Synthesis process of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate

Abstract

This invention belongs to the field of organic synthesis technology, specifically relating to a synthesis process for n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate. This invention uses 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid and n-hexanol as raw materials for esterification, employing solid acid catalyst HND-32 as the catalyst for the esterification reaction. The yield of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate obtained is consistently above 90%, with a purity above 99.5%. The single-pass conversion rate of benzoic acid is as high as 95%. Furthermore, the solid acid catalyst HND-32 can be reused more than 10 times while maintaining good catalytic performance, avoiding the defects of low yield, high cost, and high waste levels found in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, specifically relating to a synthesis process of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate. Background Technology

[0002] UVA (320nm-420nm) ultraviolet rays have strong penetrating power and are most harmful to the human body. 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl ester is a broadband oil-soluble ultraviolet absorber. It has strong absorption of the entire UVA band (320-400nm) ultraviolet rays, with a maximum absorption peak at 354nm, making it the best ultraviolet absorber in the UVA band. Compared with other ultraviolet absorbers, 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl ester has better photostability and can maintain its protective efficacy for a long time. It is widely used in sunscreens, hair care products, and medical skin care products.

[0003] There are currently reports on the synthesis methods of related substances such as 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester, such as patent CN. 105339344A, BASF’s patents CN1653035, DE10011317, EP2155660, WO2022 / 129431, EP401550 and WO2003097578, all of the above prior art uses concentrated sulfuric acid as an esterification catalyst. However, using concentrated sulfuric acid as a catalyst has the following defects: (1) The phenolic hydroxyl group in the structure of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid is easily oxidized, while concentrated sulfuric acid has strong oxidizing properties. Moreover, the reaction time is long and the temperature is high. The reaction solution is dark in color during the esterification reaction, and the target product is dark in color with high impurity content. It is difficult to separate and purify. It is necessary to go through complex separation and decolorization to obtain qualified products. The esterification yield is low. (2) After the reaction is completed, a large amount of water needs to be added and the sulfuric acid catalyst is neutralized with alkali, which will generate a large amount of saline wastewater. Patent CN112010771 discloses a method for preparing n-hexyl 2-(4-diethylamino-2-hydroxybenzoyl)benzoate, which uses a composite solid catalyst of metal oxides (tungsten trioxide and molybdenum trioxide) as the esterification catalyst. The overall yield of the process is 85.4%. Although the catalyst is changed, the esterification reaction temperature is 145-150℃, the reaction time is 5-6 hours, and the negative pressure is -0.06 to -0.09 MPa. Since the boiling point of n-hexanol is only 156-157℃, the reflux of n-hexanol is large during the esterification reaction under these conditions, resulting in high energy consumption and the need for a large amount of water washing, generating a lot of wastewater. The purification process requires cumbersome operations such as activated carbon adsorption decolorization followed by cooling and crystallization. Moreover, tungsten and molybdenum are rare metals, and compared with concentrated sulfuric acid as a catalyst, there are still three waste treatment problems, resulting in higher overall production costs. Patent CN111499529 employs a process of esterification followed by acylation of phthalic anhydride and n-hexanol. Although it does not use concentrated sulfuric acid as a catalyst, it requires the use of toxic substances such as anhydrous zinc chloride, phosphorus oxychloride, and N,N-dimethylformamide, which can easily cause harm to the human body. Furthermore, the post-reaction processing is cumbersome, and it generates a large amount of highly acidic wastewater, resulting in high costs for waste treatment.

[0004] Therefore, providing an environmentally friendly, efficient, and low-cost synthesis process for 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester has become an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a synthesis process for n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate, which uses 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid and n-hexanol as raw materials for esterification reaction, and employs solid acid catalyst HND-32 as the catalyst, thus avoiding the defects of low yield, high cost, and high waste in the prior art.

[0006] The technical solution of the present invention is as follows:

[0007] This invention provides a synthetic process for 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester, wherein the synthetic process uses 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid and n-hexanol as raw materials, and the esterification reaction is carried out under the catalysis of solid acid catalyst HND-32 to obtain 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester.

[0008] The reaction equation involved in this invention is as follows:

[0009] .

[0010] The solid acid catalyst HND-32 used in this invention has the following advantages compared with concentrated sulfuric acid:

[0011] 1) Non-corrosive, safe to use, and does not corrode equipment, requiring minimal equipment investment;

[0012] 2) The separation is simple and easy to recover. Compared with concentrated sulfuric acid, which is used once, the solid acid catalyst HND-32 can be recovered through simple filtration after use, and no alkali neutralization is required, so no saline wastewater is generated.

