Application of benzophenones to elucidate the photochemical reaction pathways of hydrogen peroxide with dimethylsulfoxide

Benzophenone ((C6H5)(2)CO) and decafluorobenzophenone ((C6F5)(2)CO) were ap plied to elucidate the photochemical reaction pathway of hydrogen peroxide (H2O2) with dimethylsulfoxide (DMSO). When a solution of benzophenone in DM SO was excited with the 355 nm laser light, three transient species were ob served in the time-resolved electron paramagnetic resonance spectra: benzop henone ketyl (C6H5)(2)COH., methyl (CH3)-C-., and methylsulfinic methyl (CH 2SOCH3)-C-. radicals. However, when decafluorobenzophenone was used with DM SO, only ketyl and methylsulfinic methyl radicals were observed under the s ame experimental conditions. When the reaction of benzophenone and DMSO was carried out in the presence of H2O2, different time profiles of (CH3)-C-. radicals were observed. In the reaction of decafluorobenzophenone-DMSO-H2O2 , the time profiles of the radicals were not affected by the presence of H2 O2. Thus, these results verify that (CH3)-C-. radicals are regenerated in a cyclic pathway, in which (CH3)-C-. radicals attack H2O2. The regeneration pathway allows us to observe f-pair polarization throughout the lifetime of (CH3)-C-. radicals, which last several microseconds, an order of magnitude longer than the T-1 relaxation time of (CH3)-C-. radicals.