Photolysis of benzotriazole in alcoholic glass at 77 K

Abstract

The photolysis of benzotriazole (1) in alcoholic glass at 254 nm has been studied by UV absorption, emission, IR, and mass spectroscopies. Bond scission of the N-NH bond of 1 originates from the S1(π,π*) state to give the azo compound 2, having an absorption band at 423 nm and an IR absorption band at 2070 cm-1. This yellow azo intermediate is decomposed thermally or photochemically. Iminocyclohexadienylidene (3) with resonance structures of a carbene (3a) and a biradical (3b) may be produced as a colorless second intermediate. On the basis of reaction product analysis from the rigid-phase photolysis of 1 at 77 K compared to those in liquid solution and gas-phase photolyses, the reaction paths of 3 to yield aniline, o-anisidine, o-ethoxyaniline, and 1-cyanocyclopentadiene are discussed in terms of the spin states of 3. © 1987 American Chemical Society.