Wurtz reaction method of synthesizing saturated hydrocarbons by the action of sodium metal on alkyl halides (usually bromides or iodides): 2RBr + 2Na → R - R + 2NaBr. B. p. discovered by S. A. Wurtz. (1855). P. Fittig distributed V. r. to the region of fatty aromatic hydrocarbons (Wurtz-Fittig reaction): C 6 H 5 Br + 2Na + BrC 4 H 9 → C 6 H 5 - C 4 H 9 + 2NaBr.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what “Wurtz reaction” is in other dictionaries:
Condensation of alkyl halides under the influence of Na (rarely Li or K) with the formation of saturated hydrocarbons: 2RHal + 2Na > RХR + 2NaHal, where Hal is usually Br or I. When used in the diet, decomp. alkyl halides (RHal and RHal) are formed... ... Chemical encyclopedia
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The Wurtz reaction, or Wurtz synthesis, is a method for the synthesis of symmetrical saturated hydrocarbons by the action of sodium metal on alkyl halides (usually bromides or chlorides). Leads to an increase in the hydrocarbon chain (summation of hydrocarbons... ... Wikipedia
The Wurtz reaction, or Wurtz synthesis, is a method for the synthesis of symmetrical saturated hydrocarbons by the action of metallic sodium on alkyl halides (usually bromides or iodides): 2RBr + 2Na → R R + 2NaBr The Wurtz reaction was discovered by S. A. Wurtz (1855). P. Fittig... ... Wikipedia
See Wurtz reaction... Chemical encyclopedia
Synthesis of org. compounds using Magniorg. halides RMgHal (Grignard reagents). The latter are usually received in a ration: RHal + Mg > RMgHal. In this case, р р RHal in diethyl ether is slowly added with stirring to a suspension of Mg in the same liquid... Chemical encyclopedia
Preparation of b hydroxycarbonate esters t interaction. aldehydes or ketones with a halocarbon esters present. Zh (so-called classical P.p.): Differ. aldehydes and ketones (saturated or unsaturated, aromatic, ... ... Chemical encyclopedia
This article is about chemical compounds. For the Canadian aluminum company, see Rio Tinto Alcan... Wikipedia
Historically established in organic chemistry, the name of a large group of reactions for the formation of complex compounds from two or more simpler ones. K. r., differing both in the nature of the reagents and in the essence of chemical transformations, ... ...
Organic compounds containing an atom of a metal directly bonded to a carbon atom. All M. s. can be divided into two groups: 1. M. s. intransitive and part of M. s. transition metals. These connections... ... Great Soviet Encyclopedia
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In industry, the substance is usually produced in large quantities, striving for maximum profitability. Often it is possible to use not a pure organic compound, but a mixture. In some cases, it is economically profitable to separate even complex mixtures, especially if it is possible to simultaneously isolate other useful substances. There are many cases where it turns out to be profitable to develop a unique synthesis method and build a special enterprise for the production of a highly profitable substance.
In the laboratory it is usually necessary to synthesize small quantities of a substance (grams and fractions of a gram). In research, chemists almost always need individual substances rather than mixtures. Unlike industry, time has more value than price. In addition, laboratory syntheses are always flexible because the researcher is not interested in repeating the studied process many times. Therefore, methods are used that make it possible to obtain the target product quickly and in high yield with a minimum content of impurities.
It is important that laboratory (but not industrial) methods, as a rule, can be extended to the entire class of synthesized compounds.
During the course of organic chemistry, the main focus is on laboratory methods of preparation. When solving problems, industrial methods should not be used, even if they are used to obtain exactly the substance whose synthesis needs to be planned. For example, if ethylene is to be synthesized during the synthesis, it must be produced using general methods for the synthesis of alkenes, although this compound is produced in huge quantities by cracking.
Alkenes and alkynes in the presence of heterogeneous catalysts such as Pt, Pd, Ni, easily add one or two moles of hydrogen with slight heating and low pressure. In this case, alkanes with the same carbon skeleton are quantitatively formed.
Halogen derivatives of saturated hydrocarbons can be reduced to alkanes with a metal in an acidic environment:
Alkanes can be prepared by hydrolysis of Grignard reagents:
The above methods allow the synthesis of alkanes that have the same carbon skeleton as in the original molecule.
Several methods are known for the synthesis of paraffins, the structure of the carbon chain of which differs from the starting substances. Monohalogen derivatives of alkanes, when interacting with sodium metal, are converted into saturated hydrocarbons by the Wurtz reaction. During the reaction, it is formed carbon-carbon bond between carbon atoms bonded in the parent compound to halogens.
