CN115010592A - Preparation method of 4-bromophthalic acid - Google Patents
Preparation method of 4-bromophthalic acid Download PDFInfo
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- C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
- C07C51/16—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation
- C07C51/21—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen
- C07C51/255—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting
- C07C51/265—Preparation of carboxylic acids or their salts, halides or anhydrides by oxidation with molecular oxygen of compounds containing six-membered aromatic rings without ring-splitting having alkyl side chains which are oxidised to carboxyl groups
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- C07C51/44—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation
- C07C51/46—Separation; Purification; Stabilisation; Use of additives by change of the physical state, e.g. crystallisation by distillation by azeotropic distillation
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Abstract
The invention discloses a preparation method of 4-bromophthalic acid, which comprises the following steps: preparing 4-bromine ortho-xylene by utilizing ortho-xylene; mixing 4-bromo-o-xylene, cobalt acetate, manganese acetate, tetrabromoethane and a solvent, heating to 150-220 ℃ in a high-pressure kettle, introducing air for 0.5-1.5 hours, introducing oxygen for 2-8 hours, and maintaining the pressure at 1.2-1.5 Mpa to perform liquid-phase oxidation reaction to obtain a reaction solution containing 4-bromo-phthalic acid; then carrying out corresponding post-treatment to obtain the 4-bromophthalic acid. The invention can obtain higher solvent recovery rate and crude product recovery rate, and realize the recovery and reuse of the solvent and the entrainer.
Description
Technical Field
The invention belongs to the technical field of organic chemical synthesis, and relates to a preparation method of 4-bromophthalic acid.
Background
4-Bromophthalic acid, having the molecular formula C 8 H 5 BrO 4 The molecular weight is 245.03, and the structural formula is shown as formula 1. In recent years, with the rapid development of aerospace, electronic technology and other fields, the demand for high-performance materials has also increased. Among them, the aromatic polyimide material is widely used in aerospace, electronics, automobile manufacturing and other fields because of its advantages of good high temperature resistance, acid and alkali resistance, radiation resistance, low dielectric property and the like. 4-bromophthalic acid is used as an important polyimide production raw material, and the demand is remarkably increased.
The currently available preparation method of 4-bromophthalic acid is as follows:
todorovic M, Schwab K D et al, in Fluorescent Iso oil Cross Chemistry A Rapid, User-friendly Stacking reaction, Angewandte Chemistry-International Edition, 2019, 58(40):14120-4, reported dropping potassium permanganate solution into 4-bromo-o-xylene, stirring at room temperature for 12h, adding KOH to dissolve it, filtering, adding EtOH to the filtrate, standing at 0 ℃ to obtain 4-bromophthalic acid with a yield of 48%. The method has low yield and poor economic benefit, and uses a large amount of potassium permanganate solution, thus being not friendly to the environment.
2. A method for synthesizing 5-bromobenzofuranone by catalytic oxidation of 4-bromoo-xylene is disclosed in fine chemical intermediates 2007, No.167(02), 44-45, wherein pure oxygen is used as an oxidant, cobalt acetate and manganese acetate are used as catalysts, and sodium bromide is used as an initiator. The mol ratio of 4-bromine o-xylene, cobalt acetate, manganese acetate and sodium bromide is 2: 1: 1:1 (namely, the mass ratio of 4-bromine o-xylene, cobalt acetate, manganese acetate and sodium bromide is 1: 48: 28%), reacting at 110 ℃ for 10h, and obtaining the yield of 69.1%. The method avoids using a strong oxidant, but has the disadvantages of large catalyst consumption, long reaction time, low yield and unsuitability for industrial production. Pure oxygen is used as an oxidant, so that the reaction speed is high, the temperature rise is high, and the safety is low. Meanwhile, if the method reduces the dosage of the composite catalyst consisting of cobalt acetate, manganese acetate and sodium bromide, the yield is obviously reduced.
3. Chinese patent application No. CN201510896105.4 discloses a method for synthesizing 4-bromophthalic anhydride, which comprises dissolving sodium hydroxide in water, adding phthalic acid, phase transfer catalyst, stirring, heating, adding 20% oleum for acidification, cooling, adding sodium bisulfite aqueous solution to remove excess bromine, adding organic solvent for extraction, distilling to remove organic solvent, and heating to obtain crude 4-bromophthalic acid. The method has complex steps, uses a large amount of fuming sulfuric acid and bromine, and is not environment-friendly.
4. Chinese patent application No. CN201410244731.0 discloses a method for synthesizing 4-bromophthalic acid, which comprises using phthalic anhydride, sodium hydroxide and sodium bromide as raw materials, mixing phthalic anhydride and sodium hydroxide uniformly, adding sodium hypochlorite aqueous solution under ultrasonic condition for reaction, and controlling the pH value of the reaction solution to obtain the target product 4-bromophthalic acid. However, reports have shown that direct bromination of phthalic acid yields a mixture of 3-bromophthalic acid, 4-bromophthalic acid and dibromophthalic acid. Although the double bromo phthalic acid can be removed by post-treatment, 3-bromo phthalic acid and 4-bromo phthalic acid are difficult to separate by rectification due to close boiling points, and the generated amount is basically the same. This results in a product with a yield and purity that are difficult to improve.
Disclosure of Invention
The invention aims to solve the technical problem of providing a preparation method of 4-bromophthalic acid, which is simple, low in cost, high in yield and good in safety.
In order to solve the technical problem, the invention provides a preparation method of 4-bromophthalic acid, which comprises the following steps:
1) preparing 4-bromine o-xylene by using o-xylene;
2) mixing 4-bromo-o-xylene, cobalt acetate, manganese acetate, tetrabromoethane and a solvent, heating to 150-220 ℃ in a high-pressure kettle, introducing air for 0.5-1.5 hours, introducing oxygen for 2-8 hours, and maintaining the pressure at 1.2-1.5 Mpa to perform liquid-phase oxidation reaction to obtain a reaction solution containing 4-bromo-phthalic acid;
the cobalt acetate accounts for 1-10 wt% (preferably 4-8%) of the 4-bromophthalic acid, and the manganese acetate accounts for 1-10 wt% (preferably 2-4%) of the 4-bromophthalic acid; tetrabromoethane accounts for 1-10 wt% (preferably 5%) of 4-bromophthalic acid;
description of the drawings: cobalt acetate and manganese acetate as catalysts, tetrabromoethane as initiator.
As an improvement of the process for producing 4-bromophthalic acid of the present invention, the process further comprises the following step 3):
3) adding an entrainer into the reaction liquid containing the 4-bromophthalic acid to carry out azeotropic distillation to remove the solvent, then carrying out solid-liquid separation to remove the liquid, adding a 3 wt% NaOH solution, heating at 60-100 ℃ for 1-5 h, filtering, adding hydrochloric acid into the obtained filtrate until no solid (white solid) is separated out, filtering, and recrystallizing the filter cake to obtain the 4-bromophthalic acid.
In the azeotropic distillation of the step, the distilled entrainer (n-heptane) returns to the reaction system through a water separator for continuous use, the distilled acetic acid leaves the system to be recovered, and the recovered acetic acid can be continuously used in the step 2); when no acetic acid is taken out from the system, stopping azeotropic distillation;
and (3) carrying out solid-liquid separation on the obtained product, wherein the separated liquid is n-heptane, adding a 3 wt% NaOH solution into the residue, heating, and filtering to respectively obtain a filter cake (a mixture of the recycled cobalt-manganese sodium salt catalyst) and a filtrate. Hydrochloric acid was added to the filtrate until no white solid precipitated, and filtered. Recrystallizing the filter cake to obtain the 4-bromophthalic acid.
As a further improvement of the process for the preparation of 4-bromophthalic acid of the present invention: when the 4-bromine o-xylene in the step 2) is 0.05mol, the amount of the 3 wt% NaOH solution in the step 3) is 50-100 ml.
As a further improvement of the process for producing 4-bromophthalic acid of the present invention, the step 1) is:
adding o-xylene, iron powder and iodine particles into a container, then adding (dropwise adding) liquid bromine, stirring at 0-5 ℃ for 4-8 h, and standing at room temperature for 10-15 h;
iron powder: 0.5 to 5 wt% (preferably 1 to 2%) of o-xylene, iodine particles: 0.5 to 5 wt% (preferably 2 to 3%) of o-xylene, liquid bromine: o-xylene ═ 1:1 to 3 (preferably 1: 1.5);
washing the reaction product with 3 wt% NaOH solution twice, separating the organic phase and vacuum distilling to obtain 4-bromo-o-xylene.
As a further improvement of the process for the preparation of 4-bromophthalic acid of the present invention: the solvent in the step 2) is acetic acid (acetic acid).
