Preparation method of ultraviolet light absorber UV-234

Abstract

The invention relates to the technical field of ultraviolet light absorbers, in particular to a preparation method of an ultraviolet light absorber UV-234, which comprises the following steps: cooling an o-nitroaniline hydrochloric acid solution, reacting with sodium nitrite, and adding urea to obtain diazonium salt; the method comprises the following steps: mixing a 2, 4-dicumyl phenol methanol solution with caustic soda flakes, dropwise adding a diazonium salt, and heating to obtain a coupling product; adding caustic soda liquid and hydrazine hydrate, keeping the temperature, adding methylbenzene, caustic soda flakes and aluminum powder, and separating to obtain a methylbenzene layer; reacting a toluene layer with hydrochloric acid and water, adding zinc powder, and washing to be neutral; the preparation method comprises the following steps: distilling to recover toluene, adding methanol for reflux, cooling, filtering, washing and drying to obtain the ultraviolet light absorber UV-234, and adopting a two-step reduction strategy of accurate temperature control to realize selective reduction of nitro and azo groups. The strategy is based on a molecular orbital theory, reduction potential differences of different functional groups are fully considered, and the electron transfer process is accurately controlled by regulating and controlling reaction conditions, so that the selectivity and the yield of a target product are greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ultraviolet absorbers, and particularly to a preparation method of an ultraviolet absorber UV-234. Background Art

[0002] As an important light stabilizer, ultraviolet absorber UV-234 is widely used in fields such as plastics, coatings, and textiles. However, the traditional preparation methods of UV-234 have many problems, which restrict its large-scale production and application.

[0003] In the prior art, the synthesis of UV-234 usually adopts a one-step reduction method, that is, after coupling o-nitroaniline with 2,4-dicumylphenol, a reduction reaction is directly carried out. Although this method is simple to operate, it has the following defects: First, it is difficult to achieve selective reduction of nitro and azo groups in one-step reduction, often resulting in over-reduction or insufficient reduction, generating a large number of by-products, seriously affecting the product purity and yield. Second, the temperature control in the diazotization and coupling reactions of the traditional method is not precise enough, easily causing the instability of diazonium salts or incomplete coupling reactions. Third, a wide variety of organic solvents are used in the conventional synthesis, which not only increases the production cost but also brings environmental pollution problems. In addition, the existing technology often adopts simple cooling crystallization in the crystallization purification stage, and it is difficult to effectively control the crystal morphology and particle size distribution, resulting in problems such as poor dispersibility and insufficient thermal stability of the product in subsequent applications. Summary of the Invention

[0004] The present invention aims to solve the above technical problems and provides an efficient, environmentally friendly, and controllable preparation method of UV-234.

[0005] The object of the present invention is to provide a preparation method of an ultraviolet absorber UV-234, comprising the following steps:

[0006] (1) Diazotization reaction: Dissolve o-nitroaniline in 30% hydrochloric acid, heat to 80 - 90 °C for dissolution, then cool to below 15 °C, add flake ice, and then slowly add a sodium nitrite solution, control the temperature to react at 5 - 10 °C, and finally add urea at -3 - 0 °C;

[0007] (2) Coupling reaction: Dissolve 2,4-dicumylphenol in methanol, heat to 55 - 65 °C for reflux, then cool to below 20 °C, add flake caustic soda, continue to cool to below 15 °C, and slowly dropwise add the diazonium salt obtained in step (1) at 10 - 15 °C, and heat to 40 - 50 °C after the reaction is completed;

[0008] (3) Alkaline reduction: Add 30% liquid caustic soda and 5 g of glucose to the solution obtained in step (2), heat up to 65 - 70 °C, slowly dropwise add 40% hydrazine hydrate, keep the temperature for reaction, then cool down to 50 °C, add toluene and flake caustic soda, slowly add aluminum powder at 50 - 60 °C, after the reaction is completed, add toluene, and separate the alcohol - water layer;

[0009] (4) Acidic reduction: Add water and 30% hydrochloric acid to the toluene layer obtained in step (3), heat up to 70 - 80 °C for reaction, then add water and 30% hydrochloric acid, heat up to 80 - 85 °C, slowly add zinc powder, after the reaction is completed, wash with water multiple times until neutral;

[0010] (5) Crystallization: Distill and recover part of the toluene from the solution obtained in step (4), then add methanol, heat up to reflux, cool down to below 10 °C and filter, wash with methanol, and dry at 80 °C to obtain the finished product of ultraviolet absorber UV - 234.

