Abstract
Here we demonstrate the synthesis of multifunctionalised benzimidazoles through the coupling of o-phenylenediamine with aldehydes by using Copper (II) hydroxide as an efficient solid catalyst in methanol at room temperature. The Copper (II) hydroxide solid catalyst gave better yields (80%-99%) in short reaction time (4-8 h). These commercially available cheap catalysts are more active than many reported expensive heterogeneous catalysts. Using the Copper hydroxide fresh catalyst, the yield of product 3a was 98%, while the recovered catalyst in the three subsequent cycles gave the yield of 94%, 90% and 88% respectively.
Highlights
Among the various nitrogen containing heterocycles, benzimidazole derivatives exhibit antiviral, antiulcer, antihypertensive and anticancer properties [1,2,3,4]
The synthesis of 2-substituted benzimidazoles involves the treatment of o-phenylenediamines with either carboxylic acids [12,13,14,15,16] or their derivatives [17,18,19], under strongly acidic conditions and sometimes combines with very high temperatures (i.e., PPA, 180 ̊C) or the use of microwave irradiation [20,21,22]
We have attempted the condensation of o-phenylenediamine 1 (1.0 mmol) with benzaldehyde 2 (R = Ph) (1.2 mmol) at room temperature in methanol condition for 6h at open oxygen atmosphere, in absence of catalyst by M.A.Chari et al, [32,33] and they have reported 27.6% of 2-phenyl benzimidazole product 3 and 0.1% of 1-benzyl-2-phenyl-1H-benzimidazoleproduct 4 at 6 h and on long reaction time (12 h) resulted the formation of a mixtures like 2-phenyl benzimidazole 3 (29.1%) and 1-benzyl-2-phenyl-1H-benzimidazole 4 (2%) as side-product
Summary
Among the various nitrogen containing heterocycles, benzimidazole derivatives exhibit antiviral, antiulcer, antihypertensive and anticancer properties [1,2,3,4]. The synthesis of 2-substituted benzimidazoles involves the treatment of o-phenylenediamines with either carboxylic acids [12,13,14,15,16] or their derivatives (nitriles, imidates or orthoesters) [17,18,19], under strongly acidic conditions and sometimes combines with very high temperatures (i.e., PPA, 180 ̊C) or the use of microwave irradiation [20,21,22].
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