Hydrocyanation of Acetylene

HYDROCYANATION 01 UNSATURATED HYDROC ARBONS 2.1.1. Hytirocyanation of Acetylene 

This reaction was once regarded as an important industrial process, since it afforded a straightforward synthesis of acrylonitrile from acetylene  

Tlte method is now obsolete for the preparation of acrylonitriles as it has been replaced by the ammonoxidation processes of propylene. The catalyst is a solution of CU2CI3 in water containing HCI and an alkali chloride. Similarly, the addition of cyanogen chloride and acetylene is a copper catalyzed reaction. 

A mechanism based on CuCN addition to the coordinated acetylene molecule has been proposed, where, in fact, the acid additive assists the Cu-C cleavage 113]. 

Prunza [14], however, has proposed an ionic copper complex wltich is suitable for direct nucleophilic substitution by the cyanide ion (Equation (14)). 

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Hydrocyanation of acetylene is catalyzed by an aqueous solution of copper(I) chloride and ammonium chloride however, byproducts are also formed, viz., acetaldehyde and vinylacetylene, the latter arising by dimerization of acetylenes. Hydrocyanation, followed by reduction of alkynes leading to secondary nitriles, is catalyzed by Co(CN)5 in the atmosphere of H2 or by Ni(CN)4 in the presence of BH4 cyanide. 

The production problems with Buna N, which is a copolymer of butadiene and acrylonitrile, required even more tenacity and optimism, but Dr. Bayer was successful in the development of a commercial process for the catalytic hydrocyanation of acetylene for the production of acrylonitrile. This process which was used worldwide for many years has been displaced by the catalytic ammoxidation of ethylene process. 

Z)-Alk-2-enenitriles are also available from the hydrocyanation of acetylenes, which occurs with cis stereospecificity when catalysed by a nickel(O) complex, and from the stereoselective cyanation of vinyl halides, catalysed by tetracyano-cobaltate(i). The latter procedure is equally applicable to the stereoselective synthesis of the corresponding ( )-isomers. Also, the ( )- and (Z)-isomers (17) and (18) react with piperidine with retention of configuration to provide (19) and (20) respectively (Scheme 30). In contrast, the corresponding reaction with sodium methoxide gives rise to the (Z)-isomer only. 

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