"Highly selective synthesis of p-cresol by gas-phase alkylation of phenol with methanol on solid acids"

MARÍA EUGENIA SAD; CRISTINA LILIANA PADRÓ; CARLOS RODOLFO APESTEGUÍA

Houston, USA

Congreso; 20th North American Catalysis Society Meeting; 2007

p-Cresol is widely employed for the synthesis of pharmaceuticals, herbicides, antioxidants, agrochemicals and dyes.  It is commercially produced by toluene dehydration via sulfonation with sulphuric acid using a four reaction steps process that poses serious environmental concerns because of the formation of significant amounts of sodium sulfite as subproduct and the use of strong liquid acid catalysts.  Thus, a number of studies have been lately devoted to explore the use of solid acids for obtaining selectively p-cresol via the alkylation of phenol with methanol (Scheme 1). However, the para-:ortho-cresol selectivity ratio on amorphous catalysts or wide pore zeolites such as HBeta, HY, and H-mordenites was always lower than 0.7.  Recently, it was reported that p:o ratios of up to 1.2 are reached by using zeolites HZSM5 and MCM22 in liquid phase [1]. In this work, we performed a detailed study of the gas-phase alkylation of phenol with methanol on samples containing only strong Brönsted acid sites (HPA/SiO2) and catalysts containing both Lewis and Brönsted acid sites of either strong (zeolites HZSM5, HBeta and ZSM22) or moderate (SiO2-Al2O3) strength.  Results will show that the primary and secondary reaction pathways leading from phenol to cresols depend on both the pore microstructure and the nature, density, and strength of surface acid sites, but the reaction para-selectivity is only dramatically increased by using zeolite ZSM22.