Heterogeneous polymer supported and soluble tantalum metal complex catalysts for acylation reaction: A kinetic study

Abstract

New soluble and insoluble Tantalum pentachloride complex catalysts are prepared by simple procedures using pyridine and polymer-supported cross-linked (poly-4-vinyl pyridine) beads (PSCPVP) respectively as supports and Tantalum pentachloride as a catalytic moiety (TaCl5). The prepared soluble Py-TaCl5 and insoluble bead-shaped PSCPVP-TaCl5 catalysts have been characterized with FT-IR, UV-Vis, SEM, TGA and elemental analysis techniques. The catalytic efficiency of these catalysts has been examined through acylation of ethanol as a model reaction under identical pseudo first order reaction condition. From the calculated kobs values, it has been noticed that both the catalysts are active and however, Py-TaCl5shown 1.65 fold has increased activity (kobs =11.42x103 min-1) than insoluble PSCPVP-TaCl5 catalyst (kobs= 6.98x103, min-1). Although, PSCPVP-TaCl5 has shown lesser activity than soluble due to its lower cost, recyclability and reusable nature up to third cycle, it has received greater recognition. Hence, in order to utilize this insoluble bead-shaped PSCPVP-TaCl5 catalyst to pack in column reactor and to carry out the same reaction for continuous mode operation at industrial level, detailed kinetics study for acylation of ethanol has been conducted under pseudo first order condition by varying the different experimental parameters and has observed that each parameter has influenced the reaction. The obtained kobs value reveals that reaction rates increase with the increase in the stirring speed, [substrate], [catalyst] and temperature. The thermodynamic parameters viz., activation energy (Ea), entropy (∆S), enthalpy (∆H) and free energy (∆G#) for the reaction are also calculated for the first time and their observed values are 35.2 kJmol-1, -64.6 kJ-1mol-1, 37.7 kJmol-1and 57.3 kJmol-1 respectively. The prepared insoluble catalyst is stable even after its use for three times in acylation without losing its efficiency, thus it is better suited for industrial applications.