Selective Photoelectrochemical Oxidation of Vicinal CyclohexanedicarboxylicAcids: A Mechanic Study

摘要

The course of photoxidation of vicinal diacids on irradiated TiO2 suspensionsproceeds via one-electron oxidative decarboxylation rather than two-electron oxidative bis-decarboxylation (which occurs on poised metal electrodes). The formation of a monocarboxylic acid as the major product indicates that trapping of an intermediate radical is competitive with further oxidation. The observed regiochemical preference in unsymmetrical diacids is rationalized by the conformational preference of the diacid adsorbed onto the photoactivated catalyst surface. The semiconductor-mediated photocatalyzed oxidation of many organic substrates proceeds through interfacial electron transfer, with an appropriate adsorbate trapping the photogenerated hole. In several cases, clear evidence exists for surface-confined organic cation radicals formed in this manner. (JES)