A uv-3 ultraviolet absorber and a method for preparing the same

Abstract

This application relates to a UV-3 ultraviolet absorber and its preparation method, belonging to the field of chemical synthesis technology. The preparation method employs a one-pot process, in which benzocaine reacts with triethyl orthoformate in xylene solvent. This step utilizes reactive distillation coupling control, continuously removing the generated alcohol distillate through a distillation separation device to promote reaction equilibrium shift, obtaining a xylene solution of the intermediate NET. Subsequently, the solution is heated to a reaction temperature of 135–145°C, and benzyl chloride is added dropwise for N-alkylation, while a tail gas absorption device absorbs byproduct gases. The reaction slurry is then cooled for crystallization, solid-liquid separation, and drying to obtain the UV-3 product. This invention simplifies the production process through a one-pot process, avoids the use of toxic DMF solvent, and solves the technical problem of raw material residues leading to subsequent side reactions in the one-pot process through reactive distillation coupling control, resulting in a final product with high purity and high yield.

Description

Technical Field

[0001] This application relates to the field of chemical synthesis technology, and in particular to a UV-3 ultraviolet absorber and its preparation method. Background Technology

[0002] UV-3 is a high-performance and widely used ultraviolet absorber. In existing preparation processes, a common method is to synthesize it using benzocaine as a starting material in a two-step process. This process typically begins by reacting benzocaine with triethyl orthoformate in a solvent such as dimethylformamide to prepare the intermediate NET. After the reaction is complete, the intermediate NET is separated and purified through crystallization, filtration, and drying. Subsequently, the dried intermediate NET is transferred to another reaction vessel, where DMF solvent and an inorganic base such as potassium carbonate are added again, and the second step reaction is carried out under heating conditions. After the reaction is complete, post-processing yields the UV-3 product.

[0003] The aforementioned existing technical solutions have significant technical drawbacks. This two-step process is lengthy, involving multiple independent unit operations such as intermediate separation, purification, drying, and material transfer. This not only significantly extends the overall production cycle and reduces equipment utilization and production efficiency, but also increases the intensity of manual operations and material losses during transfer. Furthermore, this process relies on highly toxic, high-boiling-point, and difficult-to-recover DMF as a solvent and uses potassium carbonate as the alkali agent in the reaction. This not only increases the difficulty and cost of solvent recovery, posing a threat to the environment and the safety of operators, but also generates a large amount of inorganic waste salts, increasing the burden of subsequent environmental treatment.

[0004] The inventors also discovered in their research that attempting to simplify the process by omitting intermediate separation steps and combining the two reactions into a one-pot process presents a critical technical bottleneck: the synthesis of the intermediate NET in the first step is a reversible reaction, with methanol as a byproduct. In conventional closed or reflux one-pot systems, the equilibrium of this reversible reaction cannot shift completely towards the product, inevitably leaving unreacted benzocaine feedstock in the reaction system. When this system containing residual benzocaine directly enters the subsequent high-temperature cyclization stage, the residual benzocaine undergoes unintended side reactions with the cyclizing reagent, generating a large amount of impurities. This significantly reduces the purity and molar yield of the final UV-3 product, making it difficult to obtain the high-quality target product using this simplified one-pot process.

[0005] In view of the above-mentioned related technologies, a UV-3 ultraviolet absorber and its preparation method are provided. Summary of the Invention

[0006] The purpose of this application is to provide a UV-3 ultraviolet absorber and its preparation method, aiming to improve the shortcomings of the existing UV-3 preparation technology, which has a lengthy two-step process and uses toxic DMF solvent. The simplified one-pot method has the problem of raw material residue and subsequent side reactions due to the reversible nature of the key intermediate synthesis reaction, which ultimately leads to low product purity and yield.