As a further improvement of the process for producing 4-bromophthalic acid of the present invention, the liquid-phase oxidation reaction in the step 2) is: firstly, air of 1 plus or minus 0.1h is introduced, and then oxygen of 7 plus or minus 1h is introduced to maintain the pressure of 1.3 plus or minus 0.1 MPa.
As a further improvement of the process for the preparation of 4-bromophthalic acid of the present invention:
in the step 3): the entrainer used for the azeotropic distillation was n-heptane.
In the step 3): the solvent used for recrystallization is acetic acid and water according to the weight ratio of 1: 1-2 mass ratio of the obtained mixed liquid.
The reaction equation for synthesizing 4-bromophthalic acid is as follows:
current oxidations generally use pure oxygen or air as the oxidant. If air is used as an oxidant, the temperature rise is small, but the selectivity of the reaction is low, a large number of byproducts are produced, and the reaction process is slow. If pure oxygen is used as the oxidant, the temperature rise in the initial reaction process is too severe. If oxygen is used as an oxidant, side reactions are aggravated, and the selectivity of a main product is reduced. Therefore, the present invention firstly uses air as an oxidant, which has advantages in that side reactions caused by severe reaction/temperature rise can be reduced at the initial reaction, and then oxygen is used as an oxidant after the oxidation reaction is performed for a period of time, which has advantages in that the conversion of raw materials can be promoted, and the effects of increasing the reaction rate and promoting the main reaction to proceed are achieved. Therefore, the composition-changing gas oxidizing agent of the present invention is preferably introduced with air for 1 hour and then with oxygen for 7 hours.
The technological process of preparing 4-bromophthalic acid includes the first bromination of o-xylene and the subsequent liquid phase oxidation of 4-bromoo-xylene. Compared with the multi-step reaction in the prior art, the method has the advantages of cheap and easily obtained raw materials, simplified steps, greatly reduced discharge of three wastes by liquid phase oxidation, reduced production cost, reduced environmental protection pressure, high product purity, low impurity content and high yield compared with the traditional potassium permanganate oxidation method. Meanwhile, compared with pure oxygen as an oxidant, the variable composition gas is used as the oxidant, the temperature rise in the reaction process is small (the maximum temperature rise is only 5-8 ℃ in the invention of air and oxygen, and the maximum temperature rise is 15-20 ℃ in the pure oxygen reaction), and the safety is good. The product yield of the invention reaches more than 80%, the purity reaches more than 98.5%, and the product quality is effectively improved.
In conclusion, the preparation method of the 4-bromophthalic acid has the following technical advantages:
1. the method has the advantages of low cost and easy obtainment of o-xylene as a raw material, reduction of raw material cost, high selectivity of brominated products, less by-products and reduction of separation cost.
2. The 4-bromophthalic acid is synthesized by using variable composition gas (firstly air and then oxygen) as an oxidant and performing liquid phase catalytic oxidation on the 4-bromoo-xylene, and the method has the advantages of thorough reaction, less side reaction, high product yield and environmental friendliness.
3. Tetrabromoethane is set as an initiator, so that the dosage of the catalyst is greatly reduced.
4. Screening n-heptane as entrainer, distilling to remove the azeotrope with the solvent (acetic acid) in step 2) at normal pressure, condensing, separating phase, returning n-heptane to the system for recycling, and recovering acetic acid. The process can obtain high solvent recovery rate and crude product recovery rate, and realize the recovery and reuse of the solvent and the entrainer.
Detailed Description
The invention will be further described with reference to specific examples, but the scope of the invention is not limited thereto:
in the present invention, the particle size of the iron powder is about 100-150 μm, and the particle size of the iodine particle is about 15-30 mm.
Example 1, a method of preparing 4-bromophthalic acid, sequentially performing the following steps:
1) 33.0g (0.30mol) of o-xylene, 0.33g of iron powder and 0.66g of iodine particles were charged in a three-necked flask. 24.0g (0.20mol) of liquid bromine was added dropwise thereto under stirring at 0 ℃. After the addition of the liquid bromine was completed (the addition time was about 30 minutes), the mixture was stirred at 0 ℃ for 5 hours and allowed to stand at room temperature for 14 hours. Then washed twice with 3 wt% NaOH solution (50 ml. times.2) and the organic phase (in the lower layer) was separated. The organic phases obtained by two combined washings are subjected to reduced pressure distillation at the pressure of-97 kPa to remove the o-xylene, and the fraction at the temperature of 114 ℃ and 118 ℃ is collected to obtain 0.15mol of 4-bromine-o-xylene with the yield of 75.5%.
