Kinetic study of the oxidation of ascorbic acid by aqueous copper(II) catalysed by chloride ion*

Abstract

Two methods of monitoring the chloride-catalysed oxidation of ascorbic acid by aqueous Cu^II have been developed that allow the reaction conditions to be varied more widely than previously and thereby permit a fuller elucidation of the behaviour and rate law for this system. It has been possible to study the reaction over a wide concentration range from 1.6 to 500 mM Cl^– and 4 to 100 mM Cu^II. For the first time, it is shown that the ascorbic acid (H₂asc)–Cu^II–chloride ion–Cu^I–dehydroascorbic acid (dha) system comes to equilibrium, under anaerobic conditions, with all species present and is driven towards products by chloride complexation of Cu^I. The results are consistent with the following reaction scheme (i = 0–2). The full rate law has been elucidated and values for

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various k_1i, k_–2i and k_2i/k_–1i have been determined.