[0007] By adopting the above technical solution, a UV-3 ultraviolet absorber is characterized in that it is obtained by a preparation method, wherein the preparation method uses raw materials in the following proportions:

[0008] The amount of xylene solvent used is 3.0 to 5.0 times the mass of benzocaine;

[0009] Triethyl orthoformate, wherein the molar ratio of triethyl orthoformate to benzocaine is 0.5:1 to 0.65:1;

[0010] Benzyl chloride, wherein the initial molar ratio of benzyl chloride to benzocaine is 0.5:1 to 0.6:1.

[0011] Preferably, the preparation method includes: reacting benzocaine with triethyl orthoformate at 110-140°C under controlled distillation for 12 to 16 hours, and continuously removing the generated alcohol distillate through a distillation separation device to obtain a xylene solution of intermediate NET.

[0012] Preferably, the preparation method includes: adjusting the xylene solution of intermediate NET to 135-145°C, adding benzyl chloride dropwise at this temperature for 1.0 to 6.0 hours, and maintaining the temperature for 1.0 to 3.0 hours.

[0013] A method for preparing a UV-3 ultraviolet absorber, using a one-pot process, includes the following steps:

[0014] S1. Add benzocaine and xylene solvent to the reaction vessel;

[0015] S2, add triethyl orthoformate dropwise;

[0016] S3. Perform reactive distillation coupling control, continuously remove the generated alcohol distillate through a distillation separation device to force the reversible reaction equilibrium shift and obtain a xylene solution of intermediate NET.

[0017] S4. Adjust the temperature of the xylene solution of the intermediate NET to the reaction temperature;

[0018] S5. At the reaction temperature, benzyl chloride is added dropwise to the xylene solution of the intermediate NET to carry out the reaction and generate a reaction slurry.

[0019] S6. Introduce the hydrogen chloride gas generated in step S5 into the tail gas absorption device for absorption.

[0020] S7. Cool, crystallize, separate solids and liquids and dry the reaction slurry to obtain the UV-3 ultraviolet absorber product.

[0021] Preferably, the amount of xylene used in step S1 is 3.0 to 5.0 times the mass of benzocaine;

[0022] In step S2, the molar ratio of triethyl orthoformate to benzocaine is 0.5:1 to 0.65:1;

[0023] In step S5, the initial molar ratio of benzyl chloride to benzocaine is 0.5:1 to 0.6:1.

[0024] Preferably, in step S3, the reaction distillation coupling control is carried out at 110–140°C for 12 to 16 hours.

[0025] Preferably, the reaction temperature in step S4 is 135–145°C; and the dropping time in step S5 is 1.0 to 6.0 hours, and after the dropping is completed, the reaction is kept at the temperature for 1.0 to 3.0 hours.

[0026] Preferably, the reactive distillation coupling control described in step S3 aims to achieve a conversion rate of benzocaine of 99.5% or higher and to reduce the residual amount of benzocaine raw material in the xylene solution of the intermediate NET to less than 0.5%, thereby reducing the side reactions it may initiate in step S5.

[0027] Preferably, in step S2, the triethyl orthoformate is added dropwise when the temperature inside the reactor rises to 80-100°C.

[0028] Preferably, the cooling in step S7 involves cooling the reaction slurry to 20–30°C; and the drying is carried out at 60–80°C and a vacuum degree below -0.09 MPa.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. This application adopts a one-pot process to continuously complete the synthesis of intermediate NET and subsequent reactions in xylene solvent. Compared with the existing technology that requires two-step operation, it significantly simplifies the production process, shortens the overall production cycle, and improves production efficiency.

