Kinetics and Mechanism of Chemical Reactions. Catalysis
The quantitative regularities of the effect of the concentration of promoting additive PPh3 on the rate of hydrocarbomethoxylation of cyclohexene for catalysis with Pd(OAc)2-PPh3-p-Toluenesulfonic acid system are established within the temperature range 368–383 K. It has been shown that in the studied temperature range the dependences of reaction rate on the PPh3 concentration pass through maxima. The results obtained are interpreted within a hydride mechanism of hydrocarbomethoxylation previously proposed. The values of some effective constants of the kinetic reaction equation are estimated. Using the temperature dependence of an effective rate constant, effective activation energy is estimated and, on its basis, the changes in enthalpy, entropy, and Gibbs energy in the ligand exchange reaction between the Pd(PPh3)4 and Pd(CO)2(PPh3)2, 2 complexes were estimated. It is established that this reaction is close to an equilibrium state at 373 K. Using previously obtained data for the temperatures of 363, 368, 373, 378, and 383 K, kinetic models of cyclohexene hydrocarbomethoxylation were developed, reflecting the cumulative effect of various participants in the reaction on its rate and working throughout the reaction.