Mechanism of the Wurtz reaction. What reactions are characteristic of alkanes? Wurtz reaction definition
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Nominal organic reactions
In organic chemistry, there are a huge number of reactions that bear the name of the researcher who discovered or studied a given reaction.
Named reactions can be found in many organic chemistry reference books, but I want to separate them by class of chemical compound. And, of course, these are not all nominal reactions; these are the reactions that are often encountered in the school course of organic chemistry.
Nominal reactions :
- Wurtz reaction- a “nominal” reaction of chain extension, or more precisely, doubling the number of carbon atoms:
C2H5 Cl + 2Na +Cl C2H5 → C4H10 + 2NaCl (butane was obtained from ethane)
- Konovalov's reaction: With dilute nitric acid under pressure, alkanes are nitrated:
С2H6 + HNO3 (HO-NO2) → С2H5NO2 + H2O (nitroethane)
- Another “nominal” reaction: Kolbe reaction: electrolysis of salts:
2СH3COONa -(electrolysis)-→ СH3-CH3 (ethane) + 2СO2 +2Na
Nominal reactions:
- Joining by Markovnikov's rule:
a hydrogen attaches to the most hydrogenated (= the one with the most hydrogens) carbon atom at a double bond:
C H2=C H-CH3 + H Cl = CH 3-C HCl -CH3
- Reverse reaction - dehydrogenation - Zaitsev's rule— hydrogen is taken away from the most hydrogen-unsaturated (least hydrogenated) carbon atom.
Nominal reactions:
- Kucherov's reaction
CH 3 -C≡CH + H 2 O -> (catalyst - Hg 2+) -> CH 3 -C(=O)-CH 3
Nominal reactions
- The structural formula that we now use, the “birdhouse,” is called Kekule's formula:
- Zinin's reaction- reduction of nitrobenzene and its nitrohomologues:
- Friedel-Kraftz reaction - alkylation of arenes:
How can this be applied to the Unified State Exam? Imagine, there was once a task like this in part B:
Match the nominal reaction or rule with a particular reaction or the desired rule
1. Wurtz reaction 1. 2CH3CH2OH → CH2=CH–CH=CH2 (+ H2; + 2H2O)
2. Kucherov reaction 2. R–H + HNO3 → R–NO2 (+ H2O)
3. Zelinsky reaction 3. 2C2H5I + 2Na → n-C4H10 (+ 2NaI)
4. Konovalov reaction 4. cyclo-C6H12 → C6H6 (+ 3H2)
5. Zinin reaction 5. C2H2 + H2O → CH3CHO
6. Butlerov reaction 6. C6H5NO2 + H2 (H+) → C6H5NH2
7. Markovnikov’s rule 7. CH3CH2CH(OH)CH3 → CH3CH=CHCH3 (+ H2O)
8. Zaitsev’s rule 8. CH3CH2CH=CH2 + HCl → CH3CH2–CHCl–CH3
In general, such tasks - nominal reactions - are rare in the Unified State Exam, but it’s better to know than to rack your brains over such a problem later! And repeating the basic organic reactions again is not superfluous.
![](https://i2.wp.com/distant-lessons.ru/wp-content/uploads/2012/12/obshaja-formula-arenov.png)
. P. Fittig extended the Wurtz reaction to the field of aromatic hydrocarbons
Modern approach to the Wurtz reaction
To overcome many side processes, it has been proposed to use more selective and modern methods. Major developments are being carried out on the use of non-sodium metals. To carry out the Wurtz reaction, silver, zinc, iron and pyrophoric lead are used. The latter reagent allows the reaction to be carried out in the presence of a carboxyl group.
Intramolecular Wurtz reaction
In the 90s of the XIX century. Freund and Gustafson proposed an intramolecular variant. Thus, 1,3-dibromopropane can be successfully converted into cyclopropane by the action of zinc in the presence of sodium iodide as an activator. By this route it was possible to obtain bisspirocyclopropane and bicyclobutane. Later, it was proposed to generate Grignard intermediates, which subsequently, upon the action of silver trifluoroacetate, lead to intramolecular cross-coupling. This method is not applicable for obtaining average cycles.
Links
Wikimedia Foundation. 2010.