[0031] 2. This application uses a single xylene solvent to replace the DMF and potassium carbonate system in the prior art, which not only saves the raw material cost of potassium carbonate, but also avoids the use of highly toxic, high-boiling-point, and difficult-to-recover DMF solvent, reducing solvent costs and recycling difficulties, and is more environmentally friendly;

[0032] 3. This application uses a one-pot process to eliminate the cumbersome steps of separating, purifying, drying and transferring intermediate NET, which greatly reduces manual operation steps and material transfer losses, effectively reduces the labor intensity and labor costs of workers, and also improves the overall utilization rate of reaction equipment. Detailed Implementation

[0033] Example:

[0034] Example 1:

[0035] This embodiment provides a method for preparing a UV-3 ultraviolet absorber, the steps of which are as follows:

[0036] In a reaction vessel equipped with a mechanical stirrer, temperature probe, distillation column and condenser, add 100 kg of benzocaine and 400 kg of xylene (the amount of xylene is 4.0 times the mass of benzocaine).

[0037] Start stirring, heat to 90°C, and begin adding triethyl orthoformate dropwise (molar ratio of 0.55 times that of benzocaine).

[0038] After the addition is complete, the temperature is raised to 125°C, and the distillation column is started for reactive distillation coupling control. The generated ethanol distillate is continuously removed, and the reaction is maintained in this state for 14 hours to obtain a xylene solution of the intermediate NET.

[0039] The temperature of the xylene solution of the intermediate NET was adjusted to 140°C.

[0040] At 140°C, benzyl chloride (molar ratio 0.55 times the initial molar amount of benzocaine) was added dropwise to the reactor over a period of 3.0 hours. After the addition was complete, the reaction was continued at 140°C for another 2.0 hours to produce a reaction slurry.

[0041] Throughout the process, the generated hydrogen chloride gas is introduced into a secondary sodium hydroxide alkaline solution absorption tower for absorption.

[0042] After the reaction was completed, the reaction slurry was cooled to 20°C for crystallization. Solid-liquid separation was performed using a centrifuge, and the filter cake was washed with xylene and dried to constant weight at 70°C and a vacuum of -0.095 MPa for 6 hours to obtain the UV-3 ultraviolet absorber product.

[0043] Example 2:

[0044] This embodiment provides a method for preparing a UV-3 ultraviolet absorber, the steps of which are as follows:

[0045] Add 100 kg of benzocaine and 300 kg of xylene (the amount of xylene is 3.0 times the mass of benzocaine) to the reactor.

[0046] Start stirring, heat to 80°C, and begin adding triethyl orthoformate dropwise (molar ratio of 0.50 times that of benzocaine).

[0047] After the addition is complete, the temperature is raised to 110°C, and the distillation column is started for reactive distillation coupling control. The generated ethanol distillate is continuously removed, and the reaction is maintained in this state for 12 hours to obtain a xylene solution of the intermediate NET.

[0048] The temperature of the xylene solution of the intermediate NET was adjusted to 135°C.

[0049] At 135°C, benzyl chloride (molar ratio 0.50 times the initial molar amount of benzocaine) was added dropwise to the reactor, with the addition time controlled at 1.0 hour. After the addition was complete, the reaction was continued at 135°C for another 1.0 hour to generate a reaction slurry.

[0050] Throughout the process, the generated hydrogen chloride gas is introduced into the tail gas absorption device for absorption.

[0051] After the reaction is complete, the reaction slurry is cooled to 20°C for crystallization. After solid-liquid separation and washing, it is dried to constant weight at 60°C and a vacuum of -0.09 MPa for 4 hours to obtain the UV-3 ultraviolet absorber product.

[0052] Example 3:

[0053] This embodiment provides a method for preparing a UV-3 ultraviolet absorber, the steps of which are as follows:

[0054] Add 100 kg of benzocaine and 500 kg of xylene (the amount of xylene is 5.0 times the mass of benzocaine) to the reactor.

[0055] Start stirring, heat to 100°C, and begin adding triethyl orthoformate dropwise (molar ratio of 0.65 times that of benzocaine).

[0056] After the addition was complete, the temperature was raised to 140°C, and the distillation column was started for reactive distillation coupling control. The generated ethanol distillate was continuously removed, and the reaction was maintained in this state for 16 hours to obtain a xylene solution of the intermediate NET.

