Method for efficiently preparing high chlorinated xylene from low chlorinated xylene
By using a stepwise chlorination reaction of low-chlorinated xylene with chlorine under specific conditions, the problems of low selectivity and complex equipment in the preparation of high-chlorinated xylene in the existing technology have been solved, realizing the preparation of high-chlorinated xylene with high selectivity and high yield, and simplifying equipment requirements.
Patent Information
- Application Number
- CN202410592149.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-14
- Publication Date
- 2025-11-18
AI Technical Summary
Existing technologies for preparing perchlorinated xylenes suffer from low reaction selectivity, numerous byproducts, complex equipment, and difficult maintenance, making it difficult to achieve industrial-scale production.
High-chlorinated xylene or hexachloroxylene can be prepared by stepwise chlorination of low-chlorinated xylene with chlorine at a specific temperature and in the presence of additives, controlling the proportion of intermediates. Peroxides are used as reaction promoters or catalysts, and side reaction inhibitors are used to regulate the reaction process.
This method enables the preparation of perchlorinated xylenes with high selectivity and high yield, simplifies equipment requirements, and improves reaction efficiency and product purity.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of new materials chemicals, and in particular to a new method and technology for the efficient preparation of high-chlorinated xylene or hexachloroxylene from low-chlorinated xylene or mixtures as starting materials through a stepwise chlorination reaction. Background Technology
[0002] Perchloroxylenes are an important class of fine chemical products, widely used as raw materials or intermediates in pharmaceuticals, pesticides, coatings, and dyes. For example, tetrachlorom-xylene (i.e., 1,3-di(dichloromethyl)benzene) is impurity 9 in montelukast sodium; tetrachloromethyldichlorobenzene is impurity 46 in plerusex; both can be used as impurity reference standards. p-Chlorotetrabenzene is used as an important intermediate in organic synthesis. Hexachlorom-xylene (i.e., m-di(trichloromethylbenzene)) is used as an intermediate in pesticides and pharmaceuticals. Hexachlorop-xylene (i.e., p-di(trichloromethylbenzene)) is an antischistosomiasis drug; it is also used as a raw material or intermediate in the production of pesticides, coatings, and dyes.
[0003] Isophthaloyl chloride and terephthaloyl chloride can be used as the main raw materials for preparing poly(m-phenylene isophthalamide) fiber (aramid 1313) and poly(p-phenylene terephthalamide) fiber (aramid 1414), respectively. Aramid fibers have very high molecular chain rigidity, exceptionally stable chemical structure, and are resistant to high temperatures and strong acids and alkalis. They also possess high flame retardancy and electrical insulation properties, thus being classified as strategic materials. As specialty fibers, they have significant demand in high-end application fields, such as radiation-proof clothing, bulletproof clothing, tire cords, aerospace clothing, high-temperature resistant clothing, honeycomb components, high-temperature conduits, aircraft fuel tanks, reverse osmosis membranes, or hollow fibers. However, although some literature reports the use of hexachlorom-xylene and hexachlorop-xylene as raw materials to react with the corresponding aryldicarboxylic acids to further prepare the corresponding isophthaloyl chloride and terephthaloyl chloride, achieving industrial-scale production still urgently requires further technological upgrades and innovative development.
[0004] Currently, the preparation of hexachloroxylene mostly uses xylene as a raw material, which undergoes a chlorination reaction on the methyl group with chlorine under ultraviolet light catalysis. However, on the one hand, photocatalysis requires high transmittance of the reactants; on the other hand, the selectivity of the reaction is not high, the chlorination sites are difficult to control, and there are many byproducts of chlorination on the benzene ring, which darkens the color of the reactants and reduces transmittance, thus affecting the catalysis under ultraviolet light. Furthermore, the corresponding production equipment is relatively complex and difficult to maintain.
[0005] Perchloroxylene is an important intermediate in organic synthesis, but there are few reports on efficient and systematic preparation methods for it.
