HETEROGENEOUS PHOTOCATALYSIS .15. MECHANISTIC ASPECTS OF CADMIUM SULFIDE-CATALYZED PHOTOADDITION OF OLEFINS TO SCHIFF-BASES

A methanolic suspension of cadmium sulfide powder photocatalyzes the a ddition of cyclopentene and cyclohexene to imines affording gamma,delt a-unsaturated amines and the hydrodimer of the imine as a by-product. The product ratio is not dependent on the light intensity, but changes in favor of the hydrodimer when the amount of photocatalyst is increa sed. Measurement of the imine dark adsorption reveals the presence of multilayer adsorption. At concentrations below 0.5 mmol l(-1), Langmui r behavior is observed, from which an adsorption equilibrium constant of 4400 +/- 950 l mol(-1) can be calculated for the imine; the value o btained by a novel ''in situ'' determination of the dependence of the initial rate on the imine concentration affords a value of 2000 l mol( -1). The adsorption constants of cyclopentene and cyclohexene, as dete rmined from the conventional rate-concentration dependence, are in the region of 15 l mol(-1) and suggest that both olefins adsorb onto the same surface sites. This is supported by competition experiments. (C) 1997 Elsevier Science S.A.