[0057] The temperature of the xylene solution of the intermediate NET was adjusted to 145°C.

[0058] At 145°C, benzyl chloride (molar ratio 0.60 times the initial molar amount of benzocaine) was added dropwise to the reactor over a period of 6.0 hours. After the addition was complete, the reaction was continued at 145°C for another 3.0 hours to produce a reaction slurry.

[0059] Throughout the process, the generated hydrogen chloride gas is introduced into the tail gas absorption device for absorption.

[0060] After the reaction is complete, the reaction slurry is cooled to 30°C for crystallization. After solid-liquid separation and washing, it is dried to constant weight at 80°C and a vacuum of -0.098 MPa for 8 hours to obtain the UV-3 ultraviolet absorber product.

[0061] Comparative Example 1:

[0062] Compared with Example 1, the difference is that this comparative example does not use a one-pot process, but instead uses the following existing step-by-step method:

[0063] A xylene solution of the intermediate NET according to Example 1;

[0064] The obtained solution was cooled to crystallize, then centrifuged and dried.

[0065] In another reaction vessel, crude NET, DMF (dimethylformamide), and potassium carbonate (K2CO3) are added.

[0066] Heat the mixture to the reaction point;

[0067] After the reaction was completed, the product was desolvated under reduced pressure, and then xylene was added to obtain the UV-3 product.

[0068] Comparative Example 2:

[0069] Compared with Example 1, the difference is that the distillation separation function of the distillation column is not activated, but the reaction is carried out under closed reflux conditions for 14 hours; the remaining steps are the same as in Example 1.

[0070] Comparative Example 3:

[0071] Compared with Example 1, the difference is that instead of adding benzyl chloride dropwise, potassium carbonate (K2CO3) solid in the same molar amount as benzyl chloride in Example 1 is added to the reactor, and the reaction is kept at 140°C for the same number of hours; the rest of the steps are the same as in Example 1.

[0072] Comparative Example 4:

[0073] Compared with Example 1, the difference is that no heating is performed; the addition of benzyl chloride and the heat preservation reaction are both carried out at 125°C; the remaining steps are the same as in Example 1.

[0074] Test Example 1: Comparison Test of Process Efficiency

[0075] This test case is used to compare the total process time of different preparation methods.

[0076] Experimental steps:

[0077] The preparation schemes of Example 1, Example 2, Example 3 and Comparative Example 1 were used respectively.

[0078] For Examples 1-3, the timing start point Set the time when benzocaine and xylene are added to the reactor; timing endpoint. Set the time when drying is complete and constant weight UV-3 product is obtained.

[0079] For Comparative Example 1, the starting point of the timekeeping... Set as the feeding time; timer end point Set the time when the processing and drying are completed and a constant weight UV-3 product is obtained.

[0080] Record The time is the total process time, expressed in hours.

[0081] Test results:

[0082] The test results of the total process time of Examples 1-3 and Comparative Example 1 are recorded in Table 1.

[0083] Table 1: Comparison of Total Process Duration

[0084] Test object Total process time Example 1 27.8 Example 2 22.1 Example 3 35.7 Comparative Example 1 41.2

[0085] The test results in Table 1 show that the total process time of Examples 1-3 is shorter than that of Comparative Example 1. The measured times for Examples 1-3 are 27.8h, 22.1h, and 35.7h, respectively, while the measured time for Comparative Example 1 is 41.2h.

[0086] Comparative Example 1 employs a stepwise preparation method, with its process divided into two independent chemical transformation stages. After the first stage, additional physical separation, solvent removal, and drying of the intermediate products are required. These processes consume extra time and necessitate transferring the materials from the first reactor to the second reactor for subsequent reactions.

