Studies on the oxygen atom transfer reactions of peroxomonosulfate: Catalytic effect of hemiacetal

Abstract

The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05–5.89 and at 31°C and 38°C. When formaldehyde and Ni(II) ions concentrations are ∼5.0 × 10−4 M to 10.0 × 10−4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equation is (−d[PMS])/dt = (k′2[HCHO][Ni(II)][PMS]2)/{[H+](1+K2[GLYCA])}. The number of PMS decomposed for each mole of formaldehyde (turnover number) is 5–10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni-hemiacetal reacts with another molecule of PMS in the rate-limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 642–649, 2009