2) 9.25g (0.05mol) of the 4-bromo-o-xylene, 0.37g (0.002mol) of cobalt acetate, 0.19g (0.001mol) of manganese acetate, 0.46g of tetrabromoethane and 30g of acetic acid are weighed, placed in an autoclave, and subjected to a total reaction for 8 hours under the conditions of 200 ℃, 1000rpm and 1.3MPa by firstly introducing 1 hour of air (the pressure of the autoclave is 1.3MPa) and then introducing 7 hours of oxygen to maintain the pressure of 1.3 MPa.
3) After the reaction is finished, mixing the kettle liquid with 50ml of n-heptane, then carrying out azeotropic distillation (the temperature is about 90 ℃) in a three-neck flask, returning the distilled n-heptane to the reaction system through a water separator for continuous use, leaving the distilled acetic acid from the system for recovery, and continuously using the recovered acetic acid in the oxidation reaction in the step 2); when no acetic acid is carried out in the system, the azeotropic distillation is stopped.
And (3) carrying out solid-liquid separation on the obtained product, wherein the separated liquid is n-heptane, adding 100ml of 3 wt% NaOH solution into the residue in the three-neck flask, heating at 80 ℃ for 2h, and filtering to respectively obtain a filter cake (a mixture of the recycled cobalt-manganese sodium salt catalyst) and a filtrate. Hydrochloric acid was added to the filtrate until no white solid precipitated (about 50ml hydrochloric acid amount), and filtered. The filter cake was recrystallized from 50 wt% acetic acid (100ml) by heating to 80 ℃ to give 9.87g (0.04mol) of 4-bromophthalic acid in 80.6% yield and 99% purity.
Example 2, a method of preparing 4-bromophthalic acid, sequentially performing the following steps:
1) 33.0g of o-xylene, 0.66g of iron powder and 0.66g of iodine granules are added into a three-neck flask. 24.0g of liquid bromine was added dropwise thereto under stirring at 0 ℃. After the dropwise addition, the mixture was stirred at 0 ℃ for 5 hours and allowed to stand at room temperature for 14 hours. Then, the mixture was washed twice with a 3 wt% NaOH solution, and the organic phase was separated. The organic phases obtained by two combined washings are subjected to reduced pressure distillation at the pressure of-97 kPa to remove the o-xylene, and the fraction at the temperature of 114 ℃ and 118 ℃ is collected to obtain 0.155mol of 4-bromo-o-xylene with the yield of 77.5%.
2) 9.25g of the 4-bromo-o-xylene, 0.37g of cobalt acetate, 0.37g of manganese acetate, 0.46g of tetrabromoethane and 30g of acetic acid are weighed, placed in an autoclave, and subjected to reaction for 8 hours under the conditions of 200 ℃, 1000rpm and 1.3MPa by firstly introducing 1 hour of air and then 7 hours of oxygen to maintain the pressure at 1.3 MPa.
3) Equivalent to step 3 of example 1);
9.36g (0.038mol) of 4-bromophthalic acid was obtained in a yield of 76.4%.
Example 3, a method of preparing 4-bromophthalic acid, sequentially performing the following steps:
1) 33.0g of o-xylene, 0.66g of iron powder and 0.99g of iodine granules are added into a three-neck flask. 24.0g of liquid bromine was added dropwise thereto under stirring at 0 ℃. After the dropwise addition, the mixture was stirred at 0 ℃ for 5 hours and allowed to stand at room temperature for 14 hours. Then, the mixture was washed twice with a 3 wt% NaOH solution, and the organic phase was separated. The organic phases obtained by two combined washings are subjected to reduced pressure distillation at the pressure of-97 kPa to remove the o-xylene, and the fraction at the temperature of 114 ℃ and 118 ℃ is collected to obtain 0.155mol of 4-bromo-o-xylene with the yield of 77.5%.
2) 9.25g of 4-bromo-o-xylene, 0.74g of cobalt acetate, 0.37g of manganese acetate, 0.46g of tetrabromoethane and 30g of acetic acid are weighed, placed in an autoclave, and subjected to reaction for 8 hours by firstly introducing 1 hour of air and then 7 hours of oxygen at the conditions of 200 ℃, 1000rpm and 1.3MPa to maintain the pressure of 1.3 MPa.
