Maximise equilibrium conversion in biphasic catalysed reactions: How to obtain reliable data for equilibrium constants?

For the prediction and optimisation of the equilibrium conversion in biphasic catalysed reactions, the equilibrium constant of the desired reaction and the partition coefficients of all reactants have to be known. Within this contribution we have examined the alcohol dehydrogenase-catalysed reduction of several linear and aromatic ketones in biphasic reaction media with respect to equilibrium conversion. In this example, the equilibrium constant can be expressed in terms of differences in oxidation-reduction potentials Delta E-0. However, for a large variety of organic compounds, these data are quite rare in the literature. To overcome this lack of data, we have utilised methods of computational chemistry to calculate data for the Gibbs free energy Delta G(R) leading to the equilibrium constants of a homologous series of linear ketones. To obtain comparable data for the reduction of substituted acetophenone derivatives, the Hammett relation leads to the necessary equilibrium constants. Furthermore, we compare the equilibrium conversions of a set of cofactor regeneration methods for the alcohol dehydrogenase-catalysed reductions. These results lead to a time-saving experimental design for the enantioselective reduction of 2-octanone to (R)-2-octanol on a preparative scale utilising biphasic reaction conditions.