Continuous preparation method of 2, 6-dihydroxybenzoic acid

Abstract

The invention relates to the technical field of chemical industry, and provides a continuous preparation method of 2, 6-dihydroxybenzoic acid, which comprises the following steps: S1, adding resorcinol, alkali metal salt and a solvent into a reaction kettle, and carrying out a salt forming reaction to obtain a reaction liquid I; and S2, simultaneously introducing the reaction liquid I and carbon dioxide gas introduced from the outside of the reaction kettle into a gas-liquid mixer, uniformly mixing, and carrying out continuous carboxylation reaction in a tubular reactor to obtain 2, 6-dihydroxybenzoic acid. According to the technical scheme, the problems of high production cost, long reaction time and low yield and conversion rate of 2, 6-dihydroxybenzoic acid in related technologies are solved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a continuous preparation method of 2,6-dihydroxybenzoic acid. Background Art

[0002] 2,6-Dihydroxybenzoic acid is an important organic synthesis intermediate, which is widely used in the fields of medicine, pesticides, dyes, etc. In the field of medicine, it can be used to synthesize a variety of biologically active drugs, such as antibacterial drugs, anti-tumor drugs, etc. In the field of pesticides, it can be used as a key intermediate for new pesticides, which helps to develop high-efficiency and low-toxic pesticide products; in the field of dyes, it can be used to synthesize high-performance dyes to meet the needs of the growing printing and dyeing industry.

[0003] However, the existing preparation method of 2,6-dihydroxybenzoic acid has the problems of high production cost, long reaction time, low yield and conversion rate, and cannot meet market demand. Therefore, it is necessary to develop a continuous preparation method of 2,6-dihydroxybenzoic acid. Summary of the invention

[0004] The invention provides a continuous preparation method of 2,6-dihydroxybenzoic acid, which solves the problems of high production cost, long reaction time, low yield and low conversion rate of 2,6-dihydroxybenzoic acid in the related art.

[0005] The technical solution of the present invention is as follows: The present invention provides a continuous preparation method of 2,6-dihydroxybenzoic acid, comprising the following steps: S1, resorcinol and alkali metal salt are subjected to salt-forming reaction in a solvent to obtain a reaction solution I; S2, mixing the reaction solution I and carbon dioxide in a gas-liquid manner, and then performing a continuous carboxylation reaction to obtain 2,6-dihydroxybenzoic acid.

[0006] As a further technical solution, the solvent in S1 includes one or two of an alcohol solvent and cyclopentyl methyl ether.

[0007] The alcohol solvent may be, for example, methanol or ethanol.

[0008] In the present invention, the reaction solvent not only serves as a reaction medium, but also can improve the reaction rate, the selectivity of the product, the yield of 2,6-dihydroxybenzoic acid and the purity of 2,6-dihydroxybenzoic acid.

[0009] As a further technical solution, the solvent in S1 consists of an alcohol solvent and cyclopentyl methyl ether.

[0010] In the present invention, by limiting the solvent to consist of an alcohol solvent and cyclopentyl methyl ether, the yield and purity of 2,6-dihydroxybenzoic acid can be further improved.

[0011] As a further technical solution, the mass ratio of the alcohol solvent to cyclopentyl methyl ether is 3-5:1.

[0012] As a further technical solution, the alkali metal salt includes one or more of potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

[0013] As a further technical solution, the molar ratio of resorcinol to the alkali metal in the alkali metal salt is 1:1 to 1.5.

[0014] As a further technical solution, the temperature of the salt-forming reaction in S1 is 120°C~140°C, the time is 1 h, and the pressure is 0.5~0.8 MPa.

[0015] As a further technical solution, the temperature of the continuous carboxylation reaction in S2 is 140°C to 160°C, the time is 4 to 5 hours, and the pressure is 1.3 to 1.6 MPa.

[0016] As a further technical solution, when the gas and liquid are mixed, the rate at which the reaction liquid I in S2 is introduced is 1.5~5m / s.

[0017] As a further technical solution, when the gas and liquid are mixed, the rate at which the carbon dioxide gas in S2 is introduced is 10-15 m / s.