[0006] In this application, we unexpectedly discovered that the chlorination reaction of low-chlorinated xylenes exhibits a distinct stepwise chlorination characteristic. By simply controlling some process parameters, the content ratio of these intermediates at the reaction endpoint can be adjusted, thereby achieving highly selective preparation of the corresponding high-chlorinated xylene products. This process is simple to operate and requires minimal equipment. Summary of the Invention
[0007]
[0008] This application discovers that, as shown in reaction formula (I), low-chlorinated xylene A and chlorine gas undergo a stepwise chlorination reaction via intermediate B or C under reaction conditions to finally prepare the product high-chlorinated xylene or hexachloroxylene D.
[0009] Where x, y, m, and n are the numbers 0, 1, 2, or 3 respectively; the constraints are x + y = 3, m + n = 3, and y or n cannot be 0 at the same time.
[0010] The raw material, low-chlorinated xylene A, can be a pure product or a mixture.
[0011] The reaction conditions are independent of each other, namely temperature and at least one of the additives, and no solvent needs to be added.
[0012] The temperature is 25℃-200℃; preferably, the temperature is 60℃-160℃.
[0013] The additives refer to reaction promoters, catalysts, and / or side reaction inhibitors. The amount of additive used is the catalytic amount, based on the molar amount of the reactants. Preferably, in the condition, the reaction promoter or catalyst is one or more of diisopropyl peroxide, dicyclohexyl peroxide, benzoyl peroxide, lauroyl peroxide, tert-butyl peroxide, tert-butyl pervalerate, di-tert-butyl peroxide, dicumyl peroxide, azobisisobutyronitrile, and azobisisoheptanenitrile; the amount of reaction promoter or catalyst used is 0.005 equivalents to 0.05 equivalents, based on the molar amount of the reactants. Preferably, in the condition, the side reaction inhibitor is one or more of triethanolamine, aniline, N,N-dimethylaniline, N,N-diethylaniline, N,N-dihydroxyethylaniline, 2-chloro-4,6-dinitrophenol, and 4-chloro-N,N-dimethylaniline; and the amount of reaction promoter or catalyst used is 0.005 equivalents to 0.05 equivalents based on the molar amount of the reaction raw materials.
[0014] The low-chlorinated xylene A described in this invention is any one or a mixture of two or more of the following illustrative but not limiting compounds:
[0015]
[0016] The following exemplary, but not limiting, perchloroxylenes can be prepared in relatively high yields using the techniques disclosed in this invention:
[0017]
[0018] Using the technology disclosed in this invention, as shown in reaction formulas (II-1)-(II-3), the prepared hexachloro-p-xylene D1, hexachloro-m-xylene D2, or hexachloro-o-xylene D3 can be further reacted with their corresponding terephthalic acid, isophthalic acid, or phthalic acid under the action of a catalyst to generate the corresponding terephthaloyl chloride F1, isophthaloyl chloride F2, or phthaloyl chloride F3. Preferred conditions are: no solvent is required; the catalyst is anhydrous FeCl3 or Fe2O3; and the reaction temperature is 60℃-140℃.
[0019]
[0020] Attached Figure Description
[0021] Figure 1 A schematic diagram of the stepwise chlorination reaction progress of low-chlorinated p-xylene.
[0022] Figure 2 A schematic diagram of the stepwise chlorination reaction of low-chlorinated m-xylene. Detailed Implementation
[0023] Example 1:
[0024]
[0025] As shown in reaction (III), 260 g of p-xylene (2.45 mol) and 0.26 g of triethanolamine were added to a 500 mL dry round-bottom flask, a condenser was attached, and the temperature was raised to 80 °C. An initial 50 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.3 L / min to initiate the reaction. The tail gas was absorbed with alkaline solution. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography. The temperature program and the amount and frequency of benzoyl peroxide (BPO) addition were adjusted according to Table 1.
[0026] Table 1: Parameter Control Table for Stepwise Chlorination Process of Low-Chlorinated p-Xylene
[0027]
[0028] According to the results of gas chromatography monitoring, this chlorination reaction process exhibits a very obvious stepwise chlorination characteristic. Monochloro-p-xylene (Interm.1a), dichloro-p-xylene (Interm.2a and Interm.3a), trichloro-p-xylene (Interm.4a), tetrachloro-p-xylene (Interm.5a and Interm.6a), and pentachloro-p-xylene (Interm.7a) appear sequentially, reaching a peak concentration and then gradually disappearing as chlorination continues (e.g., ...). Figure 1 (As shown). In the early stages of the reaction, relatively mild conditions are required; in the later stages, relatively vigorous conditions are needed.
