Alkylation of catechol with t-butyl alcohol over acidic zeolites Original Research Article

The catalytic properties of H-ZSM-5 in catechol alkylation with t-butyl alcohol are compared to that of other solid acid catalysts, H-USY, H-beta, γ-alumina. H-ZSM-5 zeolite shows a selectivity higher than 84% and conversion higher than 90% for 4-tert-butylcatechol (4-TBC), while 3,5-di-tert-butylcatechol (DTBC) and 3-tert-butylcatechol (3-TBC) are produced as minor byproducts, which are identified by GC/MS and 1H-NMR. When the Na cation-exchange level, Na/H, of NaH-ZSM-5 increases, the conversion and DTBC selectivity decrease rapidly and 3-tert-butylcatechol (3-TBC) selectivity grows. As the SiO2/Al2O3 ratio of H-ZSM-5 increases, the conversion and DTBC selectivity decrease. Selectivities for 4-TBC over NaH-ZSM-5 with three different Na cation-exchange levels and over ZSM-5 with three different SiO2/Al2O3 ratios are not changed significantly. Surface modification of H-ZSM-5 via CVD with tetraethylorthosilicate (TEOS) or poisoning with tributylamine (TBA) leads to the reduction of DTBC selectivity, and simultaneously, to the improvement of 4-TBC selectivity. Variations of catalytic activity over ZSM-5 catalysts are compared and discussed in terms of the concentration and strength of the acid site determined by FT-IR spectroscopy. From this result, strong Brønsted acid sites seem to be responsible for the t-butylation of catechol.