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 thirteenvarious 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 acceptorbasicity (p), hydrogen-bond donor acidity (a) and dipolarity/polarizibility (it*) do not give acceptableresults. In addition, logk does not show an acceptable dual-parameter correlation with ETN and a, ETN and13, ETN and it, a and [3, a and 7T* and p and it. Like that, three parameter and four parameter correlationsof log k vs. solvatochromic parameters don't give acceptable results. Correlations of log k vs. acceptornumber (AN), donor number (DN), relative static permittivity (a) and dipole moment (μ) are tested butdon't give reasonable results. However in case of alcoholic solvents, reaction rate constants increase withincreasing of hydrogen-bond donor acidity (a), dipolarity/polarizibility (e), normalized polarityparameter (ETN), relative static permittivity (c), dipole moment 0.0 and acceptor number (AN) anddecrease with increasing of hydrogen-bond acceptor basicity (f3) and donor number (DN). These effectsare attributed to the non-polar nature of the reactant and competitive adsorption of solvent on catalystsurface.