[0029] After a total reaction time of 38 hours, the content of hexachloro-p-xylene D1 in the reaction solution reached as high as 96.8%. The crude product was purified by slurrying with methanol to obtain 719 g (2.30 mol, purity >99%) of a purified white solid, with a yield of 93.9%.
[0030] Based on this principle, increasing the chlorination rate and accelerating the frequency of BPO addition can shorten the overall reaction time.
[0031] Example 2:
[0032]
[0033] Following the pattern observed in Example 1, 50 g of monochloro-p-xylene Interm.1a (356 mmol) and 50 mg of triethanolamine were added to a 100 mL dry round-bottom flask. A condenser was attached, and the temperature was raised to 80 °C. An initial 50 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.1 L / min to initiate the reaction. The tail gas was absorbed with alkaline solution. BPO (50 mg) was added every 3 hours. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography.
[0034] After 10 hours of reaction, the content of trichloro-p-xylene Interm.4a in the reaction solution reached 76%; the main byproducts were dichloro-p-xylene Interm.3a and tetrachloro-p-xylene Interm.6a. After cooling to room temperature, methanol was added for purification by stirring. Residual methanol was removed, and then the solution was further purified by vacuum distillation to obtain purified pure white solid trichloro-p-xylene Interm.4a (49.2 g, 235 mmol, purity >96%), with a yield of 66%.
[0035] Example 3:
[0036]
[0037] Following the pattern observed in Example 1, 50 g of a mixture of dichloro-p-xylene (Interm.2a and Interm.3a, 286 mmol) and 50 mg of triethanolamine were added to a 100 mL dry round-bottom flask. A condenser was attached, and the temperature was raised to 100 °C. An initial 50 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.1 L / min to initiate the reaction. The tail gas was absorbed with an alkaline solution. BPO (50 mg) was added every 3 hours. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography.
[0038] After 15 hours of reaction, the content of tetrachloro-p-xylene Interm.6a in the reaction solution reached 72%; the main byproducts were trichloro-p-xylene Interm.4a, the tetrachloro-p-xylene isomer Interm.5a, and a small amount of pentachloro-p-xylene Interm.7a. After cooling to room temperature, methanol was added for purification by stirring, residual methanol was removed, and then further purified by vacuum distillation to obtain purified pure white solid tetrachloro-p-xylene Interm.6a (43.9 g, 180 mmol, purity >95%), with a yield of 63%.
[0039] Example 4:
[0040]
[0041] 40 g of the tetrachloro-p-xylene mixture Interm.6a (164 mmol) prepared in Example 3 and 40 mg of triethanolamine were added to a 100 mL dry round-bottom flask. A condenser was attached, and the temperature was raised to 120 °C. An initial 60 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.1 L / min to initiate the reaction. The tail gas was absorbed with alkaline solution. BPO (60 mg) was added every 2 hours. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography.
[0042] After 12 hours of reaction, the content of pentachloro-p-xylene Interm.7a in the reaction solution reached 81%; the main byproduct was hexachloro-p-xylene D1. After cooling to room temperature, methanol was added for slurry purification. Residual methanol was removed, and then the solution was further purified by vacuum distillation to obtain purified pure white solid pentachloro-p-xylene Interm.7a (34.2 g, 123 mmol, purity >96%), with a yield of 75%.
[0043] Example 5:
[0044]
[0045] The crude hexachloro-p-xylene (204.1 g, 640 mmol, 97% purity), terephthalic acid (108.5 g, 640 mmol, 98% purity), and anhydrous ferric chloride (1 g, 6.4 mmol) prepared according to Example 1 were placed into a 1 L dry four-necked round-bottom flask, fitted with a reflux condenser and an anhydrous calcium chloride drying tube, and connected to an alkaline solution to absorb the tail gas. The mixture was stirred and heated to 110 °C for 1 hour, during which the solution gradually turned black. A sample was taken and monitored by gas chromatography, confirming that the raw materials had been completely converted. The reaction was continued at this temperature for another 1.5 hours.
