Short Communication Supported imidazole as heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO 2 Meenakshisundaram Sankar a, ⁎, Thalasseril G. Ajithkumar b , Gopinathan Sankar c , Palanichamy Manikandan a,1 a Catalysis and Inorganic Chemistry Division, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India b Central NMR Facility, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, India c Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK abstract article info Article history: Received 3 June 2014 Received in revised form 21 October 2014 Accepted 28 October 2014 Available online 01 November 2014 Keywords: Cyclic carbonates CO 2 utilization Anchored imidazole Epoxides Imidazole anchored onto a silica matrix, by means of a propyl linkage, is found to be an effective heterogeneous catalyst for the synthesis of cyclic carbonates from epoxides and CO 2 in near quantitative yield. The versatility of this catalyst is demonstrated by using different substrates (epichlorohydrin, propylene oxide, butylene oxide and styrene oxide) for this cycloaddition reaction. These CO 2 insertion reactions were typically carried out in the temperature range of 343 to 403 K at 0.6 MPa CO 2 pressure under solvent-free conditions. Several spectroscopic methods were used to characterize the catalyst and study the integrity of the fresh and spent catalysts. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Utilization of renewable feedstock to value added chemicals is an attractive and important area of research [1–3]. Carbon dioxide (CO 2 ) is an abundant, safe, inexpensive and renewable C-1 feedstock for producing a number of industrially important chemicals [3–6]. However, owing to the thermodynamic stability of CO 2 , its utilization in making organic compounds is a challenging topic [1,3,7]. Among various possible transformations, the atom-economic synthesis of cyclic carbonates from epoxides and CO 2 has been of great interest both industrially and academically (Scheme 1) [1,3,6,7]. Cyclic carbonates are used in the synthesis of many industrially important compounds like dimethyl carbonate and polycarbonates and they find applications as solvents and intermediates for the synthesis of fine chemicals [1,8–10]. Conven- tionally, these cyclic carbonates are synthesized using phosgene or CO, which are hazardous and environmentally unfriendly [3,4,7]. A number of catalysts have been reported for this method of synthe- sizing cyclic carbonate [11]. Although homogeneous catalysts are efficient in many cases, catalyst separation from the reaction mixture is difficult [12–14]. To overcome this, a number of solid catalysts have also been reported, for example, Yasuda et al. [15] have reported SmOCl-based catalyst to obtain higher selectivity without any additive under scCO 2 , but the yield was poor without an additive like DMF. Yamaguchi et al. [16] reported a mixed metal oxide catalyst, but with a higher catalyst loading for this cycloaddition reaction. Other reported heterogeneous catalysts include Nb 2 O 5 , Ti-SBA-15 and other metal oxide-based materials [17–19]. Unfortunately, these solid catalysts suffer one or more of the following disadvantages: need for solvent or co-catalyst, requirement of higher temperature and pressure, longer duration for the completion of reaction or high cost involved in the ma- terials synthesis. Initially, we reported a Zn-W polyoxometalate-based catalyst for the synthesis of cyclic carbonate with a very high turnover number, but with homogeneous 4-(N,N-dialkylamine)pyridine (DMAP) as a co-catalyst [10]. During that study, we found that DMAP (lewis-base) alone can catalyze this cycloaddition reaction [10]. Shiels et al. [18] followed up this lead and anchored DMAP in SBA-15 and reported it as an effective heterogeneous catalyst for the synthesis of cyclic carbonate. Similarly, other N-containing organic bases have been anchored on metal oxide supports as were reported as heteroge- neous catalysts for this reaction. Zhang et al. [19] anchored 1,5,7- triazabicyclo[4,4,0]dec-5-ene on fumed silica matrix and reported that as an efficient catalyst for the cyclic carbonate synthesis. However, the performance of the recovered catalysts decreased with a reduced selectivity for cyclic carbonate. Recently, Miralda et al. [20] reported a zeolitic imidazole framework-8 catalyst for the insertion of CO 2 to epichlorohydrin to form chloropropene carbonate. Although, this catalyst is active at relatively lower temperature, i.e., 353 K, the selectivity for the cyclic carbonate was reported to be less because of the formation of diol by-products. A number of groups have reported imidazolium- based ionic liquids supported on mesoporous silica [21], commercial silica surfaces [22], SBA-15 [23] and polymers [24,25] as effective Catalysis Communications 59 (2015) 201–205 ⁎ Corresponding author at: Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff CF10 3AT, UK. E-mail address: sankarncl@gmail.com (M. Sankar). 1 Current address: SABIC Technology Centre, Bangalore, India. http://dx.doi.org/10.1016/j.catcom.2014.10.026 1566-7367/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom