Reductive Activation of Arenes. XI. Reaction of Two-Electron Reduction Product of Terephthalodinitrile with Alkyl Halides in Liquid Ammonia

The product of reduction of terephthalodinitrile with two equivalents of metallic potassium reacts with alkyl halides in liquid ammonia to yield 4-alkylbenzonitriles and 2-alkylterephthalodinitriles, whose ratio strongly depends on the alkyl halide and changes in favor of the ipso-substitution product, 4-alkylbenzonitrile, in going from tertiary alkyls to primary and from iodides to chlorides. Using cyclopropylmethyl bromide as model alkylating agent, the reaction was shown to proceed by concurrent nucleophilic substitution (S_N) and electron transfer (ET) mechanisms. Change in the product ratio is the result of increased contribution of the S_N mechanism.