Investigation of the Dependence of the Rate of Cyclohexene Alkoxycarbonylation with Cyclohexanol and CO on the p-Toluenesulfonic Acid Monohydrate Concentration and Temperature

The effects of the p-toluenesulfonic acid monohydrate (TsOH∙H₂O) concentration on the alkoxycarbonylation of cyclohexene over a Pd(PPh₃)₂Cl₂–PPh₃–TsOH∙H₂O catalytic system were quantified at 363–383 K. Within this temperature range, the correlation between the cyclohexyl cyclohexanecarboxylate production rate and the TsOH∙H₂O concentration was found to be similar to an S-shaped curve. Based on these data, as well as previous findings with regard to the effects of water and TsOH∙H₂O concentrations on the cyclohexene methoxycarbonylation rate, the hydride mechanism for the alkoxycarbonylation process was updated by adding relevant ligand exchange reactions between ballast palladium complexes, specifically reactions that produce a palladium aqua complex. The accordingly-modified kinetic equation for cyclohexene alkoxycarbonylation with cyclohexanol and CO was found to be consistent with the experimental data. Effective constants were evaluated for the modified kinetic equation over the studied temperature range. A number of relevant parameters—namely, the effective activation energy and the changes in enthalpy, entropy, and Gibbs free energy during the ligand exchange between the complexes Pd(PPh₃)₂(C₆H₁₁OH)₂ and Pd(PPh₃)₂(H₂O)₂—were further evaluated in light of the activated complex theory. This reaction was found to be nearly equilibrium at 373 K.