Spin trapping of methyl radicals by the acyl nitroso compound Ph--C(= O)NO formed in the photochemical reaction between benzohydroxamic acid, dimethyl sulfoxide and hydrogen peroxide. An EPR study.

By the use of EPR spectroscopy, it has been shown that acyl nitroso compounds can act as spin traps for short-lived radicals with the formation of acyl aminoxyl radicals. The reaction was studied for the system benzohydroxamic acid [Ph--C(= O)N(H)]-dimethyl sulfoxide-hydrogen peroxide. The acyl aminoxyl radicals appeared almost immediately when the reaction mixture was irradiated in situ in the EPR cavity with UV light. The trapping reaction involved two photochemical reactions, i.e. the oxidation of the hydroxamic acid to the acyl nitroso compound Ph--C(= O)NO, and the formation of methyl radicals from dimethyl sulfoxide. The EPR spectra are superpositions of the spectra of two species of acyl aminoxyl radicals, i.e. the radicals Ph--C(= O)N(O.)H formed by oxidation of the parent benzohydroxamic acid, and the radical Ph--C(= O)N(O.)CH3, formed by trapping of methyl radicals.