Study on the stability of palladium complexes with Hemaraphos ligand and reaction kinetics in the bis-hydroalkoxycarbonylation of 1,3-butadiene

The bis-hydroalkoxycarbonylation of 1,3-butadine (BD) to synthesize dimethyl adipate offers an environmentally friendly alternative route for the production of adiponitrile. While through the study of the stability in different reaction systems proves that the nucleophilicity of "N" (pyridine group) in Hemaraphos ligand not only contributes to the stability of Pd complexes, but also promotes the formation of Pd-H active species. Moreover, based on the study of kinetics, this reaction was divided into two stages (Reaction 1: hydroalkoxycarbonylation of BD to methyl pentanoate, Reaction 2: hydroalkoxycarbonylation of methyl pentanoate to dimethyl adipate) and the qualitative kinetics for the two reaction stages was studied respectively. It was found that the reaction rate of Reaction 2 was much higher than that of Reaction 1. And even if the activation energy of the catalyst for Reaction 2 was lower than that of Reaction 1, the conversion of BD took priority when both BD and methyl pentanoate existed simultaneously in the system. Finally, the different reaction mechanisms for Hemaraphos and dtbpx was proposed and compared based on the different dynamic behaviors. The electron donor ability of "N" (pyridine group) is stronger than "O" (ester carbonyl group), which was found to be the possible reason for the two hydroalkoxycarbonylation reaction stages of Hemaraphos.