Process for synthesizing p-hydroxycinnamic acid

Abstract

The invention relates to the technical field of chemical synthesis, in particular to a p-hydroxycinnamic acid synthesis process which at least comprises the following steps: sequentially adding p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene into a reaction container, stirring, heating for reaction, cooling, and dropwise adding a potassium carbonate aqueous solution until the pH is 7-8; after stirring, taking a water phase in a split-phase manner, dropwise adding diluted hydrochloric acid into the water phase until the pH is 1-3, and filtering after stirring; washing the filtered solid until the pH value is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid; the method has the advantages that by optimizing the p-hydroxycinnamic acid synthesis process, the high yield of crude hydroxycinnamic acid is achieved under the condition of low pyridine feeding amount, the purity of subsequent products is high, the color of the products is optimized, and the subsequent application requirements are better met.

Description

Technical Field

[0001] The invention relates to the technical field of chemical synthesis, in particular to a synthesis process of p-hydroxycinnamic acid. Background Art

[0002] Para-hydroxycinnamic acid is widely found in plants (such as soybeans, wheat, corn, grapes, apples, etc.) and has a variety of biological activities (such as antioxidant, anti-inflammatory, antibacterial, anti-tumor, etc.). It plays an important role in medicine, agriculture, cosmetics, and chemical industry, and therefore has attracted much attention. In medicine, it can be used to synthesize the new expectorant drug rhododendron, to synthesize the anti-adrenergic drug esmolol, as an intermediate for the production of coronary heart disease treatment drug calcitonin, and to manufacture local anesthetics, bactericides and hemostatics, etc. It has the effect of inhibiting cervical cancer. In agriculture, it is used to produce plant growth promoters, long-acting bactericides and fruit and vegetable preservatives. In cosmetics, para-hydroxycinnamic acid has an inhibitory effect on the activity of tyrosinase monophenolase and diphenolase, which can reduce the activity of monophenolase and diphenolase by 50%, and is used in cosmetics to inhibit the formation of melanin. In the chemical industry, p-hydroxycinnamic acid is a very important flavor and fragrance, mainly used to prepare spicy cherry, apricot, honey and other spices; p-hydroxycinnamic acid is also a strong conductive material, which is widely studied in the liquid crystal display industry. The photosensitive p-hydroxypolyimide is synthesized by the grafting reaction of hydroxypolyimide and p-hydroxycinnamic acid, and the structure of the photosensitive p-hydroxypolyimide is determined by infrared and nuclear magnetic resonance. The synthesized p-hydroxypolyimide is used as a liquid crystal orientation layer in liquid crystal display devices, which proves that it has good thermal stability. In addition, p-hydroxycinnamic acid can also be used as a chemical reagent for the determination of uranium and vanadium, and for the production of vinyl cinnamic acid, the main raw material of photosensitive resin. In recent years, many scientists at home and abroad have also been committed to expanding the research on p-hydroxycinnamic acid to the fields of microbiology and medicine - the influence of cell differentiation and telomerase activity. In the future, p-hydroxycinnamic acid will be more and more used in our lives, and its development prospects and market prospects are very huge.