[0018] As a further technical solution, the mass volume ratio of resorcinol to solvent is 1g:15~20mL.

[0019] As a further technical solution, the salt-forming reaction is carried out in a reactor, the gas-liquid mixing is carried out in a gas-liquid mixer, and the continuous carboxylation reaction is carried out in a tubular reactor, that is, the continuous preparation method of 2,6-dihydroxybenzoic acid comprises the following steps: S1, resorcinol, alkali metal and solvent are put into a reaction kettle to perform salt-forming reaction to obtain reaction solution I; S2, the reaction solution I and the carbon dioxide gas introduced from the outside of the reactor are simultaneously introduced into a gas-liquid mixer and mixed evenly, and then a continuous carboxylation reaction is carried out in a tubular reactor to obtain 2,6-dihydroxybenzoic acid.

[0020] As a further technical solution, the continuous preparation method of 2,6-dihydroxybenzoic acid comprises the following steps: S1, resorcinol, alkali metal and solvent are put into a reaction kettle to perform salt-forming reaction to obtain reaction solution I; S2, the reaction solution I and the carbon dioxide gas introduced outside the reactor are simultaneously introduced into a gas-liquid mixer and mixed evenly, and then a continuous carboxylation reaction is carried out in a tubular reactor to obtain a reaction solution II, which is placed in a reaction solution storage tank; S3. After the reaction liquid II is heated, the solvent is collected at the upper port of the reaction liquid storage tank, and 2,6-dihydroxybenzoic acid is obtained at the lower port of the reaction liquid storage tank.

[0021] The present invention adopts a tubular reactor for continuous reaction, which can increase the production of 2,6-dihydroxybenzoic acid, improve product quality and product stability, realize mechanized and automated production, reduce production costs, and reduce environmental pollution. The tubular reactor has a simple and compact structure, high strength, high corrosion resistance, good impact resistance, long service life, and is easy to repair. A gas-liquid mixer is also provided to shear carbon dioxide gas into small bubbles, increase the solubility of carbon dioxide in the reaction liquid I, make the mixture fully contact in the tubular reactor, greatly shorten the reaction time, reduce the generation of by-products, and improve the yield and raw material conversion rate.

[0022] The working principle and beneficial effects of the present invention are: In the present invention, resorcinol and an alkali metal undergo a salt-forming reaction under the action of a solvent, and then undergo a carboxylation reaction with carbon dioxide to prepare 2,6-dihydroxybenzoic acid. The process route can reduce the generation of by-products, improve the yield and purity of 2,6-dihydroxybenzoic acid, and shorten the reaction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0024] Figure 1 This is a process flow chart of the continuous preparation of 2,6-dihydroxybenzoic acid in Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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.

[0026] Example 1 A continuous preparation method of 2,6-dihydroxybenzoic acid comprises the following steps: S1, 330 mL of solvent, 22 g of resorcinol and 13.8 g of potassium carbonate were put into a reactor to carry out a salt-forming reaction (temperature 120°C, time 1 h, pressure 0.5 MPa) to obtain a reaction solution I, wherein the solvent is anhydrous ethanol; S2, the reaction liquid I and the carbon dioxide gas introduced from the reactor are introduced into the gas-liquid mixer at the introduction rate of 1.5m / s and 10m / s respectively, and after being mixed evenly, a continuous reaction is carried out in a tubular reactor (the reaction temperature is 160°C, the reaction time is 5h, and the reaction pressure is 1.6MPa) to obtain a reaction liquid II, which is placed in a reaction liquid storage tank; S3, after the reaction liquid II is heated, the solvent is collected at the upper port of the reaction liquid storage tank, and the crude 2,6-dihydroxybenzoic acid is obtained at the lower port of the reaction liquid storage tank, washed with anhydrous ethanol, and then recrystallized with anhydrous ethanol and dried to obtain 29.35g of 2,6-dihydroxybenzoic acid with a yield of 94.53% and a purity of 99.2%. The process flow chart of the continuous preparation of 2,6-dihydroxybenzoic acid in this embodiment is as follows Figure 1 shown.