[0011] Specifically, in step (1), the amount of 30% hydrochloric acid used is 70 - 80 g, the amount of o - nitroaniline used is 20 - 30 g, the amount of flake ice used is 30 - 40 g, the amount of sodium nitrite used is 10 - 15 g, and the amount of urea used is 0.5 - 1.5 g.

[0012] Specifically, in step (2), the amount of methanol used is 180 - 220 g, the amount of 2,4 - dicumylphenol used is 40 - 50 g, and the amount of flake caustic soda used is 25 - 35 g.

[0013] Specifically, in step (3), the amount of 30% liquid caustic soda used is 30 - 40 g, the amount of 40% hydrazine hydrate used is 15 - 25 g, the total amount of toluene used is 180 - 200 g, the amount of flake caustic soda used is 10 - 20 g, and the amount of aluminum powder used is 7 - 11 g.

[0014] Specifically, in step (4), the amount of water added for the first time is 25 - 35 g, the amount of 30% hydrochloric acid used is 30 - 40 g, the amount of water added for the second time is 30 - 40 g, the amount of 30% hydrochloric acid used is 50 - 60 g, and the amount of zinc powder used is 5 - 7 g.

[0015] Specifically, in step (5), the amount of toluene distilled and recovered is 90 - 110 g, and the amount of methanol added is 140 - 160 g.

[0016] Specifically, in step (1), the time for the diazotization reaction is 1.5 - 2.5 hours.

[0017] Specifically, in step (2), the time for the coupling reaction is 2.5 - 3.5 hours.

[0018] Specifically, in the step (3), the total time of the alkaline reduction reaction is 3.5 - 4.5 hours.

[0019] Specifically, in the step (4), the time of the acidic reduction reaction is 1.5 - 2.5 hours, and it is washed with water until the pH value reaches 6 - 8.

[0020] Specifically, the present invention has achieved technological breakthroughs in the following ways:

[0021] The present invention provides an efficient, environmentally friendly and controllable method for preparing UV - 234. The core innovation points of this method are as follows:

[0022] 1. A two - step reduction strategy with precise temperature control is adopted to achieve the selective reduction of nitro and azo groups. This strategy is based on molecular orbital theory, fully considering the reduction potential differences of different functional groups. By regulating the reaction conditions and precisely controlling the electron transfer process, the selectivity and yield of the target product are significantly improved.

[0023] 2. The technology of low - temperature pre - dissolution and urea capturer is introduced in the diazotization reaction, significantly improving the stability and purity of diazonium salts. This innovation stems from an in - depth understanding of the diazotization reaction mechanism. By controlling the dissolution state of reactants and capturing by - products, the occurrence of side reactions is effectively inhibited.

[0024] 3. Methanol is innovatively selected as the coupling reaction solvent, which not only improves the reaction efficiency but also realizes the recycling of the solvent. This selection is based on a systematic analysis of the polarity and solubility parameters of the reaction system, optimizing the reaction conditions and embodying the concept of green chemistry.

[0025] 4. A unique crystallization process is designed. By controlling the crystallization temperature, time and stirring rate, precise regulation of the crystal morphology and particle size of UV - 234 is achieved. This process innovation stems from crystal growth theory. By optimizing the crystallization kinetics and thermodynamics conditions, the dispersibility and thermal stability of the product are significantly improved.

[0026] Through the above innovations, the present invention not only solves the technical problems in traditional methods but also brings a series of unexpected technical effects:

[0027] 1. The product purity is significantly improved, reaching more than 99.6%, far exceeding the existing technical level.

[0028] 2. The thermal stability and ultraviolet absorption performance are synergistically enhanced. The thermal decomposition temperature is increased to 286 °C, while maintaining excellent ultraviolet protection effect.

[0029] 3. The dispersibility in polymers is greatly improved, and the dispersibility score reaches 4.6 (on a 5 - point scale), which directly enhances the light - stabilizing performance of the product.

[0030] 4. The solvent residue is reduced to 32 ppm, which not only improves the product safety but also unexpectedly enhances the compatibility between UV-234 and the polymer matrix.

[0031] 5. Through a precisely controlled crystallization process, a unique crystal structure is obtained, which comprehensively optimizes multiple properties of UV-234 at the molecular and crystal scales.

