Synthetic method of p-hydroxybenzoic acid

Abstract

The invention relates to the field of liquid crystal intermediates and food preservatives, and discloses a synthetic method of p-hydroxybenzoic acid, which is characterized in that phenol, carbon monoxide and carbonate are subjected to a benzene ring carboxylation reaction under the catalytic action of a basic catalyst to generate p-hydroxybenzoic acid. The method has the advantages of cheap and easily available raw materials, simple process, convenient target product separation and high yield. According to the method for preparing p-hydroxybenzoic acid through Kolbe-Schmitt reaction, only phenol potassium salt can react with carbon dioxide to generate p-hydroxybenzoic acid, the product p-hydroxybenzoic acid can react with another molecule of phenol potassium salt to generate p-hydroxybenzoic acid potassium salt and phenol, and phenol cannot generate Kolbe-Schmitt reaction with carbon dioxide, so that the yield of p-hydroxybenzoic acid is lower than 50%. The method disclosed by the invention is different from a Kolbe-Schmitt reaction, the yield of p-hydroxybenzoic acid is greater than 85%, the emission of three wastes is less, the method has the potential of large-scale industrialization, p-hydroxybenzoic acid meeting the liquid crystal level requirement can be produced, and the method has relatively high social and economic effects.

Description

Technical Field

[0001] The invention relates to the field of liquid crystal intermediates and food preservatives, and in particular to a method for synthesizing p-hydroxybenzoic acid. Background Art

[0002] Parahydroxybenzoic acid is a widely used organic synthetic raw material. Its main application areas are preservatives and mildew inhibitors for food, cosmetics, and medicines, which can extend the shelf life of products. In 2023, the total output of major varieties of food additives in my country will be around 16 million tons. As an important component of food additives, the market demand for parahydroxybenzoic acid will grow accordingly. Parahydroxybenzoic acid is used as a pesticide intermediate for the synthesis of insecticides, fungicides, etc. Another important use of parahydroxybenzoic acid is the synthesis of liquid crystal polymers. The liquid crystal product Xydar is a polymer of parahydroxybenzoic acid, hydroquinone and phthalic acid, X-7G is a polymer of parahydroxybenzoic acid and polyethylene terephthalate in a molten state, Vectra is a molten polymer of parahydroxybenzoic acid and 2-hydroxy-6-naphthoic acid, and Tian is a polymer of parahydroxybenzoic acid, 2-hydroxy-6-naphthoic acid and hydroquinone. Driven by downstream market demand, my country's parahydroxybenzoic acid market has developed rapidly and market demand has continued to grow.

[0003] The Kolbe–Schmitt reaction (potassium phenolate and carbon dioxide carboxylation method) is currently the industrial production method of p-hydroxybenzoic acid. Only potassium phenolate can react with carbon dioxide to produce p-hydroxybenzoic acid. The product p-hydroxybenzoic acid will react with another molecule of potassium phenolate to produce potassium p-hydroxybenzoate and phenol. Phenol cannot react with carbon dioxide to undergo the Kolbe–Schmitt reaction, so the yield of p-hydroxybenzoic acid is less than 50%. In industry, p-hydroxybenzoic acid can also be obtained from salicylic acid through salt formation, transposition, and neutralization, but the cost is relatively high. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing p-hydroxybenzoic acid, which has a simple process, a high yield of the target product, is easy to separate, and has less discharge of three wastes.

[0005] The objective of the present invention is achieved through the following technical scheme: under the catalytic action of an alkaline catalyst, phenol, carbon monoxide and carbonate undergo a benzene ring carboxylation reaction to generate p-hydroxybenzoic acid.

[0006] The reaction chemical formula of the present invention is: In the above technical solution, the alkaline catalyst is a biochar-supported copper-magnesium oxide catalyst, and the mass ratio of the catalyst to phenol is 0.05:1-0.5:1, preferably 0.1:1-0.3:1.

[0007] In the above technical solution, the carbonate is one or more of lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate and magnesium carbonate.

[0008] In the above technical solution, the biochar is loaded with copper and magnesium oxide catalyst, and the biochar is yeast pyrolysis carbon; the mass percentage of copper is 1-7%, preferably 2-5%; the mass percentage of magnesium is 1-20%, preferably 4-10%.

