FREE-RADICAL FORMATION BY ULTRASOUND IN ORGANIC LIQUIDS - A SPIN-TRAPPING AND EPR STUDY

The 50-kHz sonolysis of a variety of organic liquids, including n-alka nes (C-8-C-16), n-alcohols (C-3-C-8), cyclohexane, toluene, dioxane, a nd N,N-dimethylformamide, was investigated by EPR and spin trapping. 2 ,4,6-Tri-tertbutylnitrosobenzene (3tBNB) was found to be a particularl y suitable spin trap since primary, secondary, and tertiary alkyl radi cals could be distinguished. By comparison with sonolysis of the fully deuterated analogues of the organic liquids (N,N-dimethylformamide-d( 7), n-butanol-d(10), cyclohexane-d(12), dioxane-d(8)), the absence of radicals originating from the thermal decomposition of the spin trap ( 3tBNB) under conditions of the present experiments could be establishe d. When the spin traps 3tBNB and 3,5-dibromo-4-nitrosobenzenesulfonate were compared in the sonolysis of N,N-dimethylformamide and N,N-dimet hylformamide-d(7), similar results were obtained. For the homologous s eries of n-alkanes and n-alcohols spin adduct yields with 3tBNB increa se with decreasing solvent vapor pressure. Spin trapping appears to be a promising method for investigating the mechanisms of sonochemical r eactions in organic liquids.