[0013] 3) Non-oxidizing: The phenolic hydroxyl group in the structure of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid is easily oxidized, while concentrated sulfuric acid has strong oxidizing properties. Therefore, in the traditional esterification reaction using concentrated sulfuric acid as a catalyst, the reaction solution is dark in color, there are many by-products, and there are problems such as difficulty in separation and purification. However, the solid acid catalyst HND-32 has no oxidizing properties. No oxidation reaction occurs in the esterification of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid with n-hexanol. The reaction has strong selectivity, high conversion rate, light color of reaction solution, and simple product purification process.

[0014] Furthermore, the synthesis process specifically includes:

[0015] (1) Preparation of crude 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester:

[0016] Using solid acid catalyst HND-32 as a catalyst, esterification reaction of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid and n-hexanol was carried out. After the reaction, solid acid catalyst HND-32 was recovered by hot filtration. The filtrate (esterification reaction solution) was cooled and crystallized. After crystallization, the crude product n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid was obtained by centrifugation.

[0017] (2) Preparation of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate:

[0018] The crude product obtained in (1) was recrystallized with anhydrous ethanol to obtain the qualified target product 2-(4-N,N-diethylamino-2-hydroxybenzoyl) benzoic acid n-hexyl ester.

[0019] Preferably, in (1), the molar ratio of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid to n-hexanol is 1:1.5 to 1:20; more preferably, it is 1:2.5 to 1:5.

[0020] Preferably, the esterification reaction temperature in (1) is 50-180°C; more preferably 100-160°C; and even more preferably 110-120°C.

[0021] Preferably, the esterification reaction time in (1) is 1~10h; more preferably 2~6h;

[0022] Preferably, in (1), the amount of solid acid catalyst HND-32 is not less than 10-50% of the mass of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid;

[0023] Preferably, the endpoint of the esterification reaction in (1) is controlled as follows: heating is stopped when the conversion rate of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid is greater than 95%, and the solid acid catalyst HND-32 is recovered by hot filtration and used directly in the next reaction.

[0024] Preferably, the cooling and crystallization temperature in (1) is 5–80°C; more preferably, it is 30–50°C.

[0025] Preferably, the centrifuged mother liquor in (1) is used directly as n-hexanol for the next reaction.

[0026] Preferably, during recrystallization in (2), the mass ratio of crude 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl ester to ethanol is 1:1 to 1:10, preferably 1:2 to 1:6;

[0027] Preferably, during recrystallization in (2), the crude product dissolves at a temperature of 40~70℃; more preferably, at 50~60℃.

[0028] Preferably, during recrystallization in (2), the crystallization temperature is 0~50℃; more preferably, it is 10~30℃.

[0029] The reaction vessel described in this invention is an atmospheric pressure reaction device, including a batch reactor and a tubular reactor.

[0030] The beneficial effects of this invention are as follows:

[0031] (1) The present invention uses solid acid catalyst HND-32 as catalyst. Compared with traditional concentrated sulfuric acid, the synthesis process of the present invention has a selectivity of over 98%, a single-pass conversion rate of over 95% for 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, and a single-pass yield of over 90% and a purity of over 99.5% for n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, which greatly improves the production efficiency of n-hexyl 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid.

[0032] (2) The solid acid catalyst HND-32 used in this invention is easy to recycle and utilize, the whole process is simple and easy to control, and no waste is generated in the production process, thus avoiding the defects of high waste in traditional technology.

[0033] (3) The solid acid catalyst used in this invention can be recycled and reused. It can maintain a good catalytic effect even after being reused more than 10 times, which further saves costs for the production of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester. Attached Figure Description

[0034] Figure 1 Scanning electron microscope image of solid acid HND-32 catalyst microspheres;

[0035] Figure 2 The results are the HPLC analysis results for the product in Example 1.

[0036] Figure 3 The results are the HPLC analysis results for the product in Example 2.

[0037] Figure 4 The results are the HPLC analysis results for the product in Example 3.

[0038] Figure 5 The results are the HPLC analysis results for the product in Example 4.

[0039] Figure 6 The results are the HPLC analysis results for the product in Example 5.

[0040] Figure 7 The results are the HPLC analysis results for the product in Example 6.

[0041] Figure 8 The results are the HPLC analysis results for the product in Example 7.

[0042] Figure 9 The results are the HPLC detection results of the product in Example 8;

[0043] Figure 10 The results are the HPLC analysis results for the product in Example 9.

[0044] Figure 11 The results are the HPLC analysis results for the product in Example 10.

[0045] Figure 12 The results are the HPLC analysis results for the product in Example 11.