[0046] After the reaction was completed, the apparatus was directly connected to a vacuum distillation device. Fraction 1 was collected at 100℃-105℃ to obtain 106.6g of terephthaloyl chloride with a purity of 99.7%; Fraction 2 was collected at 105℃ to obtain 81.2g of terephthaloyl chloride with a purity of 99.7%; Fraction 3 was collected at 110℃-120℃ to obtain 65.6g of terephthaloyl chloride with a purity of 99.2%. The total yield of all fractions was 253.4g, with an overall yield of 97.5%. The residue in the reaction vessel was 4.2g.
[0047] Example 6:
[0048]
[0049] As shown in reaction (IV), add m-xylene (100g, 942mmol) and N,N-dihydroxyethylaniline (100mg) to a 500mL dry round-bottom flask, attach a condenser, heat to 80℃, add the first batch of 50mg benzoyl peroxide (BPO), connect the chlorine cylinder and open the valve, controlling the chlorine flow rate at approximately 0.2L / min to start the reaction. Absorb the tail gas with alkaline solution. During the reaction, take samples every two hours for gas chromatography monitoring; and add BPO every two hours (mix 0.5mL-1mL of the reaction solution with 50mg BPO before adding it to the reaction system). Adjust the temperature according to the program in Table 2.
[0050] Table 2: Parameter Adjustment Table for Stepwise Chlorination Process of Low-Chlorinated m-Xylene
[0051] Temperature / °C Time / h Temperature rise point (reaction point) 80 4 m-Xylene content ≤20% 90 6 The content of monochloro-p-xylene (Interm.1b) is ≤20%. 100 4 The content of dichloro-p-xylene (Interm.3b) is ≤20%. 120 4 The content of trichloro-p-xylene (Interm.4b) is ≤20%. 140 4 Tetrachloro-p-xylene (Interm.6b) content ≤ 20% 150 8 The reaction ended.
[0052] According to the results of gas chromatography monitoring, this chlorination reaction process also exhibited a very obvious stepwise chlorination characteristic. Monochlorom-xylene (Interm.1b), dichlorop-xylene (Interm.2b and Interm.3b), trichlorop-xylene (Interm.4b), tetrachlorop-xylene (Interm.5b and Interm.6b), and pentachlorop-xylene (Interm.7b) appeared sequentially, reaching a peak concentration and then gradually disappearing as chlorination continued (e.g., ...). Figure 2 (As shown).
[0053] The initial reaction required relatively mild conditions, while the later stages required more vigorous conditions. After a total of 30 hours of reaction, the content of hexachloro-p-xylene D1 in the reaction solution reached as high as 90.8%. The crude product was purified by slurrying with methanol to obtain 251 g (803 mmol, purity >98%) of a purified white solid, with a yield of 85.2%.
[0054] Example 7:
[0055]
[0056] Following the pattern observed in Example 6, 50 g of monochlorom-xylene Interm.1b (356 mmol) and 50 mg of N,N-dihydroxyethylaniline were added to a 100 mL dry round-bottom flask. A condenser was attached, and the temperature was raised to 80°C. An initial 50 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.1 L / min to initiate the reaction. The tail gas was absorbed with alkaline solution. BPO (50 mg) was added every 3 hours. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography.
[0057] After 8 hours of reaction, the content of trichloro-m-xylene Interm.4b in the reaction solution reached 70%; the main byproducts were dichloro-m-xylene Interm.3b and tetrachloro-m-xylene Interm.6b. After cooling to room temperature, the product was purified by vacuum distillation to obtain purified pure light yellow oily liquid trichloro-m-xylene Interm.4b (46.2 g, 221 mmol, purity >95%), with a yield of 62%.
