A process for the preparation of 4-chlorophthalic acid
By controlling the reaction conditions and subsequent processing of phthalic anhydride, 2-benzyloxyethanol, trimethylpentane, and water with chlorine, the problem of low yield of 4-chlorophthalic acid was solved, achieving high purity and high yield preparation, which is suitable for industrial production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HEBEI DONGLI NEW MATERIAL CO LTD
- Filing Date
- 2023-03-17
- Publication Date
- 2026-05-12
AI Technical Summary
In the existing technology, the yield of 4-chlorophthalic acid is low, the content of polychlorinated phthalic acid is high, the molar yield of the target product is insufficient, and the utilization rate of sodium hypochlorite chlorination method is low, resulting in high cost and poor product purity and yield.
High-purity 4-chlorophthalic acid was obtained by reacting phthalic anhydride, 2-benzyloxyethanol, trimethylpentane and water with chlorine under closed conditions, controlling the pH value to be 1-2, the pressure to be ≤0.05MPa and the temperature to be 60-90℃. The reaction was followed by static separation, cooling and crystallization of the oil phase and centrifugation and drying.
The purity of 4-chlorophthalic acid was increased to over 98%, the molar yield reached 91-95%, the byproducts were reduced, the production cost was lowered, and the foundation for industrial application was laid.
Abstract
Description
Technical Field
[0001] This invention relates to the field of organic synthesis technology, and in particular to a method for preparing 4-chlorophthalic acid. Background Technology
[0002] Chlorophthalic anhydride is a widely used and high-value-added fine chemical product. It is an important intermediate in the preparation of biphenyl dianhydride, which is an important monomer of polyimide.
[0003] The main method for preparing chlorophthalic acid is the sodium hypochlorite chlorination method using phthalic anhydride. Sodium hypochlorite is used as the chlorinating agent. Sodium hypochlorite exists in the form of an aqueous solution, has poor thermal stability, and is not easy to store for a long time. In a slightly acidic reaction system, it is easy to decompose into hydrochloric acid and chlorine gas, resulting in low utilization. The content of 4-chlorophthalic acid is only about 70%, the content of polychlorinated phthalic acid is about 20%, and the molar yield of the target product is only about 65%, which is a low yield. Summary of the Invention
[0004] In view of this, the object of the present invention is to provide a method for preparing 4-chlorophthalic acid. The preparation method provided by the present invention yields 4-chlorophthalic acid in a high rate.
[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:
[0006] This invention provides a method for preparing 4-chlorophthalic acid, comprising the following steps:
[0007] Under closed conditions, phthalic anhydride, 2-benzyloxyethanol, trimethylpentane, chlorine and water are mixed and subjected to a chlorination reaction to obtain the 4-chlorophthalic acid.
[0008] Preferably, the mass ratio of phthalic anhydride, 2-benzyloxyethanol, trimethylpentane and water is 1:3-5:0.2-0.4:0.1-0.2.
[0009] Preferably, the pressure of the chlorination reaction is ≤0.05MPa.
[0010] Preferably, the pressure of the chlorination reaction is adjusted by the rate at which chlorine gas is introduced.
[0011] Preferably, the pH value of the chlorination reaction is 1 to 2.
[0012] Preferably, the pH value is adjusted by an inorganic base.
[0013] Preferably, the chlorination reaction is carried out at a temperature of 60–90°C, and the reaction endpoint is reached when the phthalic acid content in the aqueous phase is ≤0.1 wt%.
[0014] Preferably, after the chlorination reaction is completed, the chlorinated product is further subjected to static separation, cooling and crystallization of the oil phase, centrifugation and drying to obtain the 4-chlorophthalic acid.
[0015] Preferably, the temperature for the static separation is 60–90°C, and the time is 0.5–1 hour.
[0016] Preferably, the temperature at which the oil phase cools and crystallizes is 60–90°C.
[0017] This invention provides a method for preparing 4-chlorophthalic acid, comprising the following steps: under sealed conditions, phthalic anhydride (phthalic anhydride), 2-benzyloxyethanol (benzyl cellosolve), trimethylpentane, chlorine gas and water are mixed to carry out a chlorination reaction to obtain the 4-chlorophthalic acid.
[0018] Compared with the prior art, the present invention has the following advantages:
[0019] In this invention, phthalic anhydride is soluble in water, and the 4-chlorophthalic acid produced during the reaction process has high solubility in the mixed solvent. This allows the 4-chlorophthalic acid generated in the water to be transferred to the mixed solvent in a timely manner, thus preventing the 4-chlorophthalic acid from being replaced by chlorine again to form polychlorinated products. This reduces the generation of by-products and solves the problems of high cost and low product yield in traditional processes, laying the foundation for enterprises to open up the polyimide market.
