Application and Development Prospects of Sodium Pyrithione [Overview]
Sodium pyrithione is mainly used for anti-fungal and antibacterial products in daily chemicals (shampoos and hair care products), architectural coatings, adhesives, sealants, pesticides, textiles, leather products, metal working fluids and other fields. It is also It can prepare products such as disinfectants, detergents and medical broad-spectrum antifungal dermatological drugs. At the same time, it is also an effective fungicide and an excellent commonly used disinfectant for fruit trees, peanuts, wheat, vegetables and other crops. Its derivative product, zinc pyrithione, is also a commonly used fungicide in daily chemicals.
Sodium pyrithione can be used to synthesize copper pyrithione salt. Copper pyrithione, referred to as CPT, scientific name is 2-mercaptopyridine-N-copper oxide salt. It has the advantages of low toxicity, low solubility in water, good chemical stability, broad-spectrum bacteriostasis and mildew resistance, and is widely used in Antifouling paint for ships prevents crustaceans, seaweed and other aquatic organisms from corroding the hull. Overseas, as early as the early 1950s, Shaw et al. studied the bactericidal properties of pyrithione salts and their derivatives. The toxicity and solubility of copper pyrithione salts are far lower than other pyrithione salts. Such as sodium salt, zinc salt, etc., but there are certain technical difficulties in the large-scale production of high-quality pyrithione copper salt. At present, considerable research has been done on the preparation and application of copper pyrithione at home and abroad, and its application fields have expanded to daily chemical products, medicine, leather, wood, etc. The basic synthesis route of pyrithione copper salt is to react soluble pyrithione sodium salt with soluble copper salt at a certain temperature, and then wash, filter and dry to obtain pyrithione copper salt green powder.
The reaction medium can be water, or water plus surfactant, or organic solvent, or a mixture of these substances. Among them, the key raw materials that determine the production cost, purity and color of pyrithione copper salt are the purity of sodium pyrithione and copper salt, and determine whether the shape of pyrithione salt particles is needle-like, flaky or granular, and the surface The hydrophilic and lipophilic properties have a great relationship with the reaction medium system. The size of the copper pyrithione salt particles has a great relationship with the reaction medium and production equipment. The size of the particles can also be further adjusted by using grinding equipment in the later stage to make the distribution range narrower. At present, there are mainly four synthetic routes for pyridinethione sodium salt:
(1) Using 2-aminopyridine as the starting material;
(2) Using pyridine-2-carboxylic acid as the starting material;
(3) Using pyridine as the starting material;
(4) Use 2-chloropyridine as the starting material.
The synthetic route using 2-aminopyridine as the starting material is long and requires acylation, oxidation, hydrolysis, diazotization, chlorination, sulfhydration, and then hydrolysis to obtain sodium pyrithione. The overall yield cannot be controlled. The reaction conditions using pyridine-2-carboxylic acid and pyridine as starting materials are relatively harsh. The reaction process requires zinc carbonate hydroxide, sodium hydride or lithium hydride and argon gas, making it difficult to achieve industrial production. At present, our country mainly uses 2-chloropyridine as the initial raw material, and produces sodium pyrithione through oxidation → sulfhydration → hydrolysis.
Application and development prospects of sodium pyrithione [preparation method]
The important intermediate for the synthesis of sodium pyrithione is 2-chloropyridine nitrogen oxide (2-PCL-N-oxide), which can be catalyzed by 2-chloropyridine (2-PCL) in the presence of tungstic acid and phosphoric acid It is prepared by reacting with hydrogen peroxide under normal conditions. The catalyst needs to be recovered with a slight excess of calcium hydroxide, and then sodium carbonate is added to precipitate the remaining calcium ions. Finally, the solid calcium salt is filtered out to obtain a clear 2-chloropyridine nitrogen oxide solution, which is then processed The unreacted raw material 2-chloropyridine is removed by distillation in the distillation tower to obtain qualified products that meet corporate standards.
