Kinetics of the reaction of rhodium(II) acetate with carboxylic acids



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The kinetics of the reaction of rhodium(II) acetate with several carboxylic acids and their aqueous mixtures were studied. The rates were determined as the pseudo-first order rate constants at time zero. A rate expression was derived and proven to be in agreement with the experimentally observed results. The rate depends on the acid strength of the entering carboxylate and the ratio of the acid concentration to water concentration. Water was found to inhibit the reaction. Activation parameters for some of the systems were determined. The barrier for the reaction is significant enough to demand higher temperatures in most cases. The following mechanism is proposed. Prior to reaction, the rhodium(II) acetate forms a Lewis acid-base adduct with the entering acid and/or water. A new molecule of acid then protonates an acetate, producing acetic acid, and the entering acid replaces it as a bridging group.