Method 1: The preparation principle is that ZnSO4 · 7H2O reacts with SPT to create ZPT and sodium sulfate. Evaluate an appropriate quantity of zinc sulfate heptahydrate as well as prepare zinc sulfate solutions of 0.25 mol/L and 0.50 mol/L specifically. Measure an appropriate amount of sodium pyrithione remedy and also prepare 0.5 mol/L and 1.0 mol/L salt pyrithione remedy specifically. The technological problems of the response procedure are controlled, as well as the two are swiftly included in a three-necked flask for response at a certain quantity ratio to get Pyrithione Zinc Bar Soap crystals, which are then suction filteringed system, washed, and also vacuum-dried to get zinc pyrithione powder.
Technique 2: Using pyridine as raw material, after 30% H2O2 oxidation, N-oxidative-2-hydroxypyridine was synthesized in the system of dimethyl sulfoxide, toluene and also sulfur powder, and lastly complexed with Zn2+ to develop a salt, although this technique Simple, readily available and low-cost resources, yet the overall yield is incredibly reduced, only about 17%.
Method 3: Making Use Of 2-carboxypyridine as the raw material, the reaction conditions are reasonably severe, and stimulants such as NaH as well as LiCl are utilized in the response process, which is expensive and also has a high risk variable, and large-scale industrialization is challenging.
Technique 4: Using 2-chloropyridine as a raw material, making use of a catalytic oxidation system composed of maleic anhydride and also acetic acid, and also better controlling the mercaptolation reaction through a Na2S-NaSH barrier system, zinc pyrithione is gotten with a return of regarding 75%.
1) Synthesis of 2-chloro-N-oxypyridine (1): In a 250 mL four-necked flask equipped with mechanical stirring, a condenser tube, a constant-pressure dropping funnel, and a thermometer, 20.0 g (0.18 mol) of 2-chloropyridine was added Pyridine, 1.3 g (0.013 mol) maleic anhydride, 5.0 mL of 50% H2O2 and 50 mL of ethyl acetate were stirred to dissolve all of them. After the temperature was raised to 80 °C, 9.5 mL of H2O2 was added dropwise, and the dropwise addition was completed in 15 min. Reaction 4 h, TLC to determine the reaction endpoint. The product was washed with water and distilled under reduced pressure to obtain a pale yellow liquid.
2) Synthesis of 2-mercapto-N-oxypyridine (2): Add NaOH solution to compound 1, adjust to pH 9.0~11.0, heat up to 50 °C, protect with N2, and dropwise add 100 ℃ through a constant pressure dropping funnel The buffer solution composed of 17.6 g (0.31 mol) NaSH and 9.4 g (0.12 mol) Na2S was added dropwise for about 30 min. During the process, attention was paid to controlling the pH change, and the temperature was raised to 90 °C for 2 h. After the reaction, it was lowered to room temperature, and 1 mol/L HCl solution was added to adjust the pH to 2, and a large amount of white precipitates were produced, which was filtered and dried to obtain the product.
3) Synthesis of 2-mercapto-N-oxypyridine sodium salt (3): Add NaOH solution to compound 2, adjust to pH 6 (± 0.5), and dissolve it with slight heat to form a transparent yellow solution.
4) Synthesis of Pyrithione Zinc Bar Soap (4): Weigh 14.0 g (0.05 mol) of ZnSO4 7H2O solid, dissolve it in 150 mL of distilled water, and slowly add it dropwise to compound 3 at 50 °C through a constant pressure dropping funnel. A large amount of white precipitate formed, and stirring was continued for 2 h. Suction filtration, washed twice with water, washed with cyclohexane, and dried to obtain 22.9 g of white solid with a total yield of 68%.