The Synthesis Of Benzimidazoles Containing Nitro Or Carboxylic Substrates

Benzimidazoles and their derivatives are very useful intermediates for the development of molecules on pharmaceutical or biological interest. Because of their good biological activities and reactive activities,the research of benzimidazoles has been a hot spot. From the discovery of 5,6-dimethylbenzimidazole as a component of Vitamin B12, the research of benzimidazoles and their derivatives has been over one hundred years, we know that benzimidazoles and their derivatives have low toxicity and can inhibit bacteria, and they are used more and more widely.This dissertation used 4-nitrobenzene-1,2-diamine and 3,4-diaminobenzoic acid as raw materials, respectively with some organic acids, aldehydes, nitriles, etal. Through cyclic condensation we got different benzimidazole derivatives. At the same time we got benzimidazole cycle with good active groups, such as carboxyl and nitrogen groups, hoping to get new compounds with better activities through anti-bacteria tests.To synthesize benzimidazole derivatives, we synthesized three different kinds of benzimidazoles through 4-nitrobenzene-1,2-diamine and 3,4-diaminobenzoic acid. Compared strong acids catalysis, a classical method with microwave catalysis, discussed the reasons of difficulty and failure.1. Using 4-nitrobenzene-1,2-diamine as raw material, respectively reacted with acids and aminonitrile. 5-nitro-2-alkylbemzimidazoles and 5-nitro-2-amino benzimidazoles were synthesized. From the experiments we found that microwave catalysis can solve these faults, shorter reaction time and higher yields, which proves that microwave catalysis can replace the classical method to prepare benzimidazoles and their derivatives.2. Using acids to react with 3,4-diaminobenzoic acid can get 5-carboxylic-2- alkylbenzimidazoles, more acids can easily avoid the side products produced through reactive substrates'self-condensation. 2-(hydroxymethyl)-5-carboxylicbenzimidazole was oxidized by potassium permanganate to prepare the target product 2,5-dicarboxylicbenzimidazole. However, 1HNMR and LC-MS spectra proved that the carboxyl in the position 2 was removed, oxide was replaced with chromic oxide and the reaction temperature lowed also got the same results. Owing to this , this scheme was denied; use glyoxylic acid as material to react with 3,4-diaminobenzoic acid directly got the target molecular, also failed, the mechanism which carboxylic removed was discussed deeply.3. 1,4-(bis5-carboxylicbenzimidazole)benzene was produced by 3,4-diamino- benzoic acid and terephthalaldehyde with the ratio of 2:1. Replace carboxylic acids with aldehyde to react with 3,4-diaminobenzoic acid can moderately get target compounds, and the reaction can be moderately, quickly, post-processed easily and with high yields, little pollution. With the good selectivity of them, the side reaction of 3,4-diaminobenzoic acids'self-condensation can be avoided effectively.The structure of newly synthesized compounds was identified by 1H NMR, MS, IR and LC-MS spectra.