Aim and Objective: The benzimidazole derivatives have been obtained via weightreducing
aid (L-Carnitine) as a cheap catalyst. A wide range of aromatic aldehydes easily undergo
condensations with substituted o-phenylendiamine under mild condition to afford the target
molecular in excellent yields.
Materials and Methods: Melting points were measured on an Electrothemal X6 microscopy digital
melting point apparatus. 1H NMR and 13C NMR spectra were recorded in DMSO-d6 on a Bruker
AVANCE 400 (400 MHz) instrument with the TMS at d 0.00 ppm as an internal standard. C, H and
N analysis were performed by a Perkin-Elmer 2400 CHN elemental analyzer. Chemicals used were
of commercial grade without further purification.
An equimloar (1.0 mmol) mixture of o-phenylenediamine 1, aromatic aldehyde 2, and L-Carnitine
(10 mol%) was vigorously stirred at 60°C in EtOH (3 mL) for the specific time indicated by TLC
(petroleum: ethyl acetate ether = 4:1). After completion of the reaction, the mixture was quenched by
adding H2O (20 mL), extracted with EtOAc (3 x 10 mL), and the combined extracts were dried by
anhydrous MgSO4. The filtrate was evaporated and the corresponding benzimidazole was obtained
as the only product. The products 3a–3r were obtained in 82–95% yields. The structures of the
products 3 were identified by their IR, 1H NMR, 13C NMR and elemental analysis spectra.
Results: The products were obtained in 82–95% yields in 30–80 min. The method has several
advantages such as simple, clean and environmentally process, excellent yield and avoiding use of
inconvenient preparation of catalyst. Meanwhile, the catalyst L-Carnitine is a kind of weightreducing
aid, which might be applied to broad green catalyzed system.
Conclusion: A facile synthesis of benzimidazoles comprising the reaction of various aldehydes with
substituted o-phenylendiamine in good to excellent yield is provided using L-Carnitine as an
efficient catalyst. The protocol overcomes the earlier disadvantages like harsh reaction conditions,
tedious work-up, expensive process, wastes generation and the use of metallic oxide, which might be
applied to the synthesis of benzimidazoles pharmaceticals in order to meet friendly environmental