Isonitriles reaction with halogens

Treatment of alkylating agents with metal cyanides should in principle be the method of choice for preparing isocyanides (equation 25). But as the cyanide ion again represents an ambident nucleophile, the well-known problems already discussed will arise (Section 1.8.2.1.i). It remains to be stated that simple alkylation of alkali metal cyanides with halogen compounds or dialkyl sulfates is not useful for the preparation of isonitriles. The formation of nitriles always prevails and isocyanides are at best obtained in yields of up to 25%. " The prospects are much tetter in the alkylation of heavy metal cyanides, if the reaction is done under conditions which initially give rise to isocyanide-transition metal complexes (equation 26). These will then be transformed into isonitriles by treatment with KCN. Under optimized conditions this technique yielded 55% of ethyl isocyanide. ... 

Reactions at o -Position. Many studies have been concerned with the reactions of alkyl halides with cyanide in the presence of various metal ions, and with the direct alkylation of cyanide complexes. The classic synthesis of isonitriles was accomplished by the use of silver cyanide, whereas the corresponding reaction of organic halogen compounds with alkali cyanides yields nitriles (Equations 40 and 41) (34,36). 

Reaction XLVm. (a) Action of Alkali Cyanides on Alkyl and Acyl Halides. (Bl., [2], 50, 214.)—This reaction is capable of very wide application, all the simple alkyl halogen compounds, the acyl halides, and the halogen fatty acids come within its scope. The nitriles so formed yield acids by hydrolysis, so it is frequently the first step in the synthesis of an acid—the preparation and hydrolysis of the nitrile are often combined. The preparations of malonic, succinic, tricarballylic and other acids (Preparations 60, 61, 62) illustrate this. The extension of this reaction to acyl halides is important, and should be referred to, as should the interaction of silver cyanide, and alkyl iodides, to give isonitriles. Mercuric and silver cyanides, it may be noted, give with acyl chlorides and bromides better yields of normal acyl nitriles than do the alkali cyanides. 

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