A process for the catalytic chlorination of phenols

Abstract

The application discloses a method for synthesizing chlorinated phenol by catalytic chlorination, which comprises the following steps: reacting phenol with mixed gas of chlorine and air in water in the presence of a catalyst to obtain a chlorination reaction liquid, and then performing liquid separation and distillation dehydration on the chlorination reaction liquid to obtain a chlorinated phenol product. The method uses phenol as a raw material, and the reaction of the phenol with the mixed gas of chlorine and air in the presence of the catalyst can obviously improve the reaction rate while obtaining a higher reaction selectivity. After the improvement, pure oxygen and concentrated hydrochloric acid are no longer used, and a large amount of phenol-containing hydrochloric acid by-product is no longer generated, and the product quality and the product yield are greatly improved, and the method is more suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention relates to a method for synthesizing chlorophenols, and more particularly to a method for synthesizing chlorophenols by chlorination that can improve catalytic selectivity, belonging to the field of organic synthesis technology. Background Technology

[0002] Phenoxycarboxylic acid herbicides were the world's first commercially produced hormone-type selective herbicides and are the second most in-demand herbicides globally. They are environmentally friendly, have a short residual period, and low toxicity to humans and other organisms, rarely inducing resistance. They are mainly used in corn, wheat, rice, and other gramineous crops to control dicotyledonous weeds, sedges, and certain noxious weeds. The most widely used phenoxycarboxylic acid herbicide is 2,4-D, followed by MCPA.

[0003] 2,4-Dichlorophenol and 4-chloro-o-cresol are important intermediates in the synthesis of 2,4-D and MCPA, respectively. Currently, the common method for synthesizing 2,4-dichlorophenol and 4-chloro-o-cresol is to obtain them by chlorination of phenol and o-cresol with sulfuryl chloride or chlorine in the presence of a catalyst. This method produces a large amount of hydrochloric acid as a byproduct. Because hydrochloric acid contains phenol, it has an unpleasant and irritating odor, making it unusable for domestic use or as a raw material for the production of other products. It can only be disposed of as hazardous waste, resulting in the waste of byproduct hydrochloric acid and significantly increasing hazardous waste disposal costs. This approach is neither environmentally friendly nor economical.

[0004] In their paper "Highly Selective Synthesis of Chlorophenols under Microwave Irradiation," Yawen Xiong et al. studied the chlorination of o-cresol. They used copper chloride as a catalyst, hydrochloric acid as the chlorinating agent, and oxygen as the oxidant, achieving the selective chlorination synthesis of 4-chloro-o-cresol under microwave conditions with a selectivity of 91.7%. This research represents a significant step forward in the study of phenol chlorination processes that do not produce hydrochloric acid as a byproduct, and has great practical significance. However, we also note that their research still has many problems: (1) the selectivity still has room for improvement; (2) pure oxygen is required instead of the cheaper and more readily available air, resulting in higher costs; (3) microwave activation of the reactants is necessary, otherwise the reaction rate is very slow, and even after activation, the reaction rate is not ideal, resulting in low industrial value; (4) concentrated hydrochloric acid is consumed, but a large amount of difficult-to-use dilute hydrochloric acid is produced. These drawbacks, especially the slow reaction rate, severely limit its industrial application. Summary of the Invention

[0005] To address the above technical problems, this invention provides a method for the catalytic chlorination synthesis of chlorophenols based on a thorough and scientific analysis of the reaction mechanism. This method improves the selectivity of the chlorination reaction, increases the reaction rate, uses inexpensive and readily available raw materials, does not produce large amounts of difficult-to-process byproducts, and is more suitable for industrial production.

[0006] The specific technical solution of this invention is as follows:

[0007] A method for catalytic chlorination to synthesize chlorophenols, the method comprising the step of reacting phenol in water with a mixture of chlorine and air in the presence of a catalyst to obtain a chlorinated reaction solution.

[0008] Furthermore, in actual operation, phenol, water and catalyst are first mixed, then the mixture is heated to the reaction temperature, and a mixture of chlorine and air is continuously introduced into the mixture under vigorous stirring until the conversion rate of phenol reaches the expected value. Then the mixing is stopped and the reaction stops.

[0009] Furthermore, when the phenol conversion rate reaches 99% or higher, the phenol conversion is considered complete, reaching the expected value. The phenol conversion rate can be calculated by monitoring the reaction progress using gas chromatography (GC).

[0010] Furthermore, the phenol is one of phenol, 2-chlorophenol, 4-chlorophenol, and o-cresol. When the phenol is phenol, the main chlorination product is 2,4-dichlorophenol (the reaction can also be controlled so that the main product is 4-chlorophenol); when the phenol is 2-chlorophenol, the main chlorination product is 2,4-dichlorophenol; when the phenol is 4-chlorophenol, the main chlorination product is 2,4-dichlorophenol; when the phenol is o-cresol, the main chlorination product is 4-chloro-o-cresol.

[0011] Furthermore, the catalyst is a mixture of two different types of first and second catalysts. The first catalyst is one or both of cupric chloride and cuprous chloride; the second catalyst is one or both of 2,2'-bipyridine and 4,4'-bipyridine.

[0012] Furthermore, the amount of the first catalyst is 1% to 5% of the weight of phenol, for example, 1%, 2%, 3%, 4%, 5%, with a preferred amount of 1% to 3%.

[0013] Furthermore, the amount of the second catalyst is 0.5% to 2.5% of the weight of phenol, for example 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, with a preferred amount of 0.5% to 1.5%.

[0014] Furthermore, in the gas mixture, the volume ratio of air to chlorine is 1.25–1.5:1, for example, 1.25:1, 1.3:1, 1.35:1, 1.4:1, 1.45:1, or 1.5:1. Air acts as the oxidant, and chlorine acts as the chlorinating agent. The amount of air should not be too high, as this will reduce the utilization rate of chlorine; conversely, the amount of air should not be too low, otherwise, excessive hydrochloric acid will be generated.

[0015] Furthermore, the mixed gas is introduced into the mixture of phenol, water, and catalyst at a certain rate. To increase the reaction rate and shorten the reaction time, the rate of introduction of the mixed gas can be increased. In addition, to ensure sufficient contact and reaction between the mixed gas and the phenol in the liquid environment, the mixed gas can be introduced using methods disclosed in the prior art, such as introducing it from the bottom of the mixture, through a gas distributor, through a suction stirrer, through a Venturi device, or under turbine stirring. The reactor type can be a batch reactor, a microchannel reactor suitable for gas-liquid reactions, a packed tower, a plate tower, a bubble column, a centrifugal device, etc.

[0016] The mixed gas is added under vigorous stirring to increase the contact efficiency with phenol and improve the reaction efficiency. The stirring speed is preferably greater than or equal to 600 r / min, such as any value or a range between 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1200 r / min, 1500 r / min, 1800 r / min, 2000 r / min, 2500 r / min, and 3000 r / min. A stirring speed that is too low will significantly reduce the gas-liquid reaction rate.

[0017] Furthermore, the reaction temperature is 50–80°C, for example, 50°C, 60°C, 70°C, or 80°C. The higher the reaction temperature, the lower the selectivity of the reaction; preferably, it is 50–60°C. At the preferred temperature, the reaction selectivity is higher.

[0018] Furthermore, the reaction time is generally 0.25 to 1.0 hours.

[0019] Furthermore, the amount of water used is typically 1 to 5 times the mass of phenol, for example, 1, 2, 3, 4, or 5 times. Excessive water usage will lead to a decrease in the single-pass yield of the product. Preferably, the amount of water used is 1 to 3 times the mass of phenol, and particularly preferably, it is 1 to 1.5 times the mass of phenol.

[0020] Furthermore, after obtaining the chlorination reaction solution, the process also includes the steps of separating the chlorination reaction solution to obtain crude chlorophenol and dehydrating the crude chlorophenol to obtain the finished chlorophenol product. The chlorination reaction solution is allowed to stand and separate at a certain temperature, with the lower oil phase being the crude chlorophenol product and the upper phase being the aqueous phase; the obtained crude chlorophenol product is then dehydrated by distillation to obtain the finished chlorophenol product.

[0021] Furthermore, the separation temperature is 50-60℃. Too high a temperature is not conducive to separation, while too low a temperature may cause the phenol in the material to crystallize.

[0022] Furthermore, dehydration is preferably carried out under vacuum or reduced pressure at a temperature of 80–100°C. Too low a temperature will make it difficult to remove moisture, while too high a temperature may cause a small amount of chlorophenol to deteriorate. The absolute pressure of the system during dehydration is generally 3–5 kPa.

[0023] The preparation method provided by this invention has the following advantages:

[0024] 1) The method provided by the present invention significantly improves the selectivity of the reaction by using a synergistic catalyst, and at the same time greatly accelerates the reaction rate, so that the reaction can be completed within one hour, making it easier to industrialize.

[0025] 2) The method provided by the present invention does not require the use of oxygen, but uses a mixture of chlorine and air. Both chlorine and air are widely available materials with low cost.

[0026] 3) The method provided by this invention no longer uses hydrochloric acid as a chlorine source, and also no longer produces hydrochloric acid as a byproduct, thus solving the problem that conventional chlorophenol synthesis methods produce a large amount of phenol-containing hydrochloric acid as a byproduct.

