Kinetic isotope effects in oxidation reaction of C2H4 and C2D4 by p-benzoquinone in the Pd2+—HClO4—CH3CN—H2O system

Abstract

Kinetic isotope effects (KIE) have been measured for oxidation reactions of ethylene by p-benzoquinone in Pd²⁺—MeCN—H₂O—HClO₄ system. Under the conditions of preferred formation of complex Pd(MeCN)(H₂O)₃²⁺ the ratio between the initial reaction rates \(R_{{C_2}{H_4}} 0/R_{{C_2}{D_4}} 0\) is equal to 1.14±0.06 and is close to the KIE for classical chloride systems. Based on the obtained results and previous data for C₂H₄—C₂D₄ and H₂O—D₂O (0.97±0.12) systems, the slow step was proposed in the reaction mechanism–a trans-addition of water molecule to the cationic p-complex LPd(H₂O)₂(CH₂CH₂)²⁺ with formation of metalcarben-ium ion solvated by water molecule (LPd(H₂O)₂(CH₂CH₂O+H₂)⁺).