The mechanism of photochemical chain substitution of chlorine by sulpho group in 4-chloro-1-hydroxynaphthalene

On irradiation of 4-chloro-1-hydroxynaphthalene in aqueous solution of sodium sulphite the chain photosubstitution reaction of chlorine by sulphite is observed. There are two mechanisms of photoinitiation of a chain reaction: the interaction of the triplet molecule of substrate with its nonexcited molecule and an electron photoejection. Independently of the mechanism of photoinitiation two intermediates- a radical anion of 4-chloro-1-hydroxynaphthoxide anion and 4-chloro-1-naphthoxy radical are formed. Naphthoxy radicals react with reducing agents (sodium sulphite, potassium iodide) forming sulphite radical anions. The formation of two different radical anions leads to two competitive mechanisms of the chain substitution reaction: an S(RN)1 mechanism and a mechanism with the participation of sulphite radical anions. (C) 1997 Elsevier Science S.A.