Oxidation reactions of dibenzothiophene subjected to negative chemical ionization with oxygen

Dibenzothiophene (1) suffers surface-catalyzed oxidation under CI(O₂) conditions. While in the positive mode M^+· is the only major ion and those of the oxidation products are of minor importance in the negative mode, essentially only ions stemming from oxidized species can be seen, the sulfone ion [M + O₂]^−· being the most important one. The ion m/z 184 previously attributed to M^−· is actually the anion of 2-sulfobenzoic acid cyclic anhydride. Structures for the various oxidation products are proposed and the mechanisms leading to their formation are discussed.