Different acylating agents in the synthesis of aromatic ketones on sulfated zirconia J. Deutsch a; *, A. Trunschke a , D. Mu¨ ller a , V. Quaschning b , E. Kemnitz b , and H. Lieske a a Institut fu¨r Angewandte Chemie Berlin-Adlershof e.V., Richard-Willsta¨tter-Strasse 12, 12489 Berlin, Germany b Humboldt-Universita¨t zu Berlin, Institut fu¨r Chemie, Brook-Taylor-Strasse 2, 12489 Berlin, Germany Received 5 November 2002; accepted 27 February 2003 Sulfated zirconia (SZ) has been used as a heterogeneous catalyst in the synthesis of aromatic ketones. A number of carboxylic anhydrides andacidchloridesprovedtobeappropriateacylatingagentsinthereactionwithanisoleandchlorobenzene.Therateofanisoleacylationwas found to be dependent on the type of acylating agent used. Thus, acetic anhydride and benzoic anhydride reacted faster on SZ with anisole than benzoyl chloride. Successful SZ-catalyzed acylations of chlorobenzene were limited to acceptor substituted benzoyl chlorides as acylating agents. Acetic anhydride and benzoic anhydride did not react with chlorobenzene in the presence of SZ. KEY WORDS: sulfated zirconia; aromatics; acylation; aromatic ketones. 1. Introduction Acylation of aromatics is a key reaction in organic chemistry. The resulting aromatic ketones are used as intermediates or final compounds in the production of pharmaceuticals, cosmetics, agrochemicals, dyes, and special chemicals. Owing to economic and ecological drawbacks, such as the necessity of stoichiometrically activating the acylating agent with Lewis acids (Friedel–Crafts acylation), their irreversible loss during product isolation, and extensive formation of acid wastes, there is much effort made to substitute this widely established method. Numerous papers report attempts to turn the current stoichiometric methods into catalytic processes. For example, the synthesis of benzophenones was achieved in the presence of the homogeneous catalyst triflic acid [1,2]. Moreover, hafnium(IV) triflate is able to catalyze the formation of aromatic ketones, but the required use of the solvent system nitromethane/lithium perchlorate [3,4] is not convenient for industrial applications. Solid acids are attractive catalysts for the acylation of aromatics because of their easy separation from the reaction mixture by filtration. The acylation of anisole using common acylation agents, such as acetic anhy- dride, was performed over zeolites [5–10], clays [11–13], nafion-H on silica [14], heteropoly acids [15], and microencapsulated scandium(l11) triflate in combination with nitromethane/lithium perchlorate [16]. Modified metal oxides such as SZ [17], sulfated alumina [18], Al- promoted SZ [19], Al-promoted sulfated titania [20], and tungsten oxide on zirconia [21] were applied to the benzoylation of toluene. Currently there is a lack of detailed information about the reactivity of various acylating agents and aromatics under the conditions of heterogeneous catalysis. This paper reports on a systematic investigation of the reactivity of several acylating agents toward anisole and chlorobenzene over SZ. 2. Experimental 2.1. Chemicals Anisole (99.7%, anhydrous), chlorobenzene (99.8%, anhydrous), acetic anhydride (98%), propionic anhy- dride (97%), decanoic anhydride (98%), octadecanoic anhydride (98%), isobutyric anhydride (97%), pivalic anhydride (99%), (S)-2-methylbutyric anhydride (94%), phenylacetyl chloride (98%), 3-phenylpropionyl chloride (98%), succinic acid monomethyl ester chloride (97%), benzoyl chloride (99%), 4-methylbenzoyl chloride (98%), 4-methoxybenzoyl chloride (99%), 4- chlorobenzoyl chloride (99%), 4-nitrobenzoyl chloride (98%), and 1,3,5-benzenetricarboxylic acid trimethyl ester (98%) were purchased from Aldrich, and benzoic anhydride (97%) from Fluka. The chemicals were used without further purification. 2-Methylbutyric anhydride was synthesized from 2-methylbutyric acid (Aldrich, 98%) and N,N 0 -dicyclohexyl-carbodiimide (Aldrich 99%) according to a previous study [22]. 2.2. Catalyst preparation and characterization The catalyst, SZ, was prepared by adding aqueous ammonia to an aqueous solution of ZrOCl 2 until a pH Catalysis Letters Vol. 88, Nos. 1–2, May 2003 (# 2003) 9 1011-372X/03/0500-0009/0 # 2003 Plenum Publishing Corporation * To whom correspondence should be addressed.