A method for preparing ultraviolet absorber

Abstract

The present invention discloses a method for preparing a UV absorber, and the method for preparing the UV absorber comprises the following steps: S1, using 2-hydroxy-4-methoxy-benzophenone as a raw material to prepare a wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid; S2, drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid to obtain a UV absorber, wherein the drying process comprises first-stage drying and second-stage drying, wherein the first-stage drying comprises at least one of reduced pressure drying and microwave drying, and the second-stage drying comprises at least one of reduced pressure drying and microwave drying. The UV absorber prepared by the present invention can avoid the problems of poor thermal stability and easy hydrolysis of UV absorber BP-4 by drying process.

Description

Technical Field

[0001] The invention relates to the technical field of ultraviolet absorber preparation, and in particular to a method for preparing an ultraviolet absorber. Background Art

[0002] Sunlight can be divided into ultraviolet rays, visible light, and infrared rays according to their wavelengths. Ultraviolet rays have a good effect on producing vitamin D in the body, so long-term sunbathing is considered beneficial. However, as the ozone layer in the stratosphere is destroyed, the amount of ultraviolet rays reaching the surface of the earth has increased, and health damage caused by ultraviolet rays has gradually been recognized as a problem. Such health damage includes acute problems such as sunburn, and chronic problems such as increased risk of skin cancer and other diseases due to long-term accumulation. Therefore, it is necessary to study effective countermeasures against ultraviolet rays that are harmful to the human body.

[0003] UV absorber BP-4 is a broad-spectrum UV absorber with the advantages of high absorption efficiency, non-toxicity, no teratogenic side effects, good light and thermal stability, etc. It can absorb UV-A and UV-B at the same time. It is a Class I sunscreen approved by the US FDA. This product is an off-white or light yellow crystalline powder, easily soluble in water, ethanol, methanol, slightly soluble in ethyl acetate, and is a water-soluble UV absorber. It is widely used in sunscreen creams, creams, honeys, lotions, oils and other sunscreen cosmetics. However, UV absorber BP-4 has the problems of poor thermal stability and easy hydrolysis. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for preparing an ultraviolet absorber, aiming to solve the problem that the ultraviolet absorber BP-4 has poor thermal stability and hydrolysis caused by drying during dehydration.

[0005] To achieve the above object, the present invention provides a method for preparing an ultraviolet absorber, which comprises the following steps:

[0006] S1, using 2-hydroxy-4-methoxy-benzophenone as a raw material to prepare 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid wet fine product;

[0007] S2. Drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid to obtain an ultraviolet absorber, wherein the drying treatment includes a first stage drying and a second stage drying, wherein the first stage drying includes at least one of reduced pressure drying and microwave drying, and the second stage drying includes at least one of reduced pressure drying and microwave drying.

[0008] Optionally, the water content of the ultraviolet absorber after the first stage of drying is ≤10%.

[0009] Optionally, the water content of the ultraviolet absorber after the second stage of drying is ≤2%.

[0010] Optionally, the reduced pressure drying comprises the following steps:

[0011] First, the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid is vacuum dried for 0.5 to 2 hours, and the internal pressure is controlled at 10 to 10000 Pa to obtain a first dry solid. Then, the first dry solid is heated to 60 to 90° C. at a heating rate of 5 to 30° C. / h for drying.

[0012] Optionally, the reduced pressure drying time is 3 to 30 hours.

[0013] Optionally, the microwave drying has a flat thickness of 2 to 20 cm.

[0014] Optionally, the microwave drying temperature is 60-80°C.

[0015] Optionally, the microwave drying time is 20 to 200 minutes.