3) Equivalent to step 3 of example 1);
9.86g (0.04mol) of 4-bromophthalic acid was obtained in a yield of 80.5%.
Example 4, a method of preparing 4-bromophthalic acid, sequentially performing the following steps:
1) 16.5g of o-xylene mother liquor distilled out by reduced pressure distillation according to the method described in step 1) of example 1, 16.5g of fresh o-xylene, 0.33g of iron powder and 0.66g of iodine particles were charged into a three-necked flask. Under stirring at 0 ℃, 23.97g of liquid bromine was added dropwise. After the dropwise addition, the mixture was stirred at 0 ℃ for 5 hours and allowed to stand at room temperature for 14 hours. Then, the mixture was washed twice with a 3 wt% NaOH solution, and the organic phase was separated. The organic phases obtained by two combined washings are subjected to reduced pressure distillation at the pressure of-97 kPa to remove the o-xylene, and the fraction at the temperature of 114 ℃ and 118 ℃ is collected to obtain 0.17mol of 4-bromine-o-xylene with the yield of 85.7 percent.
2) 9.25g of the above 4-bromo-o-xylene, 0.37g of cobalt acetate, 0.19g of manganese acetate, 0.46g of tetrabromoethane and 30g of acetic acid were weighed out and placed in an autoclave. At 200 deg.C, 1000rpm, 1.3MPa, introducing air for 1h, introducing oxygen for 7h to maintain 1.3MPa, and reacting for 8 h.
3) Equivalent to step 3 of example 1);
9.87g (0.04mol) of 4-bromophthalic acid was obtained with a yield of 80.6%.
Example 5, a method of preparing 4-bromophthalic acid, sequentially performing the following steps:
1) 16.5g of o-xylene mother liquor distilled out by reduced pressure distillation according to the method described in step 1) of example 1, 16.5g of fresh o-xylene, 0.33g of iron powder and 0.66g of iodine particles were charged into a three-necked flask. Under stirring at 0 ℃, 23.97g of liquid bromine was added dropwise. After the dropwise addition, the mixture was stirred at 0 ℃ for 5 hours and allowed to stand at room temperature for 14 hours. Then, the mixture was washed twice with a 3 wt% NaOH solution, and the organic phase was separated. The organic phases obtained by two combined washings are subjected to reduced pressure distillation at the pressure of-97 kPa to remove the o-xylene, and the fraction at the temperature of 114 ℃ and 118 ℃ is collected to obtain 0.17mol of 4-bromine-o-xylene with the yield of 85.7 percent.
2) 9.25g of the above 4-bromo-o-xylene, 0.19g of cobalt acetate, 0.10g of manganese acetate, 0.46g of tetrabromoethane, and 30g of acetic acid were weighed, and 0.29g of the mixture of the cobalt manganese sodium salt catalysts recovered in example 1 was added thereto, and the mixture was placed in an autoclave. At 200 ℃, 1000rpm and 1.3MPa, firstly introducing air for 1h, then introducing oxygen for 7h to maintain the pressure at 1.3MPa, namely reacting for 8 h.
3) Equivalent to step 3 of example 1);
6.38g (0.026mol) of 4-bromophthalic acid was obtained in a yield of 52.1%.
Comparative example 1, the mass fraction of the iron powder relative to the o-xylene in the step 1) of the example 1 is changed from 1% to 0.1%, 10% and 15%; the remaining conditions were identical to step 1) of example 1. The yields of 4-bromo-o-xylene obtained in step 1) are shown in table 1 below.
TABLE 1
Comparative example 2, the mass fraction of the iodine particles relative to the o-xylene in the step 1) of the example 1 is changed from 2% to 0.1%, 10% and 15%; the rest is equivalent to step 1) of example 1. The yields obtained for 4-bromo-o-xylene obtained in step 1) are shown in Table 2 below.
TABLE 2
Comparative example 3, the mass fraction of cobalt acetate relative to 4-bromo-o-xylene in step 2) of example 1 was changed from 4% to 20%, 0.5%, 0.1%; the rest is equivalent to embodiment 1. The final 4-bromophthalic acid yields obtained are shown in table 3 below.
TABLE 3
Comparative example 4, the mass fraction of manganese acetate relative to 4-bromo-o-xylene in step 2) of example 1 was changed from 2% to 20%, 0.5%, 0.1%; the rest is equivalent to embodiment 1. The final 4-bromophthalic acid yields obtained are shown in table 4 below.
