Esterification of 4-methoxyphenylacetic acid with dimethyl carbonate over mesoporous sulfated zirconia
Mesoporous zirconia was synthesized using cetyltrimethylammonium bromide as template under hydrothermal conditions. The surfactant was removed by ethanol extraction. The resultant mesoporous material was further treated with sulfuric acid and calcined in air at 450 °C for 5 h to obtain mesoporous sulfated zirconia (MSZ). The mesoporous sulfated zirconia was characterized by XRD and N2 adsorption and desorption measurements. Esterification of 4-methoxyphenylacetic acid (4-MPAA) with dimethyl carbonate was carried out in a batch reactor under autogeneous pressure over this catalyst as a function of reaction temperature, catalyst loading and the results are also compared with conventional sulfated zirconia (CSZ). More than 98% selectivity for methyl 4-methoxyphenylacetate was observed in all the experiments. The CSZ catalyst shows very low conversion when compared to that of MSZ. This may be attributed to its low surface area, presence of micropores and non-uniform pore size distribution. The mesoporous sulfated zirconia comprises of large surface area and uniformly distributed mesopores, which facilitates the reaction of bulky organic molecules like 4-MPAA with DMC. In addition, MSZ catalyst shows higher acidity than that of CSZ catalyst and in turn a higher catalytic activity. The kinetics of the reaction over both the catalysts was studied. The rate constant for the reaction was found to be 4.7 × 10−3 min−1 and 0.5 × 10−3 min−1 for MSZ and CSZ, respectively. The activation energy of the reaction is 18.0 kcal/mol over MSZ catalyst.
Journal: Catalysis Communications - Volume 10, Issue 13, 25 July 2009, Pages 1711–1717