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

Abstract

Benzophenone ((C 6 H5),CO) and decafluorobenzophenone ((C 6Fs ) 2 CO) were applied to elucidate the photochemical reaction pathway of hydrogen peroxide (H,0 2) with dimethylsulfoxide (DMSO). When a solution of benzophenone in DMSO was excited with the 355 nm laser light, three transient species were observed in the time-resolved electron paramagnetic resonance spectra: benzophenone ketyl (C6H5)2COH', methyl 'CH 3 , and methylsulfinic methyl 'CH2SOCH3 radicals. However, when decafluorobenzophenone was used with DMSO, only ketyl and methylsulfinic methyl radicals were observed under the same experimental conditions. When the reaction of benzophenone and DMSO was carried out in the presence of H 2 02, different time profiles of 'CH 3 radicals were observed. In the reaction of decafluorobenzophenone-DMSO-H 20 2, the time profiles of the radicals were not affected by the presence of H 2 0,. Thus, these results verify that 'CH 3 radicals are regenerated in a cyclic pathway, in which 'CH, radicals attack H202 . The regeneration pathway allows us to observe f-pair polarization throughout the lifetime of 'CH 3 radicals, which last several microseconds, an order of magnitude longer than the T, relaxation time of 'CH3 radicals.

EPR studies of free radical reactions of C60 embedded in mesoporous MCM-41 materials in aqueous solution

“…Methyl radicals were generated from the attack of hydroxyl radicals on dimethylsulfoxide (DMSO). [16][17][18] Even though this is a secondary reaction, the reaction of OH radical with DMSO is practically diffusion controlled with a bimolecular rate constant of k ¼ 7.2 Â 10 9 M À1 s À1 . 19 Thus, it is feasible to generate CH 3 quantitatively for our scavenging studies.…”

“…The identity of CH 3 radical as an intermediate spin adduct (reaction ( 5)) has been established previously. [15][16][17][18] The EPR spectra of DMSO attacked by OH radicals (generated from the Fenton reaction) in the presence of DMPO are shown in Fig. 4: (1) no MCM41-NH-C 60 H was added (Fig.…”