Photoinitiation mechanism of the tris(2,2'-bipyridyl)ruthenium(II)-sensitized chain reaction of radical ion substitution of a sulpho group for bromine in 1-bromo-2-hydroxynaphthalene

V.L. Ivanov and A.B. Artyukhin

High Energy Chemistry, v.32 (5), p. 333-338 (1998), translated from Russ. Khimia Vysokikh Energii, v.32 (5), p. 372-377 (1998)

ABSTRACT. The substitution reaction of bromine by sulpho group proceeds upon irradiation of the tris(2,2'-bipyridyl)ruthenium(II) complex in the presence of 1-bromo-2- hydroxynaphthalene in an aqueous solution of sodium sulphite. This is a chain reaction because the quantum yield is higher than unity at low light intensity and at high concentrations of substrate and reagent. The quantum yield of initiation was found to depend upon, on one hand, quenching of luminescence of the ruthenium complex by both bromonaphthol and sulphite ions and, on the other hand, the yield of free radical ions from ion-radical pairs. The yield of the univalent ruthenium complex or correspondingly, the sulphite radical ion from the ion-radical pair univalent ruthenium complex with sulphite radical anion depends on sodium sulphite concentration and is 0.34 at a concentration of 0.2 mol/l. The yield of naphthoxy radicals from the ion-radical pair univalent ruthenium complex with naphthoxy radical depends only slightly on the sodium sulphite concentration and is 0.07 at a concentration of 0.2 mol/l.

Laboratory of Photochemistry