OXIDATION OF NITROBENZENE, CHLOROBENZENES AND CHLOROPHENOLS USING LIQUID-PHASE RUTHENIUM CATALYSTS

Ruthenium trichloride and various ruthenium(II) complexes, such as [Ru (H2O)(2) (L)(4)](BF4)(2) and [RuCl2(L)(4)] (L=DMSO), are effective cat alysts for the complete oxidation of substituted aromatics at ambient temperature and in the liquid phase (double phase or water with suitab le amounts of a surfactant agent) in the presence of an oxidizing agen t, preferably monopersulfate. The oxidation of benzoic acid, chloro-, bromo-, iodo- and nitrobenzene and a number of polychlorobenzenes and polychlorophenols was followed by monitoring the nature and the relati ve amounts of the final products; chlorinated substrates are mainly co nverted into hydrochloric acid and carbon dioxide. Factors such as sol vent, substrate, oxidant and concentration affect the reactions. The m ost favorable reaction conditions require the presence of polar media, like nitromethane or water. The fate of the catalyst during the vario us stages of the reactions was followed, which gave indications of the nature of the active species involved. The overall results imply that a strongly oxidizing ruthenium derivative is responsible for the effe ctive oxidation with monopersulfate, tentatively a highly reactive per oxoruthenium species [Ru-O-O-SO3H]. Oxidation of chlorobenzene is firs t order in both the substrate and the catalysts and an n (or inverse) kinetic isotope effect is measured. The rates of the oxidation of mono -substituted benzenes depend upon the degree of deactivation of the ar omatic ring, thus suggesting an initial electrophilic attack followed by a series of faster steps. Phenol and polychlorophenols are more sen sitive to oxidation than substituted benzenes.