[0003] The traditional synthesis process of p-hydroxycinnamic acid has one or more of the following problems: potential safety hazard, waste of raw materials, waste of energy and low product yield. Jin Jishu et al. synthesized p-hydroxycinnamic acid by Knoevenagel-doebner reaction using p-hydroxybenzaldehyde and malonic acid as raw materials, but the yield was only about 50%. In a Chinese patent (publication number CN101781191A), p-hydroxybenzaldehyde and malonic acid were used as raw materials, and under the action of a catalyst randomly combined from pyridine, aniline and piperidine, the reaction was carried out at a temperature of 80-100° C., and the water separation reaction was refluxed for 1 hour. The p-hydroxycinnamic acid product was prepared by filtering, washing and recrystallization, and the crude product yield was 62.71%. However, the catalyst pyridine and solvent were used in large amounts during the feeding process, and the reaction process was a solid-liquid reaction. The reaction product was easy to adhere to the wall and was not completely dissolved in the solvent, which was difficult to operate in actual production. The presence of substances such as pyridine caused potential safety hazards in material cleaning, which caused safety accidents and increased production costs invisibly. Direct application of the filtrate leads to the continuous accumulation of high-boiling substances in the solvent, affecting the color of the product (the color of the crude product obtained after filtration is yellow-green and the crude product yield is low, and the color of the product after recrystallization does not meet the requirements), and it is impossible to produce a p-hydroxycinnamic acid product that meets the standards. Wang Lei et al. disclosed the synthesis of p-hydroxycinnamic acid and the optimization of process conditions, using p-hydroxybenzaldehyde and malonic acid as raw materials, toluene as solvent, pyridine, aniline, piperidine, etc. as catalysts, reacting at 85°C for 1h, and obtaining a cinnamic acid product through alkali dissolution and acid precipitation, with a crude product yield of 80.5%. However, the molar ratio of malonic acid to pyridine in the process is too large, which makes it difficult to recover malonic acid and pyridine is very soluble in water, resulting in waste of malonic acid and pyridine, resulting in high production costs and difficulty in industrial production.

[0004] Therefore, it is an urgent problem for those skilled in the art to provide a synthesis process for p-hydroxycinnamic acid that can effectively reduce the waste of raw materials and energy while meeting the existing p-hydroxycinnamic acid production quality standards. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a synthesis process of p-hydroxycinnamic acid, which optimizes the synthesis process of p-hydroxycinnamic acid and achieves a higher crude hydroxycinnamic acid yield under the condition of a lower pyridine feed amount, and the purity of the subsequent product is high, the product color is optimized, and the subsequent application requirements are better met.

[0006] On one hand, the present invention provides a synthesis process of p-hydroxycinnamic acid, which comprises at least the following steps: adding p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene into a reaction container in sequence, stirring and heating to react, and dropping a potassium carbonate aqueous solution until the pH value is 7-8 after cooling; stirring and then separating the phases to obtain a water phase, dropping dilute hydrochloric acid into the water phase until the pH value is 1-3, stirring and then filtering; washing the filtered solid until the pH value is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid.

[0007] As a preferred technical solution, the molar ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene is 1: (1.0-1.2): (2.5-3.5): (0.5-1.0): (0.5-1.2).

[0008] As a preferred technical solution, the mass ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene is 12.2:11.4:(5.5-5.6):(0.8-0.9):(31.8-31.9).

[0009] As a preferred technical solution, the temperature of the stirring and heating reaction is 90-100°C.

[0010] As an example, the temperature of the stirring and heating reaction is 90°C, 92°C, 95°C, 98°C, and 100°C.

[0011] Preferably, the stirring and heating temperature is 95°C.

[0012] As a preferred technical solution, the stirring and heating reaction time is 1.5-2h.

[0013] As an example, the stirring and heating reaction time is 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, and 2.0h.

[0014] Preferably, the stirring and heating reaction time is 1.6-1.9h.

[0015] As a preferred technical solution, the temperature after cooling is 25-40°C.

[0016] As an example, the temperature after cooling is 25°C, 30°C, 35°C, or 40°C.

[0017] Preferably, the temperature after cooling is 30°C.

[0018] As a preferred technical solution, the mass concentration of the potassium carbonate aqueous solution is 10-25%.

[0019] As an example, the mass concentration of the potassium carbonate aqueous solution is 10%, 12.5%, 15%, 20%, and 25%.

[0020] Preferably, the mass concentration of the potassium carbonate aqueous solution is 12.5%.

[0021] As a preferred technical solution, the mass concentration of the dilute hydrochloric acid is 10-30%.

[0022] As an example, the mass concentration of the dilute hydrochloric acid is 10%, 12%, 15%, 20%, 25%, or 30%.

[0023] Preferably, the mass concentration of the dilute hydrochloric acid is 15%.

