THE KINETICS AND MECHANISM OF OXIDATION OF 3-MERCAPTOPROPIONIC ACID, 2-MERCAPTOETHANESULFONIC ACID AND 2-MERCAPTOBENZOIC ACID BY POTASSIUM FERRATE

The kinetics of the reaction of potassium ferrate with 3-mercaptopropi onic acid, 2-mercaptoethanesulfonic acid and 2-mercaptobenzoic acid we re investigated under pseudo first-order conditions. Reproducible kine tics were obtained, but each thiol formed a ferric complex when in lar ge excess which interfered with the kinetic results. The rate expressi on was very similar for 3-mercaptopropionic acid and 2-mercaptoethanes ulfonic acid, giving two terms, one of which was first-order in each o f hydrogen ion, thiol and ferrate concentration, and the other was fir st-order in just thiol and ferrate concentration. The reaction with 2- mercaptobenzoic acid gave two terms, one of which was first-order in e ach of thiol and ferrate concentration, and the other was first-order in hydrogen ion and also in ferrate concentration. The reactions were complete within 300 ms to give the fully oxidized thiols for 3-mercapt opropionic acid and 2-mercaptoethanesulfonic acid, and the sulfine for 2-mercaptobenzoic acid. The proposed mechanism for 3-mercaptopropioni c acid and 2-mercaptoethanesulfonic acid involves rate-determining ste ps between the thiol and both the protonated and unprotonated ferrate ion, whereas the rate-determining steps for 2-mercaptobenzoic acid jus t involve the unprotonated ferrate. (C) 1998 Elsevier Science S.A. All rights reserved.