[0087] Examples 1-3 of this technical solution employ a one-pot process. This process uses xylene as a single solvent system, allowing the first and second steps to be performed continuously in the same reaction vessel. This method eliminates the physical operations of separating, purifying, drying, and transferring the intermediate NET, thereby reducing the proportion of non-reaction time and shortening the total time from initial raw materials to the final product.

[0088] Test Example 2: Necessity Test of Critical Process Step (Reaction Distillation Coupling)

[0089] This test case compares the effects of reactive distillation coupling control versus closed reflux on the purity and yield of the final product in the preparation of intermediate NET.

[0090] Experimental steps:

[0091] Sample preparation:

[0092] The preparation methods of Examples 1, 2, 3 and Comparative Example 2 were followed respectively to obtain the final UV-3 dried product.

[0093] Product purity determination:

[0094] The purity of each of the above samples was determined by high performance liquid chromatography.

[0095] Instrument: Agilent 1260;

[0096] Chromatographic column: C18 column, 4.6 mm × 250 mm, 5 µm;

[0097] Mobile phase: Methanol: Water = 90:10;

[0098] Flow rate: 1.0 mL / min;

[0099] Detection wavelength: 310nm;

[0100] Column temperature: 30℃;

[0101] Calculation method: The mass percentage content of UV-3 was calculated using the peak area normalization method.

[0102] Product yield calculation:

[0103] Using benzocaine as the reference material in the initial feed, the molar yield of the final UV-3 product was calculated.

[0104] .

[0105] Test results:

[0106] Examples 1-3 and Comparative Example 2 were tested according to the above method, and the results are recorded in Table 2.

[0107] Table 2: Comparison of the effects of reactive distillation coupling control

[0108] Test object UV-3 purity (HPLC, %) UV-3 yield (%) Example 1 99.61 91.3 Example 2 99.52 90.1 Example 3 99.73 92.4 Comparative Example 2 81.24 68.7

[0109] The test results in Table 2 show that the UV-3 products prepared in Examples 1, 2, and 3 have HPLC purities of 99.61%, 99.52%, and 99.73%, respectively, and molar yields of 91.3%, 90.1%, and 92.4%, respectively. The product prepared in Comparative Example 2 has an HPLC purity of 81.24% and a molar yield of 68.7%.

[0110] In Comparative Example 2, the synthesis of intermediate NET was carried out under closed reflux conditions. The reaction of benzocaine with triethyl orthoformate to form intermediate NET is a reversible reaction, with alcohol distillate as a byproduct. In the closed system, the byproduct methanol could not be removed, and the equilibrium of the reversible reaction could not shift completely towards the product formation, resulting in unreacted benzocaine feedstock remaining in the system after 14 hours of reaction.

[0111] In the subsequent high-temperature cyclization, the residual benzocaine feedstock in Comparative Example 2 underwent an unexpected side reaction with benzyl chloride, generating impurities other than the target product UV-3. This resulted in low HPLC purity and molar yield of the final product. Examples 1-3 employed reactive distillation coupling control, continuously removing the generated alcohol distillate through a distillation separation device. This forced the reversible reaction equilibrium towards the product, promoting a high degree of conversion of the benzocaine feedstock. Consequently, the residual benzocaine in the material was extremely low, and subsequent side reactions were suppressed, ultimately yielding a high-purity and high-yield UV-3 product.

[0112] Test Example 3: Necessity Test of the Reaction System

[0113] This test case is used to compare the effects of different cyclizing agents on the purity and yield of the final product in a xylene solvent system.

[0114] Experimental steps:

[0115] Sample preparation:

[0116] The preparation methods of Examples 1, 2, 3 and Comparative Example 3 were followed respectively to obtain the final UV-3 dried product.

[0117] Product purity determination:

[0118] The purity of each of the above samples was determined by high performance liquid chromatography.

