M-chlorobenzoic acid and preparation method thereof

Abstract

The invention relates to the technical field of production of m-chlorobenzoic acid, in particular to m-chlorobenzoic acid and a preparation method thereof. The preparation method of the m-chlorobenzoic acid comprises the following preparation processes: under ultraviolet irradiation, mixing toluene and chlorine, and carrying out chlorination reaction to obtain trichlorotoluene; mixing trichlorotoluene, a sodium hydroxide solution and water, and carrying out hydration reaction to obtain sodium benzoate; mixing sodium benzoate with hydrochloric acid, and performing acidification reaction to obtain benzoic acid; the preparation method comprises the following steps: mixing benzoic acid, a sodium hydroxide solution and water, introducing chlorine, carrying out chlorination reaction, adding hydrochloric acid into the system, and acidifying to obtain m-chlorobenzoic acid. The preparation method provided by the invention has the advantages of clear process steps, easy control of reaction conditions of each step, easy operation, common equipment and low cost, and is suitable for large-scale continuous production.

Description

Technical Field

[0001] The present invention relates to the technical field of m-chlorobenzoic acid production, in particular to m-chlorobenzoic acid and a preparation method thereof. Background Art

[0002] The process for producing m-chlorobenzoic acid using toluene as the starting material primarily involves atmospheric oxidation and pressurized oxidation. The atmospheric oxidation method, proposed by Tmenov in 1977, involves catalytic oxidation of m-chlorotoluene in acetic acid containing Co(OAC)2 and NaBr at 55-105°C under pure oxygen to produce m-chlorobenzoic acid. The reaction mixture undergoes a series of separation and purification steps, resulting in a yield of 90%-95% m-chlorobenzoic acid. The advantages and disadvantages of this process are as follows: 1) Advantage: High reaction yield. 2) Disadvantage: The reaction uses pure oxygen as the oxidant, which is costly and difficult to operate.

[0003] Pressure Oxidation: In 1981, Toray Industries, Ltd. of Japan developed a synthetic route for producing m-chlorobenzoic acid by oxidizing m-chlorotoluene with air in an acetic acid solution containing a cobalt catalyst and acetaldehyde or paraldehyde. The reaction pressure was 1.013 MPa and the temperature was 120°C, resulting in an m-chlorobenzoic acid yield of approximately 86%. The synthesized acetic acid and cobalt catalyst can be recovered and recycled. The company also developed a process for producing m-chlorobenzoic acid by air oxidation using m-chlorotoluene as the raw material and cobalt bromide, cobalt naphthenate, and manganese acetate as catalysts at 130°C and a pressure of 4.0 MPa. The yield was approximately 85%, with a 1:1 ratio of m-chlorotoluene to m-chlorobenzoic acid. The advantages and disadvantages of this process are as follows: 1) Advantages: Air as the oxidant: Compared to pure oxygen, air is less expensive and safer to operate, reducing the economic burden and safety risks of the process. Catalyst and solvent recovery: The acetic acid and cobalt catalyst can be recovered and recycled, reducing resource waste and production costs, in line with the principles of green chemistry. High yield. The yields of both process routes reached over 85%, indicating high reaction efficiency and high raw material utilization. 2) Disadvantages: High-pressure conditions: The process pressure is 4.0 MPa, which places high demands on equipment, increasing equipment investment and operational difficulty; High reaction temperature: The reaction temperatures are 120°C and 130°C, respectively, which consumes high energy and may increase production costs; Catalyst cost: Cobalt catalysts are expensive, and although they can be recycled, the initial investment is large; Possible side reactions: Under high temperature and high pressure conditions, side reactions may occur, affecting product purity and yield. Summary of the Invention

[0004] The present invention aims to provide m-chlorobenzoic acid and a preparation method thereof, so as to solve the problems of high cost and great difficulty in operation of the above-mentioned m-chlorobenzoic acid preparation method.

