Metal-ion oxidations in solution. Part III. The oxidation of 2-mercaptosuccinic acid by vanadium(V)

Abstract

The oxidation of 2-mercaptosuccinic acid by the oxy-ions of vanadium(V) has been studied in the pH range 2·4–4·4 at temperatures from 0–25° with a stopped-flow technique. The reaction proceeds via the formation of a coloured intermediate complex followed by a slower electron-transfer step. The intermediate has a stability constant of ten and at 15° the observed rate constant for its formation may be expressed as k_obs=[44·5 + 465(T)] sec.^–1 where T= 2-mercaptosuccinic acid. At the same temperature the rate constant for the redox process may be written as k¹_obs=[5·0 + 40(T)] sec.^–1. The acid dissociation constants for 2-mercaptosuccinic acid have also been measured. Reaction of the intermediate leads to the formation of the disulphide, and a mechanism for the process is proposed. In the range studied, temperature has no significant effect on the rates.