[0024] As a preferred technical solution, the crude product recrystallization comprises the following steps: adding the crude product to ethanol, controlling the temperature to 70-90°C, stirring at this temperature for 0.5-1.5h, cooling to 0-10°C, stirring at this temperature for 15-30min, and filtering to obtain the product.

[0025] Preferably, the mass ratio of the crude product to ethanol is 1:(2-4), preferably 1:(2.5-3).

[0026] As a preferred technical solution, the filtrate after filtration is recovered to obtain a mixed solution of malonic acid and pyridine, and the recovery treatment comprises the following steps: adding cyclohexane to the filtrate after filtration, stirring and heating to 85-95°C, refluxing to remove water until no water is produced in the water separator, cooling to 20-30°C, filtering twice, heating the secondary filtrate after the secondary filtration to 85-95°C, and distilling at atmospheric pressure until no fraction is produced to obtain a mixed solution of malonic acid and pyridine.

[0027] Preferably, the ratio of the mass of the filtrate after filtration to the volume of cyclohexane is 10 g: (0.5-2) mL.

[0028] As a preferred technical solution, the yield of the crude product is ≥82%.

[0029] On the other hand, the present invention provides a para-hydroxycinnamic acid, which has the appearance of an off-white powder, a purity of the para-hydroxycinnamic acid ≥99.5wt%, and a moisture content of the para-hydroxycinnamic acid ≤0.03wt% (meeting the enterprise standard Q / SXYJ020-2024 of Shanxi Yongjin Group Co., Ltd.).

[0030] The p-hydroxycinnamic acid is used in medicine, agriculture, chemical industry and daily chemical industry.

[0031] At present, p-hydroxycinnamic acid is mainly synthesized from malonic acid as raw material at home and abroad, and is divided into the following types according to the synthesis conditions and raw materials: first, p-hydroxybenzaldehyde and ethyl acetate are used as raw materials, and under the catalytic action of sodium methoxide, p-hydroxycinnamic acid is generated by reaction; second, p-hydroxybenzaldehyde and malonic acid are used as raw materials, and under the catalysis of pyridine and piperidine, p-hydroxycinnamic acid is generated by reaction under microwave irradiation; third, p-hydroxybenzaldehyde and malonic acid are used as raw materials, and p-hydroxybenzaldehyde and malonic acid are used as raw materials, and cyclohexane is used as solvent, and pyridine and aniline are used as catalysts to generate p-hydroxycinnamic acid; fourth, p-hydroxybenzaldehyde and malonic acid are used as raw materials, and toluene is used as solvent, and pyridine, aniline, and piperidine are used as catalysts to generate p-hydroxycinnamic acid; fifth, p-hydroxybenzaldehyde and malonic acid are used as raw materials, and under the action of triethylamine and piperidine, p-hydroxycinnamic acid is generated. However, the above synthesis method has the problem of long reaction time (low yield at the same reaction time, and it takes a long time to meet the requirements), resulting in a large waste of energy; or the amount of malonic acid and pyridine in the raw material ratio (molar ratio) is too large, resulting in waste of malonic acid, and pyridine is soluble in water and difficult to recover. Although the reaction time is short, it causes waste of raw materials and pollutes the environment. Using toluene as a solvent is an acute poisoning, which poses a certain risk to safety control.

[0032] The synthesis process provided by the present invention realizes the low-toxic, low-cost, rapid synthesis of high-quality p-hydroxycinnamic acid products by optimizing the order of adding each raw material, coordinating the reaction condition control and the reaction molar ratio optimization, and at the same time realizes the recovery of unreacted adipic acid and pyridine in the filtrate, further reducing production costs, and improving corporate profits and competitiveness. Specifically, by controlling the mass ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline, and xylene added in sequence to 12.2:11.4:(5.5-5.6):(0.8-0.9):(31.8-31.9), coordinating the stirring and heating reaction temperature and the stirring and heating reaction time control, the yield of the obtained p-hydroxycinnamic acid crude product is ≥82%, and the subsequent recrystallization obtains a high-purity off-white to light yellow product.

[0033] Furthermore, the present invention ensures the yield of the crude p-hydroxycinnamic acid and the quality of the subsequent p-hydroxycinnamic acid product by controlling the mass concentration of the dilute hydrochloric acid in the acid precipitation.

[0034] In addition, the present invention recovers the filtered filtrate with cyclohexane and controls the recovery conditions to obtain a mixed solution of malonic acid and pyridine, with a recovery rate of ≥85.5%, which can achieve recycling and has high added value.

[0035] The synthesis process provided by the present invention has mild reaction conditions, good safety, low requirements on equipment materials, and uses low-toxic xylene as a solvent, which is less dangerous than using toluene, reduces the occurrence of safety accidents, indirectly reduces production costs, and is easy to realize large-scale industrial production.

[0036] Beneficial Effects

[0037] 1. The present invention provides a synthesis process of p-hydroxycinnamic acid. By optimizing the synthesis process of p-hydroxycinnamic acid, a higher crude yield of hydroxycinnamic acid is achieved under the condition of a lower pyridine feed amount, the purity of the subsequent product is high, the product color is optimized, and the subsequent application requirements are better met.

[0038] 2. The synthesis process provided by the present invention achieves low-toxicity, low-cost, rapid synthesis of high-quality p-hydroxycinnamic acid products by optimizing the order of adding each raw material, coordinating the reaction condition control and optimizing the reaction molar ratio, and at the same time realizes the recovery of unreacted adipic acid and pyridine in the filtrate, further reducing production costs and improving corporate profits and competitiveness.

[0039] 3. The present invention controls the mass ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene added in sequence to be 12.2:11.4:(5.5-5.6):(0.8-0.9):(31.8-31.9), and controls the stirring and heating reaction temperature and the stirring and heating reaction time, so that the yield of the obtained crude p-hydroxycinnamic acid is ≥82%, and a high-purity off-white product is obtained by subsequent recrystallization.

[0040] 4. The present invention recovers the filtrate after filtration with cyclohexane and controls the recovery conditions to obtain a mixed solution of malonic acid and pyridine with a recovery rate of ≥85.5%, which can be recycled and has high added value.

[0041] 5. The synthesis process provided by the present invention has mild reaction conditions, good safety, and low requirements on equipment materials. The solvent used is low-toxic xylene, which is less dangerous than toluene, reduces the occurrence of safety accidents, indirectly reduces production costs, and is easy to realize large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the appearance picture of the p-hydroxycinnamic acid product provided in Example 1.

[0043] Figure 2 This is the appearance picture of the p-hydroxycinnamic acid product provided in Example 2.

[0044] Figure 3 This is the appearance picture of the p-hydroxycinnamic acid product provided in Example 3.

[0045] Figure 4 This is the appearance picture of the p-hydroxycinnamic acid product provided in Comparative Example 1.

[0046] Figure 5 This is the appearance picture of the p-hydroxycinnamic acid product provided for Comparative Example 2. DETAILED DESCRIPTION

[0047] Example 1

[0048] Embodiment 1 of the present invention provides a synthesis process of p-hydroxycinnamic acid, comprising the following steps: adding 12.2 g of p-hydroxybenzaldehyde, 11.4 g of malonic acid, 5.6 g of pyridine, 0.8 g of aniline, and 31.8 g of xylene to a reaction container in sequence, stirring and heating to react, and after cooling, dropping a potassium carbonate aqueous solution until the pH is 7; after stirring, separating the phases and taking the aqueous phase, dropping dilute hydrochloric acid into the aqueous phase until the pH is 2, stirring, and filtering; washing the filtered solid with water until the pH is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid.

[0049] The stirring and heating temperature is 95° C., and the stirring and heating reaction time is 1.8 h.

[0050] The temperature after cooling is 30°C.

[0051] The mass concentration of the potassium carbonate aqueous solution is 12.5%.

[0052] The mass concentration of the dilute hydrochloric acid is 15%.

[0053] The yield of the crude product is 82.25% (based on p-hydroxybenzaldehyde), and the content of p-hydroxycinnamic acid in the crude product is 98.3847%.

[0054] The crude product recrystallization comprises the following steps: adding the crude product into ethanol, controlling the temperature to 80° C., keeping the temperature and stirring for 1 hour, then cooling to 5° C., keeping the temperature and stirring for 30 minutes, and then filtering to obtain the product.

[0055] The mass ratio of the crude product to ethanol is 1:3.

[0056] The filtrate after filtration is recovered to obtain a mixed solution of malonic acid and pyridine, and the recovery process comprises the following steps: adding 200g of cyclohexane to the filtrate after filtration, stirring and heating to 90°C, refluxing to remove water until no water is produced in the water separator, cooling to 20°C, filtering twice, heating the secondary filtrate after the secondary filtration to 90°C, and distilling at normal pressure until no fraction is produced to obtain a mixed solution of malonic acid and pyridine, with a recovery rate of 85.5%.

[0057] On the other hand, Example 1 of the present invention provides a p-hydroxycinnamic acid, wherein the p-hydroxycinnamic acid is an off-white powder (see Figure 1 ), the purity of the p-hydroxycinnamic acid is 99.7449%.

[0058] The purity detection method of the p-hydroxycinnamic acid is as follows: liquid chromatography instrument: Foley LC5090; conditions are as follows: the mobile phase is methanol and acetic acid aqueous solution (1wt%), the volume ratio of methanol: acetic acid aqueous solution (0.1wt%) = 30:70, chromatographic column model: Shim-pack GIST C18, 5um, 4.6mm×250mm, detection wavelength: 254nm, flow rate: 1mL / min.

[0059] Example 2

[0060] Embodiment 2 of the present invention provides a synthesis process of p-hydroxycinnamic acid, comprising the following steps: adding 12.2 g of p-hydroxybenzaldehyde, 11.4 g of malonic acid, 5.5 g of pyridine, 0.9 g of aniline, and 31.9 g of xylene to a reaction container in sequence, stirring and heating to react, and after cooling, dropping an aqueous solution of potassium carbonate until the pH is 7; after stirring, separating the phases and taking the aqueous phase, dropping dilute hydrochloric acid into the aqueous phase until the pH is 2, stirring, and filtering; washing the filtered solid with water until the pH is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid.

[0061] The stirring and heating temperature is 95° C., and the stirring and heating reaction time is 2 h.

[0062] The temperature after cooling is 30°C.

[0063] The mass concentration of the potassium carbonate aqueous solution is 12.5%.

[0064] The mass concentration of the dilute hydrochloric acid is 12%.

[0065] The yield of the crude product is 82.38% (based on p-hydroxybenzaldehyde), and the content of p-hydroxycinnamic acid in the crude product is 97.9663%.

[0066] The crude product recrystallization comprises the following steps: adding the crude product into ethanol, controlling the temperature to 80° C., keeping the temperature and stirring for 1 hour, then cooling to 5° C., keeping the temperature and stirring for 30 minutes, and then filtering to obtain the product.

[0067] The mass ratio of the crude product to ethanol is 1:3.

[0068] The filtrate after filtration is recovered to obtain a mixed solution of malonic acid and pyridine, and the recovery process comprises the following steps: adding 200g of cyclohexane to the filtrate after filtration, stirring and heating to 90°C, refluxing to remove water until no water is produced in the water separator, cooling to 20°C, filtering twice, heating the secondary filtrate after the secondary filtration to 90°C, and distilling at normal pressure until no fraction is produced to obtain a mixed solution of malonic acid and pyridine, with a recovery rate of 85.5%.

[0069] On the other hand, Example 2 of the present invention provides a p-hydroxycinnamic acid, wherein the p-hydroxycinnamic acid is a beige powder (see Figure 2 ), the purity of the p-hydroxycinnamic acid is 99.7576%.

[0070] The purity detection method of the p-hydroxycinnamic acid is as follows: liquid chromatography instrument: Foley LC5090; conditions are as follows: the mobile phase is methanol and acetic acid aqueous solution (1wt%), the volume ratio of methanol: acetic acid aqueous solution (0.1wt%) = 30:70, chromatographic column model: Shim-pack GIST C18, 5um, 4.6mm×250mm, detection wavelength: 254nm, flow rate: 1mL / min.

