Isotope studies of photocatalysis: TiO2-mediated degradation of dimethyl phenylphosphonate

The initial step of TiO2-mediated photocatalytic degradation of dimethyl phenylphosphonate (DMPP), labeled with 18O or deuteria in the methoxy groups, results in products due to ring hydroxylation and demethylation. The 18O labeling experiments clearly demonstrate that the methyl group is lost, rather than a methoxy group, resulting in a labeled phosphonic mono-acid. Results from deuterium isotope experiments are more ambiguous.