The important intermediate for the synthesis of Sodium Pyrithione is 2-chloropyridine nitrogen oxide (2-PCL-N-oxide), which can be prepared by reacting 2-chloropyridine (2-PCL) with hydrogen peroxide under the catalysis of tungstic acid and phosphoric acid. The catalyst needs to be recovered with a slight excess of calcium hydroxide, then sodium carbonate is added to precipitate the residual calcium ions, and finally the solid calcium salt is filtered to obtain a clear 2-chloropyridine nitrogen oxide solution, which is then rectified by a rectification tower The unreacted raw material 2-chloropyridine was removed to obtain a qualified product meeting the enterprise standard.
1 Raw materials and instruments
2-chloropyridine (2-PCL, 99.5%), Jiangsu Hengsheng Chemical Co., Ltd.; hydrogen peroxide (H2O2, 50%), Shanghai Arkema Gaoyuan Chemical Co., Ltd.; tungstic acid (H2WO4, 98%), phosphoric acid (H3PO4, 85%), Jiangyin Chengxing Industrial Group Co., Ltd.; Sodium Hydrosulfide (NaSH, Analytical Pure), Sodium Carbonate (Na2CO3, Analytical Pure), Calcium Hydroxide (Ca(OH) 2, Analytical Pure), Changshu Hongyu Calcium Ltd. Eurostar digital display 60 electric stirrer, IKA, Germany; S20K pH meter, METTLER TOLEDO; PFX195 colorimeter, Lovibond; JB-30 laboratory distillation device, Deda Tianyi.
2 Synthetic roadmap
3 synthesis method
According to the reaction route in Figure 1, add 100 g of 2-PCL, 5 g of tungstic acid, 1 g of phosphoric acid, and 50 mL of water into a 250 mL four-neck flask equipped with an electric stirrer, a thermometer, a spherical condenser and a constant pressure dropping funnel. Stir and heat up. When the temperature reaches 65 °C, start to add 65 mL of H2O2 dropwise. Control the temperature between 65 and 75 °C through a water bath. After the reaction, take samples for analysis. When the residual amount of H2O2 is less than 2%, cool the 2-PCL -N-oxide solution to 50 °C, then add about 4.5g (about 3% of the weight of the nitrogen oxide solution) Ca(OH) 2 powder, adjust the pH to 9.5-10.5, stay for 3 hours, At this time, Ca (OH) 2 is slightly excessive, add an appropriate amount of Na2CO3 and stir for 30 minutes, then filter through a filter press device to obtain a 2-PCL-N-oxide solution, and finally enter a rectification device for rectification. Subsequently, 95 mL of 38% NaSH solution was added dropwise to the rectified liquid at 80 °C, and at the same time, 32% sodium hydroxide was used to neutralize the hydrogen chloride generated by the reaction, and the pH of the solution was controlled between 9.0 and 11.5 to fully react Finally, the final product Sodium Pyrithione solution is obtained.
The addition of sodium carbonate to the intermediate 2-chloropyridine nitrogen oxide solution can significantly reduce the calcium ion content; the calcium ion in the nitrogen oxide solution can keep it stable during the rectification process; the addition of sodium carbonate will make the nitrogen oxide and The chromaticity of Sodium Pyrithione becomes worse, the higher the amount of sodium carbonate added, the worse the chromaticity of nitrogen oxides and Sodium Pyrithione, for the comprehensive consideration of the final product, the added amount of sodium carbonate is 0.4% (relative to nitrogen oxide The amount of material) is the optimal amount.