Design of Sulphate Modified Solid Acid Catalysts for Transesterification of Diethyl Malonate with Benzyl Alcohol.

Sulphate ion modified multiwalled carbon nanotubes (S-CNTs), mesoporous carbon (S-MC), zirconia (S-ZrO2), alumina (S-Al2O3) and silica (S-SiO2) were prepared by wet impregnation technique. The physico-chemical properties of the prepared materials were investigated by Powder-XRD, BET-Surface area and SEM-EDS analysis. Surface acidity of the materials was analyzed using TPD-NH3 and n-butyl amine titration methods. Catalytic activity of these materials was investigated in liquid phase transesterification of diethyl malonate with benzyl alcohol. Effect of various reaction parameters on product yield as well as recyclability of the catalysts was investigated. Kinetics of the reactions was studied and activation energy was evaluated. All the catalysts investigated in this reaction were found to be catalytically active except S-Al2O3, for the formation of transester products; benzyl ethyl malonate (BEM) and dibenzyl malonate (DBM). S-ZrO2 and S-MC resulted good % yield (70 and 73% respectively) of total transester products where as S-CNTs showed 100% selectivity towards the formation of only BEM. Acid sites with moderate acid strength are found to be catalytically active for the transesterification reaction. The catalysts were recyclable up to 5 times without significant loss in their catalytic activity except in the case of S-MC. The reaction followed first order kinetics and the energy of activation of the reaction with different catalysts was in the range of 12-58 kJ mol-1.