ASCORBATE AND TRANSITION-METAL MEDIATION OF METHANETHIOL OXIDATION TO DIMETHYL DISULFIDE AND DIMETHYL TRISULFIDE

Headspace-gas chromatography was employed to study the behavior of methanethiol in buffer solutions (pH 6.3) in the presence of transition metals and ascorbate. In the presence of Cu(II) (1 ppm), methanethiol (2 ppm) was depleted within 30 min at 30 degrees C by 70% and 30% under aerobic and anaerobic conditions, respectively. Under similar conditions, Fe(III) alone catalyzed the oxidation of methanethiol to only a very limited extent ({ 15%). However, ascorbate plus Fe(III) mediated a rapid formation of dimethyl trisulfide at 30 degrees C in a model system containing methanethiol and hydrogen sulfide. A partial inhibition of dimethyl trisulfide formation by benzoate in the ascorbate plus Fe(III) system suggested that the hydroxyl radical was involved in the pathway leading to the formation of dimethyl trisulfide.