Thermodynamics of monooxygenase system:Ru~(III)-EDTA-ascorbate-O_2 catalyzed oygen atom transfer to olefins

摘要

The kinetics and thermodynamics of Ru~(III)-EDTA-ascorbate-O_2 system catalyzed epoxidation of cis-cyclooctene,styrene and trans-stilbene were investigated in mixed aqueous acidic (pH=1.5-2.5) solvent of water:dioxane (1:2)v/v at #mu#=0.1 M KNO_3 in the temperature range 288-313 K. The kinetics of the epoxidation of olefins studied at each particular temperature as a function of variants gave first order dependence on concentration of the catalyst,ascorbate,dixygen and olefin and an inverse first order in hydrogen ion concentration. The activation parameters corresponding to rate determining steps and the thermodynamic parameters corresponding to equilibrium steps of all kinetic intermediates, spectrophotometrically and kietically characterizec,were determined.A comparison of the activation parameters and quantitative yield of epoxides formed in presence (monooxygenase) and absence (dioxygenase) of ascorbic acid indicated that monooxygenase system was more efficient for epoxidation. Both enthalpy triangle openH~# and entropy triangle openS~# of activation were found to be highly reduced in presence of ascorbate.Linear free energy relationship between triangle openH~# and triangle openS~# and between rate and equiliumconstants were also obtained.