[0027] 4) The method provided by this invention uses phenol as a raw material and reacts it with a mixture of chlorine and air under the action of a catalyst. While obtaining a high reaction selectivity, it significantly improves the reaction rate, eliminates the use of pure oxygen and concentrated hydrochloric acid, and eliminates the production of large amounts of phenol-containing hydrochloric acid as a byproduct. It also greatly improves product quality and product yield.

[0028] 5) The method provided by this invention is simple and easy to implement, with a selectivity of over 97.0% and a purity of over 97.0% for chlorophenol. Detailed Implementation

[0029] To further illustrate the present invention, the preparation method of chlorophenol provided by the present invention will be described in detail below with reference to specific embodiments.

[0030] Unless otherwise specified, all concentrations mentioned in the following embodiments are mass percentage concentrations.

[0031] Example 1

[0032] 108.4 g of 98.64% o-cresol, 109.9 g of water, 1.1 g of copper chloride, and 0.5 g of 4,4'-bipyridine were added to a 500 mL four-necked flask equipped with a suction stirrer. The mixture was heated to 50 °C with stirring, and the suction stirrer speed was adjusted to 800 r / min. Air and chlorine were mixed uniformly through a packed mixer at a volume ratio of 1.3:1 and a flow rate of 0.9 L / min. After about 1 minute of aeration, a significant temperature rise was observed in the flask. The mixture was cooled using an ice-water bath, and the reaction temperature was maintained at 50–55 °C. Samples were taken periodically during the reaction, and GC was used for monitoring. When the o-cresol conversion rate was ≥99%, the aeration was stopped. The total aeration time was 59 minutes, and the reaction was continued at this temperature for another 15 minutes to obtain the chlorinated reaction solution. The chlorinated reaction solution was sampled and analyzed by GC. The selectivity of 4-chloro-o-cresol was calculated to be 98.3%.

[0033] Reduce the stirring speed to 150 r / min, heat the chlorination reaction solution to about 55°C, stop stirring, and let it stand for 15 min while maintaining the temperature. Transfer it to a separatory funnel, let it stand for 15 min, separate the layers, and the lower oil phase is the crude chlorophenol.

[0034] The obtained crude chlorophenol was transferred to a clean 250mL four-necked flask, connected to a distillation apparatus, and heated to 80℃ under stirring at 3-5kPa absolute pressure for distillation and dehydration. A small amount of fraction (water and trace amounts of phenol) was distilled off at a gas phase temperature of approximately 32℃. As water was distilled off, the material temperature slowly rose from 80℃. When the material temperature reached 100℃, the water was almost completely distilled off, and the remaining material in the flask was 4-chloro-o-cresol. The product was weighed, yielding 139.1g of 4-chloro-o-cresol. Quantitative analysis using HPLC showed a content of 98.4%, and the product yield, calculated as o-cresol, was 97.1%.

[0035] Example 2

[0036] Add 98.7g of 98.23% phenol, 191.7g of water, 4.7g of cuprous chloride, and 0.9g of 2,2'-bipyridine to a 500mL four-necked flask equipped with a suction stirrer. Heat to 80℃ with stirring, adjust the suction stirrer speed to 1000r / min, and mix air and chlorine at a volume ratio of 1.3:1 using a packing mixer at a flow rate of 6.7L / min. After uniform mixing, the mixture is uniformly introduced into the flask. After about 1 minute of aeration, a significant temperature rise is observed in the flask. Cool using an ice-water bath and maintain the reaction temperature at 75–80℃. Samples are taken periodically during the reaction and monitored using GC. When the phenol conversion rate is ≥99%, aeration is stopped. A total of 16 minutes of aeration is performed, followed by continued temperature control for approximately 15 minutes to obtain the chlorinated reaction solution. Samples of the chlorinated reaction solution are taken and analyzed by GC. The selectivity of 2,4-dichlorophenol is calculated to be 97.1%.

[0037] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 164.5 g of 2,4-dichlorophenol product. Quantitative analysis by HPLC showed that the content was 97.6%, and the product yield was calculated to be 95.6% based on phenol.

[0038] Example 3

[0039] Add 127.9g of 98.45% 2-chlorophenol, 391.9g of water, 5.2g of copper chloride, and 2.2g of 2,2'-bipyridine to a 500mL four-necked flask equipped with a suction stirrer. Heat to 70℃ with stirring, adjust the suction stirrer speed to 600r / min, and mix air and chlorine at a volume ratio of 1.3:1 using a packing mixer at a flow rate of 2.2L / min. After uniform mixing, the mixture is uniformly introduced into the flask. After about 1 minute of aeration, a significant temperature rise is observed in the flask. Cool using an ice-water bath and maintain the reaction temperature at 65–70℃. During the reaction, samples are taken periodically and monitored using GC. When the conversion rate of 2-chlorophenol is ≥99%, stop the aeration. A total of 24 minutes of aeration was performed, followed by continued temperature control for about 15 minutes to obtain the chlorinated reaction solution. The chlorination reaction solution was sampled and analyzed by GC. The selectivity of 2,4-dichlorophenol was calculated to be 97.8%.

