Chemical Papers 66 (7) 684–690 (2012) DOI: 10.2478/s11696-012-0152-4 ORIGINAL PAPER Tungstate sulfuric acid: preparation, characterization, and application in catalytic synthesis of novel benzimidazoles Bahador Karami*, Saeed Khodabakhshi, Zahra Haghighijou Department of Chemistry, Yasouj University, 75918-74831 Yasouj, P.O. Box 353, Iran Received 17 September 2011; Revised 3 January 2012; Accepted 4 January 2012 Tungstate sulfuric acid (TSA) was prepared, characterized, and applied for direct synthesis of novel and known benzimidazoles through a condensation reaction of o-phenylenediamines with orthoesters under solvent-free conditions. TSA was characterized by powdered X-ray diffraction (XRD), X-ray fluorescence (XRF), and FTIR spectroscopy. This novel and eco-friendly method is very cheap and has many advantages such as excellent yields, recyclable and eco-friendly catalyst, and simple work-up procedure. c  2012 Institute of Chemistry, Slovak Academy of Sciences Keywords: orthoesters, o-phenylenediamine, tungstate sulfuric acid, benzimidazole, catalyst Introduction Catalytic technology plays an important role in many recent organic reactions (especially synthesis of heterocyclic compounds), therefore, preparing and employing a green catalyst can be extremely valuable (Davoodnia et al., 2011). Among heterocycles contain- ing a nitrogen atom, benzimidazole and its deriva- tives are very useful intermediates for the develop- ment of molecules of pharmaceutical and biological interest (Ogurtsov et al., 2003). For example, some benzimidazoles showed a relatively high biological ac- tivity as anti herpes (Migawa et al., 1998), anti in- fluenza (Tamm, 1957), anti fungal agents (Ku¸ s & Al- tanlar, 2003), and RAF (rapidly accelerated fibrosar- coma) kinase inhibitor (Buchstaller et al., 2011). The most prominent benzimidazole compound in nature is N-ribosyl-dimethylbenzimidazole (5,6-dimethyl-1- α-D-ribofuranosyl-1H-benzimidazole) which serves as an axial ligand for cobalt in vitamin B 12 (Barker et al., 1960). Moreover, benzimidazole derivatives are efficiently used in material science (Maiti et al., 2009), corrosion science (Roquea et al., 2008), cataly- sis (Tarte et al., 2008), etc. The discovery of novel synthetic methodologies fa- cilitating the preparation of compound libraries is a pivotal focal point of research activity in the field of modern organic synthesis. Until now, several meth- ods for the synthesis of benzimidazoles have been re- ported. However, the most commonly used method is the condensation of an o-aryldiamine with a carbonyl equivalent (Wright, 1951; Preston, 1974). Also, esters, lactones, and anhydrides are able to produce benzim- idazoles through the cyclization of amide (Niknam & Fatehi-Raviz, 2007). It should be mentioned that some of the reported methods suffer from drawbacks such as the use of toxic and expensive catalysts or organic solvents, long reaction times, low yield of the prod- ucts, and difficult work-up procedures (Sharma et al., 2009; Howarth & Hanlon, 2001; Reddy et al., 1983). Experimental All chemicals were purchased from Merck Co. (Germany), and Sigma–Aldrich Co. (USA). The re- actions were monitored by TLC (silica-gel 60 F 254 , 1-hexane–ethyl acetate). IR spectra were recorded on a FTIR Shimadzu-470 spectrometer at the scanning range of 400–4000 cm -1 (Shimadzu, Japan) and the 1 H NMR spectra were obtained on a Bruker instru- ment (400 MHz) DPX-400 Avance 2 model (Bruker, USA). Chemical shifts (δ) are reported in ppm. X-ray *Corresponding author, e-mail: karami@mail.yu.ac.ir