[0016] Optionally, step S1 includes the following steps:

[0017] S11, dissolving 2-hydroxy-4-methoxy-benzophenone in an organic solvent, heating and stirring to dissolve clearly, to obtain a mixed solution;

[0018] S12, adding a sulfonating agent to the mixed solution, heating, and obtaining a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0019] S13, cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution and crystallizing it, and filtering to obtain a crude product;

[0020] S14, mixing the crude product with a halogenated alkane and an alcohol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0021] S15, cooling the clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid and crystallizing it, filtering it to obtain a wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0022] Optionally, in step S12, the heating temperature is 50-90° C.; and / or,

[0023] The heating time is 1 to 5 hours; and / or,

[0024] In step S13, during the cooling crystallization, the temperature is lowered to 0-30°C, preferably 5-20°C; and / or,

[0025] In step S14, the halogenated alkane is a C1-C4 chloroalkane, and the alcohol solution is a C1-C4 alcohol solution; and / or,

[0026] In step S15, during the temperature reduction crystallization, the temperature is reduced to 0-30°C, preferably 5-20°C.

[0027] In the technical solution provided by the present invention, the prepared ultraviolet absorber BP-4 wet fine product is subjected to a drying treatment of segmented drying, that is, at least one drying treatment of reduced pressure drying and microwave drying, so that both free water and part of crystalline water can be removed, so that the generated BP-4 wet fine product can effectively reduce the hydrolysis phenomenon of the product during dehydration and drying, and has good thermal stability, thereby improving the product quality of the ultraviolet absorber BP-4, improving the drying efficiency of the ultraviolet absorber BP-4, and effectively reducing the turbidity of its aqueous solution. DETAILED DESCRIPTION

[0028] To make the purpose, technical scheme and advantages of the embodiment of the present invention clearer, the technical scheme in the embodiment of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiment, it is carried out according to the normal conditions or the conditions recommended by the manufacturer. If the reagents or instruments used do not specify the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, taking "A and / or B" as an example, including scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work belong to the scope of protection of the present invention.

[0029] UV absorbers are the most widely used type of light stabilizers. According to their structures, they can be divided into salicylates, benzophenones, benzotriazoles, substituted acrylonitriles, triazines, etc. Benzophenones and benzotriazoles are the most widely used in industry. As the main absorber of benzophenones, 2-hydroxy-4-methoxy-5-sulfonic acid benzophenone (BP-4) is widely used in cosmetic additives. However, the UV absorber BP-4 has the problems of poor thermal stability and easy hydrolysis.

[0030] In view of this, the present invention proposes a method for preparing an ultraviolet absorber, aiming to solve the problem that the ultraviolet absorber BP-4 has poor thermal stability and hydrolysis caused by drying during dehydration.

[0031] The present invention provides a method for preparing an ultraviolet absorber, comprising the following steps:

[0032] S1, using 2-hydroxy-4-methoxy-benzophenone as a raw material to prepare 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid wet fine product;

[0033] This step S1 specifically includes the following steps:

[0034] S11, dissolving 2-hydroxy-4-methoxy-benzophenone in an organic solvent, heating and stirring to dissolve clearly, to obtain a mixed solution;

[0035] In this step, 2-hydroxy-4-methoxy-benzophenone (BP-3) is added to a reaction kettle, and then an organic solvent is added for mixing. The organic solvent includes halogenated alkanes and halogenated aromatic hydrocarbons. Under this condition, the raw material BP-3 is fully dissolved in the organic solvent.

[0036] S12, adding a sulfonating agent to the mixed solution, heating, and obtaining a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0037] In this step, the sulfonating agent includes chlorosulfonic acid, fuming sulfuric acid, and sulfur trioxide. After the sulfonating agent is added, the temperature is raised to 50-90° C. and heated to react for 1-5 hours. Under this reaction condition, 2-hydroxy-4-methoxy-benzophenone fully reacts with the sulfonating agent to generate 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid.

[0038] S13, cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution and crystallizing it, and filtering to obtain a crude product;

[0039] It is understood that when the temperature is lowered, the solubility of the substance decreases, the solution reaches saturation, and the excess insoluble solute will precipitate. In this step, the temperature is lowered to 0-30°C, preferably 5-20°C, 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid will crystallize and precipitate, and the clear liquid is filtered out to obtain a crude substance.

