Activity of palladium-containing catalysts of hydrocarboalcoksilation

 Русская версия статьи/Russian version of the article

    Hydrocarboalcoksilation of cyclohexene is of practical interest as the reaction, present­ing the basis of the receipt of an important intermediate product in the synthesis of phar­maceuticals - methylcyclohexanecarboksilat [1]. In this regard, the research of the activi­ty of the catalysts, used for this purpose, is the actual problem. In the context of this prob­lem and in strictly comparable conditions, we studied the activity of palladium catalysts Pd(PPh₃)₂Cl₂, PdCl₂ and (CH₃COO)₂Pd, promoted by means of free triphenylphosphine and p-toluenesulfonic acid (TsOH), in the reaction of hydrocarbomethoksilation of cyclo-hexene at constant concentrations of precursors.

     The reaction is of first order in (CH₃COO)₂Pd, fractional - on Pd(PPh₃)₂Cl₂, and the dependence of reaction rate on the concentration of PdCl2 has an extreme character with a maximum at [PdCl₂] = 0,4-10^-2 mol / liter. It was established that in the studied concen­tration range of precursors (0 - 810^-3 mol / L) specific activity of (CH₃COO)₂Pd is by 6-7 times greater than the activity of Pd(PPh₃)₂Cl₂ and PdCl₂, and in the case of the latter with increasing of their concentration the formation of palladium is observed. It is shown that the formation of the latter can be suppressed by using at least 7-8 fold excess of triph-enylphosphine with respect to palladium. These differences in the behavior of predeces­sors are interpreted by the strong coordinating action of chlorine anions in comparison with the acetate anions, which cause the formation of the less active complexes in the case of chlorine-containing catalysts [2] and, consequently, decrease the rate of reaction of hydrocarbomethoksilation. This, in its turn, leads to an increase in the proportion of competing with the reaction of palladium [3, 4]. Stabilizing effect of triphenylphosphine on the catalysts was treated in terms of availability in their coordination sphere of bulk ligand PPh3, blocking the approach of palladium atoms to each other and impeding their agglom­eration.

     Thus, the use as catalysts of hydrocarboalcoksilation palladium complexes, stabilized by phosphine ligands and containing weak coordinated anions (СН₃СОО^-, TsO^- etc.), is a significant factor (6-7 times) of the increase in productivity processes for esters or of the decrease of the catalyst flow at the given productivity.

This work was supported by the Russian Foundation for Basic Research, grant№ 09-08-00890.

Sevostyanova N.T., Demerly A.M., Averyanov V.A., Batashev S.A. L.N. Tolstoy Tula State Pedagogical University, Tula, Russia