Phenylethyl halides elimination reactions

Phenylacetonitrile reacts with alkyl, allyl, and benzyl halides as one would expect (see Eq. 10.1). In the presence of excess alkylating agent and base, dialkylation is usually observed. The yield of alkylation product is usually high with normal alkyl halides (Cl, Br, I) and somewhat lower for secondary halides. There is no report of the successful alkylation of phenylacetonitrile by a tertiary alkyl halide under phase transfer conditions. This is undoubtedly due to the facile dehydrohalogenation reaction of such haloalkanes. It is probably the elimination problem which keeps 2-phenylethyl chloride from alkylating phenylacetonitrile in high yield [23], despite the fact that it is a primary halide. It is not clear why 1-phenylethyl chloride should alkylate the same substrate almost quantitatively under the same conditions [23], although the fact that the latter is a benzyl halide no doubt is part of the reason. 

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