Friedel-Crafts alkylation of resorcinol with methyl-tert-butylether over immobilized Keggin tungstophosphoric acid heterogeneous catalysts

Alkylated resorcinols are important as antioxidant and widely used in the pharmaceutical and fine chemical industries. 4-tert-butylresorcinol is used as active component in the treatment of skin diseases and as colour developer. Resorcinol alkylation to 4-tert-butylresorcinol is an electrophilic aromatic substitution, traditionally carried out in homogeneous phase using strong Brønsted acids (e. g., H2SO4). The increasing environmental concern raised the issue of developing sustainable alternatives. The use of heterogeneous solid catalysts would reduce the amount of wastes produced since they can be easily separated from the reaction mixture by filtration. However, despite the important role of alkylated dihydroxybenzenes in the chemical industry, only few works involving the use of heterogeneous catalysts have been carried out in the last years. Even though resorcinol conversion was kept high (up to 99%) the selectivity to 4-tert-butylresorcinol were low, because of the formation of the di-alkylated product 4,6-di-tert-butylresorcinol. In addition, previous works have missed to address attention to the reaction mechanism at the catalyst surface. Further, the impact of the catalyst surface chemistry on the reaction was not investigated enough. In this context, this research project aims at answering the question: how to obtain 4-tert-butylresorcinol with good resorcinol conversion and high selectivity in a clean way? The resorcinol alkylation reaction mechanism and the catalyst surface chemistry are at the core of this research. Keggin phosphotungstic acid (HPW) was chosen as active phase to catalyse the resorcinol tert-butylation. To be used in a polar liquid environment, it was heterogenized by immobilization using the hydrolytic sol-gel method following two different approaches: the not-templated synthesis and the templated synthesis using surfactants. In the first group of catalysts, obtained with the not-templated approach, different supports (SiO2, TiO2 and Zr
(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 2019