Wurtz reaction halides

Two mechanisms have been proposed for the Wurtz reaction (compare Section III,7) and for the Wurtz-Fittig reaction. According to one, sodium reacts with the alkyl halide to produce a sodium halide and a free radical, which subsequently undergoes coupling, disproportionation, etc. ... 

The coupling of alkyl halides 1 upon treatment with a metal, e.g. elemental sodium, to yield symmetrical alkanes 2, is called the Wurtz reaction. Aryl alkanes can be prepared by the Wurtz-Fittig reaction, i.e. the coupling of aryl halides with alkyl halides. 

Somewhat similar observations have been made in the reaction of alkyl halides with sodium mirrors (the Wurtz reaction) in which alkyl coupling occurs. Thus, ethane formed on treatment of methyl iodide with sodium in a field of 20 G shows n.m.r. emission (Garst and Cox, 1970). The phase is consistent with polarization via T j-S mixing,... 

It seems likely that the mechanism of the Wurtz reaction consists of two basic steps. The first is halogen-metal exchange to give an organometallic compound (RX -(- M —+ RM), which in many cases can be isolated (12-36). Following this, the organometallic compound reacts with a second molecule of alkyl halide (RX + RM —> RR). This reaction and its mechanism are considered in the next section (10-94). 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds, but it has also been carried out with many other metals, (e.g., Na, Be, Zn, Hg, As, Sb, and Sn). With sodium, the Wurtz reaction (10-93) is an important side reaction. In some cases, where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyl lead from ethyl bromide and a Pb—Na alloy. 

This is, of course, the Wurtz reaction, and support for such a mechanism involving carbanions (radicals may be involved under some conditions, however) is provided by the observation that in some cases it is possible, with optically active halides, to demonstrate inversion of configuration at the carbon atom undergoing nucleophilic attack. The carbanion, e.g. (61), can also act as a base and promote elimination ... 

The Grignard compounds react with varying ease with organic halides in the manner of the Wurtz reaction according to the equation ... 

Alkyl halides react with sodium In dry ether to give hydrocarbons containing double the number of carbon atoms present In the halide. This reaction Is known as Wurtz reaction. (Unit 13, Class XI). 

The procedure provides a good example of a high-yield intramolecular Wurtz reaction. Internjolecular Wurtz reactions normally do not give high yields of coupled products and are accompanied by formation of alkenes and alkanes corresponding to the alkyl halide.7 In contrast, intramolecular reactions of... 

Sodium displaces halogens from alkyl halides forming alkanes (Wurtz reaction) ... 

Coupling of Alkyl Halides. The Wurtz Reaction De-halogen-coupling... 

In the Wurtz Reaction, both halides are alkyl. For the Wurtz-Fittig Reaction, there is one alkyl and one aryl group, while in the Fittig Reaction, both coupling partners are aryl halides. 

As stated above, intermolecular coupling reactions between carbon atoms are of limited use. In the classical Wurtz reaction two identical primary alkyl iodide molecules are reduced by sodium. n-Hectane (C100H202), for example, has been made by this method in 60% yield (G. Stallberg, 1956). The unsymmetrical coupling of two alkyl halides can be achieved via dialkylcuprates. The first halide, which may have a branched carbon chain, is lithiated and allowed to react with copper(I) salts. The resulting dialkylcuprate can then be coupled with alkyl or aryl iodides or bromides. Although the reaction probably involves radicals it is quite stereoselective and leads to inversion of chiral halides. For example, lithium diphenyl-cuprate reacts with (R)-2-bromobutane with 90% stereoselectivity to form (S)-2-phenylbutane (G.M. Whitesides, 1969). 

The Wurtz-Fittig reaction (cf. the Wurtz reaction, Section 5.1.4, p. 478). The interaction of an aryl halide, an alkyl halide and sodium gives a reasonable yield of an alkylbenzene. 

Wurtz reaction the coupling of two alkyl halide molecules to form an alkane. 

Sodium Condensation. The coupling of an organic halide and a silicon halide by reaction with metallic sodium (the so-called Wurtz reaction) vras first applied by Pape in 1884. Silicon tetrachloride and isoamyl or isobutyl chloride were found to react with sodium at reflux temperatures when a little ethyl acetate was added to get the reaction started ... 

In this Wurtz reaction, all i groups of these all i halides will bond to each other on the second carbon and 3,4 - dimethylhexane will be formed. 

To produce 2 - methylpropane by a Wurtz reaction, which two alkyl halides should be reacted together ... 

Reduction of halides. Benzylic and allylic halides are dimerized in good yield by the complex of copper metal and cyclohexylisonitrile (Wurtz reaction). Secondary halides are dimerized in low yield, and primary halides do not react. The system is less active than Cu(I) salts and resembles potassium graphite. 

Earlier we mentioned the Wurtz reaction as being one of the simplest approaches to the formation of C-C bonds. In this reaction, the alkyl halide serves as the electrophile (carbocation equivalent) and the organometallic derivative plays the role of the nucleophile (carbanion equivalent). We have also seen that this old reaction has recently become a feasible route for the creation of C-C bonds due... 

Williamson s S3mthesis.—This reaction is known as Williamson s synthesis because, in 1851, he showed, by it, the true constitution of ether, and made possible the explanation of its preparation from alcohol and sulphuric acid as given a little later on. The reaction is similar to the Wurtz reaction between sodium and an alkyl halide by which a hydrocarbon is formed. 

Alkyl Derivatives.—When this sodium salt reacts with an alkyl halide the reaction is analogous to the Wurtz reaction, the sodium is exchanged for the alkyl radical, and an alkyl derivative of the ester is obtained. 

The coupling of alkyl halides by treatment with sodium to give a symmetrical product is called the Wurtz reaction. Side reactions (elimination and rearrangement) are so common that the reaction is seldom used. Mixed Wurtz reactions of two alkyl halides are even less feasible because of the number of products obtained. A somewhat more useful reaction (though still not very good) takes place when a mixture of an alkyl and an aryl halide is treated with sodium to give an alkylated aromatic compound (the Wurtz-Fittig reaction)... 

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