Toluene method is the first method adopted by G. fahlarg, the inventor of na saccharin. Later generations have made many improvements, becoming a simpler method for the production of na saccharin, and also an earlier method for the production of na saccharin in China. Its main raw materials include anhydrous toluene, chlorosulfonic acid, ammonia water, active carbon, liquid sodium hydroxide, hydrochloric acid, potassium permanganate, sodium sulfite and sodium bicarbonate, including chemical reactions such as chlorosulfonation, amination, oxidation, acidolysis, neutralization, etc.
The anhydrous toluene is gradually added into the chlorosulfonation pot containing chlorosulfonic acid. The reaction is carried out at low temperature for 3 hours. After the reaction, the chlorosulfonic acid is completely decomposed and the acid liquor is discharged. Then the sulfonyl chloride oil is washed with water and frozen at -15 to -20℃ for 12 hours. The para isomer crystal is filtered out and the liquid is o-toluenesulfonyl chloride. Put ammonia water in the ammoniation pot in advance, add o-toluenesulfonyl chloride, react at 60℃ for 2 h, cool, filter, decolorize the filter cake with active carbon, refine with hydrochloric acid and sodium hydroxide solution respectively in the refining pot to obtain o-toluenesulfonamide. Add o-toluenesulfonamide, water and liquid sodium hydroxide into the oxidation pot, put potassium permanganate into the oxidation pot at 25-35℃ in several times, add it, conduct heat preservation reaction for 7h, cool it to 25℃, slowly add sodium sulfite solution until the oxidation solution is colorless, filter it, wash the water containing manganese dioxide filter cake until there is no sweet taste, combine the filtrate, add diluted hydrochloric acid to pH 3, precipitate no oxide, filter it, filtrate. Add concentrated hydrochloric acid to precipitate completely, filter, wash filter cake with micro acid water, and finally get insoluble saccharin. The insoluble saccharin and sodium bicarbonate are alternately put into the neutralizing pot filled with water, and the reaction is heated to dissolve. When the reaction temperature reaches 70 ℃, adjust the reaction liquid to neutral, filter while it is hot, and the filtrate is crystallized and dried to obtain the finished product of na saccharin.
The main characteristics of toluene process are wide range of raw materials, mature technology, simple reaction and easy to master production technology. Some use chromic acid to oxidize o-toluenesulfonamide, others use electrolysis method to electrolyze o-toluenesulfonamide, so as to save raw materials, reduce pollution and reduce labor intensity.