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Production

Weigh 2mol (418g) of p-aminodimethylaniline hydrochloride, put it into a reaction kettle with a thermometer, add 6L of water to dissolve, add 0.41mol (40g) of concentrated sulfuric acid dropwise with stirring to make the solution acidic, and add it sequentially at room temperature Zinc chloride solution, aluminum sulfate solution, sodium thiosulfate solution, and 300mL of sodium dichromate solution are added, the reaction solution is heated to 40°C within 10 minutes under stirring, and the hydrochloric acid solution of N,N-dimethylaniline Put it into the reactor, then immediately add the remaining 600mL sodium dichromate solution, and heat it to 70℃ within 10 minutes; when the temperature reaches 70℃, put 2.87mol (250g) manganese dioxide into the reactor, heat to 85℃, maintain React at temperature for 30 minutes. Cool down to 50°C. Slowly add 7.14mol (700g) of concentrated sulfuric acid under stirring. After stirring, the reaction solution will be released. Place it at 4°C for 5 hours. Precipitation will be deposited. Filter by suction. Use 10% for filter cake. Wash with 600 mL of sodium chloride aqueous solution; transfer the filter cake to a 20L beaker, add 10L of water, stir and heat on an electric heating mantle until it boils, filter while hot, add 1.84mol (250g) 365bet娱乐book zinc chloride and 25.64mol (1500g) to the filtrate ) Sodium chloride, stir to dissolve, then place the solution at 4°C for 24h, filter with suction, and dry at 50°C to obtain 460g of methylene blue zinc chloride salt; dissolve the obtained zinc chloride salt in 10L of water, and add sodium carbonate 0.52 mol (55.2g), cool to room temperature, filter with suction, wash the filter cake with a small amount of water, add 17.09mol (1000g) of sodium chloride, stir to dissolve and place at 4℃ for 12 hours, filter with suction, filter cake at 40-45℃ After drying for 12 hours, 320 g of crude methylene blue was obtained (the loss on drying was about 15%, and the yield was 42.5% based on anhydrous). Put the crude methylene blue into an Erlenmeyer flask, add 1280mL of 0.1mol/L hydrochloric acid (1:4), heat to dissolve in a water bath at 60°C, place to crystallize at room temperature, and filter with suction. The filter cake is recrystallized once in the same volume and concentration of hydrochloric acid. The same volume of water was recrystallized once, and the filter cake was dried at 40-45°C for 12 hours to obtain 205 g of methylene blue with a weight loss on drying of 14.6%, and a yield of 64.3% calculated as anhydrous. The total yield calculated based on the raw material p-aminodimethylaniline hydrochloride was 27.4%.