Displacement with cyanide ion on an alkyl halide

The classical procedure for the reaction involves heating the alkyl halide (usually the chloride or bromide) with sodium or potassium cyanide in metha-nolic or ethanolic solution. The method is clearly of value for the extension of the carbon chain by one carbon atom, since the cyano group may be converted into a carboxyl group by hydrolysis (Section 5.11.2, p. 671) or into an amino-methyl group (—CH2-NH2) by reduction (Section 5.16.1, p. 771), or into a formyl group by controlled reduction to the imine followed by hydrolysis (Section 5.7.4, p. 594).  

This method has been widely used for primary and secondary halides tertiary halides undergo ready elimination under these conditions to yield the alkene and give little or no nitrile. Traces of the corresponding isonitriles (R-NC) may be formed during these displacement reactions but may be removed by virtue of 

Aprotic solvents such as dimethyl sulphoxide or dimethyl formamide significantly improve the procedure in that the less reactive alkyl chlorides are more rapidly converted into the nitriles in good yield by sodium cyanide (Expt 5.158). 

Three PTC methods are worthy of note. In the first the alkyl halide is treated with sodium cyanide in decane solution in the presence of catalytic amounts of hexadecyltributylphosphonium bromide.1673 In the second tetraethylammo-nium cyanide in molar quantities is used in dichloromethane solution with the alkyl halide.1676 In the third method, which is reported to be most satisfactory in the case of allylic and benzylic halides, a solid/liquid system of potassium cyanide and 18-crown-6 ether is employed.168 

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Displacement with cyanide ion on an alkyl halide. (Expt 5.157 and 5.158). 

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