Determination of Kinetic Order of Reaction for its Duration in the Study of Solvation Factor Effect on Cyclohexene Hydrocarbomethoxylation Catalyzed by Palladium-Phosphine Systems

The purpose of the study was to investigate homogeneous catalytic reaction of cyclohexene hydrocarbomethoxylation leading to the methyl cyclohexanecarboxylate formation. Pd(PPh3)2Cl2 and Pd(OAc)2 which were promoted by free PPh3 and p-toluenesulfonic acid were used as catalytic precursors. In the temperature range 358--393 K, we studied the methanol concentration effect on the value of kinetic order of the reaction with respect to cyclohexene for the duration of the reaction. Findings of research show that the kinetic order increased from 1 to 10 with temperature increase and methanol concentration rise. We compared the kinetic order values for the duration of the reaction and the concentration order with respect to cyclohexene, which is equal to 1, set for the initial rate region. Based on this comparison, it was suggested that the formation of inactive palladium complexes is progressed by the action of excess methanol at elevated temperatures. We found that the regularities of methanol effect on the cyclohexene hydrocarbomethoxylation rate for the duration of the reaction were agreed with the regularities discovered for the initial rate region. With consideration of the data about enthalpy change in the ligand exchange reactions between the palladium complexes with participation of CH3OH, СО and PPh3, we draw the conclusion about the dominant contribution of specific solvation to the catalyst deactivation in the conditions of high methanol concentrations