The feasibility of the enzymatic enantioselective acylation of R-2-pentanol in a solid/gas reactor was demonstrated and compared to the same reaction carried out in liquid systems. This reaction was catalysed by lipase B from Candida antarctica (CALB) through transesterification of methyl propionate and R-2-pentanol. In the present study we show that there is no effect of the organic solvent on the enantioselectivity E of CALB for this reaction neither in the solid/gas system nor in organic liquid medium. The innovative idea of this work is the replacement of the substrates and solvent concentrations by their thermodynamic activities in order to correct the differences of substrates solvation in the different media studied and to control the level of availability of the different chemical species for the enzyme. Finally, we established that the solid/gas bioreactor is a suitable tool to study the influence of organic components on the enantioselectivity of lipases because it permits to control and adjust independently thermodynamic activities of substrates, on the one hand, and of an extra-added organic component on the other hand.