[0071] Example 3

[0072] Embodiment 3 of the present invention provides a synthesis process of p-hydroxycinnamic acid, comprising the following steps: adding 12.2 g of p-hydroxybenzaldehyde, 11.4 g of malonic acid, 5.5 g of pyridine, 1.0 g of aniline, and 31.9 g of xylene to a reaction container in sequence, stirring and heating to react, and after cooling, dropping potassium carbonate aqueous solution until the pH is 7; after stirring, phase separation and taking the aqueous phase, dropping dilute hydrochloric acid into the aqueous phase until the pH is 2, stirring and filtering; washing the filtered solid with water until the pH is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid.

[0073] The stirring and heating temperature is 95° C., and the stirring and heating reaction time is 1.5 h.

[0074] The temperature after cooling is 30°C.

[0075] The mass concentration of the potassium carbonate aqueous solution is 10%.

[0076] The mass concentration of the dilute hydrochloric acid is 12%.

[0077] The yield of the crude product is 82.13% (based on p-hydroxybenzaldehyde), and the content of p-hydroxycinnamic acid in the crude product is 98.1359%.

[0078] The crude product recrystallization comprises the following steps: adding the crude product into ethanol, controlling the temperature to 80° C., keeping the temperature and stirring for 1 hour, then cooling to 5° C., keeping the temperature and stirring for 30 minutes, and then filtering to obtain the product.

[0079] The mass ratio of the crude product to ethanol is 1:3.

[0080] The filtrate after filtration is recovered to obtain a mixed solution of malonic acid and pyridine, and the recovery process comprises the following steps: adding 200g of cyclohexane to the filtrate after filtration, stirring and heating to 90°C, refluxing to remove water until no water is produced in the water separator, cooling to 20°C, filtering twice, heating the secondary filtrate after the secondary filtration to 90°C, and distilling at normal pressure until no fraction is produced to obtain a mixed solution of malonic acid and pyridine, with a recovery rate of 85.5%.

[0081] On the other hand, Example 3 of the present invention provides a p-hydroxycinnamic acid, wherein the p-hydroxycinnamic acid is a beige powder (see Figure 3 ), the purity of the p-hydroxycinnamic acid is 99.6638%.

[0082] The purity detection method of the p-hydroxycinnamic acid is as follows: liquid chromatography instrument: Foley LC5090; conditions are as follows: the mobile phase is methanol and acetic acid aqueous solution (1wt%), the volume ratio of methanol: acetic acid aqueous solution (0.1wt%) = 30:70, chromatographic column model: Shim-pack GIST C18, 5um, 4.6mm×250mm, detection wavelength: 254nm, flow rate: 1mL / min.

[0083] Comparative Example 1

[0084] Comparative Example 1 of the present invention provides a synthesis process of p-hydroxycinnamic acid, comprising the following steps: adding p-hydroxybenzaldehyde 12.2g, malonic acid 11.4g, toluene 46.1g, pyrimidine 12.7g, and aniline 0.9g to a reaction container in sequence, stirring and heating to 80°C, reacting for 1h and cooling to 15°C, filtering by suction, rinsing the filter cake with toluene three times, the filtrate is light yellow, and the solid obtained by suction filtration is a crude p-hydroxycinnamic acid product (the yield is 62.71%, based on p-hydroxybenzaldehyde; the content of p-hydroxycinnamic acid in the crude product is 95.1534%), the solid is yellow-green, and after drying, 3 times ethanol is added for recrystallization (the recrystallization process is the same as in Example 1), and the light yellow-green solid particles obtained are the p-hydroxycinnamic acid product (see Figure 4 , purity is 99.5651%).

