Synthesis of cresols by alkylation of phenol with methanol on solid acids M.E. Sad, C.L. Padro ´, C.R. Apesteguı ´a * Catalysis Science and Engineering Research Group (GICIC), Instituto de Investigaciones en Cata ´lisis y Petroquı ´mica-INCAPE-(UNL-CONICET), Santiago del Estero 2654, (3000) Santa Fe, Argentina Available online 1 February 2008 Abstract The gas-phase alkylation of phenol with methanol to obtain cresols was studied at 473 K on SiO 2 –Al 2 O 3 , Al-MCM-41, tungstophosphoric acid (HPA) supported on silica, and zeolites HBEA, HZSM5 and HY. The nature, density and strength of surface acid sites were probed by temperature- programmed desorption (TPD) of NH 3 coupled with infrared spectra of adsorbed pyridine. Anisole, o-cresol and p-cresol were primary reaction products while m-cresol, xylenols and methylanisoles were secondary products. O- and p-cresols were formed via direct C-alkylation of phenol, and also by conversion of anisole intermediate obtained by O-alkylation of phenol. C-alkylation of phenol was predominant as compared to O- alkylation over all the catalysts, excepting HPA/SiO 2 . Zeolites HBEA and HY were the most active catalysts for obtaining cresols because both reaction pathways leading from phenol to cresols were particularly promoted by the simultaneous presence of strong Lewis and Bro ¨ nsted acid sites. However, zeolite HY was rapid and severely deactivated on stream. Phenol methylation was controlled by intracrystalline diffusion on HZSM5 and the narrow channels of this zeolite hindered the formation of bulky intermediates involved in the overalkylation of cresols to xylenols. In contrast, the cresol isomer distribution was practically the same on zeolites HBEA and HZSM5 because HZSM5 did not improve the relative formation of p-cresol by shape selectivity. # 2007 Elsevier B.V. All rights reserved. Keywords: Cresol synthesis; Solid acids; Phenol alkylation; Phenol methylation 1. Introduction Cresols (or methylphenols) are widely employed for the synthesis of pharmaceuticals, herbicides, antioxidants, agro- chemicals and dyes [1]. For example, o-cresol is chlorinated to 4-chloro-o-cresol (PCOC), the starting material for important selective herbicides, and highly pure o-cresol is increasingly processed to epoxy-o-cresol resins (ECN resins), which are used as sealing materials for integrated circuits (chips). m- Cresol is a raw material for both contact and pyrethroid type insecticides and for producing photoresistant compounds and thermal recording materials; besides, selective methylation of pure m-cresol with methanol gives 2,3,6-trimethylphenol that is employed in the vitamin E synthesis. p-Cresol can be alkylated with tert-butanol to obtain 2,6-di-tert-butyl-p-cresol, commer- cially known as butylated hydroxyl toluene (BHT) which is widely used in the manufacture of phenolic resins, antioxidants and polymerization inhibitors [2,3]. p-Cresol is also used to produce anisaldehyde, a key intermediate for the synthesis of important pharmacological products such as the coronary therapeutical diltiazem or the chemotherapeutical trimethoprim [1]. p-Hydroxybenzonitrile ( p-HBN) is another industrially important product used in agrochemicals that can be obtained from p-cresol [4]. At present, o-cresol is obtained together with 2,6 xylenol by gas-phase alkylation of phenol with methanol on MgO-based catalysts at temperatures between 673 and 773 K [5]. p-Cresol is commercially produced by toluene oxidation via sulfonation with sulphuric acid using a four reaction step 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 [6]. Finally, m-cresol is obtained by alkaline chlorotoluene hydrolysis or cymene hydroperoxide cleavage, but both processes use dangerous reactants and produce environmentally aggressive effluents [1]. In an attempt www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 133–135 (2008) 720–728 * Corresponding author. Tel.: +54 342 4555279; fax: +54 342 4531068. E-mail address: capesteg@fiqus.unl.edu.ar (C.R. Apesteguı ´a). URL: http://www.ceride.gov.ar/gicic 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.12.074