[0046] Figure 13 The results are HPLC analysis of the product in Example 12. Detailed Implementation

[0047] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0048] The solid heteropolyacids, HND-260, HND-32, Amberlyst-35, and Amberlyst-36 used in the catalysts of this invention were purchased from Jiangyin Nanda Synthetic Chemical Co., Ltd.; QSE-2 was purchased from Zibo Rongke Chemical Technology Co., Ltd.; and SAC-5 was purchased from Jinzhijian High-Tech Materials Co., Ltd.

[0049] Example 1

[0050] In a 1000ml three-necked flask, add 328g of n-hexanol, 250g of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, and 80g of solid acid catalyst (HND-32). Purge with nitrogen, start stirring, and gradually raise the temperature inside the flask to 110-115℃, maintaining the temperature for 4 hours. After the temperature maintenance, hot filter the mixture. Wash the filter cake with 80g of hot n-hexanol to recover 94g of solid acid catalyst (HND-32). Stir and cool the filtrate to 40℃, and maintain the temperature at 40℃ for 2 hours. Filter under vacuum to obtain 358g of crude 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl ester, and recover 243g of the filtrate. Transfer the crude product to a 2000ml three-necked flask, add 1074g of anhydrous ethanol, stir, and raise the temperature to... At 50℃, after stirring until completely dissolved, heating was stopped, the stirring speed was slowed down, and the temperature was slowly lowered. When the internal temperature dropped to 15℃, the cooling was stopped, and the mixture was kept at 15℃ with stirring for 4 hours. The mixture was then filtered, and the filter cake was washed with ice-cold ethanol. The filter cake was then vacuum dried at 50℃ for 6 hours to obtain 289 g of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester white solid powder, with a single-pass yield of 90.21% and a purity of 99.5%. The HPLC chromatogram of this example is shown below. Figure 1 As shown.

[0051] Example 2

[0052] In a 5L reactor, 1.64 kg of n-hexanol, 1.25 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, and 0.40 kg of solid acid catalyst (HND-32) were added. Nitrogen gas was introduced, and stirring was started. The temperature inside the reaction flask was gradually raised to 110–115 °C and maintained for 4 hours. After the temperature maintenance, the mixture was hot-filtered. The filter cake was washed with 0.4 kg of hot n-hexanol, and 0.47 kg of solid acid catalyst (HND-32) was recovered. The filtrate was stirred and cooled to 40 °C, and then stirred at 40 °C for 2 hours. After vacuum filtration, 1.82 kg of crude 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester was obtained, and 1.20 kg of esterification filtrate was recovered. The obtained crude product was added to a 10L reactor, and 5.5 g of anhydrous ethanol was added. 5 kg of the mixture was stirred and heated to 50°C until completely dissolved. Heating was then stopped, the stirring speed was slowed, and the temperature was gradually lowered. When the internal temperature dropped to 15°C, cooling was stopped, and the mixture was kept at 15°C with stirring for 4 hours. The mixture was then filtered, and the filter cake was washed with ice-cold ethanol. The filter cake was then vacuum-dried at 50°C for 6 hours to obtain 1.46 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester white solid powder, with a single-pass yield of 91.61% and a purity of 99.5%. The HPLC chromatogram of this example is shown below. Figure 2 As shown.

[0053] Example 3

[0054] In a 5L reactor, 1.20 kg of the esterification filtrate recovered in Example 2, 0.44 kg of n-hexanol, 1.25 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, and 0.47 kg of the solid acid catalyst (HND-32) recovered in Example 2 were added. Stirring was started, and the temperature inside the reaction vessel was gradually raised to 110–115°C and maintained for 4 hours. After the temperature maintenance, hot filtration was performed. The filter cake was washed with 0.40 kg of hot n-hexanol, and 0.46 kg of the solid acid catalyst (HND-32) was recovered. The filtrate was stirred and cooled to 40°C, and then stirred at 40°C for 2 hours. The mixture was then filtered to obtain 1.90 kg of crude 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester, and 1.21 kg of the filtrate was recovered. The obtained crude product was added to a 10L reactor, and 5.70 g of anhydrous ethanol was added. Kg, stirred and heated to 50℃, stirred until completely dissolved, then heating was stopped, stirring speed was slowed down, and the temperature was slowly lowered. When the internal temperature dropped to 15℃, cooling was stopped, and the mixture was kept at 15℃ and stirred for 4 hours. The mixture was then filtered, and the filter cake was washed with ice-cold ethanol. The filter cake was then dried in positive air at 50℃ for 6 hours to obtain 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester white solid powder, with a single-pass yield of 92.87% and a purity of 99.5%. The HPLC chromatogram of this example is shown below. Figure 3 As shown.

