The role of onium salts in the oxidation of hydrocarbons by O-2 catalysed by cationic phase-transfer reagents

Experimental and theoretical evidence is presented that cationic phase-tran sfer catalysts promote the homolytic decomposition of hydroperoxide initiat ors into radicals, this being a fundamental step in the catalysis of the ox idation of hydrocarbons by O-2. Such decomposition of the model substance t ert-butyl hydroperoxide (t-BHP) results in O-2, tert-butanol (90-95%) di-te rt-butyl peroxide (5-10%) and traces of CO2. The stoichiometric ratio Delta [t-BHP]/Delta O-2 was found to have a value of 2, independently of the natu re of the counteranion present. It is assumed that the interaction between hydroperoxide and onium cation is mainly electrostatic in nature and that i ts effectivity depends on the positive charge density on the onium cation, which is controlled by the nature and dimensions of the counteranion. The r ole of water in the decomposition of t-BHP is also elucidated.