[0040] S14, mixing the crude product with a halogenated alkane and an alcohol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0041] In this step, the halogenated alkane is a C1-C4 chloroalkane, including monochloropropane, monochlorobutane, dichloromethane, dichloroethane, dichloropropane, dichlorobutane, etc.; the alcohol solution is an aqueous solution of C1-C4 alcohol, including methanol, ethanol, propanol or butanol, etc. In order to obtain a purer ultraviolet absorber BP-4, in this step, the crude product obtained above is dissolved in an organic solvent dichloropropane and an aqueous solution of ethanol, and after heating, impurities are filtered out while hot to obtain a pure 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid (BP-4) clear solution.

[0042] S15, cooling the clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid and crystallizing it, filtering to obtain a white solid wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid, with fast filtration speed and high production efficiency;

[0043] In this step, the temperature is lowered again to 0-30°C, preferably 5-20°C, to obtain a purer white solid wet product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid BP-4 with good crystal form.

[0044] S2. Drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid to obtain an ultraviolet absorber, wherein the drying treatment includes a first stage drying and a second stage drying, wherein the first stage drying includes at least one of reduced pressure drying and microwave drying, and the second stage drying includes at least one of reduced pressure drying and microwave drying.

[0045] In this step, the drying treatment includes at least one of reduced pressure drying and microwave drying. Specifically, the reduced pressure drying includes the following steps: first vacuum drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid for 0.5 to 2 hours, controlling the internal pressure to 10 to 10000 pa, to obtain a first dried solid, and then heating the first dried solid to 60 to 90°C at a heating rate of 5 to 30°C / h for drying. The reduced pressure drying time is 3 to 30 hours; after reduced pressure drying, the water content of the ultraviolet absorber is ≤10%. By strictly controlling the conditions of reduced pressure drying, the ultraviolet absorber BP-4 will not decompose during dehydration, and has good stability, while the water content of the ultraviolet absorber is controlled within a reasonable range. In order to further dry the ultraviolet absorber BP-4, preferably, microwave drying is performed after reduced pressure drying. The operating steps of microwave drying are: the ultraviolet absorber BP-4 dried under reduced pressure is spread in a microwave drying container with a thickness of 2 to 20 cm, and dried at 60 to 80° C. for 20 to 200 minutes. The moisture content of the ultraviolet absorber BP-4 dried by microwave is ≤2%. The ultraviolet absorber BP-4 after microwave drying has further controlled moisture content, better stability, less prone to decomposition, and longer storage, thereby improving the product quality of the ultraviolet absorber BP-4, improving the drying efficiency of the ultraviolet absorber BP-4, and effectively reducing the turbidity of its aqueous solution.

[0046] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0047] Example 1

[0048] (1) Weigh 300 g of 2-hydroxy-4-methoxy-benzophenone and 1200 g of ethylene dichloride, mix them, heat and stir until dissolved, and obtain a mixed solution;

[0049] (2) adding 160 g of chlorosulfonic acid to the mixed solution, heating to 70° C., and stirring for 2 h to obtain a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0050] (3) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution to 10° C. for crystallization, and filtering to obtain a crude product;

[0051] (4) mixing the crude product with 1100 g of dichloromethane and 200 g of propanol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0052] (5) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid clear solution to 10° C. for crystallization, and filtering to obtain a wet fine product;

[0053] (6) The wet fine product is subjected to vacuum drying for 0.5 h, the internal pressure is controlled at 1000 MPa, the temperature is increased to 75° C. at a heating rate of 10° C. / h, and the total time is a reduced pressure drying treatment of 20 h.

[0054] (7) After microwave drying at a layer thickness of 6 cm, a temperature of 60° C., and a time of 20 min, 386.2 g of ultraviolet absorber was obtained with a total yield of 95.36%. The turbidity of its aqueous solution was 1.8 EBC.

[0055] Example 2

[0056] (1) Weigh 300 g of 2-hydroxy-4-methoxy-benzophenone and 1200 g of dichloropropane, mix them, heat and stir until dissolved, and obtain a mixed solution;

[0057] (2) adding 160 g of chlorosulfonic acid to the mixed solution, heating to 85° C., and stirring for 2.5 h to obtain a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0058] (3) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution to 15° C. for crystallization, and filtering to obtain a crude product;

[0059] (4) mixing the crude product with an aqueous solution of 1200 g of dichloropropane and 300 g of ethanol, heating, and filtering out insoluble matter to obtain a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0060] (5) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid clear solution to 15° C. for crystallization, and filtering to obtain a wet fine product;

[0061] (6) The wet fine product is vacuum dried for 0.8 h, the internal pressure is controlled at 8000 Pa, the temperature is increased to 80° C. at a heating rate of 15 h° C. / h, and the total time is 8 h of reduced pressure drying treatment.