[0032] In summary, the preparation method of UV-234 provided by the present invention not only overcomes the limitations of the prior art but also makes breakthrough progress in terms of product performance, production efficiency, and environmental friendliness. These innovations and advantages open up new possibilities for the application of UV-234 in harsh environments such as high temperature and strong light, and at the same time point out a new direction for the technological development in the field of ultraviolet absorbers. Detailed implementation manners

[0033] Example 1: A preparation method of ultraviolet absorber UV-234

[0034] This example provides a preparation method of ultraviolet absorber UV-234, which comprises the following steps:

[0035] (1) Diazotization reaction: First, add 25 g of o-nitroaniline to 78 g of 30% hydrochloric acid, start stirring, heat up to 80 °C, and keep warm for 2 hours to ensure complete dissolution of the raw materials. Subsequently, cool the reaction solution to below 15 °C and add 35 g of flake ice. Then, slowly dropwise add the pre-prepared sodium nitrite solution (13 g of sodium nitrite dissolved in 26 g of water). After the addition is complete, control the reaction temperature at 5 °C and continue the reaction for 2 hours. Finally, add 1 g of urea at -3 °C and stir for 15 minutes to obtain a yellow-brown transparent diazonium salt solution.

[0036] (2) Coupling reaction: Add 198 g of methanol to the reaction kettle, start stirring, and add 45 g of 2,4-dicumylphenol. After installing the condenser, raise the temperature to 55 °C and keep stirring under reflux for 1 hour to ensure complete dissolution of the raw materials. Subsequently, cool the reaction solution to below 20 °C and add 30 g of flake caustic soda. Continue to cool to below 15 °C, and then slowly dropwise add the diazonium salt solution obtained in step (1) in the temperature range of 10 - 15 °C, and the dropping time is about 1 hour. After the addition is complete, continue the reaction at 10 - 15 °C for 3 hours to finally obtain a dark red thick coupling product.

[0037] (3) Alkaline reduction: Add 35 g of 30% liquid caustic soda and 5 g of glucose to the coupling product, and heat up to 65 °C. Then slowly dropwise add 19 g of 40% hydrazine hydrate solution, and keep the reaction solution in a fine reflux state. After the addition is complete, continue the reaction at this temperature for 2 hours. When it is observed that the red color disappears and yellow materials precipitate, lower the temperature to 50 °C, and successively add 48 g of toluene and 15 g of flake caustic soda. Subsequently, slowly add 9 g of aluminum powder at 50 - 55 °C, and keep the reflux state during the addition. After the feeding is completed, continue the reaction at 55 °C for 2 hours until the solution turns light yellow. Finally, add 139 g of toluene, stir for 15 minutes and then stand still for 10 minutes to separate the alcohol-water layer.

[0038] (4) Acidic reduction: Add 30 g of water and 35 g of 30% hydrochloric acid to the toluene layer obtained in step (3), heat up to 70 °C, stir and react for 15 minutes, and separate the water layer after standing. Then add 35 g of water and 55 g of 30% hydrochloric acid, and heat up to 80 °C. Slowly add 6 g of zinc powder under reflux state, and continue the reaction at 80 - 85 °C for 2 hours after the addition. Judgment of the reaction end point: Take a small amount of the reaction solution and drop it on the filter paper. When it is observed that the material is bright white, the reaction is complete.

[0039] (5) Crystallization: First, wash the reaction solution obtained in step (4) with water multiple times until the pH value reaches 6 - 7. Then distill and recover 100 g of toluene, lower the temperature to 68 °C, and add 150 g of methanol. Heat up to the reflux state and keep it warm for 1 hour. Subsequently, lower the temperature below 10 °C, filter, and wash with a small amount of cold methanol until the filter cake turns white. Finally, dry the filter cake at 80 °C to obtain the finished product of ultraviolet absorber UV-234.

[0040] In this example, by precisely controlling the temperature of the diazotization reaction, the diazonium salt intermediate can be effectively stabilized, and the reaction selectivity can be improved. In the coupling reaction, using methanol as the solvent not only increases the solubility of 2,4-dicumylphenol but also facilitates the subsequent solvent recovery and utilization, embodying the concept of green chemistry. The two-step reduction strategy of alkaline reduction and acidic reduction can achieve the selective reduction of nitro and azo groups, effectively avoiding the by-products caused by over-reduction.

[0041] Example 2: A preparation method of ultraviolet absorber UV-234

[0042] The preparation method of ultraviolet absorber UV-234 provided in this example includes the following steps:

[0043] (1) Diazotization reaction: Take 70 g of 30% hydrochloric acid, add 20 g of o-nitroaniline, heat up to 90 °C to dissolve, and keep the temperature for 2.5 hours. After cooling to 10 °C, add 30 g of flake ice. Slowly dropwise add sodium nitrite solution (10 g of sodium nitrite dissolved in 20 g of water). Control the temperature at 10 °C and react for 1.5 hours. Finally, add 0.5 g of urea at 0 °C and stir for 10 minutes.

