Photo-substitution of 1,2,4,5-tetracyanobenzene by toluene

Abstract

A novel photo-induced reaction involving charge-transfer excitation is described. Irradiation of a solution of 1,2,4,5-tetracyanobenzene in toluene with a medium-pressure mercury arc gave 1-benzyl-2,4,5-tricyanobenzene with a small amount of bibenzyl. Irradiation at the frequency of a charge-transfer band of the 1,2,4,5-tetracyanobenzene–mesitylene system with acetone-filtered u.v. light gave the analogous product, indicating that the reaction proceeds through a charge-transfer mechanism. The reaction was quenched in the presence of trifluoroacetic acid. The structure of the intermediate was deduced on the basis of results obtained by using [α-²H₃]toluene. Substituted toluenes underwent the same type of reaction; the effect of substituents on product yields is discussed.