Effects of solvents polarity parameters on heterogeneous catalytic hydrogenation of cyclohexene in molecular solvents

Heterogeneous catalytic hydrogenation of cyclohexene, catalyzed by Pt/A1203, was carried out in thirteen various solvents (four alcoholic solvents, six aprotic polar solvents and three non polar solvents) at 25 °C. Single-parameter correlations of logk vs. normalized polarity parameter (ETN), hydrogen-bond acceptor basicity (p), hydrogen-bond donor acidity (a) and dipolarity/polarizibility (it*) do not give acceptable results. In addition, logk does not show an acceptable dual-parameter correlation with ETN and a, ETN and 13, ETN and it, a and [3, a and 7T* and p and it. Like that, three parameter and four parameter correlations of log k vs. solvatochromic parameters don't give acceptable results. Correlations of log k vs. acceptor number (AN), donor number (DN), relative static permittivity (a) and dipole moment (μ) are tested but don't give reasonable results. However in case of alcoholic solvents, reaction rate constants increase with increasing of hydrogen-bond donor acidity (a), dipolarity/polarizibility (e), normalized polarity parameter (ETN), relative static permittivity (c), dipole moment 0.0 and acceptor number (AN) and decrease with increasing of hydrogen-bond acceptor basicity (f3) and donor number (DN). These effects are attributed to the non-polar nature of the reactant and competitive adsorption of solvent on catalyst surface.