Decomposition of aqueous dithionite. Part II. A reaction mechanism for the decomposition of aqueous sodium dithionite

Abstract

The decomposition of dilute aqueous sodium dithionite has been studied in unbuffered solutions by means of continuous polarography, accompanied by recorded pH values. The decomposition–time curve began with a slow "induction" period followed by an S-shaped rapid phase. The pH values decreased slightly during the induction period and increased considerably during the rapid phase. The addition of a solution of fresh decomposition products eliminated the induction phase. The addition of sulfide also eliminated the induction period and catalyzed the reaction. The accepted stoichiometry (2) of the reaction was confirmed. The following sequence of reactions is proposed[Formula: see text][Formula: see text]In the presence of H2S and possibly S formed in side reactions which consume H+, reaction [5] is catalyzed and may be represented as[Formula: see text]and[Formula: see text]The rate equation is represented as[Formula: see text]Reaction [4] is rate limiting during the induction period and reaction [5] (catalyzed), during the rapid phase of decomposition.