[0055] In this embodiment, the esterification filtrate recovered in Example 2 was used as a partial hexanol, and the solid acid catalyst recovered in Example 2 was used. The yield was higher than that in Example 2, which may be because the filtrate itself contained some product. The yield and purity of this embodiment were both good, indicating that the solid acid catalyst (HND-32) used in this invention has good reproducibility.

[0056] Example 4

[0057] The operation of Example 3 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 3. Any deficiency was supplemented with new n-hexanol. The catalyst was the one recovered in Example 3. Other feed and operation procedures were the same as in Example 3. The final yield was 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl white solid powder, with a single-pass yield of 92.96% and a purity of 99.6%. The HPLC chromatogram of this example is shown below. Figure 4 As shown.

[0058] Example 5

[0059] The operation of Example 4 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 4. Any deficiency was supplemented with new n-hexanol. The catalyst was the esterification catalyst recovered in Example 4. Other feed and operation were the same as in Example 4. The final yield was 1.47 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl white solid powder, with a single-pass yield of 92.24% and a purity of 99.5%. The HPLC chromatogram of this example is shown below. Figure 5 As shown.

[0060] Example 6

[0061] The operation of Example 5 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 5. Any deficiency was supplemented with new n-hexanol. The catalyst was the esterification catalyst recovered in Example 5. Other feed and operation procedures were the same as in Example 5. The final product was 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester, a white solid powder, with a single-pass yield of 92.96% and a purity of 99.6%. The HPLC chromatogram of this example is shown below. Figure 6 As shown.

[0062] Example 7

[0063] The operation of Example 6 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 6. If insufficient, new n-hexanol was added to make up the difference. The catalyst was the esterification catalyst recovered in Example 6. Other feed and operation were the same as in Example 6. Finally, 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester white solid powder was obtained, with a single-pass yield of 93.05% and a purity of 99.7%. The HPLC chromatogram of this example is shown below. Figure 7 As shown.

[0064] Example 8

[0065] The operation of Example 7 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 7. Any deficiency was supplemented with new n-hexanol. The catalyst was the esterification catalyst recovered in Example 7. Other feed and operation procedures were the same as in Example 7. The final product was 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester, a white solid powder, with a single-pass yield of 92.96% and a purity of 99.6%. The HPLC chromatogram of this example is shown below. Figure 8 As shown.

[0066] Example 9

[0067] The operation of Example 8 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 8. Any deficiency was supplemented with new n-hexanol. The catalyst was the esterification catalyst recovered in Example 8. Other feed and operation procedures were the same as in Example 8. The final yield was 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester, a white solid powder, with a single-pass yield of 93.05% and a purity of 99.7%. The HPLC chromatogram of this example is shown below. Figure 9 As shown.

[0068] Example 10

[0069] The operation of Example 9 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 9. If insufficient, new n-hexanol was added to make up the difference. The catalyst was the esterification catalyst recovered in Example 9. Other feed and operation were the same as in Example 9. Finally, 1.47 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester white solid powder was obtained, with a single-pass yield of 92.52% and a purity of 99.8%. The HPLC chromatogram of this example is shown below. Figure 10 As shown.

[0070] Example 11

[0071] The operation of Example 10 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 10. If insufficient, new n-hexanol was added to make up the difference. The catalyst was the esterification catalyst recovered in Example 10. Other feed and operation were the same as in Example 10. Finally, 1.48 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl ester white solid powder was obtained, with a single-pass yield of 92.80% and a purity of 99.7%. The HPLC chromatogram of this example is shown below. Figure 11 As shown.

[0072] Example 12

[0073] The operation of Example 11 was repeated, with the added n-hexanol mainly derived from the esterification filtrate recovered in Example 11. Any shortfall was made up with fresh n-hexanol. The catalyst was the esterification catalyst recovered in Example 11. Other feed and operation procedures were the same as in Example 11. The final yield was 1.47 kg of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoate n-hexyl white solid powder, with a single-pass yield of 92.27% and a purity of 99.8%. The HPLC chromatogram of this example is shown below. Figure 12 As shown.

[0074] The solid acid catalyst used in this embodiment was the 10th time it had been reused. The yield and purity of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester were both good, indicating that the solid acid catalyst used in this invention can still maintain good catalytic effect even after being reused more than 10 times.

[0075] Example 13: The effects of different catalysts on conversion and selectivity were investigated. Different catalysts were used for catalysis, and the results are shown in Table 1.

[0076] Table 1. Effects of different solid acid catalysts on the conversion and selectivity of this reaction.

[0077] catalyst Catalyst type Conversion rate / % Selectivity / % solid heteropoly acids phosphotungstic acid 70.5 57.5 QSE-2 Phosphate 64.3 69.0 SAC-5 Sulfonic acid type 69.5 76.2 HND-260 Sulfonic acid type 80.5 90.3 HND-32 Sulfonic acid type 95.0 99.3 Amberlyst-35 Sulfonic acid type 85.6 78.9 Amberlyst-36 Sulfonic acid type 88.1 80.5

[0078] As shown in Table 1, the esterification reaction can be achieved using different solid acid catalysts, but the catalytic effects of different catalysts vary significantly. Sulfonic acid solid acid catalysts are relatively mature solid acid catalysts and have achieved good application results in many reactions. The esterification reaction was studied using sulfonic acid catalysts of different specifications. The experimental results show that the conversion rate and selectivity of sulfonic acid catalysts of different structures and specifications have a significant impact on the reaction. When the catalyst is HND32, its conversion rate and selectivity are the best, with a conversion rate of up to 95% and a selectivity of up to 99.3%. The conversion rate and selectivity of other solid acid catalysts are not ideal.

[0079] The reason for this result is that the surface of γ-Al₂O₃ calcined at 800℃ can have five types of hydroxyl groups, corresponding to five acid centers with different acid strengths. There are usually multiple acid centers of different strengths on the same solid surface, and their numbers vary. Based on the acid strength range of certain solid acids, it can be seen that SiO₂-Al₂O₃, B₂O₃-Al₂O₃, etc., are strong acids, with acid strength equivalent to that of a 90% or higher concentration of sulfuric acid aqueous solution. When the same reaction is carried out on the same type of catalyst, the catalytic activity is related to the acidity of the catalyst. However, most solid acid catalysts are porous materials. In addition to considering the acidity of their surface, the influence of the pore structure on the compatibility of the reactants, i.e., the substrate, must also be considered. Higher compatibility results in better catalytic effect, while lower compatibility results in poorer catalytic effect. Therefore, different solid acid catalysts will have different effects.

[0080] Example 14: Investigating the effect of different reaction temperatures on conversion and yield.

[0081] The conversion rate, single-pass yield, and product content of the reaction were carried out at different temperatures, as shown in Table 2.

[0082] Table 2. Effect of reaction temperature on the conversion and yield of the reaction.

[0083] Reaction temperature / ℃ <![CDATA[Conversion rate / % ② > One-way yield / % Product content % 50 60.01 40.20 99.5 80 75.83 60.50 99.5 90 80.59 70.14 99.5 100 88.12 79.83 99.6 120 98.88 90.71 99.5 130 98.85 90.70 99.6 160 99.01 90.60 99.5 180 99.15 91.00 99.5

[0084] As shown in Table 2, when the reaction temperature is 50℃, the conversion rate is low and there is a lot of raw material residue due to the low reaction temperature, resulting in a low single-pass yield. As the reaction temperature increases, the conversion rate increases significantly. However, when the temperature reaches 110℃, further increasing the reaction temperature to 160℃ does not result in a significant change in the conversion rate. Continuing to increase the temperature, using a pressure vessel to raise the reaction temperature to 180℃, the conversion rate of the raw material 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid does not significantly increase compared to 160℃. Therefore, considering production costs, a reaction temperature of 100~160℃ is better, with 110~120℃ being optimal.

Claims

The synthesis process of 1,2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid hexyl ester, characterized in that, The steps are as follows: (1) Using solid acid catalyst HND-32, which contains no less than 10-50% by mass of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid, 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid and n-hexanol in a molar ratio of 1:2.5-1:5, an esterification reaction is carried out at 110-120℃ for 2-6 hours; heating is stopped when the conversion rate of 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid is greater than 95%, and the dissolution temperature of the crude product is 40-70℃. (2) After the reaction is completed, the solid acid catalyst HND-32 is recovered by hot filtration and directly used in the next reaction. The esterification reaction solution is cooled to 30-50℃ to crystallize. After crystallization, the crude product 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester is obtained by centrifugation. The mother liquor of centrifugation is used directly as n-hexanol in the next reaction. (3) The crude product 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester obtained in (2) is recrystallized with anhydrous ethanol to obtain the qualified target product 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester; during recrystallization, the mass ratio of the crude product 2-(4-N,N-diethylamino-2-hydroxybenzoyl)benzoic acid n-hexyl ester to ethanol is 1:2 to 1:6, the dissolution temperature of the crude product is 50 to 60°C, and the crystallization temperature is 10 to 30°C.

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