Liquid-Phase Oxidation of Deactivated Methylbenzenes by Aqueous Sodium Hypochlorite Catalyzed by Ruthenium Salts under Phase-Transfer Catalytic Conditions

Toluene and methylbenzene ring substituted with electron-withdrawing substituents were oxidized to the corresponding carboxylic acids. The oxidation system is biphasic consisting of an organic substrate phase and an aqueous sodium hypochlorite phase with both ruthenium and quaternary ammonium salts acting as catalysts. Yields are essentially quantitative after 2 h at room temperature with a stoichiometric ratio hypochlorite/toluene of 4.5:1 provided the pH of the aqueous phase is between 8.0 and 10.5. Kinetic studies show the reaction to be of first order in the substrate, zero order in sodium hypochlorite, and combined first order in the catalysts. The reaction mechanism consists of a Ru0₄-catalyzed hydride abstraction and a phase-transfer-catalyzed proton-dependent step.