[0119] Instrument: Agilent 1260;

[0120] Chromatographic column: C18 column, 4.6 mm × 250 mm, 5 µm;

[0121] Mobile phase: Methanol: Water = 90:10;

[0122] Flow rate: 1.0 mL / min;

[0123] Detection wavelength: 310nm;

[0124] Column temperature: 30℃;

[0125] Calculation method: The mass percentage content of UV-3 was calculated using the peak area normalization method.

[0126] Product yield calculation:

[0127] Using benzocaine as the reference material in the initial feed, the molar yield of the final UV-3 product was calculated.

[0128] .

[0129] Test results:

[0130] Examples 1-3 and Comparative Example 3 were tested according to the above method, and the results are recorded in Table 3.

[0131] Table 3: Comparison of the effects on the reaction system

[0132] Test object UV-3 purity (HPLC, %) UV-3 yield (%) Example 1 99.61 91.3 Example 2 99.52 90.1 Example 3 99.73 92.4 Comparative Example 3 5.41 0.8

[0133] The test results in Table 3 show that the UV-3 products prepared in Examples 1, 2, and 3 all have HPLC purity higher than 99.5% and molar yield higher than 90.0%. The product prepared in Comparative Example 3 has an HPLC purity of 5.41% and a molar yield of only 0.8%.

[0134] In the preparation method of Comparative Example 3, in the one-pot xylene solvent system, the inorganic base potassium carbonate was used instead of benzyl chloride. Potassium carbonate is an inorganic salt and is insoluble in xylene, a nonpolar solvent. Furthermore, at the reaction temperature of 140°C, it cannot form an effective solid-liquid interface or phase transfer system to promote the reaction. Therefore, the conversion of intermediate NET to UV-3 is hindered, and the reaction essentially does not occur.

[0135] The technical solutions employed in Examples 1-3 involve the use of a specific benzyl chloride in the xylene solvent system. This benzyl chloride is compatible with the xylene solvent system and can effectively promote the ring-closure reaction of the intermediate NET at a high temperature of 135–145°C, generating the target product UV-3, while simultaneously producing hydrogen chloride gas that can be absorbed and treated by the tail gas system. This system compatibility is a prerequisite for achieving high conversion rates in the second step of the one-pot process, thereby obtaining a high-purity final product.

[0136] Test Example 4: Necessity Test of Reaction Temperature Conditions

[0137] This test case is used to compare the effects of using high-temperature conditions of 135–145°C versus lower-temperature conditions on the purity and yield of the final product during the reaction step.

[0138] Experimental steps:

[0139] Sample preparation: The preparation methods of Examples 1, 2, 3 and Comparative Example 4 were followed respectively to obtain the final UV-3 dried product.

[0140] Product purity determination:

[0141] The purity of each of the above samples was determined by high performance liquid chromatography.

[0142] Instrument: Agilent 1260;

[0143] Chromatographic column: C18 column, 4.6 mm × 250 mm, 5 µm;

[0144] Mobile phase: Methanol: Water = 90:10;

[0145] Flow rate: 1.0 mL / min;

[0146] Detection wavelength: 310nm;

[0147] Column temperature: 30℃;

[0148] Calculation method: The mass percentage content of UV-3 was calculated using the peak area normalization method.

[0149] Product yield calculation:

[0150] Using benzocaine as the reference material in the initial feed, the molar yield of the final UV-3 product was calculated.

[0151] .

[0152] Test results:

[0153] Examples 1-3 and Comparative Example 4 were tested according to the above method, and the results are recorded in Table 4.

[0154] Table 4: Comparison of the effects of reaction temperature

[0155] Test object UV-3 purity (HPLC, %) UV-3 yield (%) Example 1 99.61 91.3 Example 2 99.52 90.1 Example 3 99.73 92.4 Comparative Example 4 88.98 80.5

[0156] The test results in Table 4 show that the UV-3 products prepared in Examples 1, 2, and 3 all have an HPLC purity higher than 99.5% and a molar yield higher than 90.0%. The product prepared in Comparative Example 4 has an HPLC purity of 88.98% and a molar yield of 80.5%.