[0062] (7) After microwave drying at a layer thickness of 10 cm, a temperature of 70° C., and a time of 60 min, 392.3 g of ultraviolet absorber was obtained with a total yield of 96.86%. The turbidity of its aqueous solution was 2.1 EBC.

[0063] Example 3

[0064] (1) Weigh 300 g of 2-hydroxy-4-methoxy-benzophenone and 1200 g of dichloropropane, mix them, heat and stir until dissolved, and obtain a mixed solution;

[0065] (2) adding 160 g of chlorosulfonic acid to the mixed solution, heating to 80° C., and stirring for 3 h to obtain a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0066] (3) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution to 20° C. for crystallization, and filtering to obtain a crude product;

[0067] (4) mixing the crude product with 1250 g of dichloropropane and 220 g of ethanol solution, heating, and filtering out insoluble matter to obtain a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0068] (5) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid clear solution to 20° C. for crystallization, and filtering to obtain a wet fine product;

[0069] (6) The wet fine product is subjected to vacuum drying for 1.0 h, the internal pressure is controlled at 5000 Pa, the temperature is increased to 85° C. at a heating rate of 20° C. / h, and the total time is 3 h of reduced pressure drying treatment.

[0070] (7) After microwave drying at a layer thickness of 20 cm, a temperature of 80° C., and a time of 150 min, 391.0 g of ultraviolet absorber was obtained with a total yield of 96.54%. The turbidity of its aqueous solution was 1.6 EBC.

[0071] Example 4

[0072] (1) Weigh 300 g of 2-hydroxy-4-methoxy-benzophenone and 1200 g of chlorobenzene, mix them, heat and stir until dissolved, and obtain a mixed solution;

[0073] (2) adding 160 g of chlorosulfonic acid to the mixed solution, heating to 50° C., and stirring for 5 h to obtain a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0074] (3) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution to 5° C. for crystallization, and filtering to obtain a crude product;

[0075] (4) mixing the crude product with 1300 g of ethylene dichloride and 250 g of propanol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0076] (5) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid clear solution to 5° C. for crystallization, and filtering to obtain a wet fine product;

[0077] (6) The wet fine product is subjected to vacuum drying for 2.0 h, the internal pressure is controlled at 500 Pa, the temperature is increased to 60° C. at a heating rate of 5° C. / h, and the total time is 30 h of reduced pressure drying treatment.

[0078] (7) After microwave drying at a layer thickness of 18 cm, a temperature of 65° C., and a time of 200 min, 385.8 g of ultraviolet absorber was obtained with a total yield of 95.26%. The turbidity of its aqueous solution was 2.2 EBC.

[0079] Example 5

[0080] (1) Weigh 300 g of 2-hydroxy-4-methoxy-benzophenone and 1200 g of chloroform, mix them, heat and stir until dissolved, and obtain a mixed solution;

[0081] (2) adding 160 g of chlorosulfonic acid to the mixed solution, heating to 90° C., and stirring for 1 h to obtain a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution;

[0082] (3) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution to 30° C. for crystallization, and filtering to obtain a crude product;

[0083] (4) mixing the crude product with 1400 g of ethylene dichloride and 300 g of methanol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid;

[0084] (5) cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid clear solution to 30° C. for crystallization, and filtering to obtain a wet fine product;

[0085] (6) The wet fine product is subjected to vacuum drying for 1.5 hours, the internal pressure is controlled at 10000 Pa, the temperature is increased to 90° C. at a heating rate of 30° C. / h, and the total time is 15 hours of reduced pressure drying treatment.

[0086] (7) After microwave drying at a layer thickness of 15 cm, a temperature of 75° C., and a time of 100 min, 387.0 g of ultraviolet absorber was obtained with a total yield of 95.55%. The turbidity of its aqueous solution was 2.0 EBC.

