
According to the nature of the hydrocarbon substituents, amines are divided into
General structural features of amines
Just like in the ammonia molecule, in the molecule of any amine, the nitrogen atom has an unshared electron pair directed to one of the vertices of the distorted tetrahedron:
For this reason, amines, like ammonia, have significantly pronounced basic properties.
So, amines, like ammonia, reversibly react with water, forming weak bases:
The bond of the hydrogen cation with the nitrogen atom in the amine molecule is implemented using the donor-acceptor mechanism due to the lone electron pair of the nitrogen atom. Limit amines are stronger bases compared to ammonia, because. in such amines, hydrocarbon substituents have a positive inductive (+I) effect. In this regard, the electron density on the nitrogen atom increases, which facilitates its interaction with the H + cation.
Aromatic amines, if the amino group is directly connected to the aromatic nucleus, exhibit weaker basic properties compared to ammonia. This is due to the fact that the lone electron pair of the nitrogen atom is shifted towards the aromatic π-system of the benzene ring, as a result of which the electron density on the nitrogen atom decreases. In turn, this leads to a decrease in the basic properties, in particular the ability to interact with water. So, for example, aniline reacts only with strong acids, and practically does not react with water.
Chemical properties of saturated amines
As already mentioned, amines react reversibly with water:
Aqueous solutions of amines have an alkaline reaction of the environment, due to the dissociation of the resulting bases:
Saturated amines react with water better than ammonia due to their stronger basic properties.
The main properties of saturated amines increase in the series.
Secondary limiting amines are stronger bases than primary limiting amines, which in turn are stronger bases than ammonia. As for the basic properties of tertiary amines, when it comes to reactions in aqueous solutions, the basic properties of tertiary amines are much worse than those of secondary amines, and even slightly worse than those of primary ones. This is due to steric hindrances, which significantly affect the rate of amine protonation. In other words, three substituents "block" the nitrogen atom and prevent its interaction with H + cations.
Interaction with acids
Both free saturated amines and their aqueous solutions interact with acids. In this case, salts are formed:
Since the basic properties of saturated amines are more pronounced than those of ammonia, such amines react even with weak acids, for example coal:
Amine salts are solids that are highly soluble in water and poorly soluble in non-polar organic solvents. The interaction of amine salts with alkalis leads to the release of free amines, similar to how ammonia is displaced by the action of alkalis on ammonium salts:
2. Primary limiting amines react with nitrous acid to form the corresponding alcohols, nitrogen N 2 and water. For example:
A characteristic feature of this reaction is the formation of gaseous nitrogen, in connection with which it is qualitative for primary amines and is used to distinguish them from secondary and tertiary. It should be noted that most often this reaction is carried out by mixing the amine not with a solution of nitrous acid itself, but with a solution of a salt of nitrous acid (nitrite) and then adding a strong mineral acid to this mixture. When nitrites interact with strong mineral acids, nitrous acid is formed, which then reacts with an amine:
Secondary amines give oily liquids under similar conditions, the so-called N-nitrosamines, but this reaction in real USE assignments does not occur in chemistry. Tertiary amines do not react with nitrous acid.
Complete combustion of any amine leads to the formation carbon dioxide, water and nitrogen:
Interaction with haloalkanes
It is noteworthy that exactly the same salt is obtained by the action of hydrogen chloride on a more substituted amine. In our case, during the interaction of hydrogen chloride with dimethylamine:
Getting amines:
1) Alkylation of ammonia with haloalkanes:
In the case of a lack of ammonia, instead of an amine, its salt is obtained:
2) Reduction by metals (to hydrogen in the activity series) in an acidic medium:
followed by treatment of the solution with alkali to release the free amine:
3) The reaction of ammonia with alcohols by passing their mixture through heated aluminum oxide. Depending on the proportions of alcohol / amine, primary, secondary or tertiary amines are formed:
Chemical properties of aniline
Aniline - the trivial name of aminobenzene, which has the formula:
As can be seen from the illustration, in the aniline molecule the amino group is directly connected to the aromatic ring. In such amines, as already mentioned, the basic properties are much less pronounced than in ammonia. So, in particular, aniline practically does not react with water and weak acids such as carbonic.
The interaction of aniline with acids
Aniline reacts with strong and moderately strong inorganic acids. In this case, phenylammonium salts are formed:
Reaction of aniline with halogens
As already mentioned at the very beginning of this chapter, the amino group in aromatic amines is drawn into the aromatic ring, which in turn reduces the electron density on the nitrogen atom, and as a result increases it in the aromatic nucleus. An increase in the electron density in the aromatic nucleus leads to the fact that electrophilic substitution reactions, in particular, reactions with halogens, proceed much more easily, especially in the ortho and para positions relative to the amino group. So, aniline easily interacts with bromine water, forming a white precipitate of 2,4,6-tribromoaniline:
This reaction is qualitative for aniline and often allows you to determine it among other organic compounds.
The interaction of aniline with nitrous acid
Aniline reacts with nitrous acid, but due to the specificity and complexity of this reaction, it does not occur in the real exam in chemistry.
Aniline alkylation reactions
With the help of sequential alkylation of aniline at the nitrogen atom with halogen derivatives of hydrocarbons, secondary and tertiary amines can be obtained:
Chemical properties of amino acids
Amino acids name compounds in the molecules of which there are two types functional groups- amino (-NH 2) and carboxy- (-COOH) groups.
In other words, amino acids can be considered as derivatives carboxylic acids, in the molecules of which one or more hydrogen atoms are replaced by amino groups.
Thus, the general formula of amino acids can be written as (NH 2) x R(COOH) y, where x and y are most often equal to one or two.
Since amino acids have both an amino group and a carboxyl group, they exhibit Chemical properties similar to both amines and carboxylic acids.
Acidic properties of amino acids
Formation of salts with alkalis and alkali metal carbonates
Esterification of amino acids
Amino acids can enter into an esterification reaction with alcohols:
NH 2 CH 2 COOH + CH 3 OH → NH 2 CH 2 COOCH 3 + H 2 O
Basic properties of amino acids
1. Formation of salts upon interaction with acids
NH 2 CH 2 COOH + HCl → + Cl -
2. Interaction with nitrous acid
NH 2 -CH 2 -COOH + HNO 2 → HO-CH 2 -COOH + N 2 + H 2 O
Note: interaction with nitrous acid proceeds in the same way as with primary amines
3. Alkylation
NH 2 CH 2 COOH + CH 3 I → + I -
4. Interaction of amino acids with each other
Amino acids can react with each other to form peptides - compounds containing in their molecules a peptide bond -C (O) -NH-
At the same time, it should be noted that in the case of a reaction between two different amino acids, without observing some specific synthesis conditions, the formation of different dipeptides occurs simultaneously. So, for example, instead of the reaction of glycine with alanine above, leading to glycylanine, a reaction leading to alanylglycine can occur:
In addition, a glycine molecule does not necessarily react with an alanine molecule. Peptization reactions also take place between glycine molecules:
And alanine:
In addition, since the molecules of the resulting peptides, like the original molecules of amino acids, contain amino groups and carboxyl groups, the peptides themselves can react with amino acids and other peptides due to the formation of new peptide bonds.
Individual amino acids are used to produce synthetic polypeptides or so-called polyamide fibers. So, in particular, using the polycondensation of 6-aminohexanoic (ε-aminocaproic) acid, nylon is synthesized in industry:
The nylon resin obtained as a result of this reaction is used for the production of textile fibers and plastics.
Formation of internal salts of amino acids in aqueous solution
In aqueous solutions, amino acids exist mainly in the form of internal salts - bipolar ions (zwitterions).