[0020] Data from the examples show that the purity of the 4-chlorophthalic acid obtained by this invention reaches over 98%, and the molar yield reaches 91-95%. Furthermore, the method is reliable and controllable, which is beneficial for industrial promotion and application. Detailed Implementation
[0021] This invention provides a method for preparing 4-chlorophthalic acid, comprising the following steps:
[0022] Under closed conditions, phthalic anhydride, 2-benzyloxyethanol, trimethylpentane, chlorine and water are mixed and subjected to a chlorination reaction to obtain the 4-chlorophthalic acid (4-chlorophthalic acid, CAS: 89-20-3, chemical formula: C8H5ClO4).
[0023] In this invention, the preferred mass ratio of phthalic anhydride, 2-benzyloxyethanol, trimethylpentane and water is 1:3-5:0.2-0.4:0.1-0.2. In specific embodiments of this invention, a more preferred ratio is 74:260:25:8, 74:360:25:14 or 74:300:20:14.
[0024] In this invention, the pressure of the chlorination reaction is preferably ≤0.05MPa.
[0025] In this invention, the pressure of the chlorination reaction is preferably adjusted by the rate at which chlorine gas is introduced.
[0026] In this invention, the pH value of the chlorination reaction is preferably 1 to 2, more preferably 1.1 to 1.8, and most preferably 1.5.
[0027] In this invention, the pH value is preferably adjusted by an inorganic base, which preferably includes sodium hydroxide or potassium hydroxide.
[0028] In this invention, the inorganic base is preferably used in the form of an aqueous solution of inorganic base. This invention does not have a special limitation on the concentration of the aqueous solution of inorganic base, as long as it can reach the pH value. Specifically, the mass concentration of the aqueous solution of inorganic base is 20-30%.
[0029] In this invention, the temperature of the chlorination reaction is preferably 60-90°C, more preferably 80-90°C, and the reaction endpoint is preferably ≤0.1wt% phthalic acid content in the aqueous phase.
[0030] In this invention, after the chlorination reaction is completed, it is preferable to further subject the obtained chlorinated product to static separation, cooling and crystallization of the oil phase, centrifugation and drying in sequence to obtain the 4-chlorophthalic acid.
[0031] In this invention, the preferred temperature for the static separation is 60–90°C, and the preferred time is 0.5–1 hour.
[0032] In this invention, the preferred temperature for cooling and crystallization of the oil phase is 60–90°C.
[0033] The present invention does not impose any particular limitation on the specific methods of centrifugation and drying; any method known to those skilled in the art can be used.
[0034] To further illustrate the present invention, the preparation method of 4-chlorophthalic acid provided by the present invention will be described in detail below with reference to examples, but these should not be construed as limiting the scope of protection of the present invention.
[0035] Example 1
[0036] 74g of phthalic anhydride, 260g of benzyl cellosolve, 25g of trimethylpentane, and 8g of water were added to a closed reactor. The temperature was raised to 90℃, and chlorine gas was introduced. The reaction temperature was controlled at 90℃, and the pressure of chlorine gas introduced into the reactor was controlled at ≤0.05MPa. A 20wt% liquid alkali was used to control the pH value at 1.5. The reaction was carried out for 6.5 hours. The phthalic acid content in the water was measured to be 0.09wt%. The reaction was completed, and 98.2g of liquid alkali was consumed. The mixture was allowed to stand at 90℃≤0.05MPa for separation. The oil phase was cooled to 15℃≤0.05MPa to crystallize, centrifuged, and dried to obtain 94.2g of 4-chlorophthalic acid. The purity of 4-chlorophthalic acid was measured to be 98.8%, the purity of 3-chlorophthalic acid was 0.19%, the content of dichlorophthalic acid was 0.68%, and the content of phthalic acid was 0.15%, with a molar yield of 93.97%.
[0037] Example 2
[0038] 74g of phthalic anhydride, 360g of benzyl cellosolve, 25g of trimethylpentane, and 14g of water were added to a closed reactor. The temperature was raised to 80℃, and chlorine gas was introduced. The reaction temperature was controlled at 80℃, and the pressure of chlorine gas introduced into the reactor was controlled to be ≤0.05MPa. A 20wt% liquid alkali was used to control the pH value of the system to 1.1. The reaction was carried out for 6 hours. The phthalic acid content in the water was measured to be 0.09wt%. The reaction was completed, and 101.1g of liquid alkali was consumed. The mixture was allowed to stand at 60℃ for separation. The oil phase was cooled to 15℃ to crystallize, centrifuged, and dried to obtain 92.1g of 4-chlorophthalic acid. The purity of 4-chlorophthalic acid was measured to be 98.1%, the purity of 3-chlorophthalic acid was 0.11%, the content of dichlorophthalic acid was 1.71%, the content of phthalic acid was 0.08%, and the molar yield was 91.87%.