[0058] Example 8:
[0059]
[0060] Following the pattern presented in Example 6, 50 g of a mixture of dichloro-m-xylene (Interm.2b and Interm.3b, 286 mmol) and 50 mg of N,N-dihydroxyethylaniline were added to a 100 mL dry round-bottom flask. A condenser was attached, and the temperature was raised to 100°C. An initial 50 mg of benzoyl peroxide (BPO) was added, the chlorine cylinder was connected, and the valve was opened. The chlorine flow rate was controlled at approximately 0.1 L / min to initiate the reaction. The tail gas was absorbed with alkaline solution. BPO (50 mg) was added every 3 hours. During the reaction, samples were taken periodically, and the reaction progress was monitored using gas chromatography.
[0061] After 12 hours of reaction, the content of tetrachloro-m-xylene Interm.6b in the reaction solution reached 68%; the main byproducts were trichloro-m-xylene Interm.4b, the tetrachloro-m-xylene isomer Interm.5b, and a small amount of pentachloro-p-xylene Interm.7b. After cooling to room temperature, methanol was added for purification by stirring, residual methanol was removed, and then further purified by vacuum distillation to obtain purified pure white solid tetrachloro-p-xylene Interm.6b (42.0 g, 172 mmol, purity >95%), with a yield of 60%.
[0062] Example 9:
[0063]
[0064] The pure hexachloro-m-xylene (62.6 g, 200 mmol), isophthalic acid (33.2 g, 200 mmol), and anhydrous ferric chloride (0.195 g, 1.2 mmol) prepared according to Example 6 were placed into a 500 mL dry four-necked round-bottom flask, fitted with a reflux condenser and an anhydrous calcium chloride drying tube, and connected to an alkaline solution to absorb the tail gas. The mixture was first heated to 60 °C, where the hexachloro-m-xylene melted from a solid state. After the solid was completely melted and stirred evenly, the temperature was raised to 80 °C, and the reaction was allowed to proceed for 1 hour, during which the solution turned black. A sample was taken and monitored by gas chromatography, which showed that the raw materials had been completely converted. The reaction was continued at this temperature for another hour.
[0065] After the reaction was completed, the sample was directly placed into a vacuum distillation apparatus. Fraction 1 was collected at 95°C to obtain 23.7 g of isophthaloyl chloride with a purity of 99.6%; Fraction 2 was collected at 100°C to obtain 19.1 g of isophthaloyl chloride with a purity of 99.2%; Fraction 3 was collected at 100°C-130°C to obtain 34.2 g of isophthaloyl chloride with a purity of 97.9%. The total amount of all fractions was 76.9 g, the overall yield was 94.7%, and the residue in the reaction vessel was 3.63 g.
[0066] It should be emphasized that the above embodiments are merely exemplary and not limiting. Based on the disclosure of this application, any adjustments or changes to the reaction conditions or parameters that a person skilled in the art might normally adopt will not deviate from the spirit of the invention. The scope of protection of this patent shall be determined by the relevant claims.
Claims
1. A method for efficiently preparing high-chlorinated xylene from low-chlorinated xylene, as shown in reaction formula (I), wherein low-chlorinated xylene A and chlorine gas undergo a stepwise chlorination reaction via intermediate B or C under reaction conditions, and finally the product high-chlorinated xylene or hexachloroxylene D is obtained. in, x, y, m, and n are the numbers 0, 1, 2, or 3 respectively; the constraints are x + y = 3, m + n = 3, and y or n cannot be 0 at the same time. The raw material, low-chlorinated xylene A, is a single substance or a mixture thereof. The reaction conditions are independent of each other, namely, temperature and additives.
2. According to claim 1, the temperature is 25℃-200℃. The additives refer to reaction promoters, catalysts, and / or side reaction inhibitors. The representative structural formula of the low-chlorinated xylene A is as follows:
3. According to claim 1, the following compounds can be prepared via the process disclosed in this invention, but are not limited to:
4. According to claim 1, the hexachloro-p-xylene, hexachloro-m-xylene, or hexachloro-o-xylene prepared by the process disclosed in this invention can be used as raw materials to react with the corresponding aryl dicarboxylic acid to further prepare the corresponding terephthaloyl chloride, isophthaloyl chloride, or phthaloyl chloride.