Kinetics and mechanism of the reaction of aqueous europium(II) ion with pyruvic acid

Article abstract of DOI:10.1021/ic00131a024

Eu^II ion reacts with pyruvic acid in air-free, aqueous, acidic solutions. The only organic product is lactic acid, which forms after a two-electron reduction of the keto form of pyruvic acid. The overall stoichiometry is 2:1, metal ion to organic acid, respectively. The kinetics were studied in detail by the stopped-flow technique. Under conditions of excess Eu^II ion over pyruvic acid, two stages are observed: a fast stage, which corresponds to the reduction of all available keto form in equilibrium with the hydro form of pyruvic acid, and a slow stage, during which hydrated pyruvic acid reacts only after being transformed to the carbonyl form by an acid-catalyzed reaction, which under these conditions is the rate-determining step. A mechanism is proposed and compared to the mechanisms of the corresponding reactions of the d elements Cr²⁺, V²⁺, and Ti³⁺.