The Wurtz reaction can be used exclusively for the synthesis of symmetrical alkanes (R-R) with an even number of carbon atoms. To avoid the formation of mixtures of alkanes, only one halogen derivative must be introduced into this reaction.
The limitations of the Wurtz reaction are clear from the following example.
The reaction produces a mixture of propane, ethane and n-butane. Since the reaction rates are similar, it is impossible to propose conditions under which propane formation would be the predominant process. Consequently, two thirds of the starting materials will be wasted. In addition, the difficult problem of separating the reaction products arises.
Caution must be exercised when extending the Wurtz reaction to more complex halogen derivatives. Alkali metals are very reactive. If a molecule contains functional groups in addition to the halogen atom, in most cases the reaction of sodium or potassium with them will proceed faster than with the halogen. It makes no sense to even try to carry out the Wurtz reaction if the molecule, along with the halogen, contains hydroxy- (OH), carboxy- (COOH), sulfo- (SO 3 H) and many other groups.
One of the methods for producing alkanes is the decarboxylation reaction (elimination of CO 2) of salts of carboxylic acids. In some cases, this process occurs very easily even with slight heating. Saturated carboxylic acids of the aliphatic series remove the carboxyl group only when their salts are calcined with an alkali.
As a result of decarboxylation, an alkane is formed containing one less carbon atom than was present in the original acid.
If a salt of a carboxylic acid of an aliphatic series is subjected to electrolysis (Kolbe anodic synthesis), then at the anode the carboxylate anion donates one electron to the electrode, turning into an unstable radical. The release of CO 2 leads to an alkyl radical. When two alkyl radicals recombine, a symmetrical alkane with an even number of carbon atoms is formed.
Lecture No. 8
Hydrocarbons
· Alkenes. Homologous series, nomenclature, types of isomerism. Geometric isomerism in the series of alkenes. Cis- And trance- isomers, E,Z nomenclature. Reasons for the lack of free rotation relative to the double bond. Physical properties, patterns of their changes in the homologous series and spectral characteristics of alkenes.
· Preparation methods: dehydrogenation of alkanes, petroleum cracking, partial hydrogenation of alkynes, dehalogenation, dehydrohalogenation of haloalkanes and dehydration of alcohols (Zaitsev’s rule).
Alkenes (olefins, ethylene hydrocarbons)
Alkenes - open-chain hydrocarbons corresponding to the general formula C n H 2 n and containing one double bond (p-bond) in the molecule .
Compared to alkanes, the corresponding ethylene hydrocarbons form a greater number of isomers, which is due not only to differences in carbon skeletons, but also to the location of the double bond and the geometry of the molecule.
Let's consider the isomerism of alkenes with four carbon atoms. In addition to structural isomers, there are isomers of the position of the double bond (butene-1 and butene-2). Butene-2 can exist in the form of two isomers, differing in the spatial arrangement of substituents relative to the double bond. Since free rotation about the p-bond is impossible (barrier 60 kcal) and the entire fragment of the molecule lies in the same plane, the methyl groups can be located either on one side of the double bond or on opposite sides. The first names use the prefix cis- (on the one hand - lat.), on the second - trance- (via – lat.). This type of spatial isomerism is called geometric.
2.1. Reaction of Butlerov A.M.
Preparation of sugars from formaldehyde under the action of alkalis:
The reaction results in a mixture of sugars.
2.2. Wagner's reaction E.E.
Oxidation of alkenes in cis - α - glycols by the action of a dilute solution of potassium permanganate in an alkaline medium (hydroxylation):
2.3. Wurtz reaction
Preparation of hydrocarbons by condensation of alkyl halides under the action of metallic sodium:
2.4. Wurtz-Grignard reaction
Formation of hydrocarbons during the reaction of alkyl (aryl) halides with a Grignard reagent:
2.5. Wurtz-Fittig reaction
Preparation of fatty aromatic hydrocarbons by condensation of aromatic halogen derivatives with alkyl halides in the presence of sodium:
2.6. Harries' reaction
Oxidative cleavage of alkenes by ozonation and subsequent hydrolysis (ozonolysis):
2.7. Gutterman-Koch reaction
The reaction of formylation of aromatic hydrocarbons by the action of carbon monoxide and hydrogen chloride in the presence of AlCl 3:
2.8. Gell-Volhard-Zelinsky reaction
Preparation of α-halogenated acids by the action of chlorine or bromine in the presence of phosphorus:
2.9. Hoffmann reaction
Preparation of aliphatic amines by alkylation of ammonia with alkyl halides:
2.10. Hoffmann reaction (rearrangement)
Rearrangement of acid amides into primary amines with the loss of one carbon atom in a solution of hypochlorites:
2.11. Grignard reactions (organomagnesium synthesis)
Reactions for the synthesis of organic compounds based on the addition of a Grignard reagent to the >C = O bond:
2.12. Diels-Alder reaction (diene synthesis)
Addition of compounds with an activated double bond (dienophiles) to conjugated dienes to form cyclic structures. The connection is made according to type 1.4:
2.13. Sandmeyer reaction
Replacement of a diazo group in aromatic compounds with a halogen or another group by the action of monovalent copper salts:
2.14. Zelinsky's reaction
Preparation of α - amino acids from aldehydes or ketones by the action of a mixture of potassium cyanide and ammonium chloride (ammonium cyanide):
2.15. Zinin's reaction
Reduction of aromatic nitro compounds into amines:
Zinin used ammonium sulfide for reduction; in industry, cast iron shavings are used in an acidic environment to reduce nitro compounds.