[0009] In the above technical solution, the molar ratio of phenol to carbonate is 1:1-1:2, preferably 1:1-1:1.5; the pressure of carbon monoxide is 0.1-10MPa, preferably 0.1-5MPa.

[0010] In the above technical solution, the reaction temperature is 150-290°C, preferably 200-280°C; the reaction time is 2-24h, preferably 6-18h.

[0011] Preparation process of yeast pyrolysis carbon: In an inert atmosphere, yeast dry powder is pyrolyzed at 600-1000°C for 1-4h, preferably 700-800°C, preferably 1-2h; ground into powder to obtain yeast biochar. The yeast biochar prepared as above is used as a carrier, and the active metal is loaded by impregnation method. Then it is roasted in an air atmosphere at a temperature of 350-550°C for 1-4h, preferably 400-500°C, preferably 1-2h. The soluble copper salt is one or more of copper chloride, copper nitrate, copper sulfate, copper phosphate or copper acetate; the soluble magnesium salt is one or more of magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium phosphate or magnesium acetate; the inert atmosphere is one or more of nitrogen or argon; Compared with the prior art, the present invention has the following beneficial effects: (1) The method of the present invention is different from the Kolbe-Schmitt reaction. The yield of p-hydroxybenzoic acid is 85%, the product is easy to separate, and the color is good. The discharge of three wastes is small, and it has the potential for large-scale industrialization. It can produce p-hydroxybenzoic acid that meets the requirements of liquid crystal level, and has a high social and economic effect. (2) The raw materials of the present invention are cheap and readily available, the process is simple, the target product is easy to separate, and the yield is high. DETAILED DESCRIPTION

[0012] The technical scheme of the present invention is described in detail below in conjunction with the embodiments, but the scope of the present invention is not limited to the following embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] Example 1

[0014] Take 10 g of yeast powder in a quartz boat, place the quartz boat in a tube furnace, and pass nitrogen for 30 minutes at room temperature (gas flow rate of 10 mL / min). Then keep the nitrogen gas flow rate unchanged and raise the temperature to 700℃ (heating rate of 5℃ / min). Still keep the nitrogen gas flow rate unchanged, keep pyrolysis at 700℃ for 1h, and then slowly cool it to 30℃ (cooling rate of 5℃ / min). Grind the black solid in the quartz boat into powder in an agate mortar to obtain biochar carrier 1, with a mass of 3.7g.

[0015] Take 10 g of yeast powder in a quartz boat, place the quartz boat in a tube furnace, and pass nitrogen for 30 minutes at room temperature (gas flow rate of 10 mL / min). Then keep the nitrogen gas flow rate unchanged and raise the temperature to 800°C (heating rate of 5°C / min). Still keep the nitrogen gas flow rate unchanged, keep pyrolysis at 800°C for 1 hour, and then slowly cool down to 30°C (cooling rate of 5°C / min). Grind the black solid in the quartz boat into powder in an agate mortar to obtain biochar carrier 2, with a mass of 3.8 g.

[0016] 0.1260 g of copper nitrate and 0.2630 g of magnesium nitrate were dissolved in 10 mL of deionized water, and 2 g of the above-mentioned biochar carrier 1 was added, stirred for 12 hours, and filtered. The impregnated biochar was dried in a hot oven at 120 °C for 12 hours, then placed in a quartz tube, calcined in an air atmosphere at 400 °C for 2 hours, cooled to room temperature, then ground and sieved to obtain catalyst 1.

[0017] 0.1947 g of copper nitrate and 0.8131 g of magnesium nitrate were dissolved in 10 mL of deionized water, and 2 g of the above-mentioned biochar carrier 2 was added, stirred for 12 hours, and filtered. The impregnated biochar was dried in a hot oven at 120 ° C for 12 hours, then placed in a quartz tube, calcined in an air atmosphere at 450 ° C for 2 hours, cooled to room temperature, then ground and sieved to obtain catalyst 2.

