OXIDATIVE DECARBOXYLATION OF BENZOIC-ACID BY PEROXYL RADICALS

A chemical model based on the thermal decomposition of AAPH (2,2'-azob is(2-amidinopropane) dihydrochloride is used for the production of per oxyl radicals. Peroxyl radicals induces the decarboxylation of [7-C-13 ]benzoic acid and the production of (CO2)-C-13, which is measured by g as chromatography-isotope ratio mass spectrometry (GC-IRMS). The decar boxylation depends on temperature; AAPH, and benzoic acid concentratio ns. The decarboxylation also depends on the presence of oxygen. Electr on spin resonance studies are performed to confirm the presence of per oxyl radicals under oxygen and of carbon-centered radicals in the abse nce of oxygen. Decarboxylation rates are measured in the presence of v arious antioxidants: ascorbate, dimethylsulfoxide, mannitol, and uric acid, It turns out that the decarboxylation is inhibited by each of th ese antioxidants. The ratio of decarboxylation rates, with and without the antioxidant, varies linearly with the antioxidant concentration. HPLC and GC-MS analyses of reaction products between benzoic acid and AAPH-derived radicals do not detect the presence of radical substituti on products on the aromatic ring or the products derived from benzoic acid. There is no doubt that GC-IRMS is a powerful technique to invest igate the effects of peroxyl radicals on benzoic acid. In addition, it is possible to follow the degradation of C-13-labeled chemical target s exposed to peroxyl radicals through the production of (CO2)-C-13. (C ) 1998 Elsevier Science Inc.