Ascorbate-induced oxidation of formate by peroxodisulfate: Product yields, kinetics and mechanism

Abstract

The slow reaction between peroxodisulfate and formate is significantly accelerated by ascorbate at room temperature. The products of this induced oxidation, CO2 and oxalate (C2O42-), were analyzed by several methods and the kinetics of this reaction were measured. The overall mechanism involves free radical species. Ascorbate reacts with peroxodisulfate to initiate production of the sulfate radical ion (SO 4.-), which reacts with formate to produce carbon dioxide radical ion (CO2.-) and sulfate. The carbon dioxide radical reacts with peroxodisulfate to form CO2 or self-combines to form oxalate. Competition occurring between these two processes determines the overall fate of the carbon dioxide radical species. As pH decreases, protonation of the carbon dioxide radical ion tends to favor production of CO2.