Applied Catalysis A: General 433–434 (2012) 265–274 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata Atom efficient Friedel–Crafts acylation of toluene with propionic anhydride over solid mesoporous superacid UDCaT-5 Ganapati D. Yadav ∗ , Shashikant B. Kamble Department of Chemical Engineering, Institute of Chemical Technology (ICT), Matunga, Mumbai 400019, India article info Article history: Received 11 March 2012 Received in revised form 30 April 2012 Accepted 21 May 2012 Available online 30 May 2012 Keywords: Friedel–Crafts acylation Heterogeneous catalysis Solid superacids Kinetics 4 ′ -Methylpropiophenone Green chemistry abstract Friedel–Crafts acylation is ubiquitous in industry and is typically carried out by using more than stoichio- metric quantities of homogeneous catalysts. This creates pollution. In this work, acylation of toluene was studied in liquid phase with propionic anhydride with a variety of solid superacids to produce 4 ′ -methylpropiophenone (4 ′ -MPP). The solid superacids were modified versions of zirconia, namely, UDCaT-4, UDCaT-5 and UDCaT-6 developed in our laboratory; amongst which UDCaT-5 was the most active, selective and robust catalyst. The effects of various reaction parameters on the rate of reaction and selectivity were investigated to deduce the intrinsic kinetics of the reaction. The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically con- trolled. The acylation conditions were: temperature 180 ◦ C, toluene to propionic anhydride molar ratio 5:1, catalyst loading 0.06 g cm -3 , speed of agitation 1000 rpm, under autogenous pressure in a stainless steel autoclave reactor. Propionic acid generated in situ also reacts sequentially with toluene to give 4 ′ -MPP. A conversion of 62% of priopionic anyhydride is obtained after 3 h, with 100% mono-acylated product containing 67% 4 ′ -MPP. Water is the only co-product of the overall reaction. A suitable kinetic model was developed. The reactions were carried out without using any solvent in order to make the process cleaner and greener. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Liquid acids have been extensively used as catalysts in a vari- ety of chemical and allied industries. Green chemistry approach involves the replacement of corrosive and toxic liquid acids such as HF and H 2 SO 4 by environmentally benign heterogeneous solid acids. The production of various pharmaceuticals, agrochemicals, dyes and pesticides involves the synthesis of aromatic ketones and their derivatives. The common routes for preparation of these ketones proceed via Friedel–Crafts acylation of the concerned aromatic hydrocarbon with derivates of carboxylic acids, which are traditionally catalyzed by either Lewis acids such as AlCl 3 , FeCl 3 and BF 3 or Brønsted acids such as HF or H 3 PO 4 [1].4 ′ - Methylpropiophenone (4 ′ -MPP) is found to have wide applications in the area of fine chemicals, pharmaceuticals, resins, drugs, per- fumes and specialty chemical synthesis. The classical production of 4 ′ -MPP is performed by Friedel–Crafts acylation process of toluene with propionic anhydride or propionyl chloride, using sto- ichiometric quantities of conventional homogeneous Lewis acid ∗ Corresponding author. Tel.: +91 22 3361 1001/1111/2222; fax: +91 22 3361 1002/1020. E-mail addresses: gdyadav@yahoo.com, gd.yadav@ictmumbai.edu.in (G.D. Yadav). catalyst, AlCl 3 , FeCl 3 or BF 3 [2]. Use of these catalysts is fraught with a numerous drawbacks and operational problems. More than stoichiometric amount of Lewis acid is required. The reaction com- plexes formed are rather stable and their break-up to obtain the desired product leads to the loss of the catalyst [1,3]. The corro- sive nature of homogeneous acids results in premature ageing of the processing equipment and associated transfer lines, which is expensive. Use of solid acids such as shape selective zeolites in acylation with carboxylic acids is more attractive [4]. In recent years, efforts have been directed toward the promotion of solid acid catalysts and several synthetic procedures have been reported. Heterogeneous solid acids are advantageous over conven- tional homogeneous acid catalysts [5–7]. They are non-corrosive; presenting fewer disposal problems, and their separation from fluid phase is much easier, which allows their repeated use. They permit the use of cheaper and non-polluting reagents, and offer several different reactor configurations [3]. In addition, physical and chemical properties of solid acids can be tailored and tuned to promote reactivity and selectivity and prolonged catalyst life [7]. Nakamura et al. [8] described the propionylation and butyryla- tion of toluene with propionic anhydrides and butyric anhydrides over SO 4 /ZrO 2 , SO 4 /SnO 2 , Pt-SO 4 /ZrO 2 , and Ru-SO 4 /ZrO 2 ; yields of 7–9% o- and 91–93% p-isomers were 31, 26, 32, and 44% for pro- pionylation and 46, 29, 44, and 55% for butyrylation, respectively obtained. 0926-860X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2012.05.031