Cesium exchanged heteropoly tungstate supported on zirconia as an efficient and selective catalyst for the preparation of unsymmetrical ethers K.T. Venkateswara Rao, P.S.N. Rao, P.S. Sai Prasad, N. Lingaiah * Catalysis Laboratory, I&PC Division, Indian Institute of Chemical Technology, Hyderabad, A.P. 500 607, India article info Article history: Received 23 December 2008 Received in revised form 2 March 2009 Accepted 8 March 2009 Available online 14 March 2009 Keywords: Unsymmetrical ethers Alcohol Heteropoly tungstate Cesium Zirconia abstract Zirconia supported cesium exchanged 12-tungstophosphoric acid catalysts were prepared and studied for the synthesis of unsymmetrical ethers from alcohols. The techniques of powder X-ray diffraction, FT- infrared and temperature programmed desorption of ammonia were employed to investigate the struc- tural characteristics of the catalysts. The supported heteropoly tungstate catalysts were highly active for the synthesis of wide range of unsymmetrical ethers from primary and secondary alcohols. Optimum per- formance of the catalysts depends upon the extent of Cs substitution to TPA, which is related to the avail- ability of surface acidic sites. The catalyst is reusable without any loss in catalytic activity. Ó 2009 Published by Elsevier B.V. 1. Introduction Preparation of ethers is an important reaction in organic chem- istry as these compounds are used as fragrance precursors and oxygenates in reformulated gasoline [1,2]. A wide variety of meth- ods are available for the synthesis of ethers and among them the Williamson ether synthesis is the best general method for the preparation of symmetrical and unsymmetrical ethers [3]. This method of preparation involves converting alcohols into corre- sponding halides under strong basic conditions and is not effective with secondary and tertiary alcohols, which paves way for elimina- tion reaction [4]. Alternatively, ethers are also prepared from alco- hols using Bronsted acid catalysts [5]. The reactions using Bronsted acid are often conducted under harsh conditions that lead to the formation of mixture of products. Moreover these are predomi- nantly focused on the synthesis of symmetrical alkyl ethers. Different catalytic systems based on transition metals as prom- ising method are reported for etherification of alcohols [6,7]. Yi Len et al. reported the etherification of benzyl alcohols with various primary aliphatic alcohols to unsymmetrical ethers in good yields over Rh (I) catalyst [8]. Etherification of aliphatic and benzylic alco- hols with primary and secondary aliphatic alcohols was reported using FeCl 3 as catalyst [9]. In most of the reported methodologies the reaction requires stoichiometric amounts of the reagent [10]. The Lewis acid reagents used for the preparation of ethers are in homogeneous phase and suffer from reusability. Moreover some of the Lewis acid catalysts are deactivated by water, which is pro- duced during the reaction. Water compatible gold catalyst was re- ported for the synthesis of unsymmetrical ethers from alcohols [11]. In spite of the high activity of this catalyst for converting ben- zylic and tertiary alcohols it suffers from reusability. In order to overcome the difficulties associated with homoge- neous catalysts, usage of heterogeneous catalysts has been re- ported [12–14]. AlPW 12 O 40 as a heterogeneous Lewis acid catalyst was reported for the etherification of benzyl alcohols [13]. Even though this catalyst showed activity in the presence of water, it is partially soluble in water. A general method for the preparation of ethers using water resistant Sn and Zn containing silicates as Lewis acid catalyst was reported [14]. Despite the cat- alyst is water resistant, it is active at high reaction temperatures and requires long reaction times. Moreover, there are no reports about its reusability. The usage of heterogeneous Bronsted acid catalysts for the preparation of unsymmetrical ethers is scare. Heteropoly compounds with Keggin structure are promising materials as they are used as catalysts for various acid catalyzed reactions [15,16]. The utility of heteropoly acids (HPA) as catalysts has stimulated considerable interest due to a unique combination of their stability, acidity and structural accessibility. The most sta- ble and strongest acid in the HPA series is tungstophosphoric acid (H 3 PW 12 O 40 ; TPA). Even though several advantages are associated with HPAs there are some disadvantages like low thermal stability, low surface area (2 m 2 /gm) and solubility in polar solvents. The acid strength of HPAs can be tuned by the exchange of protons with metal cation. When large monovalent cations like Cs + are substituted for the protons of TPA, an increased surface area, 1566-7367/$ - see front matter Ó 2009 Published by Elsevier B.V. doi:10.1016/j.catcom.2009.03.004 * Corresponding author. Tel.: +91 40 27193163; fax: +91 40 27160921. E-mail address: nakkalingaiah@iict.res.in (N. Lingaiah). Catalysis Communications 10 (2009) 1394–1397 Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom