Preparation background and overview of zinc pyrithione
Zinc pyrithione (ZPT) has strong penetrating power, inhibits abnormal cell growth and has antimicrobial effects. It is a safe and efficient anti-dandruff and anti-itching agent, and can delay hair aging and reduce hair loss. Delays the generation of gray hair, and as an organic chemical intermediate, it is widely used in fields such as medicine, pesticides, dyes, catalysis, and shipbuilding heavy industry. Currently, commercially available zinc pyrithione products generally have larger particle sizes, and some products with smaller particle sizes are obtained by mechanical slicing and grinding. They have shortcomings such as irregular particles and wide particle size distribution.
According to literature reports, domestic researchers used hydrogen peroxide and acetic acid as catalysts respectively, and found that the material ratios to 2-chloropyridine were (1.50~1.75):1 and (0.84~1.34):1 respectively. Thiolation When the pH value of the system is adjusted to 9.7~10.7, when the zinc salt is formed, the pH value of the system is adjusted to 4.0~5.0. The quality of the synthesized ZPT is better; Zheng Zhanmiao et al. used pyridine as raw material to prepare ZPT; some researchers used 2-halogen Using substituted pyridines as raw materials, the preparation of N-oxide-2-pyridinone zinc salt was studied; American scholars used 2-halopyridines as raw materials to prepare ZPT.
Preparation and sterilization mechanism of zinc pyrithione
Pyrithione acts on bacterial cells, and its bactericidal mechanism is slightly different under different pH levels. Under neutral or acidic conditions, pyrithione takes K + out of bacterial cells and brings H+ into bacterial cells; under alkaline conditions, pyrithione takes K + or Mg2 + is brought out of the bacterial cell, and Na + is brought into the bacterial cell. By eliminating the ion gradient for bacteria to obtain nutrients, the cells are eventually “starved”. Therefore, the bactericidal mechanism of zinc pyrithione is different from that of many bactericides. It kills bacteria while not being consumed itself.
Preparation and application of zinc pyrithione
Zinc pyrithione is a complex of pyrithione and zinc, which has the characteristics of high efficiency, safety and broad-spectrum bactericidal properties. This substance has excellent anti-scaling and anti-seborage properties in the field of daily chemicals, and can effectively kill fungi that cause dandruff; in the field of coatings, it can be compounded and used in ship antifouling coatings to effectively prevent marine life Attached to the hull; in the field of pesticides, it is mainly used to prevent and control apple leaf curl disease and scab disease.
In addition, the antifungal agent zinc pyrithione also has certain applications on fabrics. Experiments have studied the antifungal agent zinc pyrithione on cotton fabrics and polyester/polyester fabrics under different mass concentrations, baking times and baking temperatures. For application on cotton fabrics, the optimal process conditions are determined through single factor and orthogonal experiments. The anti-mildew process parameters for cotton fabrics are: mass concentration of zinc pyrithione 0.04g/L, baking time 3 minutes, baking temperature 120°C, liquid removal rate 80%, liquor ratio 1:25; anti-mildew process parameters for polyester-cotton fabrics are: : The mass concentration of zinc pyrithione is 0.03g/L, the baking time is 3 minutes, the baking temperature is 130°C, the liquid removal rate is 80%, and the liquor ratio is 1:25. Under this process condition, the antifungal agent zinc pyrithione can exert the best antifungal effect.
In addition, zinc pyrithione has been widely used in the daily chemical industry. It is often used in shampoos to remove dandruff. It can inhibit the growth of Gram-positive and negative bacteria and mold, and can also be used as a preservative for cosmetics. . However, its application in latex paint has only started in recent years and is not very widespread. It is still in the exploratory stage. Some experiments have conducted research on the anti-mold and anti-algae properties of zinc pyrithione in latex paint. The results show that pyrithione Zinc and other compound anti-mildew and anti-algae agents can provide comprehensive anti-mildew and anti-algae effects for products and maintain product quality. However, zinc pyrithione has unique advantages in environmental protection and bactericidal durability. It has long-term application prospects in the future of continuous environmental protection of latex paint.
Preparation of zinc pyrithione
Method 1: The preparation principle is that ZnSO4·7H2O reacts with SPT to generate ZPT and sodium sulfate. Weigh an appropriate amount of zinc sulfate heptahydrate and prepare 0.25 mol/L and 0.50 mol/L zinc sulfate solutions respectively. Measure an appropriate amount of sodium pyrithione solution and prepare 0.5 mol/L and 1.0 mol/L sodium pyrithione solutions respectively. Control the process conditions of the reaction process and quickly add the two separately at a certain volume ratio.React in a three-necked flask to obtain zinc pyrithione crystals, which are then suction filtered, washed, and vacuum dried to obtain zinc pyrithione powder.
Method 2: Using pyridine as raw material, after 30% H2O2 oxidation, synthesize N in a system of dimethyl sulfoxide, toluene and sulfur powder – Oxidation of 2-hydroxypyridine, and finally combined with Zn2 + to form a salt. Although this method is simple, the raw materials are easily available and cheap, the overall yield is extremely low, only about 17%.
Method 3: Using 2-carboxypyridine as the raw material, the reaction conditions are relatively harsh. Catalysts such as NaH and LiCl are used during the reaction. It is expensive and has a high risk factor, making large-scale industrialization difficult.
Method 4: Using 2-chloropyridine as raw material, using a catalytic oxidation system composed of maleic anhydride and acetic acid, and further controlling the sulfhydrylated transdicarbonate through the Na2S-NaSH buffer system Tert-butyl ester reacts to obtain zinc pyrithione with a yield of about 75%.
1) Synthesis of 2-chloro-N-oxypyridine (1): In a 250 mL four-necked flask equipped with mechanical stirring, condenser tube, constant pressure dropping funnel, and thermometer, add 20.0 g (0.18 mol) 2-chloropyridine, 1.3 g (0.013 mol) maleic anhydride, 5.0 mL 50% H2O2 and 50 mL ethyl acetate, stir to dissolve them all. After the temperature was raised to 80 °C, 9.5 mL H2O2 was added dropwise. The dropwise addition was completed in 15 min. The reaction was continued for 4 h. The reaction end point was determined by TLC. The product was washed with water and distilled under reduced pressure to obtain a light yellow liquid.
2) Synthesis of 2-mercapto-N-oxypyridine (2): Add NaOH solution to compound 1, adjust to pH 9.0~11.0, raise temperature to 50°C, protect with N2 and pass through constant pressure dropping funnel Add dropwise 100 mL of a buffer solution composed of 17.6 g (0.31 mol) NaSH and 9.4 g (0.12mol) Na2S. Complete the dropwise addition in about 30 minutes. Pay attention to control the change of pH during the process and raise the temperature to 90 ℃, react for 2 hours. After the reaction was completed, the reaction was reduced to room temperature, and 1 mol/L HCl solution was added to adjust to pH 2. A large amount of white precipitate was produced. The product was obtained by suction filtration and drying.
3) Synthesis of 2-mercapto-N-oxopyridine sodium salt (3): Add NaOH solution to compound 2 sodium bicarbonate, adjust to about pH 6 (± 0.5), heat slightly to dissolve it all to form Clear yellow solution.
4) Synthesis of zinc pyrithione (4): Weigh 14.0 g (0.05mol) ZnSO4·7H2O solid and dissolve it in 150 mL distilled water , slowly add compound 3 at 50 °C dropwise through a constant pressure dropping funnel. A large amount of white precipitate will appear. Continue stirring for 2 h. Filter, wash twice with water, wash with cyclohexane, and dry to obtain 22.9 g of white solid, with a total yield of 68%.
