Metal complexes as antioxidants. III. Reaction of nickel dialkyldithiocarbamates and nickel dialkyldithiophosphates with alkyl hydroperoxides

Abstract

Alkyl hydroperoxides are shown to react with nickel dialkyldithiocarbamates and nickel dialkyldithiophosphates in the liquid-phase at 30 °C to generate free radicals. These radicals are capable of inducing the decomposition of the hydroperoxide and destroying the nickel complex. Rates of radical generation, as determined from hydrocarbon autoxidation, are similar to rates of complex disappearance and are ca. 1/5th rates of hydroperoxide disappearance. Rates of disappearance of both reactants are retarded by the addition of hydrogen atom donating antioxidants, the rate of hydroperoxide disappearance is reduced to the rate of radical generation and the rate of complex disappearance is significantly less than the rate of radical generation. These results are consistent with a mechanism for decomposition which involves cycling of the nickel complex. Decomposition of cumene hydroperoxide to α-cumyl alcohol, α-methylstyrene and acetophenone suggests the intermediacy of cumyloxy radicals in this system while the electron spin resonance spectroscopic method indicates that alkylperoxy radicals are also transient intermediates.