[0027] Example 2 A continuous preparation method of 2,6-dihydroxybenzoic acid comprises the following steps: S1. 400 mL of solvent, 22 g of resorcinol and 23 g of potassium bicarbonate were put into a reactor to carry out a salt-forming reaction (temperature: 135° C., time: 1 h, pressure: 0.7 MPa) to obtain a reaction solution I, wherein the solvent is anhydrous ethanol; S2, the reaction liquid I and the carbon dioxide gas introduced from the outside of the reactor are introduced into the gas-liquid mixer at the introduction rate of 3m / s and 12m / s respectively, and after being mixed evenly, a continuous reaction is carried out in a tubular reactor (reaction temperature is 150°C, reaction time is 4.5h, reaction pressure is 1.5MPa), to obtain reaction liquid II, which is placed in a reaction liquid storage tank; S3. After the reaction liquid II is heated, the solvent is collected at the upper port of the reaction liquid storage tank. After the crude 2,6-dihydroxybenzoic acid is obtained at the lower port of the reaction liquid storage tank, it is washed with anhydrous ethanol, recrystallized with anhydrous ethanol, and dried to obtain 29.32 g of 2,6-dihydroxybenzoic acid with a yield of 94.34% and a purity of 99.1%.

[0028] Example 3 A continuous preparation method of 2,6-dihydroxybenzoic acid comprises the following steps: S1. Put 440 mL of solvent, 22 g of resorcinol and 25.2 g of sodium bicarbonate into a reactor to carry out salt-forming reaction (temperature: 140°C, time: 1 h, pressure: 0.8 MPa) to obtain reaction solution I, wherein the solvent is anhydrous ethanol; S2, the reaction liquid I and the carbon dioxide gas introduced from the reactor are introduced into the gas-liquid mixer at the introduction rate of 5m / s and 15m / s respectively, and after being mixed evenly, a continuous reaction is carried out in a tubular reactor (the reaction temperature is 145°C, the reaction time is 4h, and the reaction pressure is 1.3MPa) to obtain a reaction liquid II, which is placed in a reaction liquid storage tank; S3. After the reaction liquid II is heated, the solvent is collected at the upper port of the reaction liquid storage tank. After the crude 2,6-dihydroxybenzoic acid is obtained at the lower port of the reaction liquid storage tank, it is washed with anhydrous ethanol, recrystallized with anhydrous ethanol, and dried to obtain 29.41 g of 2,6-dihydroxybenzoic acid with a yield of 94.72% and a purity of 99.2%.

[0029] Example 4 The difference between this embodiment and embodiment 1 is that the solvent is cyclopentyl methyl ether.

[0030] Result: 29.48 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 94.95% and a purity of 99.2%.

[0031] Example 5 The only difference between this embodiment and embodiment 1 is that the solvent consists of anhydrous ethanol and cyclopentyl methyl ether in a mass ratio of 2:1.

[0032] Result: 29.63 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 95.53% and a purity of 99.3%.

[0033] Example 6 The only difference between this embodiment and embodiment 1 is that the solvent consists of anhydrous ethanol and cyclopentyl methyl ether in a mass ratio of 6:1.

[0034] Result: 29.71 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 95.88% and a purity of 99.4%.

[0035] Example 7 The only difference between this embodiment and embodiment 1 is that the solvent consists of anhydrous ethanol and cyclopentyl methyl ether in a mass ratio of 3:1.

[0036] Result: 29.97 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 96.72% and a purity of 99.4%.

[0037] Example 8 The only difference between this embodiment and embodiment 1 is that the solvent consists of anhydrous ethanol and cyclopentyl methyl ether in a mass ratio of 4:1.

[0038] Result: 30.28 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 97.92% and a purity of 99.6%.

[0039] Example 9 The only difference between this embodiment and embodiment 1 is that the solvent consists of anhydrous ethanol and cyclopentyl methyl ether in a mass ratio of 5:1.

[0040] Result: 30.12 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 97.30% and a purity of 99.5%.