[0157] In the preparation method of Comparative Example 4, the reaction was carried out at a temperature of 125°C, which is lower than the temperature range of 135–145°C specified in this technical solution. The formation reaction of UV-3 is a condensation ring-closing reaction, and the rate of this reaction is positively correlated with temperature. At the lower reaction temperature of 125°C, the frequency and energy of effective collisions between reactant molecules are insufficient to completely convert the intermediate NET into the target product UV-3 within the set reaction time (6.0 hours of dropwise addition + 3.0 hours of holding), resulting in insufficient cyclization conversion.

[0158] In Examples 1-3, the temperature was adjusted to 135–145°C before the addition and reaction of benzyl chloride. This high temperature effectively increased the thermodynamic activation energy of the reaction system, enabling the intermediate NET and benzyl chloride to complete a high-conversion closed-loop reaction in a relatively short time. This demonstrates that controlling the reaction temperature at 135–145°C is a key technical feature for achieving high conversion rates and high product purity in a one-pot process.

[0159] Test Example 5: Overall Performance Comparison

[0160] This test case is used to comprehensively compare the total process time, product purity, and product yield of Examples 1-3 and Comparative Examples 1-4.

[0161] Experimental steps:

[0162] Sample acquisition:

[0163] The preparation methods of Examples 1, 2, 3, 1, 2, 3 and 4 were followed respectively to obtain their respective UV-3 drying products.

[0164] Data collection:

[0165] Record the total process time for each preparation method according to the timing method in Test Example 1.

[0166] The UV-3 purity of each sample was determined according to the HPLC method disclosed in Test Example 2.

[0167] Calculate the UV-3 molar yield for each sample according to the yield calculation method disclosed in Test Example 2.

[0168] Data Summary:

[0169] All the test data mentioned above are summarized in Table 5.

[0170] Test results:

[0171] Examples 1-3 and Comparative Examples 1-4 were tested according to the above method, and the results are recorded in Table 5.

[0172] Table 5: Results of Comprehensive Performance Comparison Test

[0173] Test object Total process time (h) UV-3 purity (HPLC, %) UV-3 yield (%) Example 1 27.8 99.61 91.3 Example 2 22.1 99.52 90.1 Example 3 35.7 99.73 92.4 Comparative Example 1 41.2 99.15 85.6 Comparative Example 2 27.5 81.24 68.7 Comparative Example 3 27.9 5.41 0.8 Comparative Example 4 28 88.98 80.5

[0174] Table 5 shows that the samples from Examples 1-3 exhibited significant differences from Comparative Examples 1-4 in terms of product purity, yield, and total process time. Comparative Example 1, using a stepwise preparation method, had a significantly longer total process time and lower yield than Examples 1-3. This is because the one-pot process of Examples 1-3, by continuously executing multiple reactions in a single solvent system, eliminates physical operations such as the separation, transfer, and drying of intermediate products, thereby shortening non-reaction time and reducing material transfer losses.

[0175] Comparative Example 2 used the same one-pot process as Examples 1-3, but employed closed reflux in the intermediate NET synthesis step. Its purity and yield were significantly lower than those of Examples 1-3. This result indicates that the reversible reaction equilibrium in the intermediate synthesis step is a key factor affecting the feasibility of the one-pot process. The reactive distillation coupling control used in Examples 1-3, by continuously removing the byproduct alcohol distillate, forces the reversible reaction equilibrium towards the product, enabling the benzocaine feedstock to complete the reaction with high conversion. This, in turn, suppresses side reactions caused by feedstock residue in the subsequent high-temperature cyclization step, which is the technical basis for obtaining high-purity and high-yield products.