[0044] (2) Coupling reaction: Add 180 g of methanol and 40 g of 2,4-dicumylphenol to the reaction kettle. Heat up to 65 °C and reflux for 1.5 hours. Cool down to 15 °C, add 25 g of flake caustic soda. Dropwise add the diazonium salt solution at 12 - 15 °C, and the dropping time is 1.5 hours. After reacting for 2.5 hours, heat up to 45 °C.

[0045] (3) Alkaline reduction: Add 30 g of 30% liquid caustic soda and 5 g of glucose, heat up to 70 °C. Dropwise add 15 g of 40% hydrazine hydrate and react for 2.5 hours. Cool down to 50 °C, add 40 g of toluene and 10 g of flake caustic soda. Add 7 g of aluminum powder at 60 °C and react for 1.5 hours. Add 150 g of toluene and separate the alcohol-water layer.

[0046] (4) Acidic reduction: Add 25 g of water and 30 g of 30% hydrochloric acid to the toluene layer and react at 75 °C. Then add 30 g of water and 50 g of 30% hydrochloric acid, add 5 g of zinc powder at 85 °C and react for 1.5 hours.

[0047] (5) Crystallization: Wash with water until the pH is 8, distill and recover 110 g of toluene. Add 140 g of methanol at 68 °C and reflux for 0.5 hours. Filter at 5 °C and dry at 80 °C to obtain the product.

[0048] In this example, by increasing the temperature and prolonging the reaction time of the diazotization reaction, the complete dissolution and conversion of o-nitroaniline can be ensured, thereby improving the efficiency of subsequent reactions. Using a relatively high reflux temperature in the coupling reaction helps to accelerate the reaction rate and shorten the overall reaction time. In the reduction step, by adjusting the dosage of the reducing agent and the reaction time, the reduction degree can be better controlled and the product quality can be optimized.

[0049] Example 3: A preparation method of ultraviolet absorber UV-234

[0050] The preparation method of ultraviolet absorber UV-234 provided in this example includes the following steps:

[0051] (1) Diazotization reaction: Dissolve 23 g of o-nitroaniline with 75 g of 30% hydrochloric acid, keep the temperature at 85 °C for 2.2 hours. Cool to 12 °C, add 33 g of flake ice. Dropwise add sodium nitrite solution (12 g dissolved in 23 g of water). React at 7 °C for 1.8 hours, and add 0.8 g of urea at -2 °C.

[0052] (2) Coupling reaction: Dissolve 43 g of 2,4-dicumylphenol in 190 g of methanol, reflux at 60 °C for 1.2 h. Cool to 18 °C, add 28 g of sodium hydroxide flakes. Dropwise add the diazonium salt at 13 - 15 °C over 1.2 h. React for 3 h, then raise the temperature to 48 °C.

[0053] (3) Alkaline reduction: Add 33 g of 30% liquid caustic soda and 5 g of glucose, dropwise add 17 g of 40% hydrazine hydrate at 68 °C, react for 2.2 h. Cool to 50 °C, add 44 g of toluene and 13 g of sodium hydroxide flakes. Add 8 g of aluminum powder at 55 °C, react for 1.8 h. Add 145 g of toluene and separate.

[0054] (4) Acidic reduction: Add 28 g of water and 33 g of 30% hydrochloric acid, react at 73 °C. Then add 33 g of water and 53 g of 30% hydrochloric acid, add 5.5 g of zinc powder at 83 °C, react for 1.8 h.

[0055] (5) Crystallization: Wash with water until pH 7, recover 105 g of toluene. Add 145 g of methanol at 68 °C, reflux for 0.8 h. Filter at 8 °C and dry at 80 °C.

[0056] In this example, by finely tuning the reaction temperature and time of each step, it is possible to optimize energy consumption and production efficiency while ensuring complete reaction. Especially in the reduction step, by precisely controlling the dosage of the reducing agent and reaction conditions, the reaction rate and selectivity can be better balanced, thereby improving product quality and yield.

[0057] Example 4: A preparation method of ultraviolet absorber UV-234

[0058] The preparation method of ultraviolet absorber UV-234 provided in this example includes the following steps:

[0059] (1) Diazotization reaction: Dissolve 30 g of o-nitroaniline in 80 g of 30% hydrochloric acid, keep warm at 88 °C for 2 h. Cool to 14 °C, add 40 g of flake ice. Dropwise add the sodium nitrite solution (15 g dissolved in 30 g of water). React at 8 °C for 2 h, add 1.5 g of urea at -1 °C.

