One-pot Syhesis Of Benzimidazols From 2-nitroaniline And Alcohols Over Heterogeneous Catalyst

Benzimidazole derivatives are an important class of pharmaceuticals intermediates,and its derivatives have physiology efficacy of anti-fungal,anti-tumor,lowering blood pressure and treatment of hypoglycemia.Benzimidazole derivatives can also be used surfactant treatment agent,epoxy Mring agent,chemiluminescence and other areas.Due to their broad application value and market prospects,thus preparation of the benzimidazole and its derivatives has an important significance in organic synthesis.The traditional methods for the synthesis of benzimidazoles and their derivatives were mainly involved in the use of o-phenylenediamine derivatives as substrates.Although use of o-nitroaniline as the starting material by reductive cyclization for the synthesis of benzimidazole was frequently reported in the literature,most methods were used the complex acidic liquid catalyst and oxidants which were environmentally unfriendly,multi-step reaction and tedious separation procedures,thus there are harmful to the environment and higher energy consumption.In this dissertation,the direct synthesis of benzimidazoles in one pot from o-nitroaniline and alcohol in aqueous media catalyzed by 5%M-5%Pd/Al2O3 solid catalyst was studied.The reaction can be successfully completed in a single step,thus greatly simplifies the experiment and work-up steps.It has the advantage of low-cost,meeting the practical requirements,and using water as a green solvent,which provides a new method for the synthesis of benzimidazole compounds.The M-Pd catalyst as the main catalytic active component controls the steps of dehydrogenation and hydrogenation,whereas the acidic Al2O3 also plays an important role in the reaction.The conditions of direct synthesis of benzimidazoles from o-nitroaniline and ethanol are optimized and the best conditions are as follows:0.8g 5%M-5%Pd/Al2O3 catalyst,o-nitroaniline 8g,ethanol 120 mL,water 80 mL,T = 453 K,P = 3.5 MPa,reaction time 8 h.Under this condition,the yield of 2-methylbenzimidazole could up to about 98.0%.Catalyst(5wt%M-5wt%Pd/Al2O3)was characterized and evaluated.The results showed that the catalyst has a certain catalytic activity and surface metal alloy form.The catalyst could be reused for six times whereas the catalytic activity did not significantly down.It is obvious to clarify that this catalyst has high stability.By using o-nitrophenol,o-nitrobenzaldehyde,o-nitro thiophenol,these o-nitrophenyl derivatives can also give the corresponding products,which shows that this method has a broader value.