1 Raw materials and equipment
2-Chloropyridine (2-PCL, 99.5%), Jiangsu Hengsheng Chemical Co., Ltd.; hydrogen peroxide (H2O2, 50%), Shanghai Ah Kema Gaoyuan Chemical Co., Ltd.; Tungstic acid (H2WO4, 98%), phosphoric acid (H3PO4, 85%), Jiangyin Chengxing Industrial Group Co., Ltd.; sodium hydrosulfide (NaSH, analytical grade), sodium carbonate (Na2CO3, analytical Pure), calcium hydroxide (Ca(OH) 2, analytical grade), Changshu Hongyu Calcide Co., Ltd. Eurostar digital display 60 electric mixer, IKA, Germany; S20K pH meter, METTLER TOLEDO; PFX195 colorimeter, Lovibond; JB-30 laboratory distillation device, Deda Tianyi.
2 Synthesis Roadmap
3 Synthesis method
According to the reaction route in Figure 1, add 100 g2-PCL, 5 g tungstic acid, and 1 g phosphoric acid into a 250 mL four-necked flask equipped with an electric stirrer, thermometer, spherical condenser and constant pressure dropping funnel. Stir and heat up 50 mL of water. When the temperature reaches 65 °C, start adding 65 mL of H2O2 dropwise. Control the temperature between 65 and 75 °C through a water bath. After the reaction is completed, take samples for analysis. When the residual amount of H2O2 is less than 2%, cool down. Bring 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, and adjust the pH to 9. 5~ 10. 5, stay for 3 hours. At this time, there is a slight excess of Ca (OH)2. Add an appropriate amount of Na2CO3 and stir for 30 minutes. Finally, the 2-PCL-N-oxide dissolved propyl carbonate liquid is obtained by filtering through a filter press device, and finallyThen it enters the rectification device for rectification. Subsequently, 95 mL of 38% NaSH solution was added dropwise to the distillate at 80°C, and 32% sodium hydroxide was used to neutralize the hydrogen chloride generated by the reaction. 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 ions in the nitrogen oxide solution can keep it stable during the distillation process; the addition of sodium carbonate will make the nitrogen The chromaticity of nitrogen oxides and sodium pyrithione becomes worse. The higher the amount of sodium carbonate added, the worse the chromaticity of nitrogen oxides and sodium pyrithione becomes. For the comprehensive consideration of the final product, the amount of sodium carbonate added 0.4% (relative to the amount of nitrogen oxides) is the optimal amount.
Application and development prospects of sodium pyrithione [Application and development prospects]
With the emphasis on ecological balance and marine water environment in recent years, the use of cuprous oxide powder as the main bactericide in ship antifouling primers was banned after 2012, while pyrithione salt due to its low toxicity and good Bactericidal and anti-fouling effects will be widely used. Most of the currently synthesized copper pyrithione has a granular and needle-like crystal structure. The platelet shape has a higher surface area than the needle-like structure, which provides higher insecticidal protection and is therefore more beneficial to copper pyrithione. It is used for antifouling in coatings and other products. At the same time, the particles with a flaky structure can obtain favorable packing density, dispersion, and are easy to grind. It is worth in-depth study to prepare copper pyrithione with a lamellar structure of about 2 μm for antifouling and antibacterial use, and to prepare composite copper pyrithione particles to enhance the antifouling effect of copper pyrithione on hard dirt.
Application and development prospects of sodium pyrithione [Reference materials]
[1] Ge Haifeng, Zhang Wei. Effect of sodium carbonate on the color of 2-chloropyridine nitrogen oxide and sodium pyrithione [J]. Guangzhou Chemical Industry, 2017, 45(22): 59-60+78 .
[2]Ren Huanyu. Preparation and application of pyridinethione copper salt[J]. Shanghai Paint, 2013, 51(08):30-33.
[3]Ludwig Strauch.Process and Device for the Isolation of Fractions of a Substance Mixture Electrophoretically Separated in a Carrier Ge［l P］.US 3533933, 1970-10-13.