[0060] (2) Coupling reaction: Dissolve 50 g of 2,4-dicumylphenol in 220 g of methanol, reflux at 58 °C for 1 h. Cool to 19 °C, add 35 g of sodium hydroxide flakes. Dropwise add the diazonium salt at 14 - 15 °C over 1 h. React for 3.5 h, then raise the temperature to 50 °C.

[0061] (3) Alkaline reduction: Add 40 g of 30% liquid caustic soda and 5 g of glucose, dropwise add 25 g of 40% hydrazine hydrate at 67 °C, react for 2 h. Cool to 50 °C, add 52 g of toluene and 20 g of sodium hydroxide flakes. Add 11 g of aluminum powder at 58 °C, react for 2 h. Add 140 g of toluene and separate.

[0062] (4) Acidic reduction: Add 35 g of water and 40 g of 30% hydrochloric acid, and react at 78 °C. Then add 40 g of water and 60 g of 30% hydrochloric acid, and add 7 g of zinc powder at 82 °C, and react for 2 hours.

[0063] (5) Crystallization: Wash with water until the pH is 6 - 7, and recover 90 g of toluene. Add 160 g of methanol at 68 °C, reflux for 1 hour. Filter at 10 °C and dry at 80 °C.

[0064] In this example, by using a raw material solution with a higher concentration and a larger temperature gradient, the reaction rate can be accelerated and the production efficiency can be improved. At the same time, by increasing the dosage of the reducing agent and prolonging the reaction time, the completeness of the reaction can be ensured, thereby improving the product purity. In addition, using more methanol in the crystallization process helps to improve the crystallization effect and further enhance the product quality.

[0065] By adjusting the reaction conditions and raw material ratios of each step, the process can be optimized according to the actual production requirements to achieve efficient, environmentally friendly, and high-quality production of UV-234.

[0066] Comparative Example 1: A preparation method of ultraviolet absorber UV-234

[0067] This comparative example aims to verify the importance of controlling the diazotization reaction temperature and is compared with Example 1. The preparation method includes the following steps:

[0068] (1) Diazotization reaction: Add 25 g of o-nitroaniline to 78 g of 30% hydrochloric acid, start stirring, and directly react at room temperature (about 25 °C), slowly dropwise add the pre-prepared sodium nitrite solution (13 g of sodium nitrite dissolved in 26 g of water). After the dropping is completed, continue to react for 2 hours. Finally, add 1 g of urea and stir for 15 minutes.

[0069] (2) Coupling reaction to (5) Crystallization: The same as in Example 1.

[0070] Result analysis: In this comparative example, due to the failure to effectively control the diazotization reaction temperature, the diazonium salt is unstable and partially decomposed. This not only reduces the yield of the diazonium salt but also affects the effect of the subsequent coupling reaction. The yields and purities of the final products are lower than those in Example 1, fully demonstrating the importance of precise temperature control for improving reaction selectivity and product quality.

[0071] Comparative Example 2: A preparation method of ultraviolet absorber UV-234

[0072] This comparative example aims to verify the importance of selecting the coupling reaction solvent and is compared with Example 2. The preparation method includes the following steps:

[0073] (1) Diazotization reaction: The same as in Example 2.

[0074] (2) Coupling reaction: Dissolve 40 g of 2,4 - dicumylphenol in 180 g of water (replacing methanol), and the remaining steps are the same as in Example 2.

[0075] (3) Alkaline reduction to (5) Crystallization: The same as in Example 2.

[0076] Result analysis: Using water as the solvent for the coupling reaction can reduce costs, but the low solubility of 2,4 - dicumylphenol in water leads to incomplete reactions and a decrease in the yield of the coupling product. At the same time, the aqueous phase system also increases the difficulty of subsequent separation and purification. This result proves the superiority of using methanol as the solvent, which not only improves the reaction efficiency but also facilitates the subsequent solvent recovery and utilization, embodying the green chemistry concept of the present invention.

[0077] Comparative Example 3: A preparation method of ultraviolet absorber UV - 234

[0078] This comparative example aims to verify the necessity of the two - step reduction strategy and is compared with Example 3. The preparation method includes the following steps:

[0079] (1) Diazotization reaction and (2) Coupling reaction: The same as in Example 3.

[0080] (3) One - step reduction: Combine the alkaline reduction and acidic reduction in Example 3 into one step. Add 33 g of 30% liquid caustic soda, 17 g of 40% hydrazine hydrate, 8 g of aluminum powder, and 5.5 g of zinc powder to the coupling product simultaneously, and react at 70 °C for 3 hours.

[0081] (4) Crystallization: The same as in Example 3.

