Kinetic studies on the metal(II) tartarate–peroxomonosulfate reaction

The kinetics of oxidation of tartaric acid (TAR) by peroxomonosulfate (PMS) in the presence of Cu(II) and Ni(II) ions was studied in the pH range 4.05–5.20 and also in alkaline medium (pH ∼12.7). The rate was calculated by measuring the [PMS] at various time intervals. The metal ions concentration range used in the kinetic studies was 2.50 × 10 −5 to 1.00 × 10 −4 M [Cu(II)], 2.50 × 10 −4 to 2.00 × 10 −3 M [Ni(II)], 0.05 to 0.10 M [TAR], and µ = 0.15 M. The metal(II) tartarates, not TAR/tartarate, are oxidized by PMS. The oxidation of copper(II) tartarate at the acidic pH shows an appreciable induction period, usually 30–60 min, as in classical autocatalysis reaction. The induction period in nickel(II) tartarate is small. Analysis of the [PMS]–time profile shows that the reactions proceed through autocatalysis. In alkaline medium, the Cu(II) tartarate–PMS reaction involves autocatalysis whereas Ni(II) tartarate obeys simple first‐order kinetics with respect to [PMS]. The calculated rate constants for the initial oxidation ( k 1 ) and catalyzed oxidation ( k 2 ) at [TAR] = 0.05 M, pH 4.05, and 31°C are Cu(II) (1.00 × 10 −4 M): k 1 = 4.12 × 10 −6 s −1 , k 2 = 7.76 × 10 −1 M −1 s −1 and Ni(II) (1.00 × 10 −3 M): k 1 = 5.80 × 10 −5 s −1 , k 2 = 8.11 × 10 −2 M −1 s −1 . The results suggest that the initial reaction is the oxidative decarboxylation of the tartarate to an aldehyde. The aldehyde intermediate may react with the alpha hydroxyl group of the tartarate to give a hemi acetal, which may be responsible for the autocatalysis. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 620–630, 2011