Highly selective conversion of guaiacol to tert-butylphenols in supercritical ethanol over a H(2)WO(4) catalyst

The conversion of guaiacol is examined at 300 °C in supercritical ethanol over a H(2)WO(4) catalyst. Guaiacol is consumed completely, meanwhile, 16.7% aromatic ethers and 80.0% alkylphenols are obtained. Interestingly, tert-butylphenols are produced mainly with a high selectivity of 71.8%, and the overall selectivity of 2,6-di-tert-butylphenol and 2,6-di-tert-butyl-4-ethylphenol is as high as 63.7%. The experimental results indicate that catechol and 2-ethoxyphenol are the intermediates. Meanwhile, the WO(3) sites play an important role in the conversion of guaiacol and the Brønsted acid sites on H(2)WO(4) enhance the conversion and favour a high selectivity of the tert-butylphenols. The recycling tests show that the carbon deposition on the catalyst surface, the dehydration and partial reduction of the catalyst itself are responsible for the decay of the H(2)WO(4) catalyst. Finally, the possible reaction pathways proposed involve the transetherification process and the alkylation process during guaiacol conversion.