[0176] The results of Comparative Examples 3 and 4 further confirmed the compatibility of the reaction conditions. Comparative Example 3 showed that in the xylene nonpolar solvent system, the inorganic base potassium carbonate is not reactive and cannot achieve cyclization. The benzyl chloride used in Examples 1-3 is compatible with the xylene system. Meanwhile, the comparison between Comparative Example 4 and Examples 1-3 shows that the reaction temperature is another controlling factor; the temperature range of 135–145°C provides the necessary activation energy, ensuring a high conversion rate within the set time. In summary, this technical solution solves the side reaction and conversion rate problems in the one-pot reaction through specific process control and a matched reaction system.

Claims

1. A UV-3 ultraviolet absorber, characterized in that, Obtained by a preparation method, wherein the preparation method uses raw materials in the following proportions: The amount of xylene solvent used is 3.0 to 5.0 times the mass of benzocaine; Triethyl orthoformate, wherein the molar ratio of triethyl orthoformate to benzocaine is 0.5:1 to 0.65:1; N-alkylation, wherein the initial molar ratio of N-alkylation to benzocaine is 0.5:1 to 0.6:

1.

2. The UV-3 ultraviolet absorber according to claim 1, characterized in that, The preparation method includes: reacting benzocaine with triethyl orthoformate at 110-140°C to N-alkylate by distillation, continuing the reaction for 12 to 16 hours, and continuously removing the generated alcohol distillate through a distillation separation device to obtain a xylene solution of intermediate NET.

3. The UV-3 ultraviolet absorber according to claim 1, characterized in that, The preparation method includes: adjusting the xylene solution of intermediate NET to 135-145°C, adding benzyl chloride dropwise at this temperature for 1.0 to 6.0 hours, and maintaining the temperature for 1.0 to 3.0 hours.

4. A method for preparing a UV-3 ultraviolet absorber, wherein the UV-3 ultraviolet absorber according to any one of claims 1-3 is characterized in that, The one-pot process includes the following steps: S1. Add benzocaine and xylene solvent to the reaction vessel; S2, add triethyl orthoformate dropwise; S3. Perform reactive distillation coupling control, continuously remove the generated alcohol distillate through a distillation separation device to force irreversible equilibrium shift, and obtain a xylene solution of intermediate NET. S4. Adjust the temperature of the xylene solution of the intermediate NET to the N-alkylation temperature; S5. At the reaction temperature, benzyl chloride is added dropwise to the xylene solution of the intermediate NET to carry out the reaction and generate a reaction slurry. S6. Introduce the hydrogen chloride gas generated in step S5 into the tail gas absorption device for absorption. S7. Cool, crystallize, separate solids and liquids and dry the reaction slurry to obtain the UV-3 ultraviolet absorber product.

5. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that: The amount of xylene used in step S1 is 3.0 to 5.0 times the mass of benzocaine; In step S2, the molar ratio of triethyl orthoformate to benzocaine is 0.5:1 to 0.65:1; In step S5, the initial molar ratio of benzyl chloride to benzocaine is 0.5:1 to 0.6:

1.

6. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that, In step S3, the reaction distillation coupling control is carried out at 110–140°C for 12 to 16 hours.

7. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that, The reaction temperature in step S4 is 135–145°C; and the dropping time in step S5 is 1.0 to 6.0 hours, and after the dropping is completed, the reaction is kept at the temperature for 1.0 to 3.0 hours.

8. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that, The reaction-distillation coupling control described in step S3 aims to achieve a conversion rate of benzocaine of over 99.5% and to keep the residual amount of benzocaine raw material in the xylene solution of the intermediate NET below 0.5%, thereby avoiding the occurrence of side reactions in step S5.

9. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that, In step S2, when the temperature inside the reactor rises to 80-100°C, the triethyl orthoformate is added dropwise.

10. The method for preparing a UV-3 ultraviolet absorber according to claim 4, characterized in that, The cooling mentioned in step S7 is to cool the reaction slurry to 20-30°C; and the drying is carried out at 60-80°C and a vacuum degree below -0.09MPa.