Heterogeneous catalytic hydrogenation of cyclohexene, catalyzed by Pt/Al2O3, was carried out in solutions of 2-hydroxyethylammonium formate (a room temperature ionic liquid, RTIL) mixed with methanol, ethanol and propan-2-ol at 25 degrees C. The rate constants of the reaction in ionic liquid alcohol mixtures were higher than alcohol alone. First-order rate constant of the reaction in the RTIL relative to propan-2-ol is approximately 28. Furthermore, the rate constant of the reaction increases with the mole fraction of the ionic liquid. Single-parameter correlations of log k vs. normalized polarity parameter (E-T(N)), hydrogen-bond acceptor basicity (beta) and hydrogen-bond donor acidity (alpha) do not give acceptable results in the solutions. In addition, log k does not show an acceptable dual-parameter correlation with pi* (dipolarity/polarizibility, one of the Kamlet-Taft parameters for solvent that shows the dipolarity of the solvent) and alpha, pi* and and E-T(N) and beta. However single-parameter correlation of log k vs. pi* gives reasonable results. The increase of the reaction rate with pi* is attributed to the non-polar nature of the reactants. (c) 2008 Elsevier B.V. All rights reserved.