ACYLATION OF ANISOLE WITH LAURIC ACID OVER ZEOLITE BETA

Abstract

ABSTRACT Friedel-Crafts acylation of aromatic compounds is used in the production of many pharmaceutical, agrochemical, and fragrance compounds. Friedel-Crafts acylation proceeds in the presence of acid catalysts. The present industrial practice involves the use of stoichiometric (or more) amounts of metal halides (Lewis acids, like AlCl3, FeCl3) as the catalysts and acyl chlorides as acylatinssg agents, which results in substantial by-product formation besides operational difficulties due to the corrosive nature of the acids and halides. To eliminate corrosion and environmental problems, the replacement of the conventional mineral acids by solid acid catalysts has become a necessity. There are many types of solid acids, such as zeolites, heteropolyacids, sulfonated resins and sulfated metal oxides that possess different acidities. Among these, zeolites are widely used as solid acid catalysts in petroleum and petrochemical processes. The wide pore zeolites, Y, beta and mordenite have found to be especially suitable for applications in the synthesis of fine chemicals. In this work, the Friedel-Crafts acylation of anisole with a long chain carboxylic acid (lauric acid) over zeolite beta (BEA) is reported. The parent zeolite obtained from a commercial source was modified by various treatments, such as, dealumination, desilication and ion-exchange to increase its activity in the acylation reaction. In the present study, the SiO2/Al2O3 ratio (SAR = 25) of the parent BEA was altered by dealumination with HNO3 (to SAR, 58, 88 and 170), and by desilication with tetrapropyl ammonium hydroxide (TPOH). Acidity was altered by exchanging the parent NH4-form with Ce3+, Zn2+ and Fe3+ - ions. The samples were characterized by powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), N2 adsorption isotherm and temperature programmed desorption (TPD) of ammonia. XRD results showed that the BEA structure was maintained after the various treatments. All the catalysts were tested in the Friedel-Crafts acylation of anisole with lauric acid. The reactions were carried out at 155oC and atmospheric pressure in two necked RB flux. Gas Chromatographic analysis of the products revealed the formation of mainly the para isomer of the ketone a [1-(4-methoxyphenyl)dodecane-1-one] as the product. The o- and m- isomers were formed in much smaller amounts. The by-products of the reaction were small amounts of phenol, methanol and unidentified compounds. While mild dealumination increased the activity, severe dealumination decreased the activity. Similarly, desilication and ion-exchange treatments also increased the activity of the zeolite. The activity was highest for Zn-exchanged BEA. Conversion (wt %, based on lauric acid) over the parent sample (SAR = 25) was 38 %, and conversion over the other samples was: i) dealuminated BEA, 52 % for SAR 58 > 11 % for SAR 88 > 5 % for SAR 170; ii) desilicated BEA 54 % for DS1, 48 % for DS2 and iii) meta exchanged samples, 72 % for Zn-BEA, 67 % for Fe-BEA and 59 % for Ce-BEA. Likely reasons for the observed changes in activity on dealumination, desilication and ion-exchange treatments are presented.