Purification method of high-purity p-chloromethyl styrene

Abstract

The invention discloses a purification method of high-purity p-chloromethylstyrene, which mainly comprises the following steps: by taking p-chloromethylstyrene with the purity of lower than 90% as a main raw material, carrying out reflux water diversion, primary crystallization and secondary recrystallization to obtain p-chloromethylstyrene with the purity of higher than 99.5%. The method provided by the invention overcomes the conventional rectification purification operation, and avoids polymerization impurities caused by high temperature, serious influence on the yield and incapability of obtaining a high-purity product; according to the process, a new purification mode is adopted, a small amount of undehydrated raw materials are removed through reflux dehydration, the product purity is improved, two times of recrystallization impurity removal are conducted, mother liquor is continuously recycled and reused, the overall recovery rate can be improved, and parachloromethyl styrene is effectively purified to 99.5% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical material preparation, and particularly relates to a purification method for high-purity p-chloromethylstyrene. Background Art

[0002] Due to its special functional group structure, p-chloromethylstyrene has many important chemical properties, so it has very important applications in the chemical industry and is an indispensable chemical raw material. Its application fields include coatings, inks, pharmaceuticals, pesticides, dyes, pigments, etc.

[0003] Due to the wide application of polymer materials at the present stage, p-chloromethylstyrene has a very wide range of applications. Especially, high-purity products are used more widely and precisely. For example, p-chloromethylstyrene can be polymerized on the surface of a silicon material with double bonds, and then quaternized to prepare a new type of strong anion chromatography column packing; it can also be grafted onto the surface of carbon nanotubes after polymerization, realizing the chemical modification of carbon nanotubes; related derivatives of p-chloromethylstyrene can also be used as organic photosensitive materials to replace inorganic selenium photosensitive materials, etc.

[0004] However, due to the structure of p-chloromethylstyrene itself, isomer impurities and polymerization impurities are very likely to be generated during the production process, and it is very difficult to obtain a product with a purity greater than 95.0%.

[0005] There are mainly the following several synthesis or purification methods for chloromethylstyrene: 1. Using the phase transfer catalysis method, with p-chloromethyl-α-bromoethylbenzene and potassium hydroxide as raw materials, toluene as a solvent, and adding a phase transfer catalyst to synthesize p-chloromethylstyrene:

[0006] 2. Dissolving 1-(2-chloroethyl)-4-(chloromethyl)benzene in a tetrahydrofuran solvent and carrying out an elimination reaction under alkaline conditions to synthesize p-chloromethylstyrene:

[0007] 3. Under the catalysis of a Lewis acid, directly carrying out chloromethylation on styrene to obtain p-chloromethylstyrene:

[0008] This synthesis process has a short route and easily available raw materials, but the yield is low, and the direct chloromethylation has poor selectivity and difficult separation in the later stage, and it is not suitable for producing high-purity p-chloromethylstyrene. Summary of the Invention

[0009] The present invention overcomes the conventional distillation purification operation, avoiding the polymerization impurities caused by high temperature, which seriously affect the yield and cannot obtain high-purity products. This process uses a new purification method, removing a small amount of un-dehydrated raw materials by reflux dehydration to improve the product purity. Then, through two recrystallizations for impurity removal, the mother liquor is continuously recycled, which can not only improve the overall recovery rate but also effectively purify the product to over 99.5%.

[0010] The object of the present invention is to solve the problems in conventional distillation purification, such as the generation of a large amount of polymerization impurities and the difficulty in separating isomeric impurities. It can refine the crude product with a purity lower than 90% to over 99.5%, and the comprehensive recovery rate reaches over 60%.

