Metal ions can also act as potent inhibitors of autoxidation,[14, 28-30] by means of
reactions 12 and 13 in Scheme 1.1. Reaction 12 commonly occurs for Mn2+ and Co2+
metal salts and this reaction can completely suppress autoxidation when the concentration
of metal ions is higher than the hydroperoxide concentration.[14, 15] Particularly for
manganese(II) complexes, reaction 12 is one of the causes for the induction time that is
often observed for metal-catalysed autoxidation reactions. To eliminate this induction
time, the [Mn2+]/[ROOH]0 ratio has to be less than one.[31] Higher valent metals might be
able to inhibit autoxidation (at low oxygen concentration) by scavenging carbon radicals,
reaction 13 in scheme 1.1. Cu2+ and Fe3+ ions have been shown to readily reduce certain
carbon radicals.