See what the “Wurtz reaction” is in other dictionaries:
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
Method for the synthesis of saturated hydrocarbons by the action of metallic sodium 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. on the… … Great Soviet Encyclopedia
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
- ... Wikipedia
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
See Wurtz reaction... Chemical encyclopedia
Preparation of b hydroxycarbonate esters t interaction. aldehydes or ketones with a halocarbon esters present. Zh (the so-called classical P.p.): Differ. aldehydes and ketones (saturated or unsaturated, aromatic, ... ... Chemical encyclopedia
In organic chemistry, there are a huge number of reactions that bear the name of the researcher who discovered or studied a given reaction. Often the names of several scientists appear in the name of the reaction: these may be the authors of the first publication (for example, ... ... Wikipedia
This article is about chemical compounds. For the Canadian aluminum company, see Rio Tinto Alcan... Wikipedia
Charles Adolphe Würtz Charles Adolphe Würtz ... Wikipedia
Books
- The life of remarkable devices, Arkady Iskanderovich Kuramshin, How can a chemist become famous? Very simple! A reaction he discovered, a new substance, or even a reagent may be named after him! But if this is not enough, then such a scientist has one more... Category: Chemical Sciences Series: Scientific Pop of Runet Publisher: AST,
- Life of remarkable devices, Kuramshin A., How can a chemist become famous? Very simple! A reaction he discovered, a new substance, or even a reagent may be named after him! But if this is not enough, then such a scientist has one more... Category:
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, with its help, saturated hydrocarbons with a long carbon chain are obtained, it is especially useful in obtaining individual hydrocarbons of high molecular weight, and, as can be seen from the above diagram, 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
, condensation of alkyl halides under the influence of Na (rarely Li or K) with the formation of saturated hydrocarbons:2RHal + 2Na -> R-R + 2NaHal,
where Hal is usually Br or I. When used in the district, decomp. alkyl halides (RHal and R"Hal) a difficult-to-separate mixture of all possible products (R-R, R"-R", R"-R) is formed.
V. r. proceeds easily if the alkyl halide has a large mol. mass, and the halogen is bonded to the primary C atom. The process is carried out at low temperatures in solvating solutions. Thus, in THF the reaction occurs quickly and with good yield even at -80 °C.
It is assumed that the reaction mechanism includes the formation of radical ions and radicals:
However, the fact that the configuration of certain optically active alkyl halides (for example, 2-chlorooctane in solution with Na) is reversed does not exclude the possibility of heterolytic. mechanism.
the reaction was discovered by S. Wurtz in 1855 and is used mainly for the production of hydrocarbons with a long carbon chain. In other cases, especially when preparing unsymmetrical alkanes, decomp. modifications of V. r., discussed below.
For the synthesis of fatty aromatic. conn. use the Fittig modification (Wurtz-Fittig solution):
ArHal + RHal + 2Na -> Ar-R + 2NaHal
reaction discovered by R. Fittig in 1855. Alkanes are often formed in good yield using the Grignard reagent, e.g.:
Unsymmetrical saturated hydrocarbons are obtained using copperorg. conn.:
A solution similar to V. r. is used for the synthesis of elementoorg. conn. and bicyclic. connection, e.g.:
Lit.: Reactions of organometallic compounds as redox processes, M., 1981, p. 16-38. E.G. Ter-Gabriel.
Useful Internet resources:
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 produce 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, with its help, saturated hydrocarbons with a long carbon chain are obtained, it is especially useful in the preparation of individual hydrocarbons of high molecular weight, and, as can be seen from the above diagram, to obtain a given hydrocarbon, only one alkyl halide should be taken, since when condensing two alkyl halides, a mixture of all three possible coupling products is obtained.
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):
![](https://i2.wp.com/krugosvet.ru/images/1012431_image004.gif)
Other strained carbocyclic systems can be constructed. For example, from 1,3-dibromoadamantane, using a sodium-potassium alloy, 1,3-dehydroadamantane can be obtained:
![](https://i1.wp.com/krugosvet.ru/images/1012431_image006.gif)
And the interaction of 1-bromo-3-chloro-cyclobutane with sodium leads to bicyclobutane:
![](https://i2.wp.com/krugosvet.ru/images/1012431_image008.gif)
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:
![](https://i2.wp.com/krugosvet.ru/images/1012431_image010.gif)
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.
Sources: Internet resources
http://www.krugosvet.ru/enc/nauka_i_tehnika/himiya/REAKTSIYA_VYURTSA.html