Studies on MCM-41: Effect of sulfate on nitration of phenol

The mesoporous molecular sieve MCM-41 was synthesized by sol–gel method using tetraethyl orthosilicate (TEOS), cetyl trimethyl ammonium bromide (CTAB), aqueous NH3 and water. A series of sulfate modified MCM-41 was prepared by incipient wetness impregnation method using H2SO4 as sulfatising agent. The samples were characterized by BET surface area, X-ray diffraction, FT-IR and TG–DTA. The catalytic activity of the samples was evaluated for nitration of phenol with nitric acid in dichloro ethane (DCE) medium, at room temperature. The effect of reaction parameters, i.e. time, concentration of nitric acid and phenol/nitric acid ratio were also investigated. Modification with sulfate opened new opportunities to generate active Brønsted and Lewis acid sites in the stabilized nanostructure MCM-41. Among the catalysts screened, 4 wt.% sulfated MCM-41 showed maximum activity (93%), with 90% selectivity towards ortho-nitrophenol.

S/MCM-41 is an efficient catalyst for nitration of phenol, which is an electrophilic substitution reaction. The electrophile, i.e. nitronium ion was generated by the reaction between HNO3 and the Brønsted acid sites of S/MCM-41. It attacked phenol and gave ortho- and para-nitrophenol. Between these two products ortho-nitrophenol was the major product. Figure optionsDownload as PowerPoint slide