Temperature Aspect of CH3OH effect on the rate of cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)2–PPh3–p-toluenesulfonic acid system

Resumo

In the temperature range of 353–368 K, quantitative characteristics of the effect of the CH₃OH concentration on cyclohexene hydrocarbomethoxylation catalyzed by the Pd(OAc)₂–PPh₃–p-toluenesulfonic acid system are determined. It is shown that, in the temperature range covered, the dependence of the reaction rate on the CH₃OH concentration passes through a maximum. The results are interpreted in terms of a catalytic cycle involving hydride–, alkyl–and acyl–palladium complexes of cationic type as intermediates, supplemented by ligand exchange reactions that transfer part of the catalyst into an inactive form. The effective constants for the earlier obtained kinetic equation are estimated. Based on the temperature dependences of the effective constants and the activated complex theory, the effective activation energies, as well as the enthalpy, entropy, and Gibbs energy changes for the ligand exchange reactions between the Pd(CH₃OH)₂(PPh₃)₂ and Pd(CO)₂(PPh₃)₂ complexes are estimated. It is established that, at 373 K, this reaction is close to the state of equilibrium.