Synthesis of Hydroquinone Monomethyl Ether from Hydroquinone and Methanol over Heteropolyacids Supported on Clay: Kinetics and Mechanism

Hydroquinone mono methyl ether (HMME) is industrially a very important anti-oxidant, produced by environmentally undesirable routes. In the current studies, HMME was synthesized from hydroquinone and methanol catalyzed by various solid acids using montmorillonite clay (K10) as a support with different loadings of dodecatungstophosphoric acid (DTP), AlCl3, FeCl3, and ZnCl2. Among these, 40% DTP/K10 with benzoquinone as cocatalyst was the most active and selective. The reaction mechanism suggests that benzoquinone couples with protonated methanol on the catalyst site to yield an intermediate, which reacts with hydroquinone adjacent to the site. The surface reaction between the intermediate and chemisorbed hydroquinone controls the overall rate of reaction. There is 100% selectivity toward HMME. The experimental data are well correlated with the model. Excess of methanol favors the formation of HMME.