Butylation of phenol on medium pore AlPO 4 –11, –31 and –41 structures: Effect of silicon incorporation C.V. Satyanarayana*, U. Sridevi and B.S. Rao Catalysis Division, National Chemical Laboratory, Pune-411 008, India. Butylation of phenol with tert-butylalcohol as the alkylating agent is reported on three medium pore aluminophosphates AlPO 4 –11, AlPO 4 –31 and AlPO 4 –41. Activity of these molecular sieves has been compared with their silicon substituted versions SAPO-11, SAPO- 31 and SAPO-41. Surprisingly, AlPO 4 frameworks without silicon substitution were found to be active. Apparently, terminal hydroxyls in AlPO 4 ’s are active for butylation of phenol. The highest activity of AlPO 4 -31 is attributed to the presence of large concentration of terminal hydroxyls, a result of its small crystallite size. In addition to weak terminal hydroxyls, bronsted acid sites generated upon silicon substitution into AlPO 4 framework also contribute to the over all activity. All the catalysts, including SAPO’s deactivate at a faster rate. SAPO- 11 with higher concentration of silicon deactivates at a slower rate. 1. INTRODUCTION Alkyl phenols, particularly 4-tert-butylphenol (4-TBP), 2,4-di-tert-butylphenol (2,4- DTBP) and 2,6-di-tert-butylphenol (2,6-DTBP) have great commercial significance. 4-tert- butylphenol is used on a large scale for the production of a variety of phenol-formaldehyde resins. It also has antioxidant properties and is used as a stabilizer in rubber and chlorinated hydrocarbons. Whereas 2,4-DTBP is mainly used in the manufacture of its triphosphite which is employed as a (co-)stabilizer for polyvinyl chloride. 2,6-DTBP is a very important building block in the synthesis of higher molecular mass antioxidants and light protection agents for plastics and polyolefins [1]. The catalysts used, thus far for the preparation of butylphenols, consist of mainly liquid acids [2], aluminium phenoxide [3,4], metal oxides [5], ion-exchange resins[6,7] and clays [8]. Though cation exchange resins are good catalysts for this purpose, they can not be used at higher temperatures. On the otherhand, it may be possible to prepare 4-TBP and 2,4- DTBP with very high selectivities employing environmentally benign molecular sieve catalysts. There are some reports in recent years, on the use of molecular sieve catalysts in the alkylation of phenols. Xu et al. have employed sodium exchanged HY zeolites to obtain 4- TBP with 85% selectivity at a phenol conversion of 69% [9]. Butylphenols with high para selectivity were reported to be obtained when phenol was alkylated with iso-butylalcohol over large pore zeolites ZSM-12, beta and MCM-22 [10]. Zhang et al. in their study on beta zeolite catalysts have reported that strong acid sites are responsible for the formation of 2,4- DTBP, while medium and weak acid sites facilitate the formation of 4-TBP and 2-TBP respectively [11]. In their study using HY zeolites, Corma et al. concluded that C-alkylation requires stronger acidity than the O-alkylation [12]. Butylation of phenol over mesoporous