[0085] Comparative Example 2

[0086] Comparative Example 2 of the present invention provides a synthesis process of p-hydroxycinnamic acid. In a reaction container, 20 g of p-hydroxybenzaldehyde, 25.5 g of malonic acid, 23.8 g of toluene, 35.4 g of pyrimidine, 1.5 g of aniline, and 0.4 g of piperidine are added in sequence, the temperature is raised to 80° C. with stirring, the temperature is lowered to 30° C. after reacting for 1 hour, and a 25 wt % potassium carbonate aqueous solution is added dropwise until the pH is 77; the aqueous phase is taken after stirring and phase separation, and 12 wt % dilute hydrochloric acid is added dropwise until the pH is 2, the solid is filtered after stirring, and the filtered solid is washed with water until the pH is neutral, and a crude product is obtained after drying (the yield is 80.5%, based on p-hydroxybenzaldehyde; the content of p-hydroxycinnamic acid in the crude product is 98.2188%), and the crude product is recrystallized (the recrystallization process is the same as in Example 1) to obtain p-hydroxycinnamic acid, and the obtained off-white solid particles are p-hydroxycinnamic acid (see Figure 5 , purity is 99.6352%).

[0087] The content of p-hydroxycinnamic acid in the crude product and the purity of p-hydroxycinnamic acid in the above embodiments and comparative examples were tested with reference to the enterprise standard Q / SXYJ020-2024 of Shanxi Yongjin Group Co., Ltd.

Claims

1. A process for synthesizing p-hydroxycinnamic acid, characterized in that: The method comprises at least the following steps: adding p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene into a reaction container in sequence, stirring and heating to react, and after cooling, dropping a potassium carbonate aqueous solution until the pH value is 7-8; after stirring, phase separation and taking a water phase, dropping dilute hydrochloric acid into the water phase until the pH value is 1-3, stirring and filtering; washing the filtered solid until the pH value is neutral, drying to obtain a crude product, and recrystallizing the crude product to obtain p-hydroxycinnamic acid.

2. The synthesis process of p-hydroxycinnamic acid according to claim 1, characterized in that: The molar ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene is 1:(1.0-1.2):(2.5-3.5):(0.5-1.0):(0.5-1.2).

3. The synthesis process of p-hydroxycinnamic acid according to claim 2, characterized in that: The mass ratio of p-hydroxybenzaldehyde, malonic acid, pyridine, aniline and xylene is 12.2:11.4:(5.5-5.6):(0.8-0.9):(31.8-31.9).

4. The synthesis process of p-hydroxycinnamic acid according to claim 3, characterized in that: The temperature of the stirring and heating reaction is 90-100° C., and the time of the stirring and heating reaction is 1.5-2 hours.

5. The synthesis process of p-hydroxycinnamic acid according to claim 4, characterized in that: The mass concentration of the dilute hydrochloric acid is 10-30%.

6. The process for synthesizing p-hydroxycinnamic acid according to claim 5, characterized in that: The yield of the crude product is ≥82%.

7. The process for synthesizing p-hydroxycinnamic acid according to claim 6, characterized in that: The crude product recrystallization comprises the following steps: adding the crude product into ethanol, controlling the temperature to 70-90° C., stirring at the temperature for 0.5-1.5 hours, cooling to 0-10° C., stirring at the temperature for 15-30 minutes, and filtering to obtain the product.

8. The process for synthesizing p-hydroxycinnamic acid according to claim 7, characterized in that: The mass ratio of the crude product to ethanol is 1:(2-4).

9. The process for synthesizing p-hydroxycinnamic acid according to claim 8, characterized in that: The filtrate after filtration is recycled to obtain a mixed solution of malonic acid and pyridine, and the recycling process comprises the following steps: adding cyclohexane to the filtrate after filtration, stirring and heating to 85-95° C., refluxing to remove water until no water is produced in the water separator, cooling to 20-30° C., secondary filtration, heating the secondary filtrate after the secondary filtration to 85-95° C., and distilling at atmospheric pressure until no fraction is produced to obtain a mixed solution of malonic acid and pyridine.

10. The process for synthesizing p-hydroxycinnamic acid according to claim 9, characterized in that: The ratio of the mass of the filtrate after filtration to the volume of cyclohexane is 10 g: (0.5-2) mL.

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