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

Headspace-gas chromatography was employed to study the behavior of met hanethiol in buffer solutions (pH 6.3) in the presence of transition m etals 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 conditi ons, Fe(III) alone catalyzed the oxidation of methanethiol to only a v ery limited extent ({ 15%). However, ascorbate plus Fe(III) mediated a rapid formation of dimethyl trisulfide at 30 degrees C in a model sys tem 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 p athway leading to the formation of dimethyl trisulfide.