The kinetics of the oxidation of 3-mercaptopropionic acid with potassium ferricyanide

The kinetics of the oxidation of 3-mercaptopropionic acid with potassium ferricyanide in aqueous solution have been investigated under a variety of conditions, using a spectrophotometric method. In the pH range 3.83-C78, the rate law -d-(ferricyanide)/dt = k(ferricyanide)(2) Was found to apply. The observed rate constant (k) was found to increase with increasing thiol concentration and pH, to decrease with increasing initial ferricyanide ion concentration and with added potassium ferrocyanide, and to be unaffected by added dithiodipropionic acid. These results are discussed in terms of a mechanism in which an initial reversible electron transfer is followed by another, irreversible one.