[0041] Example 10 The only difference between this embodiment and embodiment 1 is that the solvent is water.

[0042] Result: 29.11 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 93.19% and a purity of 98.6%.

[0043] Comparative Example 1 The difference between this comparative example and Example 1 is only S2. In this comparative example: S2, the reaction liquid I and the carbon dioxide gas introduced from the outside of the reactor are simultaneously introduced into the gas-liquid mixer and mixed evenly, and then a carboxylation reaction is carried out in the reactor to obtain a reaction liquid II, which is placed in a reaction liquid storage tank.

[0044] Result: 28.71 g of 2,6-dihydroxybenzoic acid was obtained with a yield of 91.16% and a purity of 97.8%.

[0045] Compared with Example 1, no tubular reactor was used in Comparative Example 1. As a result, the yield of 2,6-dihydroxybenzoic acid in Comparative Example 1 was lower than that in Example 1, indicating that the use of a tubular reactor in the preparation process of 2,6-dihydroxybenzoic acid can improve the yield and purity of 2,6-dihydroxybenzoic acid.

[0046] In Examples 1, 4 and 10, the solvent of Example 1 is anhydrous ethanol, the solvent of Example 4 is cyclopentyl methyl ether, and the solvent of Example 10 is water. As a result, the yield of 2,6-dihydroxybenzoic acid in Examples 1 and 4 is higher than that in Example 10, indicating that when the solvent is anhydrous ethanol or cyclopentyl methyl ether, the yield of 2,6-dihydroxybenzoic acid can be increased, and 2,6-dihydroxybenzoic acid has a higher purity.

[0047] The yield of 2,6-dihydroxybenzoic acid in Example 5 is higher than that in Example 1 and Example 4, indicating that when the solvent is composed of anhydrous ethanol and cyclopentyl methyl ether, the yield of 2,6-dihydroxybenzoic acid can be further improved, and 2,6-dihydroxybenzoic acid has a higher purity.

[0048] Compared with Example 5, Examples 6 to 9 changed the mass ratio of anhydrous ethanol and cyclopentyl methyl ether. As a result, the yield of 2,6-dihydroxybenzoic acid in Examples 7 to 9 was higher than that in Examples 5 to 6, indicating that when the mass ratio of anhydrous ethanol and cyclopentyl methyl ether was 3 to 5:1, the yield of 2,6-dihydroxybenzoic acid could be further improved, and 2,6-dihydroxybenzoic acid had a higher purity.

[0049] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A continuous preparation method of 2,6-dihydroxybenzoic acid, characterized in that: The following steps are involved: S1, resorcinol and alkali metal salt are subjected to salt-forming reaction in a solvent to obtain a reaction solution I; S2, mixing the reaction solution I and carbon dioxide in a gas-liquid manner, and then performing a continuous carboxylation reaction to obtain 2,6-dihydroxybenzoic acid.

2. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: The solvent in S1 includes one or two of an alcohol solvent and cyclopentyl methyl ether.

3. A continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 2, characterized in that, The solvent in S1 consists of an alcohol solvent and cyclopentyl methyl ether.

4. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 3, characterized in that: The mass ratio of the alcohol solvent to cyclopentyl methyl ether is 3-5:

1.

5. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: The alkali metal salt includes one or more of potassium carbonate, sodium bicarbonate, and potassium bicarbonate.

6. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: The molar ratio of the resorcinol to the alkali metal in the alkali metal salt is 1:1-1.

5.

7. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: The temperature of the continuous carboxylation reaction in S2 is 140° C. to 160° C., the time is 4 to 5 hours, and the pressure is 1.3 to 1.6 MPa.

8. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: When the gas and liquid are mixed, the rate at which the reaction liquid I is introduced is 1.5-5 m / s.

9. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: When the gas and liquid are mixed, the rate of carbon dioxide introduction is 10-15 m / s.

10. The continuous preparation method of 2,6-dihydroxybenzoic acid according to claim 1, characterized in that: The mass volume ratio of the resorcinol to the solvent is 1g:15-20mL.

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