[0005] To achieve the above object, the present invention provides a method for preparing m-chlorobenzoic acid, comprising the following preparation process:

[0006] (1) Mixing toluene and chlorine gas under ultraviolet light to undergo chlorination reaction to obtain trichlorotoluene;

[0007] (2) mixing benzotrichloride, sodium hydroxide solution and water, and performing hydration reaction to obtain sodium benzoate;

[0008] (3) mixing sodium benzoate with hydrochloric acid and performing an acidification reaction to obtain benzoic acid;

[0009] (4) Benzoic acid, sodium hydroxide solution and water are mixed, and chlorine gas is introduced to carry out a chlorination reaction to obtain m-chlorobenzoic acid.

[0010] In the present invention, the mass ratio of toluene to chlorine in step (1) is 1:4-4.5.

[0011] In the present invention, the temperature of the chlorination reaction in step (1) is 108-112° C., and the time of the chlorination reaction is 7-9 hours.

[0012] In the present invention, the by-product of the chlorination reaction in step (1) is hydrogen chloride, which can be used as a hydrochloric acid solution after recovery.

[0013] In the present invention, the mass ratio of trichlorotoluene, sodium hydroxide solution and water in step (2) is 1:2-2.2:1.9-2; the mass concentration of the sodium hydroxide solution is 25%-35%.

[0014] In the present invention, the temperature of the hydration reaction in step (2) is 85-95° C., and the hydration time is 1-2 h.

[0015] In the present invention, after the hydration reaction in step (2) is completed, the system is cooled to 45-50° C. and allowed to stand. After the aqueous phase and the oil phase are separated, hydrochloric acid is added dropwise to the system to adjust the pH of the system to 4-5 to obtain benzoic acid.

[0016] In the present invention, the mass concentration of the hydrochloric acid in step (3) is 25-35%, and the temperature of the acidification reaction is 45-50° C. The amount of hydrochloric acid added is not limited, and it can be used until the pH of the system reaches 4-5.

[0017] In the present invention, the mass ratio of benzoic acid, sodium hydroxide solution and water in step (4) is 1:2.3-2.8:2.5-2.8.

[0018] In the present invention, the mass ratio of chlorine gas to benzoic acid in step (4) is 1:2.8-3.2, and the temperature of the chlorination reaction is 68-72°C.

[0019] In the present invention, the mass concentration of the hydrochloric acid in step (4) is 25%-35%, and the temperature of the acidification reaction is 40-50° C. The amount of hydrochloric acid added is not limited, as long as the pH of the system is 3-4.

[0020] In the present invention, after the acidification in step (4), centrifugation is performed and the centrifuged solid is dried to obtain m-chlorobenzoic acid.

[0021] The present invention also provides meta-chlorobenzoic acid prepared by the above-mentioned method for preparing meta-chlorobenzoic acid.

[0022] The present invention has the following beneficial effects

[0023] The invention provides a preparation method of m-chlorobenzoic acid, which comprises the following preparation steps: mixing toluene and chlorine gas under ultraviolet light irradiation, carrying out a chlorination reaction to obtain trichlorotoluene; mixing trichlorotoluene, a sodium hydroxide solution and water, carrying out a hydration reaction to obtain sodium benzoate; mixing the sodium benzoate and hydrochloric acid, carrying out an acidification reaction to obtain benzoic acid; mixing the benzoic acid, the sodium hydroxide solution and water, introducing chlorine gas, carrying out a chlorination reaction, and subsequently adding hydrochloric acid to the system, carrying out acidification to obtain m-chlorobenzoic acid.

[0024] The entire preparation process provided by the present invention is carried out at atmospheric pressure, eliminating the need for high-pressure equipment and reducing safety risks such as leakage and explosion associated with high pressure. The low reaction temperature not only reduces energy consumption but also minimizes the probability of raw material or product decomposition and side reactions at high temperatures, thereby improving product purity.

[0025] The present invention uses chlorine as the oxidant, avoiding the risks associated with the storage, transportation, and use of pure oxygen in atmospheric pressure oxidation processes, resulting in a safer operating environment. Furthermore, organic solvents such as acetic acid are not used (or are used only in small quantities), thereby avoiding atmospheric pollution caused by solvent volatilization and energy consumption during the recovery process, thereby reducing environmental impact.