[0011] To achieve the above object, the present invention discloses the following technical content: A purification method for high-purity p-chloromethylstyrene, characterized by the following steps: (1) Dehydration reaction: Using xylene with a volume of 5 - 10 times as the solvent, mixing the crude p-chloromethylstyrene and the polymerization inhibitor according to a weight ratio of 1:0.001 - 1:0.005, reacting at 100 - 135°C for 8 - 15 hours. After the reaction is completed, cool down and filter. Concentrate the mother liquor until there is basically no residual xylene, add methanol with a volume of 0.1 - 2 times, cool down to -20 - 0°C for crystallization. The mother liquor is recycled, and the wet product is dried to obtain the p-chloromethylstyrene after the first crystallization; (2) Second recrystallization: Using toluene as the solvent, the p-chloromethylstyrene after the first crystallization adsorbs impurities in the presence of the adsorbent, and then filters and crystallizes to obtain high-purity p-chloromethylstyrene. The polymerization inhibitor mentioned refers to p-tert-butylcatechol (TBC); the adsorbent mentioned refers to silica gel.

[0012] The second recrystallization mentioned in the present invention refers to using toluene with a volume of 1 - 3 times as the crystallization solvent, adding the p-chloromethylstyrene after the first crystallization into it, heating to 40 - 110°C and stirring to dissolve, then adding the adsorbent according to a weight ratio of 1:0.01 - 1:0.05 for mixing, maintaining the temperature at 40 - 110°C for 1 - 5 hours, then filtering. Cool down the mother liquor to -20 - 0°C for crystallization. The mother liquor is recycled, and the wet product is dried to obtain high-purity p-chloromethylstyrene.

[0013] The present invention further discloses the application of the purification method for high-purity p-chloromethylstyrene in effectively treating the crude p-chloromethylstyrene with a purity lower than 90%, or even lower. The experimental results show that through the first crystallization, the purity can be increased to 90 - 95%, and the recovery rate reaches 80 - 90%. After the second crystallization, the purity can be further increased to over 99.5%, and the recovery rate reaches 80 - 90%. The comprehensive recovery rate of the two crystallizations reaches over 60%.

[0014] A more detailed description of the present invention is as follows: First, the crude p-chloromethylstyrene with a purity lower than 90% is dehydrated first in the presence of xylene as a solvent to remove the undehydrated impurities, then filtered. After concentration, methanol is added for crystallization, and after drying, a primary refined product is obtained. Then, it is dissolved in toluene, adsorbed by silica gel, and then recrystallized, and after drying, p-chloromethylstyrene with a purity higher than 99.5% is obtained.

[0015] Dehydration reaction: Using xylene as a solvent, the crude p-chloromethylstyrene undergoes a dehydration reaction in the presence of an inhibitor. The specific formula is as follows: Using 5 - 10 times the volume of xylene as a solvent, the crude p-chloromethylstyrene and the inhibitor are mixed in a weight ratio of 1:0.001 - 1:0.005, kept at 100 - 135 °C for reaction for 8 - 15 hours. After the reaction is completed, the temperature is lowered and filtered. The mother liquor is concentrated until there is basically no xylene residue, 0.1 - 2 times the volume of methanol is added, the temperature is lowered to -20 - 0 °C for crystallization, the mother liquor is recycled and reused, and the wet product is dried to obtain the p-chloromethylstyrene of the first crystallization, with a yield of 80 - 90% and a purity of 90% - 95%.

[0016] (2) Secondary recrystallization: Using toluene as a solvent, the p-chloromethylstyrene of the first crystallization adsorbs impurities in the presence of an adsorbent, and then is filtered and crystallized to obtain high-purity p-chloromethylstyrene. Specifically as follows: Using 1 - 3 times the volume of toluene as the crystallization solvent, the p-chloromethylstyrene of the first crystallization is added thereto, heated to 40 - 110 °C and stirred for dissolution, and then an adsorbent is added in a weight ratio of 1:0.01 - 1:0.05 for mixing, kept at 40 - 110 °C for 1 - 5 hours, then filtered. The mother liquor is cooled to -20 - 0 °C for crystallization, the mother liquor is recycled and reused, and the wet product is dried to obtain high-purity p-chloromethylstyrene, with a yield of 80 - 90% and a purity greater than 99.5%.

