The Ni(II) ion catalyzed thermal decomposition of peroxomonosulfate (PMS) was studied in the pH range 3.42-5.89. The rate is first order in [PMS] and Ni(II) ion concentrations. At pH greater than or equal to 5.23, the reaction becomes zero order in [PMS] and this changeover in the order of the reaction occurs at a higher concentration of nickel ions. The first-order kinetics in PMS can be explained as a rate-limiting step and is the transformation of nickel peroxomonosulfate into nickel peroxide. This peroxide intermediate reacts rapidly with another PMS to give oxygen and Ni(II). The formation of nickel peroxide is associated with a small negative or nearly zero entropy of activation. The zero-order kinetics in [PMS] can be explained by the fact that the hydrolysis of aquated nickel(II) ions into hydroxocompounds is the rate-limiting step. The turnover number is 2 at pH 3.42 and increases with pH.

The kinetics of oxidation of the dipeptide glycylglycine by peroxomonosulfate (PMS) was studied in the pH range of 3.42-5.89. The rate is first order in [PMS], glycylglycine concentration, and inverse first order in [H + ]. The kinetic data suggest that SO 2− 5 reacts, with glycylglycine, faster than H SO − 5 by five orders of magnitude. The observed kinetics can be explained as due to the formation of an intermediate by the nucleophilic interaction of peroxide with the terminal protonated amine of glycylglycine, which then decomposes in the rate-limiting step to the product aldehyde. The thermodynamic parameters are evaluated. The reaction is catalyzed by Ni(II) ions only when pH ≤ 4.63, and above this pH the rate is zero order with respect to [Ni(II)]. Perusal of the enhanced rate constant values suggests that the Ni-peroxide intermediate also reacts with glycylglycine. The Ni-dipeptide complex is not oxidized by PMS, and this complex in fact inhibits the formation of Ni-peroxide intermediate.