Researches On Synthesis Of 5-Aminobenzimidazolone By Reduction

5-Aminobenzimidazolone is an important intermediate for the synthesis of benzimidazolone organic pigments.The reduction of 5-aminobenzimidazolone via 5-nitrobenzimidazolone is a key step in the synthesis process.At present,The main reduction methods used in industry include iron powder reduction method,catalytic hydrogenation reduction method and hydrated hydrazine reduction method.However,these methods have some problems in application: Iron reduction method has serious problem of environmental pollution;Catalytic hydrogenation reduction method requires high equipment and expensive catalyst;Hydrated hydrazine is volatile and toxic,and is not suitable for mass production.Therefore,it is important to find else excellent method for the preparation of 5-aminobenzimidazolone.In this paper,several new methods were used to study the synthesis of 5-aminobenzimidazolone by 5-nitrobenzimidazolone.The optimum reduction conditions of the methods were determined through experiments,and the yield and purity was calculated.In which the yield was 84.3% with zinc powder-ammonium chloride;the yield was 80.5% with sodium hyposulfite;the yield was 94.2% with thiourea dioxide.The yield with sodium sulfide alone was not ideal,but the yield improved to 92.5% when combined thiourea dioxide and sodium sulphide,and overcomed many of the disadvantages of the method with sodium sulphide.The purity of the products obtained by the method above is higher than 99%.Analyze and characterize the reduced products,measuring melting point,nuclear magnetic resonance spectrum,infrared spectrum and mass spectrometry the product certificated to be 5-aminobenzimidazolone.The methods used in the experiment were evaluated by comparing the cost of raw materials,the synthesis process,the requirements for equipment and the degree of environmental pollution.Analysis shows that zinc powder method has high raw material costs and complicated process flow;The sodium hyposulfite method,the thiourea dioxide method and combined thiourea dioxide and sodium sulphide method has the advantages of low reduction cost,simple production process,little environmental pollution,high yield,and has a good industrialization prospect.