[0082] Result analysis: Although one - step reduction simplifies the operation process, it is difficult to achieve selective reduction of nitro and azo groups. This leads to problems of over - reduction or insufficient reduction, generating more by - products and reducing the purity and yield of the target product. This result fully proves the scientific nature and necessity of the two - step strategy of alkaline reduction and acidic reduction adopted in the present invention.

[0083] Comparative Example 4: A preparation method of ultraviolet absorber UV - 234

[0084] This comparative example aims to verify the importance of the choice of reducing agent and is compared with Example 4. The preparation method includes the following steps:

[0085] (1) Diazotization reaction and (2) Coupling reaction: The same as in Example 4.

[0086] (3) Alkaline reduction: Replace hydrazine hydrate and aluminum powder with 25 g of sodium borohydride, and the remaining steps are the same as in Example 4.

[0087] (4) Acidic reduction and (5) crystallization: The same as in Example 4.

[0088] Result analysis: Although sodium borohydride is a strong reducing agent that can rapidly reduce nitro and azo groups, its reducing ability is too strong to control, easily leading to over-reduction. At the same time, the use of sodium borohydride also increases costs and safety risks. In contrast, the combination of hydrazine hydrate and aluminum powder used in the present invention not only has a mild and controllable reduction effect, but also is more economical and environmentally friendly, fully demonstrating the innovation and superiority of the present invention in the selection of reducing agents.

[0089] Comparative Example 5: A preparation method of ultraviolet absorber UV-234

[0090] This comparative example aims to verify the importance of solvent selection during crystallization by comparing with Example 1. The preparation method includes the following steps:

[0091] (1) Diazo reaction to (4) acidic reduction: The same as in Example 1.

[0092] (5) Crystallization: Use 150 grams of ethanol to replace methanol for crystallization, and the remaining steps are the same as in Example 1.

[0093] Result analysis: Although ethanol is also a commonly used crystallization solvent, in this reaction system, the product obtained by using ethanol for crystallization has smaller particles and is prone to solvent residues. In contrast, using methanol can not only obtain larger and more regular crystals, which is beneficial to improving the product purity, but also is easier to dry, reducing solvent residues. This result verifies the rationality of the present invention in the selection of crystallization solvents.

[0094] Comparative Example 6: A preparation method of ultraviolet absorber UV-234

[0095] This comparative example aims to verify the necessity of urea addition by comparing with Example 2. The preparation method includes the following steps:

[0096] (1) Diazo reaction: Conducted according to the method of Example 2 without adding urea.

[0097] (2) Coupling reaction to (5) crystallization: The same as in Example 2.

[0098] Result analysis: In the diazo reaction product without added urea, there may be excessive nitrous acid. These residual nitrous acids may cause side reactions in the subsequent coupling reaction, affecting the product purity and yield. In contrast, adding a small amount of urea in the present invention can effectively capture excessive nitrous acid, prevent side reactions from occurring, and thus improve the product quality. This result fully demonstrates the importance of adding urea, a small but crucial step, in the diazo reaction of the present invention.

[0099] Through these six specifically designed comparative examples, the innovative points and advantages of the present invention in aspects such as reaction condition control, solvent selection, reduction strategy, crystallization optimization, etc. can be clearly seen. These comparative examples verify the scientific nature and necessity of each step of the present invention from different perspectives. The results show that the UV-234 preparation method provided by the present invention has significant advantages in terms of reaction efficiency, product quality, economy, and environmental protection, fully reflecting its creativity and practical value.

[0100] Performance test experimental design:

[0101] 1. Product purity test

[0102] Experimental method: The purity of UV-234 was determined by high performance liquid chromatography (HPLC).

[0103] Experimental conditions: Column C18, mobile phase methanol / water (80:20, v / v), flow rate 1.0 mL / min, detection wavelength 313 nm.

[0104] 2. Ultraviolet absorption performance test

[0105] Experimental method: The absorbance of UV-234 at different wavelengths was measured using an ultraviolet-visible spectrophotometer.

[0106] Experimental conditions: The sample was dissolved in ethyl acetate at a concentration of 10 mg / L, and the scanning range was 280 - 400 nm.

[0107] 3. Thermal stability test

[0108] Experimental method: The thermal stability of the sample was determined by thermogravimetric analysis (TGA).

[0109] Experimental conditions: Heating rate 10 °C / min, temperature range 25 - 500 °C, nitrogen atmosphere.

[0110] 4. Dispersibility test

[0111] Experimental method: The UV-234 sample was dispersed in polypropylene (PP), and its dispersibility was observed using an optical microscope.

[0112] Experimental conditions: The mass ratio of UV-234 to PP was 1:1000. After mixing, it was melt-mixed at 180 °C for 5 minutes to form a film, and the magnification was 500 times.