2.16. Jocić's reaction
Preparation of alkynylmagnesium halides (Jocic reagents) using the Grignard reagent:
2.17. Cannizzaro's reaction
Redox disproportionation of two molecules of aromatic aldehyde into the corresponding alcohol and acid under the action of alkalis. This reaction also involves aliphatic and heterocyclic aldehydes that do not contain mobile hydrogen in the α position:
Cannizzaro cross reaction
2.18. Claisen reaction (condensation)
Preparation of cinnamic acid esters by condensation of aromatic aldehydes with carboxylic acid esters and carbonyl compounds.
2.19. Kolbe reaction
Production of hydrocarbons by electrolysis of solutions of alkaline salts of aliphatic carboxylic acids:
At the anode, the acid anion is discharged into an unstable acid radical, which decomposes with the release of carbon dioxide, and the resulting alkyl radicals couple into a hydrocarbon:
2. 20. Kolbe-Schmitt reaction
Preparation of aromatic hydroxy acids by thermal carboxylation of alkali metal phenolates with carbon dioxide:
2. 21. Konovalov’s reaction
Nitration of aliphatic, alicyclic and fatty-aromatic compounds with nitric acid (12-20%):
2.22. Kucherov's reaction
Catalytic hydration of acetylene, its homologues and derivatives with the formation of aldehydes and ketones:
a) when acetylene is hydrated, acetaldehyde is obtained:
b) hydration of acetylene homologues produces ketones:
2.23. Lebedev's reaction
Preparation of butadiene by catalytic pyrolysis (450˚C) of ethyl alcohol:
2.24. Perkin reaction
Preparation of α,β - unsaturated acids by condensation of aromatic aldehydes with carboxylic acid anhydrides:
2.25. Raschig reaction
Industrial production of phenol by catalytic chlorination of benzene followed by hydrolysis of chlorobenzene with water vapor:
2.26. Reformatsky's reaction
Preparation of β - hydroxycarboxylic acids by the interaction of aldehydes or ketones with esters of α - halocarboxylic acids under the influence of metallic zinc:
2.27. Rodionov's reaction
Preparation of β - amino acids by condensation of aldehydes with malonic acid and ammonia in an alcohol solution:
2.28. Tishchenko's reaction
Condensation of aldehydes to form esters under the influence of aluminum alcoholates:
2.29. Favorsky's reaction
Interaction of alkynes with aldehydes and ketones:
2.30. Friedel-Crafts reaction
Alkylation or acylation of aromatic compounds with alkyl or acyl halides in the presence of aluminum chloride:
a) alkylation:
b) acylation:
2.31. Chichibabin reaction
Reaction of pyridine with sodium amide (α-amination):
2.32. Chugaev-Tserevitinov reaction
The interaction of organic compounds containing a mobile hydrogen atom with the Grignard reagent with the release of methane:
2.33. Schiff reaction
The interaction of aldehydes with amines in the presence of alkali leads to the formation of azomethines (Schiff bases):
2.34. Strecker reaction
Preparation of α - amino acids from aldehydes and ketones by the action of ammonia and hydrocyanic acid, followed by hydrolysis of the resulting aminonitriles:
2.35. Yuryev's reaction
Wurtz reaction
The Wurtz reaction is of limited use because it results in the joining of two alkyl groups and thus an alkane with more carbon atoms than the starting materials. In this way, ethane can be obtained from methyl bromide, n-butane from ethyl bromide, and 2,3-dimethylbutane from isopropyl bromide.
