The hydrogenation of (E)-2-methyl-2-butenoic acid (tiglic acid), using a commercial 5 wt% Pd/Al2O3 catalyst (Engelhard) doped with cinchonidine (CD) (P = 4.0 MPa, T= 298 K) was investigated in depth to evidence the nature of the interaction CD:acid and the specific role of the solvent polarity on the enantiomeric excess (e.e.). Previous results reported in the literature on the same substrate or on similar unsaturated short chain acids have been verified for a feasible industrial application. A linear correlation between the dielectric constant of the solvent (epsilon) and the e.e. was observed, with a decrease in e.e. by increasing E. The highest enantionteric excess (e.e. = 48%) was obtained with n-hexane. (c) 2005 Elsevier B.V. All rights reserved.