The influence of composition of binary solvent CH3CN-H2O on the kinetics of oxidation of cyclohexene by p-BENZOQUINONES in solutions of cationic palladium(II) complexes
During the study of cyclohexene oxidation by p-benzoquinones into cyclohexanone in water-organic solutions of cationic complexes of palladium(II) it was demonstrated that the initial reaction rate R0 depends complicatedly on water molar fraction for three studied solvents: acetonitrile (AN), dimethylformamide, and dimethylsulfoxide. In order to explain the obtained bimodal dependence for the example of AN-water system, modeling of phase equilibrium in the studied system was performed. The existence of two- and three-phase immiscibility areas as well as a three-component heteroazeotrope was found. By UV spectroscopy it was stated that varying of water molar fraction in the binary solvent substantially changes the state of starting cationic complexes [Pd(АН)x(H2O)4-x]2+. For mathematical description of medium effect on R0 value three models were proposed taking into account different factors, such as: a) physico-chemical properties of binary solvent; b) composition of possible associates AN-water; c) composition of starting [Pd(АН)x(H2O)4-x]2+ complexes. The adequate description of bimodal dependency was obtained in the model considering the changes of [Pd(АН)x(H2O)4-x]2+ complexes composition with simultaneous presence of an associate of (АН)2(H2O) composition.