[0026] The preparation method provided by the present invention has clear process steps, the reaction conditions of each step are easy to control, easy to operate, and the equipment is commonly used. The cost is low and it is suitable for large-scale continuous production.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is an infrared spectrum of trichlorotoluene prepared in step (1) of Example 1 of the present invention;

[0029] Figure 2 is an infrared spectrum of benzoic acid prepared in step (3) of Example 1 of the present invention;

[0030] Figure 3This is the infrared spectrum of m-chlorobenzoic acid prepared in step (4) of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention is further described below with reference to the accompanying drawings and examples. Unless otherwise defined, technical or scientific terms used herein shall have the same meanings as those commonly understood by persons of ordinary skill in the art to which the present invention pertains. The above-mentioned features or features described in the specific examples of the present invention may be combined in any manner. These specific examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention.

[0032] Example 1

[0033] A method for preparing m-chlorobenzoic acid comprises the following preparation steps:

[0034] (1) 494 kg of toluene was transferred to a chlorination reactor. Under ultraviolet light, the reactor jacket was heated to 110° C., 2068 kg of chlorine gas was introduced into the reactor, and the chlorination reaction was carried out for 8 hours to obtain 890 kg of trichlorotoluene (purity 86%).

[0035] (2) 890 kg of trichlorotoluene was transported to a hydrolysis reactor, mixed with 1800 kg of a 30% sodium hydroxide solution and 1750 kg of water, and then introduced into reactor No. 2. The mixture was heated to 90° C. and subjected to a hydration reaction for 1.5 hours to obtain sodium benzoate.

[0036] (3) The system temperature was cooled to 45°C and allowed to stand for 30 min. The aqueous phase was separated first, and then the oil phase was separated. 30% hydrochloric acid was added dropwise from the top of reactor No. 2 to adjust the pH of the system to 4. Acidification reaction was carried out to obtain 697 kg of benzoic acid (purity 99.3%), which was then taken out;

[0037] (4) Then, 360 kg of benzoic acid, 900 kg of 30% sodium hydroxide solution, and 1000 kg of water were added to the No. 2 reactor. After mixing, the reactor was heated to 70°C using the reactor interlayer. 120 kg of chlorine gas was introduced into the reactor to carry out a chlorination reaction. Then, the system temperature was lowered to 40°C, and a 30% hydrochloric acid solution was added dropwise from the top of the reactor to adjust the pH of the system to 4. Acidification reaction was carried out, centrifugation was performed, and the centrifuged solid was dried with air at 80°C to obtain 330 kg of m-chlorobenzoic acid (purity 99.1%).

[0038] Example 2

[0039] A method for preparing m-chlorobenzoic acid comprises the following preparation steps:

[0040] (1) 500 kg of toluene was transported to a chlorination reactor. Under ultraviolet light, the reactor jacket was heated to 108°C. 2000 kg of chlorine gas was introduced into the reactor. The chlorination reaction was carried out for 9 hours to obtain 900 kg of trichlorotoluene (purity 85.3%).

[0041] (2) 900 kg of trichlorotoluene was transported to a hydrolysis reactor, mixed with 1800 kg of a 25% sodium hydroxide solution and 1800 kg of water, and then introduced into reactor No. 2. The mixture was heated to 85° C. and subjected to a hydration reaction for 1 hour to obtain sodium benzoate.

[0042] (3) The system temperature was cooled to 45°C and allowed to stand for 30 min. The aqueous phase was separated first, and then the oil phase was separated. 25% hydrochloric acid was added dropwise from the top of reactor No. 2 to adjust the pH of the system to 4. Acidification reaction was carried out to obtain 750 kg of benzoic acid (purity 99.2%), which was then taken out;

[0043] (4) 360 kg of benzoic acid, 970 kg of 25% sodium hydroxide solution, and 1000 kg of water were added to reactor No. 2 and mixed. The temperature was raised to 68° C. using the reactor interlayer. 120 kg of chlorine gas was introduced into the reactor to carry out a chlorination reaction. The system temperature was then lowered to 40° C. A 25% hydrochloric acid solution was added dropwise from the top of the reactor to adjust the pH of the system to 3. The reaction was acidified and centrifuged. The centrifuged solid was dried with air at 80° C. to obtain m-chlorobenzoic acid (99.1%).

