1. Preparation of sodium hydrosulfide: 3250 mL of anhydrous ethanol was added to 5 L of high-pressure reactor, and 110 g (1.60 mol) of sodium ethoxide was added at once under stirring. After the addition was completed, the inlet was sealed, and the reaction temperature was controlled below 25 °C by jacketed cooling water. Under stirring, high-pressure hydrogen sulfide gas was introduced, and the reaction pressure was maintained in the range of 0.3-0.5 MPa for about 30 min until the solution pH reached 6.5-7.5.
2. Thiolation reaction: After completion of the reaction, release the pressure inside the kettle, open the lid, and add 230.3 g (0.75 mol) of sodium 2,3-dibromopropanesulfonate. Seal the lid of the kettle, control the internal temperature at 23-25 ℃, and pass the high-pressure hydrogen sulfide gas again under stirring, maintain the pressure at 0.3-0.5 MPa, and react for 90 min. After depressurization, the hydrogen sulfide gas was driven off by vacuum (the exhaust gas was absorbed by caustic solution and activated carbon in series). The reaction solution was transferred to another reaction flask, and the pH was adjusted to 4.6-4.7 by slowly adding 36% glacial acetic acid dropwise at room temperature, and the stirring was continued for 30 min until the pH stabilized. Subsequently at 10 ℃ below the stationary 4 hours, filtration to remove sodium acetate, to obtain the clarified thiolation reaction solution.
3. Lead salt reaction: 284.5 g of lead acetate trihydrate was dissolved in 625 mL of distilled water preheated to 50-55 °C. The reaction was carried out in the same manner as the reaction solution. Transfer the above thiolated reaction solution to a 5 L reaction flask, warm up to 50 °C with stirring, and slowly add the aqueous lead acetate solution. After addition, stirring was continued for 1 h. After aging for 2 h, it was filtered. The crude lead salt cake was washed with 50 °C hot water (800 mL + 600 mL + 400 mL) in three times, drained and washed with 1000 mL of hot water of the same temperature with stirring for 30 minutes. Finally, it was washed once with 400 mL of cold anhydrous ethanol with agitation, and dried under vacuum at 50 ℃ until constant weight, obtaining 264.7 g of 2,3-dimercaptopropanesulfonic acid lead salt complex, with a yield of 70.8% (in terms of sodium 2,3-dibromopropanesulfonate).
4. Lead desalting: 250 g of 2,3-Dimercaptopropanesulfonic acid lead salt complex was added into a 3 L reaction flask, 2000 mL of anhydrous ethanol was added, and hydrogen sulfide gas was slowly introduced under stirring at room temperature until the yellow lead salt particles completely disappeared and were transformed into black lead sulfide precipitate. After standing for 1 hour, the temperature was raised to 35°C to drive off the residual hydrogen sulfide gas. 60°C was heated and activated carbon was added, stirred to decolorize for 15 minutes, and filtered. Ground sodium bicarbonate powder was slowly added to the filtrate to adjust the pH to 4.3, and after neutralization, stirring was continued for 15 minutes until the pH was stable. After filtration, the filtrate was cooled and crystallized in a refrigerator below 1°C overnight. The crystals were filtered, washed once with cold anhydrous ethanol and dried under vacuum to obtain 97.8 g of crude sodium 2,3-dimercaptopropanesulfonate, with a content of 95.6% and a yield of 81.04% (in terms of lead salts).
5. Refining: 95.0 g of crude sodium 2,3-dimercaptopropanesulfonate was added into a reaction flask, 1300 mL of 90% ethanol was added, and the temperature was raised to 65-70 ℃ to make it completely dissolved. Powdered activated carbon was added, and the product was decolorized by stirring for 15 min and then filtered. The clarified filtrate was cooled and crystallized in a refrigerator at 10 °C overnight, filtered, washed and dried to obtain 78.8 g of white sodium 2,3-dimercaptopropanesulfonate finished crystals.
