Thermodynamics of the lipase-catalyzed transesterification of (−)-menthol and dodecyl dodecanoate in organic solvents

The thermodynamics of the lipase-catalyzed transesterification reaction(−)-menthol(sln)+dodecyl dodecanoate(sln)=(−)-menthyl dodecanoate(sln)+1-dodecanol(sln)have been studied. Equilibrium measurements were performed as a function of temperature with n-heptane, toluene and 2,2,4-trimethylpentane as solvents. The results of the equilibrium measurements were used to calculate the standard molar Gibbs energy ΔrGmo, enthalpy ΔrHmo and entropy ΔrSmo changes for the above reaction in these three solvents at the temperature T=298.15 K. The values of the ΔrGmo and ΔrHmo in these solvents ranged, respectively, from 1.5 to 2.6 kJ mol−1 and from 0.2 to 4.0 kJ mol−1. The (hexane+water) partition coefficients of the reactants and products were also determined at T=298.15 K. A thermochemical cycle calculation was then used to calculate a value for the equilibrium constant K=(2.4±0.7)×10−3 and ΔrGmo=(14.9±0.7) kJ mol−1 for the above reaction in water. However, the average value of the equilibrium constant for reaction (1) in the organic solvents is remarkably constant, namely 〈K〉=0.372 (estimated standard deviation of the mean=0.014). Thus, the thermodynamics of this reaction in water are substantially different than in the organic solvents studied herein.