[0018] 0.3472 g of copper nitrate and 1.4504 g of magnesium nitrate were dissolved in 10 mL of deionized water, and 2 g of the above-mentioned biochar carrier 2 was added, stirred for 12 hours, and filtered. The impregnated biochar was dried in a hot oven at 120 ° C for 12 hours, then placed in a quartz tube, calcined at 500 ° C in an air atmosphere for 2 hours, cooled to room temperature, then ground and sieved to obtain catalyst 3.

[0019] Example 2

[0020] 9.4 g of phenol, 0.94 g of catalyst 1 prepared in Example 1, and 13.8 g of potassium carbonate were added to a 100 mL autoclave, and 0.1 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 280 ° C for 6 h. After the reaction was completed, it was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, and the catalyst was recovered by centrifugation. The catalyst was washed with deionized water 3 times (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid by mass concentration. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 85% (11.73 g, purity: 99.6%).

[0021] Example 3

[0022] 9.4 g of phenol, 2.82 g of catalyst 2 prepared in Example 1, and 15.9 g of sodium carbonate were added to a 100 mL autoclave, and 5 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 200 ° C for 18 h. After the reaction was completed, the mixture was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, and the catalyst was recovered by centrifugation. The catalyst was washed with deionized water 3 times (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 86% (11.9 g, purity: 99.5%).

[0023] Example 4

[0024] 9.4 g of phenol, 1.2 g of catalyst 3 prepared in Example 1, and 8.1 g of lithium carbonate were added to a 100 mL autoclave, and 0.5 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 230 °C for 10 h. After the reaction was completed, the reaction was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, the catalyst was recovered by centrifugation, and the catalyst was washed 3 times with deionized water (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 86% (11.9 g, purity: 99.8%).

[0025] Example 5

[0026] 9.4 g of phenol, 1 g of catalyst 2 prepared in Example 1, and 8.5 g of magnesium carbonate were added to a 100 mL autoclave, and 2 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 260 ° C for 12 h. After the reaction was completed, the reaction was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, and the catalyst was recovered by centrifugation. The catalyst was washed with deionized water 3 times (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 88% (12.2 g, purity: 99.4%).

[0027] Example 6

[0028] 9.4 g of phenol, 2 g of catalyst 1 prepared in Example 1, and 33 g of cesium carbonate were added to a 100 mL autoclave, and 0.2 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 210 °C for 8 h. After the reaction was completed, the reaction was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, the catalyst was recovered by centrifugation, and the catalyst was washed 3 times with deionized water (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and para-hydroxybenzoic acid was obtained by suction filtration with a yield of 92% (12.7 g, purity: 99.7%).

[0029] Example 7

[0030] 9.4 g of phenol, 2 g of catalyst 3 prepared in Example 1, and 24 g of rubidium carbonate were added to a 100 mL autoclave, and 0.1 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 150 °C for 24 h. After the reaction was completed, the reaction was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, the catalyst was recovered by centrifugation, and the catalyst was washed 3 times with deionized water (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 93% (12.8 g, purity: 99.7%).

[0031] Example 8

[0032] 9.4 g of phenol, 2 g of catalyst 1 prepared in Example 1, and 13.8 g of potassium carbonate were added to a 100 mL autoclave, and 10 MPa of carbon monoxide was charged into the autoclave. The reaction was carried out at 290 °C for 2 h. After the reaction was completed, the reaction was cooled to room temperature and excess carbon monoxide was slowly released. 30 mL of deionized water was added to the reaction system, the catalyst was recovered by centrifugation, and the catalyst was washed 3 times with deionized water (10 mL each time). The water layers were combined, and the pH was adjusted to 3 using 10% sulfuric acid. A white solid was precipitated and p-hydroxybenzoic acid was obtained by suction filtration with a yield of 91% (12.6 g, purity: 99.6%).

[0033] Comparative Example 1. Compared with the Kolbe–Schmitt reaction (Chem. Rev. 1957, 583-620), potassium phenolate can react with carbon dioxide to produce p-hydroxybenzoic acid by Kolbe–Schmitt reaction, while phenol does not react. The product p-hydroxybenzoic acid will react with potassium phenolate to produce potassium p-hydroxybenzoate and phenol, so the yield of p-hydroxybenzoic acid is less than 50%. The method disclosed in the present invention is different from the Kolbe–Schmitt reaction. In the presence of a catalyst, phenol directly reacts with potassium carbonate and carbon monoxide to produce p-hydroxybenzoic acid with a yield greater than 85%.

