THE MECHANISM OF PHOTOCHEMICAL CHAIN SUBSTITUTION OF CHLORINE BY SULFO 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 s ulphite is observed. There are two mechanisms of photoinitiation of a chain reaction: the interaction of the triplet molecule of substrate w ith its nonexcited molecule and an electron photoejection. Independent ly of the mechanism of photoinitiation two intermediates- a radical an ion of 4-chloro-1-hydroxynaphthoxide anion and 4-chloro-1-naphthoxy ra dical are formed. Naphthoxy radicals react with reducing agents (sodiu m sulphite, potassium iodide) forming sulphite radical anions. The for mation of two different radical anions leads to two competitive mechan isms of the chain substitution reaction: an S(RN)1 mechanism and a mec hanism with the participation of sulphite radical anions. (C) 1997 Els evier Science S.A.