[0113] 5. Light stability test

[0114] Experimental method: UV-234 was added to PP to form a film, and accelerated aging test was carried out in a xenon lamp aging chamber.

[0115] Experimental conditions: The addition amount of UV-234 is 0.5%, the film thickness is 50 μm, the irradiation intensity of the xenon lamp is 0.55 W / m 2 , the temperature is 65 °C, the relative humidity is 50%, and the test time is 1000 hours.

[0116] 6. Solvent residue test

[0117] Experimental method: Gas chromatography (GC) was used to determine the methanol residue in the sample.

[0118] Experimental conditions: FID detector, HP-5 chromatographic column, injection port temperature 250 °C, column temperature 80 °C, detector temperature 280 °C.

[0119] The test results are shown in the following table:

[0120] Table 1. Performance test results of UV-234 samples

[0121]

[0122]

[0123] Note: The dispersibility score uses a 1-5 scale, with 5 indicating the best dispersibility.

[0124] The results are analyzed as follows:

[0125] 1. Product purity: The product purity of Examples 1-4 of the present invention is above 99.3%, significantly higher than that of the comparative example products. This is mainly due to the innovations of the present invention in aspects such as the control of the diazotization reaction temperature, the selection of the coupling reaction solvent, and the two-step reduction strategy. In particular, Example 4 reached a high purity of 99.6%, demonstrating the excellent performance of this method.

[0126] 2. Ultraviolet absorption performance: The maximum absorption wavelengths of all samples are in the range of 310-314 nm, which conforms to the characteristics of UV-234. However, the sample examples of the present invention generally show stronger absorption intensity and more accurate maximum absorption wavelengths, which may be related to the high purity and crystal quality of the product.

[0127] 3. Thermal stability: The thermal decomposition temperatures of the sample examples are generally higher than those of the comparative example samples. This result may be due to the better control of the reaction conditions in the reduction process of the present invention, reducing the generation of unstable impurities. The thermal decomposition temperature of Example 4 is the highest, reaching 286 °C, demonstrating excellent thermal stability.

[0128] 4. Dispersibility: The sample examples of the present invention show better dispersibility in PP, and the scores are all

[0129] Above 4.3. This may be related to the crystal form and particle size distribution of the product, reflecting the advantages of the present invention in the control of the crystallization process.

[0130] 5. Light stability: After 1000 hours of accelerated aging test on the example samples, the color retention rate of the PP film is significantly higher than that of the comparative example samples. Especially for Example 4, the color retention rate is as high as 96%, demonstrating excellent light stability performance. This result verifies that the UV-234 produced by the present invention has excellent ultraviolet absorption and protection capabilities.

[0131] 6. Solvent residue: The solvent residue amounts of the example samples are generally lower than those of the comparative example samples. Especially for Example 4, the residue amount is only 32 ppm. This reflects the optimization effect of the present invention in the crystallization and drying processes, not only improving the product purity but also enhancing the product safety.

[0132] Based on the above test results, Example 4 can be recognized as the best example. It shows optimal or nearly optimal performance in various aspects such as product purity, ultraviolet absorption performance, thermal stability, dispersibility, light stability, and solvent residue.

[0133] Unexpected technical effects:

[0134] 1. Synergistic enhancement of thermal stability and ultraviolet absorption performance: The present invention not only improves the purity of UV-234 but also unexpectedly enhances its thermal stability. This may be because in the two-step reduction process, not only the selective reduction of the target group is achieved, but also the spatial configuration of the molecule is optimized, making it more stable at high temperatures. This improvement in thermal stability and the enhancement of ultraviolet absorption performance form a beneficial complement, enabling the product to maintain excellent ultraviolet protection effect in high-temperature environments.

[0135] 2. Positive correlation between dispersibility and light stability: The test results show that samples with better dispersibility tend to have higher light stability. This finding implies that the distribution state of UV-234 molecules in the polymer matrix has a significant impact on its long-term protection performance. By optimizing the crystallization process, the present invention not only improves the product purity but also enhances its dispersibility in the polymer, thereby optimizing the protection effect of UV-234 at the microscale.

[0136] 3. Substantial reduction of solvent residue amount: While ensuring high purity, the present invention achieves a significant reduction in the solvent residue amount. This not only improves the product safety but also unexpectedly improves the compatibility of UV-234 in the polymer. The low solvent residue may reduce the interfacial tension between UV-234 molecules and the polymer matrix, further promoting its uniform dispersion and thus enhancing the overall performance of the product macroscopically.