[0034] 2. Compared with the literature report (Chem. Commun., 2005, 486-488), the present invention has obvious advantages and differences: (1) The present invention does not use precious metal catalysts and has low cost; (2) The product selectivity is greater than 80%, while the selectivity of the literature (Chem. Commun., 2005, 486-488) is only 59%; (3) The present invention does not use oxygen; (4) The precious metal catalyst used in the literature (Chem. Commun., 2005, 486-488) is difficult to recycle and reuse.

[0035] 3. Compared with the reaction without using a catalyst (the process and conditions are the same as Example 7, except that no catalyst is added during the reaction), the reaction does not occur when no catalyst is used.

[0036] 4. Compared with the results of other reaction temperatures, the reaction temperature of the present invention (150-290°C) has obvious advantages. When the reaction temperature is lower than 150°C (the process and conditions are the same as those in Example 7, except that the reaction temperature is lower than 140°C), the product yield is 22%; when the reaction temperature is higher than 290°C (the process and conditions are the same as those in Example 7, except that the reaction temperature is higher than 290°C), the product yield is 65%, and a large amount of tar is produced.

[0037] 5. Compared with catalysts prepared using other carriers and other active metals, the catalyst of the present invention has obvious advantages. The catalyst preparation scheme is the same as the preparation method of catalyst 3 of the present invention, except that the type and content of the carrier or active metal used are different. The catalytic reaction process and conditions are the same as Example 7, except that (Table 1 Product yields of different catalysts) different catalysts are used.

[0038] Table 1 Product yields of different catalysts

Claims

1. A method for synthesizing p-hydroxybenzoic acid, It is characterized in that Under the catalytic action of biochar-supported copper-magnesium oxide catalyst, phenol, carbon monoxide, and carbonate undergo benzene ring carboxylation reaction to produce p-hydroxybenzoic acid. The mass ratio of catalyst to phenol is 0.05:1-0.5:1; The molar ratio of phenol to carbonate is 1:1-1:2, and the pressure of carbon monoxide is 0.1-10 MPa; The reaction temperature is 150-290°C, and the reaction time is 2-24h; The biochar-loaded copper-magnesium oxide catalyst is yeast pyrolysis carbon; the mass percentage of copper is 1-7%; the mass percentage of magnesium is 1-20%; Catalyst preparation process: In an inert atmosphere, yeast dry powder is pyrolyzed at 600-1000°C for 1-4 hours, ground into powder, and yeast biochar is obtained; The prepared yeast biochar is used as a carrier, and the active metal is loaded by an impregnation method; then, the carrier is calcined in an air atmosphere at a temperature of 350-550° C. for 1-4 hours.

2. The synthesis method according to claim 1, Features: The biochar-loaded copper-magnesium oxide catalyst has a mass ratio of the catalyst to phenol of 0.1:1-0.3:

1.

3. The synthesis method according to claim 1, Features: The carbonate is one or more of lithium carbonate, sodium carbonate, potassium carbonate, rubidium carbonate, cesium carbonate and magnesium carbonate.

4. The synthesis method according to claim 1, Features: The biochar is loaded with copper and magnesium oxide catalyst, and the biochar is yeast pyrolysis carbon; the mass percentage of copper is 2-5%; and the mass percentage of magnesium is 4-10%.

5. The synthesis method according to claim 1 or 3, Features: The molar ratio of phenol to carbonate is 1:1-1:1.

5.

6. The synthesis method according to claim 1, Features: The pressure of carbon monoxide is 0.1-5MPa.

7. The synthesis method according to claim 1, Features: The reaction temperature is 200-280°C; the reaction time is 6-18h.

8. The synthesis method according to claim 1, Features: In the process of loading active metals by impregnation, the soluble copper salt used is one or more of copper chloride, copper nitrate, copper sulfate, copper phosphate or copper acetate; the soluble magnesium salt is one or more of magnesium chloride, magnesium nitrate, magnesium sulfate, magnesium phosphate or magnesium acetate.

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