EFFECTS OF WATER AND ONIUM ION PHASE-TRANSFER CATALYST ON THE RATE OFLIQUID-PHASE OXIDATION OF HYDROCARBONS

The liquid-phase oxidations of tetralin, cumene, cyclohexene and methy lcyclohexane were investigated in the presence of water and different types of surfactants. It was found that water first increases, then de creases, the rate of oxidation. Aromatic compounds are oxidised more r eadily than non-aromatic ones. [H2O]max is mostly determined by the co ncentration of hydroperoxide present, and it does not depend on the na ture of the hydrocarbon. H2O and D2O have similar catalytic effects; b oth inhibit the oxidation when applied in a larger excess. Anionic and non-ionic surfactants reduce the catalytic effect of water, because a ccess to the hydroperoxide molecules by the water droplets is consider ably hindered by the surrounding surfactant ions or molecules. In cont rast, cationic surfactants catalyse the oxidation, their efficiencies largely depend on the nature of their anions. It is assumed that the w ater catalysis arises from the H-bonding interaction of the hydroperox ide with the discrete or less-associated water molecules. Water and on ium ion have a joint catalytic effect. The onium-ion pair attacks at t he more nucleophilic O-atom of the hydroperoxide, while the outer O-at om is activated by water, through H-bond formation.