Tungstophosphoric acid supported on MCM-41 mesoporous silicate: An efficient catalyst for the di-tert-butylation of cresols with tert-butanol in supercritical carbon dioxide

Tungstophosphoric acid (HPW) supported on MCM-41 mesoporous silicate was an excellent catalyst for the tert-butylation of cresols in supercritical CO2. The tert-butylation of p-cresol gave 2,6-di-tert-butyl-4-methylphenol (2,6-DTBPC) in high yield (the best yield: 58%) in supercritical CO2; however, zeolites, H-Y and H-beta, gave only 2-tert-butyl-4-methylphenol (2-TBPC) because of their limitation in pore size. The yield of 2,6-DTBPC over HPW(30)/MCM-41 was maximum at 110 °C, and further increase in temperature decreased the yield. There was the optimal CO2 pressure on the yield of 2,6-DTBPC at 10 MPa, and further increase of the pressure resulted in rapid decrease in the yield.Thermogravimetric analysis of used catalysts showed that the deactivation is minimized in supercritical CO2 compared to the other reaction media such as hexane as solvent and without solvent under N2 atmosphere. HPW(30)/MCM-41 was recyclable without significant loss of catalytic activity, and retained mesoporous structure even after three recycles.The tert-butylation of o- and m-cresols over HPW(30)/MCM-41 gave the 2,4-di-tert-butyl-6-methylphenol, 2,4-di-tert-butyl-5-methylphenol, respectively, in good to moderate yields.