The azobis(isobutyronitrile)-initiated autoxidation of γ-terpinene in acetonitrile at 50 °C yields onlyp-cymene and hydrogen peroxide (1:1) in a chain reaction carried by the hydroperoxyl radical, HOO. (Foti, M. C.; Ingold, K. U. J. Agric. Food Chem. 2003, 51, 2758-2765). This reaction is retarded by very low (μM) concentrations of FeCl3 and CuCl 2. The kinetics of the FeCl3-inhibited autoxidation are consistent with chain-termination via the following: Fe3+ + HOO . ⇄ [FeIV-OOH]3+ and [Fe IV-OOH]3+ + HOO. → Fe3+ + H2O2 + O2. Thus, FeCl3 in acetonitrile can be regarded as a very effective (and very simple) superoxide dismutase. The kinetics of the CuCl2-inhibited autoxidation indicate that chain transfer occurs and becomes more and more important as the reaction proceeds, i.e., the inhibition is replaced by autocatalysis. These kinetics are consistent with-reduction of Cu2+ to Cu+ by HOO . and then the reoxidation of Cu+ to Cu2+ by both HOO. and the H2O2 product. The latter reaction yields HO. radicals which continue the chain.
Date de publication
American Chemical Society
Journal of Organic Chemistry68, nº 23 : 9162–9165.