OXIDATION OF AQUEOUS SULFIDE SOLUTIONS BY DIOXYGEN .1. AUTOXIDATION REACTION

The autoxidation of aqueous sulfide solutions by dioxygen is studied a t pH 9 and 14 and at initial sulfide concentrations between 1 and 100 mM. Disulfide as a primary intermediate is proposed to enhance the sul fide oxidation by autocatalytically forming polysulfides. The postulat e is supported by the observed acceleration of the process at increasi ng pH favoring the presence of disulfide rather than that of sulfur. T he final reaction products thiosulfate and sulfate are proposed to res ult from the hydrolysis of the highly instable intermediate polythiosu lfite in parallel reaction pathways, assuming probabilities for breaki ng the sulfur chain at the alpha (sulfate) and beta (thiosulfate) posi tions to be responsible for the selectivity. A reaction scheme is prop osed, considering all experimental observations.