Synthesis Of 2-Methylbenzimidazole In One-step From O-Nitroaniline And Alcohol Over Heterogeneous Catalyst

Benzimidazole compounds are crucial structures which are contained in numerous pharmaceuticals. Many benzimidazole compounds have significant biological activities, and its significant medical value in anti-tumor, anti-cancer, anti-viral, bactericidal, anti-inflammatory and anti-parasitic. There have been many materials and methods for the synthesis of benzimidazole compounds, but the traditional synthesis techniques have rigorous demands for equipments, particularly the use of inorganic acid as a catalyst producing large amounts of wastewater, which leads to environmental pollution. Moreover, the existing synthetic processes mostly adopt a batch production, and they have problems in complicated workup procedures and difficult recycle of catalysts.One step synthesis of benzimidazole compounds from aliphatic alcohol and o-nitroaniline is catalyzed by solid catalyst. This method has the advantages of high yield and high selectivity, but also has the shortcomings, such as low activity of the catalyst, prolonged reaction times, easy to produce high boiling point byproducts, the quality of product is poor, which is not conducive to industrial applications. In this thesis, a series of novel catalysts have been prepared used in synthesis of 2-methylbenzimidazole compounds from alcohol and o-nitroaniline to develop a catalyst with highly activity and stability.A series of modified 5wt%Cu-5wt%Pd/Al2O3 catalysts were prepared, the effects of additive type, additive content, reaction time, reaction temperature on the catalytic performance of the catalyst were investigated. The catalysts were characterized by TPR, XRD, TEM, TPD, Py-IR techniques. The effects of additives on Cu-Pd/Al2O3 catalyst, synthesis of benzimidazole in trickle-bed reactor and the reasons for deactivation of the catalyst were also studied.In the autoclave, the Mg-modified 5wt%Cu-5wt%Pd/Al2O3 catalyst showed the highest reactivity and selectivity, under the conditions of 5w% Mg, 453 K, 3.5 MPa, 6 h with the conversion of o-nitroaniline and yield of 2-methylbenzimidazole 100% and 98.2% respectively. Catalyst’s characterization results showed that catalyst had the formation of CuPd alloy, and Mg additives promoted the formation of CuPd alloy and changed the surface acidity of the catalyst, which promoted dehydrogenation of ethanol and accelerated the whole reaction rate. Using the method, 3, 3’-dinitrobenzidine as starting material, can also get the corresponding bis-benzimidazole. The results showed that the process had a wide application value.In trickle-bed reactor, with K-modified 5wt%Cu-5wt%Pd/Al2O3 as catalyst, under the conditions: reaction temperature, 433 K, N2 pressure, 5 MPa, WHSV, 0.28 h-1, volume ratio of water and alcohol, 1:3, conversion of o-nitroaniline and selectivity of 2-methyl-benzimidazole were 100% and 98.2% respectively, but after the reaction time reached 42 h, the catalyst appeared the deactivation phenomenon. Characterization results of deactivated catalyst indicated the catalyst crystal changed, catalyst surface was covered by carborn deposition and a bit of CO poisoned active component of the catalyst. This was the main reason for the deactivation of catalyst. After the deactivated catalyst was calcined and reduced at high temperature, its activity can get better recovery.