ISSN: 3272-6856 European Journal of Advanced Chemistry, 2011, 3 (4):50-54 ______________________________________________________________________________        Asad Ali 1* , Mohammad Lutful Ahsan 2 , Iqbal Ahmed 1 1 Department of Chemistry, University of Chittagong, Chittagong, Bangladesh 2 Lecturer, Department of Chemistry, Comilla Residential College, Comilla, Bangladesh * E-mail: asadcu@gmail.com Received on 12 May, 2011 and accepted on 6 August, 2011 _________________________________________________________________________ ABSTRACT An expeditious synthesis of Synthesis of Various benzimidazole derivatives under micro-wave irradiation from simple and substituted ortho phenylenediamines (OPDA) with various arylaldehydes using zncl 2 / sio 2 as catalyst is described and proceeds efficiently in the absence of organic solvent under thermal condition and microwave irradiation with high yields. The structure of synthesized compounds have been established on the basis of spectral and analytical data. Keywords: Benzimidazole , OPD, ZnCl 2, Silicon Dioxide, Solvent Free. ___________________________________________________________________________ INTRODUCTION Benzimidazole is a heterocyclic aromatic organic compound having imidazole ring fused with benzene. The most prominent benzimidazole compound in nature is N-ribosyl-dimethyl benzimidazole, which serves as an axial ligand for cobalt in vitamin B12. Extensive biochemical and pharmacological studies have confirmed that benzimidazole molecules are effective against various strains of microorganisms[1,2]. Benzimidazoles are regarded as a promising class of bioactive heterocyclic compounds that exhibit a range of biological activities. Specifically, its derivatives possessed various biological activities such as antioxidant, antiparasitic, antihelmintics, antiproliferative, anti-HIV, anticonvulsant, anti-inflammatory, antihypertensive, antineoplastic, analgesic, and antitrichinellosis activities. Owing to the immense importance and varied bioactivities exhibited by benzimidazoles, efforts have been made from time to time to generate libraries of these compounds and screened them for potential biological activities[3]. These methods for the synthesis of benzimidazole derivatives include the coupling of o- phenylenediamine with aldehydes or β-keto ester or carboxylic acid in presence of various catalysts like CAN[4], p-TsOH[5], NaHSO 4 ·SiO 2 [6], Fecl 3 /Al 2 O 3 [7], PS-PyCl-XAlCl 3 [8], T-(o-Cl)PPFe III Cl b , FeCl 3 ·SiO 2 [9]: Co(NO 3 ) 2 /H 2 O 2 , Ni(NO 3 ) 2 /H 2 O 2 [10]; Fe/MgO, sulfamic acid[11]; Yb(OTf) 3 , Sc(OTf) 3 , KHSO 4, HfCl 4 , H 2 O 2 ·HCl, FeBr 3 [12]; oxalic acid, L-preline, glyoxalic acid, SDS[13], N- halosuccinamide (X = Cl, Br, I)[13]; using solvents like ethanol, methanol, DMSO, THF, DMF, PEG, CHCl 3 , HCl, polyphosphoric acid, CH 2 Cl 2 , DCM, CH 3 CN, H 2 O 2 , acetic acid. However, in above some reported methods suffer from one or more drawbacks such as prolonged reaction times, use of environmentally 50