TABLE 4
Comparative example 5-1, the "1.3 MPa oxygen retention pressure of 1.3MPa after 1h of air and 7h of oxygen in step 2) of example 1 was changed to" 1.3MPa oxygen retention pressure of 8h, and the rest was the same as in example 1. The final 4-bromophthalic acid yield was 50.8%.
Comparative example 5-2, the "1.3 MPa pressure maintained by introducing air first for 1 hour and then oxygen for 7 hours" in step 2) of example 1 was changed to "1.3 MPa pressure maintained by introducing air first for 2 hours and then oxygen for 6 hours", and the rest was the same as in example 1. The final 4-bromophthalic acid yield was 42.5%.
Comparative example 6, the azeotropic agent used in the azeotropic distillation in step 3) of example 1 was changed from n-heptane to cyclohexane and n-octane, and the rest was the same as in example 1. The final 4-bromophthalic acid yields obtained are shown in Table 5 below.
TABLE 5
Comparative example 7, the azeotropic distillation in step 3) of example 1 was changed to direct distillation, and the rest was the same as example 1. The final yield of 4-bromophthalic acid obtained was 50.2%, and the recovery of acetic acid was 32.4%.
Finally, it is also noted that the above-mentioned lists merely illustrate a few specific embodiments of the invention. It is obvious that the invention is not limited to the above embodiments, but that many variations are possible. All modifications which can be derived or suggested by a person skilled in the art from the disclosure of the present invention are to be considered within the scope of the invention.
Claims (7)
- The preparation method of the 1.4-bromophthalic acid is characterized by comprising the following steps:1) preparing 4-bromine o-xylene by using o-xylene;2) mixing 4-bromo-o-xylene, cobalt acetate, manganese acetate, tetrabromoethane and a solvent, heating to 150-220 ℃ in a high-pressure kettle, introducing air for 0.5-1.5 hours, introducing oxygen for 2-8 hours, and maintaining the pressure at 1.2-1.5 Mpa to perform liquid-phase oxidation reaction to obtain a reaction solution containing 4-bromo-phthalic acid;1-10 wt% of cobalt acetate and 1-10 wt% of manganese acetate in the 4-bromophthalic acid; tetrabromoethane accounts for 1-10 wt% of 4-bromophthalic acid.
- 2. The process for producing 4-bromophthalic acid according to claim 1, characterized by further comprising step 3) of:3) adding an entrainer into a reaction liquid containing 4-bromophthalic acid to perform azeotropic distillation to remove a solvent, performing solid-liquid separation to remove the liquid, adding a 3 wt% NaOH solution, heating at 60-100 ℃ for 1-5 h, filtering, adding hydrochloric acid into the obtained filtrate until no solid is separated out, filtering, and recrystallizing a filter cake to obtain the 4-bromophthalic acid.
- 3. The method of producing 4-bromophthalic acid according to claim 2, characterized in that: when the 4-bromine o-xylene in the step 2) is 0.05mol, the amount of the 3 wt% NaOH solution in the step 3) is 50-100 ml.
- 4. The method for producing 4-bromophthalic acid according to any of claims 1 to 3, characterized in that the step 1) is:adding o-xylene, iron powder and iodine particles into a container, adding liquid bromine, stirring at 0-5 ℃ for 4-8 hours, and standing at room temperature for 10-15 hours;iron powder: 0.5-5 wt% of o-xylene, and iodine particles: 0.5-5 wt% of o-xylene, liquid bromine: o-xylene ═ 1:1 to 3 molar ratio;washing the reaction product with 3 wt% NaOH solution, separating the obtained organic phase, and distilling under reduced pressure to obtain 4-bromo-o-xylene.
- 5. The method of producing 4-bromophthalic acid according to claim 4, characterized in that: the solvent in the step 2) is acetic acid.
- 6. The method of producing 4-bromophthalic acid according to claim 5, characterized in that:the liquid-phase oxidation reaction in the step 2) comprises the following steps: firstly, air of 1 plus or minus 0.1h is introduced, and then oxygen of 7 plus or minus 1h is introduced to maintain the pressure of 1.3 plus or minus 0.1 MPa.
- 7. The method of producing 4-bromophthalic acid according to claim 6, characterized in that:in the step 3): the azeotropic agent used for azeotropic distillation is n-heptane;in the step 3): the solvent used for recrystallization is acetic acid and water according to a ratio of 1: 1-2 mass ratio of the obtained mixed liquid.
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