Kinetics and mechanism of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2-PPh3-p-toluenesulfonic acid system

Abstract

Quantitative characteristics of the influence of the Pd(OAc)2-PPh3-p-toluenesulfonic acid (TsOH) system and the reagents on cyclohexene hydrocarbomethoxylation are established. It is shown that the reaction is of first order in the cyclohexene concentration and that the dependences of the reaction rate on the CO pressure and the CH3OH, PPh3, and TsOH concentrations exhibit extreme behavior, with maxima at 1 MPa and 0.3, 0.03, and 0.065 mol/L, respectively. These results are interpreted in terms of a catalytic cycle involving hydride-, alkyl-, and acyl-palladium cationic complexes, as intermediates, and ligand exchange reactions deactivating part of the catalyst. Based on the steady-state concentration method, a kinetic equation is derived closely describing the experimental data. Evaluation of the effective parameters of the kinetic equation led to the conclusion that the reactivity of methanol in the nucleophilic attack on the acyl-palladium intermediate is higher than that of cyclohexanol.