[0039] Example 3
[0040] 74g of phthalic anhydride, 300g of benzyl cellosolve, 20g of trimethylpentane, and 14g of water were added to a closed reactor. The reactor was heated to 80°C, and chlorine gas was introduced. The reaction temperature was controlled at 80°C. The pressure of the sealed reactor was controlled at ≤0.05MPa for the addition of 360g of chlorinated cellosolve and 14g of water. A 20wt% liquid alkali was used to control the pH value at 1.8. The reaction was carried out for 7 hours. The phthalic acid content in the water was measured to be 0.09wt%. The reaction was completed, and 99.1g of liquid alkali was consumed. The mixture was allowed to stand at 70°C for separation. The oil phase was cooled to 15°C to crystallize, centrifuged, and dried to obtain 91.8g of 4-chlorophthalic acid. The purity of 4-chlorophthalic acid was 98.63%, the purity of 3-chlorophthalic acid was 0.12%, the content of dichlorophthalic acid was 0.87%, and the content of phthalic acid was 0.21%, with a molar yield of 91.57%.
[0041] Comparative Example 1
[0042] 74g of phthalic anhydride and 200g of water were added to a closed reactor, heated to 90℃, and chlorine gas was introduced. The reaction temperature was controlled at 90℃, and the pressure of chlorine gas introduced into the reactor was controlled at ≤0.05MPa. 20wt% liquid alkali was used to control the pH value of the system at 1.5. The reaction was carried out for 5 hours. The phthalic acid content in the water was measured to be 0.15wt%. The reaction was completed, and 142.2g of liquid alkali was consumed. The mixture was cooled to 15℃ for crystallization for 1 hour, centrifuged, and dried to obtain 74.1g of 4-chlorophthalic acid. The purity of 4-chlorophthalic acid was measured to be 65.2%, the purity of 3-chlorophthalic acid was 1.21%, the content of dichlorophthalic acid was 33.47%, the content of phthalic acid was 0.12%, and the molar yield was 73.91%.
[0043] Comparative Example 2
[0044] 74g of phthalic anhydride, 200g of water, and 300g of methyl acetate were added to a closed reactor. The temperature was raised to 35℃, and 427g of 10wt% sodium hypochlorite was added dropwise. The reaction temperature was controlled at 90℃, and the pressure of chlorine gas entering the reactor was controlled at ≤0.05MPa. The pH value of the control system was 1.5 using 20wt% liquid alkali. The reaction was carried out for 5 hours, and the phthalic acid content in the water was measured to be 0.32wt%. The reaction was completed, and 8.9g of liquid alkali was consumed. The mixture was cooled to 15℃ for 1 hour to crystallize, centrifuged, and dried to obtain 73.4g of 4-chlorophthalic acid. The purity of 4-chlorophthalic acid was measured to be 65.2%, the purity of 3-chlorophthalic acid was 2.13%, the content of dichlorophthalic acid was 34.86%, the content of phthalic acid was 0.51%, and the molar yield was 73.22%.
[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing 4-chlorophthalic acid, characterized in that, Includes the following steps: Under closed conditions, phthalic anhydride, 2-benzyloxyethanol, trimethylpentane, chlorine and water are mixed and subjected to a chlorination reaction to obtain the 4-chlorophthalic acid. The mass ratio of phthalic anhydride, 2-benzyloxyethanol, trimethylpentane, and water is 1:3~5:0.2~0.4:0.1~0.2; The pressure of the chlorination reaction is ≤0.05 MPa; The pH value of the chlorination reaction is 1 to 2, and the pH value is adjusted by an inorganic base; The chlorination reaction is carried out at a temperature of 60-90°C, and the reaction endpoint is reached when the phthalic acid content in the aqueous phase is ≤0.1wt%.
2. The preparation method according to claim 1, characterized in that, The pressure of the chlorination reaction is adjusted by the rate at which chlorine gas is introduced.
3. The preparation method according to claim 1, characterized in that, After the chlorination reaction is completed, the chlorinated product is subjected to static separation, cooling and crystallization of the oil phase, centrifugation and drying to obtain the 4-chlorophthalic acid.
4. The preparation method according to claim 3, characterized in that, The temperature for the static separation is 60~90℃, and the time is 0.5~1h.
5. The preparation method according to claim 3, characterized in that, The temperature at which the oil phase crystallizes after cooling is 60~90℃.