Reactions of iron(II) and titanium(III) with organic radicals

In situ radiolysis-esr experiments on acid solutions (0.8 N H₂SO₄) of malonic acid have established that the main reaction of OH is abstraction of a CH hydrogen to produce ĊH(CO₂H)₂ but that approximately 10% of the reaction leads to the radical ĊH₂CO₂H by decarboxylation. (In basic solution, decarboxylation of CH₂(CO₂^-)₂ by OH was not observed and, at most, can account for 0.5% of the total reaction.) The fact that the main reaction occurs by abstraction is in apparent disagreement with previous results of rapid-mixing experiments in which only the esr spectrum of ĊH₂CO₂H was found. Radiolysis experiments in which Ti^III was added to the solution before irradiation showed that ĊH(CO₂H)₂ reacts with the metal ion while, at the concentrations used, ĊH₂CO₂H does not. This extra radical destruction reaction can explain, in part at least, the absence of detectable signals of the former radical in the rapid-mixing experiments. Radiation chemical experiments were carried out to further investigate the reaction of organic radicals with the reduced metal ions Ti^III and Fe^II. Measurement of the yields of Ti^VI and Fe^III in solutions containing various organic solutes showed that while a number of types of radicals such as those derived from alcohols and carboxylic acids as well as alkyl radicals can oxidize Ti^III only those of type RR′ĊCO₂H appear to be able to oxidize Fe^II. Methane was confirmed as the organic product of the reaction of ĊH₃ with Ti^III.