[0044] Example 3

[0045] A method for preparing m-chlorobenzoic acid comprises the following preparation steps:

[0046] (1) 450 kg of toluene was transferred to a chlorination reactor. Under ultraviolet light, the reactor jacket was heated to 112°C. 2025 kg of chlorine gas was introduced into the reactor. The chlorination reaction was carried out for 7 hours to obtain 792 kg of trichlorotoluene (purity 85.2%).

[0047] (2) 792 kg of trichlorotoluene was transported to a hydrolysis reactor, mixed with 1742 kg of a 35% sodium hydroxide solution and 1504 kg of water, and then introduced into reactor No. 2. The mixture was heated to 90° C. and subjected to hydration reaction for 2 h to obtain sodium benzoate.

[0048] (3) The system temperature was cooled to 50°C and allowed to stand for 30 min. The aqueous phase was separated first, and then the oil phase was separated. 35% hydrochloric acid was added dropwise from the top of reactor No. 2 to adjust the pH of the system to 5. Acidification reaction was carried out to obtain 665 kg of benzoic acid (purity 99%), which was then taken out;

[0049] (4) Then, 305 kg of benzoic acid, 705 kg of 35% sodium hydroxide solution, and 850 kg of water were added to the No. 2 reactor. After mixing, the reactor was heated to 72° C. using the reactor interlayer. 107 kg of chlorine gas was introduced into the reactor to carry out a chlorination reaction. Then, the system temperature was lowered to 50° C., and a 35% hydrochloric acid solution was added dropwise from the top of the reactor to adjust the pH of the system to 4. Acidification reaction was carried out, centrifugation was performed, and the centrifuged solid was dried with air at 80° C. to obtain m-chlorobenzoic acid (99.1%).

[0050] Characterization testing

[0051] The benzotrichloride, benzoic acid and m-chlorobenzoic acid obtained in Example 1 were detected by Fourier transform infrared spectrometer. The results were as follows: Figure 1 、 Figure 2 and Figure 3 As shown. Figure 1-Figure 3 It can be seen that the preparation method provided by the present invention can successfully synthesize m-chlorobenzoic acid products, and the characteristic peaks of the intermediate product are consistent with those of trichlorotoluene and benzoic acid.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing m-chlorobenzoic acid, characterized in that: The preparation process includes the following: (1) Mixing toluene and chlorine gas under ultraviolet light to undergo chlorination reaction to obtain trichlorotoluene; (2) mixing benzotrichloride, sodium hydroxide solution and water, and performing hydration reaction to obtain sodium benzoate; (3) mixing sodium benzoate with hydrochloric acid and performing an acidification reaction to obtain benzoic acid; (4) After mixing benzoic acid, sodium hydroxide solution and water, chlorine gas is introduced to cause chlorination reaction, and then hydrochloric acid is added to the system for acidification to obtain m-chlorobenzoic acid.

2. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass ratio of toluene to chlorine in step (1) is 1:4-4.

5.

3. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The temperature of the chlorination reaction in step (1) is 108-112° C., and the time of the chlorination reaction is 7-9 hours.

4. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass ratio of trichlorotoluene, sodium hydroxide solution and water in step (2) is 1:2-2.2:1.9-2; the mass concentration of the sodium hydroxide solution is 25%-35%.

5. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The temperature of the hydration reaction in step (2) is 85-95° C., and the hydration time is 1-2 h.

6. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass concentration of the hydrochloric acid in step (3) is 25-35%, and the temperature of the acidification reaction is 45-50°C.

7. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass ratio of benzoic acid, sodium hydroxide solution and water in step (4) is 1:2.3-2.8:2.5-2.

8.

8. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass ratio of chlorine gas to benzoic acid in step (4) is 1:2.8-3.2, and the temperature of the chlorination reaction is 68-72°C.

9. The method for preparing m-chlorobenzoic acid according to claim 1, wherein The mass concentration of the hydrochloric acid in step (4) is 25%-35%, and the temperature of the acidification reaction is 40-50°C.

10. Meta-chlorobenzoic acid prepared by the method for preparing meta-chlorobenzoic acid according to any one of claims 1 to 9.

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