Kinetic aspects of the influence of concentrations of methanol and the trans-2,3-bis(diphenylphosphinomethyl)norbornane promoting additive on the hydrocarbomethoxylation of cyclohexene catalyzed by the Pd(OAc)2/p-toluenesulfonic acid system

Abstract

The effects of temperature, the concentrations of methanol and the trans-2,3-bis(diphenylphosphinomethyl)norbornane (TBDPN) promoting additive on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2/p-toluenesulfonic acid system were studied. It was found that in the 358–383 K temperature range, the increase in the CH3OH concentration from 0 to 0.15 mol/L induces a virtually linear increase in the reaction rate, which slows down as the methanol concentration further increases. In the temperature range of 343–373 K, the dependences of the reaction rate on the TBDPN concentration pass through maxima at [TBDPN] = (3.0–4.0) × 10−3 mol/L. The results were interpreted in terms of the hydride mechanism that included diphosphinepalladium complexes as intermediates and was supplemented by ligand exchange reactions, resulting in a decrease in the activity of the palladium catalyst. The effective constants of the previously derived kinetic equation in the temperature range of 343–383 K were estimated by the least-squares method. The effective activation energies were determined and used to evaluate the enthalpy change in the ligand exchange reaction between the complexes Pd(TBDPN)3 and [HPd(TBDPN)(CH3OH)]OTs. The zerovalent complex Pd(TBDPN)3 was concluded to be more stable than the hydride complex [HPd(TBDPN)(CH3OH)]OTs.