Thermodynamics of monooxygenase system: Ru^III-EDTA-ascorbate-O₂ catalyzed <span style="font-size:12.0pt;line-height:115%;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";color:#1A1A1A;mso-ansi-language:EN-IN; mso-fareast-language:EN-IN;mso-bidi-language:HI" lang="EN-IN">oxygen atom transfer to olefins</span>

Abstract

<span style="font-size:12.0pt;line-height: 115%;font-family:" times="" new="" roman";mso-fareast-font-family:"times="" roman";="" color:#515151;mso-ansi-language:en-in;mso-fareast-language:en-in;mso-bidi-language:="" hi"="" lang="EN-IN">The kinetics and thermodynamics of Ru^III-EDTA-ascorbate-O₂ system catalyzed epoxidation of <i style="mso-bidi-font-style:normal">cis</i>-cyclooctene, styrene and <i style="mso-bidi-font-style:normal">trans</i>-stilbene were investigated in mixed aqueous acidic (pH= 1.5-2.5) solvent of water: dioxane (1:2) v/v at μ=0.1 M KNO₃ the temperature range 288-313K. The kinetics of the epoxidation of olefin studied at each particular temperature as a function of variants gave first order dependence on concentration of the catalyst, ascorbate, dioxygen 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 kinetically characterized, 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 monoxygenase system was more efficient for epoxidation. Both enthalpy Δ<i style="mso-bidi-font-style:normal">H</i>^# and entropy Δ<i style="mso-bidi-font-style:normal">S</i>^# of activation were found to be highly red uced in presence of ascorbate. Linear free energy relationship between ΔH^# and ΔS^# and between rate and equilibrium constants were also obtained.</span>