[0087] Comparative Example 1

[0088] Except that step (6) in Example 1 is not performed, the other steps are the same.

[0089] Comparative Example 2

[0090] Except that step (7) in Example 1 is not performed, the other steps are the same.

[0091] Test methods and results

[0092] The product was weighed and the total yield of the product was calculated. The statistical results are shown in Table 1.

[0093] Table 1 Total yield of products

[0094] sample Total yield / % Turbidity of aqueous solution / EBC Example 1 95.36％ 1.8 Example 2 96.86％ 2.1 Example 3 96.54％ 1.6 Example 4 95.26％ 2.2 Example 5 95.55％ 2.0 Comparative Example 1 94.68％ 4.5 Comparative Example 2 94.72％ 3.8

[0095] Note: The total yield refers to the total yield of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid UV absorber prepared from 2-hydroxy-4-methoxybenzophenone as raw material; the turbidity of the aqueous solution was measured using a TL2300 turbidity meter.

[0096] Compared with Comparative Examples 1 and 2, the total yield of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid obtained in the present invention is as high as 95% or more, and the turbidity of its aqueous solution is lower than 2.2EBC. From the above results, it can be seen that the ultraviolet absorber prepared by the preparation method provided by the present invention has high stability, is not easy to decompose during dehydration and drying, has a high yield, and has low turbidity of its aqueous solution.

[0097] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A method for preparing an ultraviolet absorber, characterized in that: The following steps are involved: S1, using 2-hydroxy-4-methoxy-benzophenone as a raw material to prepare 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid wet fine product; S2, drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid to obtain an ultraviolet absorber, wherein the drying process includes a first stage drying and a second stage drying, wherein the first stage drying is reduced pressure drying, and the second stage drying is microwave drying; The reduced pressure drying comprises the following steps: firstly vacuum drying the wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid for 0.5-2 hours, controlling the internal pressure at 10-10000 Pa to obtain a first dried solid, and then heating the first dried solid to 60-90° C. at a heating rate of 5-30° C. / h for drying; The time of the reduced pressure drying is 3 to 30 hours; The microwave drying temperature is 60-80°C; The microwave drying time is 20 to 200 minutes.

2. The method for preparing the ultraviolet absorber according to claim 1, characterized in that: The water content of the ultraviolet absorber after the first stage of drying is ≤10%.

3. The method for preparing the ultraviolet absorber according to claim 1, characterized in that: The water content of the ultraviolet absorber after the second stage drying is ≤2%.

4. The method for preparing the ultraviolet absorber according to claim 1, characterized in that: The microwave drying has a flat thickness of 2 to 20 cm.

5. The method for preparing the ultraviolet absorber according to claim 1, characterized in that: Step S1 includes the following steps: S11, dissolving 2-hydroxy-4-methoxy-benzophenone in an organic solvent, heating and stirring to dissolve clearly, to obtain a mixed solution; S12, adding a sulfonating agent to the mixed solution, heating, and obtaining a 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution; S13, cooling the 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid solution and crystallizing it, and filtering to obtain a crude product; S14, mixing the crude product with a halogenated alkane and an alcohol solution, heating, filtering out insoluble matter, and obtaining a clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid; S15, cooling the clear solution of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid to crystallize, and filtering to obtain wet fine product of 2-hydroxy-4-methoxybenzophenone-5-sulfonic acid.

6. The method for preparing the ultraviolet absorber according to claim 5, characterized in that: In step S12, the heating temperature is 50-90° C.; and / or, The heating time is 1 to 5 hours; and / or, In step S13, during the cooling crystallization, the temperature is lowered to 0-30°C; and / or, In step S14, the halogenated alkane is a C1-C4 chloroalkane, and the alcohol solution is a C1-C4 alcohol solution; and / or, In step S15, during the temperature reduction crystallization, the temperature is reduced to 0-30°C.

7. The method for preparing the ultraviolet absorber according to claim 6, characterized in that: In step S13, during the cooling crystallization, the temperature is lowered to 5-20°C; and / or, In step S15, during the temperature reduction crystallization, the temperature is reduced to 5-20°C.