Selectivity Engineering in Synthesis of Thymol Using Sulfated ZrO2–TiO2

Selective synthesis of thymol (6-isopropyl-3-methylphenol), a perfumery chemical, is challenging and was studied in this work by a continuous vapor phase alkylation of m-cresol using isopropyl alcohol over different solid acids. A series of novel zirconia–titania mixed sulfated oxides were prepared by the hydrothermal method and tested for isopropylation of m-cresol to prepare thymol. A sulfated catalyst with 2:1 mol ratio for zirconia/titania showed the best conversion and selectivity for thymol in a continuous fixed bed vapor phase reactor. The catalyst is stable and active for a long period of time, up to 20 h (TOS). Isopropylation of m-cresol was carried out in a continuous fixed bed vapor phase reactor under N2 as a carrier gas, 6.72/h WHSV, and 1:3 mol ratio of m-cresol to IPA at 220 °C. Reaction mechanism and kinetic model were developed. The reaction is kinetically controlled having an activation energy of 8.27 kcal/mol.