A thermodynamic study of ketoreductase-catalyzed reactions 3. Reduction of 1-phenyl-1-alkanones in non-aqueous solvents

Abstract

The equilibrium constants K for the reactions (1-phenyl-1-alkanone + 2-propanol = 1-phenyl-1-alkanol + acetone) in the solvents n-pentane and n-hexane have been determined by using gas chromatography at the temperature 298.15 K. The 1-phenyl-1-alkaones included in this study were: 1-phenyl-1-ethanone, 1-phenyl-1-propanone, 1-phenyl-1-butanone, 1-phenyl-1-pentanone, 1-phenyl-1-hexanone, and 1-phenyl-1-heptanone. The equilibrium constants for the reaction involving 1-phenyl-1-ethanone were measured in the solvent n-hexane as a function of temperature (288 K to 308 K). The calculated thermodynamic quantities for the 1-phenyl-1-ethanone reaction at T = 298.15 K are: K = 0.2177 ± 0.0018; the standard molar Gibbs free energy change, Δ r G m ∘ = ( 3.78 ± 0.02 ) kJ · mol - 1 , the standard molar enthalpy change, Δ r H m ∘ = ( 4.53 ± 0.87 ) kJ · mol - 1 , and the standard molar entropy change, Δ r S m ∘ = ( 2.5 ± 2.9 ) J · K - 1 · mol - 1 . The equilibrium constants of 1-phenyl-1-alkanone with an odd number of carbons in alkyl side chain are higher than the equilibrium constants of the preceding 1-phenyl-1-alkanone having an even number of carbons in the side chain and follow a zig-zag pattern with increasing carbon number in the alkyl side chain.