The Wurtz reaction is only suitable for the synthesis of symmetrical alkanes R-R. For example, propane cannot be obtained with good yield using this method. If sodium reacts with a mixture of methyl bromide and ethyl bromide, propane is indeed formed; but it will be mixed with ethane, formed by combining two methyl groups, and n-butane, formed from two ethyl groups. A significant amount of reagents is spent on the formation of unnecessary products; In addition, the problem of separation arises. Therefore, the Wurtz reaction is unsuitable for the synthesis of unsymmetrical R-R alkanes (R and R are different alkyl groups).
Although many reactions of simple alkyl halides can be extended to more complex halogen-containing compounds, this is not the case with the Wurtz reaction. Sodium metal is a very reactive substance, and it will react not only with a halogen, but with any other group that may be present in a more complex compound. For example, the Wurtz reaction cannot be used for compounds that contain an HO group in addition to a halogen, since sodium will react with the hydroxyl group faster than with the halogen.
The mechanism of the Wurtz reaction is complex and not yet fully understood, but it is clear that the reaction first produces an organosodium compound similar to the organomagnesium compound described above, RX + +2Na = RNa + NaX, which then reacts with a second alkyl halide molecule RNa + RX = R ?R+NaX (Grignard reagent is less reactive than organosodium: it reacts only with some very reactive organic compounds.)
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WURZ REACTION– a chemical reaction that allows one to obtain the simplest organic compounds - saturated hydrocarbons.
The Wurtz reaction itself consists of the condensation of alkyl halides under the action of metallic Na, Li, or less commonly K:
2RHal + 2Na ® R–R + 2NaHal.
Sometimes it is interpreted as the interaction of RNa or RLi with R"Hal.
The reaction was discovered by the French organic chemist Charles Wurtz (1817–1884) in 1855 while attempting to obtain ethyl sodium from ethyl chloride and sodium metal.
Although the Wurtz reaction results in the formation of a new carbon-carbon bond, it is not often used in organic synthesis. Basically, it is used to obtain saturated hydrocarbons with a long carbon chain, it is especially useful in obtaining individual hydrocarbons of high molecular weight, and, as can be seen from the diagram above, to obtain a given hydrocarbon, only one alkyl halide should be taken, since the condensation of two alkyl halides results in a mixture all three possible combination products. Therefore, if an alkyl halide and sodium are used, the Wurtz reaction can only produce hydrocarbons with an even number of carbon atoms. The Wurtz reaction occurs most successfully with primary alkyl iodides. Very low yields of the target product are obtained using the Wurtz method for secondary alkyl halides. The reaction is usually carried out in diethyl ether. The use of hydrocarbons as solvents reduces the selectivity of the reaction.
However, if you use a pre-prepared organometallic compound, for example alkyllithium, you can also obtain asymmetrical condensation products:
RLi + R"Hal ® R – R" + LiHal
In both cases, the reaction is accompanied by the formation of a large number of by-products due to side processes. This is illustrated by an example of the interaction of ethyl lithium with 2-bromooctane:
In this case, 3-methylnonane and a number of by-products in the indicated molar ratios are formed as a product of the Wurtz reaction.
In addition to sodium, metals such as silver, zinc, iron, copper and indium were used in the Wurtz reaction.
The Wurtz reaction has been successfully used for intramolecular condensations to construct carbocyclic systems. Thus, cyclopropane can be obtained from 1,3-dibromopropane under the action of metallic zinc and sodium iodide (as a reaction promoter):
Other strained carbocyclic systems can be constructed. For example, from 1,3-dibromoadamantane, using a sodium-potassium alloy, 1,3-dehydroadamantane can be obtained:
And the interaction of 1-bromo-3-chloro-cyclobutane with sodium leads to bicyclobutane:
There are a number of known varieties of the Wurtz reaction, which have received their own names. These are the Wurtz–Fittig reaction and the Ullmann reaction. The first involves the condensation of an alkyl and aryl halide under the action of sodium to form an alkyl aromatic derivative. In the case of the Ullmann reaction, aryl iodides are usually introduced into the condensation, and freshly prepared copper is used instead of sodium; this reaction makes it possible to obtain various biaryl derivatives in high yield, including unsymmetrical ones containing a substituent in one of the aromatic nuclei:
The Wurtz reaction mechanism is believed to consist of two main stages:
1) formation of an organometallic derivative (if a metal is used and not a pre-prepared organometallic compound):
RHal + 2Na ® R–Na + NaHal,
2) interaction of the organosodium compound formed, in this case, with another alkyl halide molecule:
RHal + R–Na ® RR + NaHal.
Depending on the nature of R and the reaction conditions, the second stage of the process can proceed by an ionic or radical mechanism.
Vladimir Korolkov