[0017] The present invention mainly examines the refining process of the crude p-chloromethylstyrene. The key point is to solve the situation in the traditional production process where it is impossible to purify to more than 99%. The difficulty of the invention lies in using different refining processes to remove different impurities, especially isomer impurities with similar melting and boiling points, eliminating impurities with incomplete dehydration, and polymer impurities affected by high temperature.

[0018] The present invention makes the following investigations on the selection of inhibitors and adsorbents: (1)Common inhibitors for styrene and related products were investigated, such as: p-tert-butylcatechol (TBC), 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (4-hydroxy TEMPO), phenothiazine, etc. During the experiment, it was found that during the process of using 4-hydroxy TEMPO as an inhibitor, 4-5% of polymerization impurities were generated; during the process of using phenothiazine as an inhibitor, 3-4% of polymerization impurities were generated; while during the process of using TBC as an inhibitor, 1-2% of polymerization impurities were generated, showing an obvious inhibition effect.

[0019] (2)Common impurity adsorbents were investigated, such as: silica gel, activated carbon, activated alumina, etc. During the experiment, it was found that during the process of using silica gel as an adsorbent, the purity could be increased from 94% to over 99.5%; during the process of using activated carbon as an adsorbent, the purity could be increased from 94% to ~98%; during the process of using activated alumina as an adsorbent, the purity could be increased from 94% to ~96%. After comprehensive evaluation, silica gel had an obvious adsorption effect.

[0020] Conclusion: During the process of using TBC as an inhibitor, less polymerization impurities are generated; during the process of using silica gel as an adsorbent, the purification effect is the best.

[0021] The innovation points of the purification method of high-purity p-chloromethylstyrene disclosed in the present invention compared with the prior art are as follows: (1)The present invention uses xylene as a solvent and adds an appropriate amount of inhibitor, which can remove all the impurities that have not been completely eliminated, and at the same time remove a large amount of isomer impurities by one crystallization; at the same time, using a suitable adsorbent for impurity adsorption can effectively remove polymerization impurities, and the overall recovery rate is above 60%, and the purity is greater than 99.5%.

[0022] (2)The present invention can effectively process crude products with a purity lower than 90%, or even lower purity; at the same time, the purity after refining can reach above 99.5%; in addition, the recycling and rational utilization of the mother liquor can effectively increase the product recovery rate to above 60%. Specific Embodiments

[0023] The present invention will be described below through specific implementation examples. Unless otherwise specified, the technical means used in the present invention are all methods well-known to those skilled in the art. In addition, the implementation examples should be understood as illustrative rather than limiting the scope of the present invention. The essence and scope of the present invention are only defined by the claims. For those skilled in the art, various changes or modifications to the material components and dosages in these implementation examples without departing from the essence and scope of the present invention also belong to the protection scope of the present invention. The raw materials and reagents used in the present invention are all commercially available. Examples

[0024] Step 1: Charge 500 g of crude p - (chloromethyl)styrene (purity 84%) into a reaction flask, add 2500 g of xylene, and then add 1 g of p - tert - butylcatechol (TBC). Control the temperature at 125 - 135 °C and carry out reflux and water separation for 6 hours. Cool down to 50 - 60 °C, filter. The mother liquor is distilled under reduced pressure at 60 - 70 °C to remove xylene until no distillate is obtained. Then cool down, add 100 g of methanol, slowly cool down to - 20 - 15 °C, keep stirring for 2 h, filter, and dry under reduced pressure to obtain the once - crystallized p - (chloromethyl)styrene. Weigh it: 420 g, yield 84%, purity 94%.

