In the hydrogenation reaction kettle by adding 50 g 1 - methyl -5 - nitro - 1H - benzimidazole -2 - butyric acid ethyl ester, 2.5 g 5% palladium/carbon, 1.3 L methanol, 475 ml ethyl acetate, hydrogen pressure control in the 0.1 - 0.2 mpa, reaction solution is 25 °C reaction 15 hours, TLC monitoring endpoint of the reaction to the reaction is complete. The fluid in a 35 °C decompression filter collects the filtrate; the filtrate is concentrated under reduced pressure to dry after adding 75 ml ethyl acetate, 70 °C stirring for 0.5 hours. After that, the mixture was to 5 °C stirring for 0.5 hours, for 5 °C standing crystallization for 2 hours, filtering, washing the filter cake with acetic acid ethyl ester, filtration cake at 50 °C decompression drying for 5 hours to afford 1-Methyl-5-amino-1H-benzimidazole-2-butanoic acid ethyl ester 35 g, yield 77.8%.
