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
demands.
Las an Efficient Catalyst for Synthesis of Aldimines at Ambient Temperature Condition
