Characteristics of cationic phase-transfer catalysts in the oxidation of hydrocarbons by O-2

The oxidation of tetralin and cyclohexene by O-2 was investigated in the pr esence of cationic phase-transfer catalysts (PTCs). It was found that the o xidation takes place analogously to the recently investigated catalysed dec ompositions of hydroperoxide initiator molecules. The natures of both the o nium cation and the counteranion are determining factors. The catalytic act ivity of the onium salt is determined by the effective charge on the onium ion and by the size and polarizability of the anion. For both hydrocarbons, the primary product of oxidation is the corresponding hydroperoxide, which may undergo further oxidation. For tetralin, tetralyl hydroperoxide underw ent disproportionation into O-2 and tetralol, and reuse of the O-2 thus pro duced resulted in a considerable "overoxidation'' in the closed reactor. Te tralone was formed in a smaller amount. The main products in the oxidation of cyclohexene were its hydroperoxide, cyclohexene oxide and 2-cyclohexen-1 -ol. In contrast to the oxidation of tetralin, "overoxidation'' did not occ ur here, and the formation of 2-cyclohexen-1-one was never observed. The ox idations of these hydrocarbons in the presence of cationic PTCs proved to b e strongly influenced by the concentration of homogeneously dissolved water . The oxidation products of these hydrocarbons also exerted considerable in fluence on the progress of the oxidation.