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The kinetics of the oxidation reaction of malonic acid by ceric ion in 1 M sulfuric acid solution at 20℃ have been investigated by spectrophotometric method. The reaction rate at a large excess of malonic acid was found to be pseudo-first order. The observed pseudo-first order rate constants, kobs, are dependent on the concentration of malonic acid, [MA], of which relationship has been found to be kobs = (0.592[MA])/(1+14.5[MA]2). A mechanism for the reaction has been suggested on the basis of the above rate equation. The rate determining step may be the electron transfer reaction between enolate type malonate anion, which is formed by the acid dissociation reaction of malonic acid, and Ce(Ⅳ). The rate depression in the range of high concentration of MA has been explained by the formation of 1 : 2 chelate between Ce(Ⅳ) and malonate. According to the mechanism, the pH dependence of the rate, which was studied by Sengupta et al., has also been explained.
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