Wurtz reaction mechanism

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. ... 

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). 

The mechanism is not known with certainty. It seems likely that it is basically a two-step process, similar to that of the Wurtz reaction (10-93), which can be represented schematically by... 

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 ... 

Richards, R. B. Mechanism of the Wurtz reaction. Transactions of the Faraday Society 1940, 36, 956-960. 

Malinovskii, M. S., Yavorovskii, A. A. Mechanism of the Grignard-Wurtz reaction. I. Synthesis of some alkaromatic hydrocarbons from benzyl chloride, a-bromoethylbenzene, and a-bromo-a-methylethylbenzene. Zh. Ohshch. Khim. 1955, 25, 2169-2173. 

This mechanism for -elimination is supported by the fact that other processes which would be expected to produce carbanions beta to groups easily displaced also cause elimination to occur. It is well known that Grignard and Wurtz reactions of 0-haloethers lead to olefins. Tetra-hydrofurfuryl chloride, for example, gives 4-pentene-l-ol on treatment with sodium,8 and 0-bromoethyl phenyl ether yields phenol and ethylene4 when it is allowed to react with magnesium in dry ether. Presumably the mechanisms are ... 

It has been pointed out by Morton, however, that although a free radical mechanism has been neither proved nor disproved, it is nevertheless possible to interpret the Wurtz reaction on the basis of the two steps, A and B,7... 

The mechanism of Freund reaction is more likely as same as the Wurtz reaction, a free-radical mechanism. In the presence of iodide ions, the pathways might be a combination of substitution (SnI or Sn2) with a free-radical mechanism. ... 

Faraday, in 1834, was the first to encounter Kolbe-electrolysis, when he studied the electrolysis of an aqueous acetate solution [1], However, it was Kolbe, in 1849, who recognized the reaction and applied it to the synthesis of a number of hydrocarbons [2]. Thereby the name of the reaction originated. Later on Wurtz demonstrated that unsymmetrical coupling products could be prepared by coelectrolysis of two different alkanoates [3]. Difficulties in the coupling of dicarboxylic acids were overcome by Crum-Brown and Walker, when they electrolysed the half esters of the diacids instead [4]. This way a simple route to useful long chain l,n-dicarboxylic acids was developed. In some cases the Kolbe dimerization failed and alkenes, alcohols or esters became the main products. The formation of alcohols by anodic oxidation of carboxylates in water was called the Hofer-Moest reaction [5]. Further applications and limitations were afterwards foimd by Fichter [6]. Weedon extensively applied the Kolbe reaction to the synthesis of rare fatty acids and similar natural products [7]. Later on key features of the mechanism were worked out by Eberson [8] and Utley [9] from the point of view of organic chemists and by Conway [10] from the point of view of a physical chemist. In Germany [11], Russia [12], and Japan [13] Kolbe electrolysis of adipic halfesters has been scaled up to a technical process. 

Chemical "affinity" remained part of the tool kit of the chemist, however badly defined and understood. Affinity cannot simply be explained away as heat, insisted Wurtz, a leading advocate of chemical and physical atomism in France in the generation following Dumas.58 As we will see in chapter 5, "energy" replaced "affinity" in the late 1800s as the driving force of chemical reactions. In addition, the concepts of spontaneity and irreversibility entered the domain of physics, undermining the classical mechanics of matter and force in which processes are, in principle, reversible. Conceptually, the notions of spontaneity and irreversibility were more closely allied with experimental results in classical chemistry than in classical physics. 

Summary Reacticm of a-heteroatom-substituted oligosilanes with potassium alkoxides is of interest to obtain insight into the mechanism of the Wurtz type polymerization of halosilanes. It also provides access to building blocks with unique reactivity. Reactions with fluoro- and methoxy-substituted silanes exhibited initial formation of silylenoid species which can undergo self-condensation. This property is less pronounced with the alkoxysilanes, which allowed for the isolation and structural characterization of an a-methoxy-silyl potassium compound (3). 

The mechanism of the Wurtz coupling is not well understood, and the currently accepted mechanism involves two steps 1) formation of a carbanionic organosodium compound via metal-halogen exchange and 2) the displacement of the halide ion by the organosodium species in an Sn2 reaction. Alternatively, a radical process can also be envisioned, although to date there has been no experimental evidence to support this assumption. 

Gilman, H., Wright, G. F. Mechanism of the Wurtz-Fittig reaction. The direct preparation of an organo-sodium (potassium) compound from an RX compound. J. Am. Chem. Soc. 1933, 55, 2893-2896. 

Emblem, H. G., Ridge, D., Todd, M. Mechanism of the Wurtz-Fittig reaction between organic halides, tetrachlorosilane, and sodium. Chem. Ind. 1955, 905-906. 

Anteunis, M., van Schoote, J. Grignard reaction. VII. Mechanism of the Grignard reagent formation and the Wurtz side reaction in ether. 

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