Selective synthesis of p-cresol by methylation of phenol

The selective synthesis of p-cresol by gas-phase alkylation of phenol with methanol was studied on SiO2-Al2O3 and zeolites HBEA, HZSM5 and HMCM22. Cresols were formed from phenol alkylation of methanol via two parallel pathways: the direct C-alkylation of phenol and the conversion of anisole intermediate obtained by O-alkylation of phenol. Methylation of o- and p-cresol led to the formation of 2,6- and 2,4-xylenols while anisole produced methylanisoles either by alkylation with methanol or by disproportionation. Regarding the cresol isomers distribution, p- and o-cresol were the major products on all the samples while m-cresol formation remained always lower than 6%. SiO2-Al2O3, HBEA and HZSM5 exhibited similar initial p-cresol:o-cresol ratios, between 0.6 and 0.8. In contrast, p-cresol was the predominant product on HMCM22 because the narrow sinusoidal 10-membered ring channels of this zeolite were particularly suitable for improving by shape selectivity the formation of p-cresol. Thus, we report here that p-cresol yields of 55% and p-cresol:o-cresol ratios of 4 are obtained on HMCM22 by gas-phase alkylation of phenol with methanol at 473 K, atmospheric pressure and contact time of 350 g h/mol phenol. (c) 2008 Elsevier B.V. All rights reserved.