[0025] Step 2: Charge 420 g of the once - crystallized p - (chloromethyl)styrene into a reaction flask, add 500 g of toluene, heat up to 40 - 50 °C until it dissolves clearly, add 15 g of silica gel, control the temperature at 40 - 50 °C, keep stirring for 2 hours, cool down and filter. The mother liquor is slowly cooled down to - 20 - 15 °C, keep stirring for 2 h, filter, and dry under reduced pressure to obtain high - purity p - (chloromethyl)styrene. Weigh it: 360 g, yield 85.7%, total yield 72.0%, purity 99.7%. Example

[0026] Step 1: Charge 1500 g of crude p - (chloromethyl)styrene (purity 82%) into a reaction flask, add 7500 g of xylene, and then add 20 g of p - tert - butylcatechol (TBC). Control the temperature at 125 - 135 °C and carry out reflux and water separation for 8 hours. Cool down to 50 - 60 °C, filter. The mother liquor is distilled under reduced pressure at 60 - 70 °C to remove xylene until no distillate is obtained. Then cool down, add 1500 g of methanol, slowly cool down to - 20 - 15 °C, keep stirring for 2 h, filter, and dry under reduced pressure to obtain the once - crystallized p - (chloromethyl)styrene. Weigh it: 1215 g, yield 81%, purity 93%.

[0027] Step 2: Charge 1215 g of the once - crystallized p - (chloromethyl)styrene into a reaction flask, add 2000 g of toluene, heat up to 40 - 50 °C until it dissolves clearly, add 200 g of silica gel, control the temperature at 40 - 50 °C, keep stirring for 2 hours, cool down and filter. The mother liquor is slowly cooled down to - 20 - 15 °C, keep stirring for 2 h, filter, and dry under reduced pressure to obtain high - purity p - (chloromethyl)styrene. Weigh it: 1015 g, yield 83.5%, total yield 67.7%, purity 99.6%. Example

[0028] Comparative experiment Conclusion: Through the optimization of the inhibitor and adsorbent in the present invention, the polymerization impurities can be effectively reduced to 1 - 2% during the reaction stage, while the purity of the crude product is increased to over 90%. Using silica gel for impurity adsorption during the purification process can increase the total yield to over 60% and the purity exceeds 99.5%. After the preferred embodiments of the detailed description, those skilled in the art can clearly understand that various changes and modifications can be made without departing from the scope and spirit of the above-mentioned patent application. Any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention all fall within the scope of the technical solution of the present invention. Moreover, the present invention is not limited by the implementation manners of the examples given in the specification.

Claims

1. A method for purifying high-purity p-chloromethylstyrene, characterized in that Proceed as follows: (1) Dehydration reaction: using 5 to 10 times the volume of xylene as solvent, the crude para-chloromethylstyrene and the polymerization inhibitor are mixed in a weight ratio of 1:0.001 to 1:0.005, and the mixture is kept at 100 to 135°C for reaction for 8 to 15 hours. After the reaction is completed, the mixture is cooled and filtered, and the mother liquor is concentrated until there is substantially no xylene residue. 0.1 to 2 times the volume of methanol is added, and the mixture is cooled to -20 to 0°C for crystallization. The mother liquor is recovered and reused, and the wet product is dried to obtain primary crystallized para-chloromethylstyrene; (2) Secondary recrystallization: using toluene as solvent, the primary crystallized p-chloromethylstyrene is subjected to adsorption of impurities in the presence of an adsorbent, and then filtered and crystallized to obtain high-purity p-chloromethylstyrene; the inhibitor is p-tert-butylcatechol (TBC); and the adsorbent is silica gel.

2. The method for purifying high-purity p-chloromethylstyrene according to claim 1, characterized in that The secondary recrystallization refers to using 1 to 3 times the volume of toluene as the crystallization solvent, and adding the primary crystallized p-chloromethylstyrene therein. The temperature is raised to 40-110°C and stirred to dissolve, and then the adsorbent is added in a weight ratio of 1:0.01-1:0.05 for mixing, and the temperature is kept at 40-110°C for 1-5 hours, and then filtered, the mother liquor is cooled to -20-0°C for crystallization, the mother liquor is recovered and reused, and the wet product is dried to obtain high-purity p-chloromethylstyrene.

3. Use of the high-purity p-chloromethylstyrene purification method according to claim 1 for effectively treating crude p-chloromethylstyrene with a purity of less than 90% or even lower purity.

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