[0137] 4. Comprehensive Impact of Crystal Morphology on Multiple Properties: By optimizing the crystallization process, the present invention not only improves the product purity but also unexpectedly affects the crystal morphology of UV-234. This unique crystal structure may be the key factor leading to the comprehensive improvement of thermal stability, dispersibility, and photo-stability. It implies that by precisely controlling the crystallization process, multiple properties of UV-234 can be regulated at the molecular and crystal scales.

[0138] Through an innovative synthesis route and fine process control, the present invention not only achieves the high-purity preparation of UV-234 but also significantly improves its performance in multiple aspects such as thermal stability, photo-stability, and dispersibility. These excellent properties stem from the synergistic effect of structural optimization at the molecular level and process innovation at the macroscopic scale. In particular, the discoveries of the synergistic enhancement of thermal stability and UV protection performance, and the positive correlation between dispersibility and photo-stability provide new possibilities for the application of UV-234 in harsh environments such as high temperature and strong light. These unexpected technical effects not only confirm the innovation and practical value of the present invention but also point out a new research direction for the future development of ultraviolet absorbers.

[0139] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and changes can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for preparing an ultraviolet absorber UV-234, characterized in that: The following steps are involved: (1) Diazotization reaction: o-nitroaniline is dissolved in 30% hydrochloric acid, heated to 80-90°C to dissolve, then cooled to below 15°C, flake ice is added, and then sodium nitrite solution is slowly added, the temperature is controlled at 5-10°C to react, and finally urea is added at -3-0°C; (2) Coupling reaction: dissolve 2,4-dicumylphenol in methanol, heat to 55-65°C and reflux, then cool to below 20°C, add caustic soda flakes, continue to cool to below 15°C, slowly dropwise add the diazonium salt obtained in step (1) at 10-15°C, and heat to 40-50°C after the reaction is completed; (3) Alkaline reduction: add 30% liquid caustic soda and 5 g glucose to the solution obtained in step (2), raise the temperature to 65-70°C, slowly dropwise add 40% hydrazine hydrate, keep the temperature to react, then cool to 50°C, add toluene and caustic soda flakes, slowly add aluminum powder at 50-60°C, add toluene after the reaction is complete, and separate the alcohol-water layer; (4) Acidic reduction: add water and 30% hydrochloric acid to the toluene layer obtained in step (3), heat to 70-80°C for reaction, then add water and 30% hydrochloric acid, heat to 80-85°C, slowly add zinc powder, and after the reaction is completed, wash with water several times until neutral; (5) Crystallization: distill the solution obtained in step (4) to recover part of the toluene, then add methanol, heat and reflux, cool to below 10°C, filter, wash with methanol, and dry at 80°C to obtain the finished product of ultraviolet absorber UV-234.

2. The preparation method according to claim 1, characterized in that: In the step (1), the amount of 30% hydrochloric acid is 70-80 grams, the amount of o-nitroaniline is 20-30 grams, the amount of flake ice is 30-40 grams, the amount of sodium nitrite is 10-15 grams, and the amount of urea is 0.5-1.5 grams.

3. The preparation method according to claim 1, characterized in that: In the step (2), the amount of methanol used is 180-220 grams, the amount of 2,4-dicumylphenol used is 40-50 grams, and the amount of caustic soda flakes used is 25-35 grams.

4. The preparation method according to claim 1, characterized in that: In the step (3), the amount of 30% liquid caustic soda is 30-40 grams, the amount of 40% hydrazine hydrate is 15-25 grams, the total amount of toluene is 180-200 grams, the amount of flake caustic soda is 10-20 grams, and the amount of aluminum powder is 7-11 grams.

5. The preparation method according to claim 1, characterized in that: In the step (4), the amount of water added for the first time is 25-35 grams, the amount of 30% hydrochloric acid is 30-40 grams, the amount of water added for the second time is 30-40 grams, the amount of 30% hydrochloric acid is 50-60 grams, and the amount of zinc powder is 5-7 grams.

6. The preparation method according to claim 1, characterized in that: In the step (5), the amount of toluene recovered by distillation is 90-110 g, and the amount of methanol added is 140-160 g.

7. The preparation method according to claim 1, characterized in that: In the step (1), the diazotization reaction time is 1.5-2.5 hours.

8. The preparation method according to claim 1, characterized in that: In the step (2), the coupling reaction time is 2.5-3.5 hours.

9. The preparation method according to claim 1, characterized in that: In the step (3), the total time of the alkaline reduction reaction is 3.5-4.5 hours.

10. The preparation method according to claim 1, characterized in that: In the step (4), the acidic reduction reaction time is 1.5-2.5 hours, and the mixture is washed with water until the pH value reaches 6-8.

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