. INTRODUCTION Coumarin, the simplest member of the group of oxygen heterocycles and a class of lactones; which is an indispensable heterocyclic unit to both the chemists and the biochemists. Coumarins occur naturally in plants and microorganisms, approximately1000 coumarin derivatives have been isolated from over 800 species of plants and microorganisms 1 . Coumarin itself was first isolated from tonka bean, Coumarounaodorata by Vogel in 1820 2 . Coumarins are structurally diverse, which includes simple substituted coumarins, those that have substituents in the benzene ring, five and six-membered fused coumarins such as furocoumarins and pyranocoumarins and coumarin dimers, which usually consists of two coumarin units linked together such as dicoumarol. A study of antimicrobial properties of such naturally occurring and synthetic coumarins has been reported recently 3 . Several coumarin derivatives were also recently reviewed for their natural occurrence, anti- microbial, anti-inflammatory, anticancer, anti-HIV and other miscellaneous properties 4 . Among the various coumarin deri- vatives, 7-substituted coumarins are important group of coumarin derivatives showing various bioactivities and also other applications 5 . For example, 7-hydroxy 4-methyl coumarin (β-methyl umbelliferone) is used as fluorescent brightener, efficient laser dye, standard for fluorometric determination of enzymatic activity and as a starting material for the preparation of insecticide and furano coumarins 6-8 . Moreover, 7-amino-4- methyl coumarin is mainly used as laser dye and intermediate Brønsted-Acidic Imidazolium Ionic Liquid [bmim(SO 3 H)][OTf]: A Mild Catalyst for Highly Efficient Synthesis of Coumarins YUVARAJ HALDORAI 1,* , RAJESH G. KALKHAMBKAR 2 and JAE-JIN SHIM 1 1 School of Chemical Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Republic of Korea 2 Department of Chemistry, Karnatak University’s Karnatak Science College, Dharwad-580 001, India *Corresponding author: E-mail: yuvraj_pd@yahoo.co.in (Received: 15 May 2013; Accepted: 25 September 2013) AJC-14184 The use of Brønsted-acidic imidazolium ionic liquid [bmim(SO3H)][OTf] as a catalyst for the high yielding synthesis of a wide variety of coumarins under mild conditions via Pechmann condensation has been demonstrated. This method is simple and has benefits from the easy way to isolate coumarins in good yields. In comparison with the classical Pechmann condensation, this new method consistently has the advantage of high yields and good purity. Key Words: Coumarins, Brønsted-acidic imidazolium ionic liquid, Pechmann condensation. Asian Journal of Chemistry; Vol. 25, No. 16 (2013), 9379-9383 http://dx.doi.org/10.14233/ajchem.2013.15772 for the synthesis of bioactive compounds 9 . Coumarins could be synthesized by various methods, such as Pechmann 10 , Perkin 11 , Knoevenagel 12 , Reformatsky 13 , Witting 14 , Claisen 15 and flash vacuum pyrolysis reaction 16 . However, the Pechmann reaction is one of the most widely applied method for the synthesis of coumarins and its derivatives, which involves the condensation of phenols with β-ketoesters in the presence of a variety of acidic condensing agents. Several acid catalysts have been used in the conventional procedure, such as H2SO4 10 , AlCl3 17 , P2O5 18 , CF3COOH 19 , HClO4 20 . However, these catalysts have to be used in large excess and hence the disposal of acidic waste leads to environmental pollution. The moisture sensi- tivity of the majority of Lewis acids to the water produced in the Pechmann reaction renders them unsuitable for use in large- scale applications and these methods also generate strongly acidic by-products. Due to the environmental concerns and as a tool to green chemistry, many catalysts such as, Bi(NO3)3·5H2O 21 , Sm(NO3)3·6H2O 22 , ZrCl4 23 , KAl(SO4)2·12H2O (alum) 24 , silica- bonded s-sulfonic acid 25 and silica triflate 26 have been used as effective catalysts for coumarin synthesis in solvent free condition in the last decade. The use of ionic liquids (ILs) as reaction media and catalyst can offer a solution to solvent emission and catalyst recycle problems 27 . Ionic liquids possess the advantages like negligible vapour pressure; reasonable thermal stability, recyclability, dissolves many organic and inorganic substrates and they are tunable to specific chemical tasks 28 . Recently ionic liquids have been successfully employed as solvents with catalytic activity for a variety of reactions 29 .