[0040] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 155.8 g of 2,4-dichlorophenol product. Quantitative analysis by HPLC showed that the content was 98.3%, and the product yield was calculated to be 95.9% based on phenol.

[0041] Example 4

[0042] Add 133.3g of 98.17% 4-chlorophenol, 523.6g of water, 3.9g of cuprous chloride, and 1.4g of 4,4'-bipyridine to a 500mL four-necked flask equipped with a suction stirrer. Heat to 60℃ with stirring, adjust the suction stirrer speed to 800r / min, and mix air and chlorine at a volume ratio of 1.3:1 using a packing mixer at a flow rate of 2.5L / min. After uniform mixing, the mixture is uniformly introduced into the flask. After about 1 minute of aeration, a significant temperature rise is observed in the flask. Cool using an ice-water bath and maintain the reaction temperature at 55–60℃. During the reaction, samples are taken periodically and monitored using GC. When the conversion rate of 4-chlorophenol is ≥99%, stop the aeration. A total of 22 minutes of aeration was performed, followed by continued temperature control for approximately 15 minutes to obtain the chlorinated reaction solution. The chlorination reaction solution was sampled and analyzed by GC. The selectivity of 2,4-dichlorophenol was calculated to be 98.3%.

[0043] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 161.5 g of 2,4-dichlorophenol product. Quantitative analysis by HPLC showed that the content was 98.7%, and the product yield was calculated to be 96.1% based on phenol.

[0044] Example 5

[0045] Add 93.6 g of 98.23% phenol, 459.7 g of water, 1.9 g of copper chloride, and 1.8 g of 4,4'-bipyridine to a 500 mL four-necked flask equipped with a suction stirrer. Heat to 50 °C with stirring. Adjust the suction stirrer speed to 800 r / min. Mix air and chlorine gas at a volume ratio of 1.3:1 using a packed mixer at a flow rate of 1.9 L / min, then uniformly introduce the mixture into the flask. After approximately 1 minute of aeration, a significant temperature rise is observed in the flask. Cool using an ice-water bath and maintain the reaction temperature at 50–55 °C. Periodically sample and monitor the reaction using GC. When the phenol conversion rate is ≥99%, stop the aeration. A total of 55 minutes of aeration was performed, followed by a continued incubation for approximately 15 minutes to obtain the chlorinated reaction solution. Sample the chlorinated reaction solution and perform GC analysis. The selectivity of 2,4'-dichlorophenol was calculated to be 98.6%.

[0046] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 154.6 g of 2,4-dichlorophenol product. Quantitative analysis by HPLC showed that the content was 99.2%, and the product yield was calculated to be 96.3% based on phenol.

[0047] Examples 6-11

[0048] Add 98.64% o-cresol, water, copper chloride, and 4,4'-bipyridine to a 500 mL four-necked flask equipped with a suction stirrer. Raise the mixture to the reaction temperature with stirring, and adjust the suction stirrer speed to 800 rpm. Mix air and chlorine at a volume ratio of 1.4:1 using a packed mixer at a flow rate of 2.1 L / min, and then uniformly introduce the mixture into the flask. After approximately 1 minute of aeration, a significant temperature rise is observed in the flask. Cool the mixture using an ice-water bath while maintaining the reaction temperature. Samples are taken periodically during the reaction and monitored using GC. Stop aeration when the o-cresol conversion rate is ≥99%. A total of 26 minutes of aeration was completed, followed by a 15-minute incubation period to obtain the chlorinated reaction solution. Samples of the chlorinated reaction solution are then analyzed by GC, and the selectivity of 4-chloro-o-cresol is calculated.

[0049] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 4-chloro-o-cresol product. Quantitative analysis was performed using HPLC to obtain the content and yield.

[0050] 4-Chloro-o-cresol was prepared according to the conditions in Table 1, and the results are shown in Table 2.

[0051]

[0052]

[0053] Examples 12-14

[0054] Add 98.64% o-cresol, water, cuprous chloride, and 4,4'-bipyridine to a 500 mL four-necked flask equipped with a suction stirrer. Heat to 50°C with stirring, and adjust the suction stirrer speed to 800 rpm. Mix air and chlorine at a volume ratio of 1.4:1 using a packed mixer at a flow rate of 2.1 L / min, and then uniformly introduce the mixture into the flask. After approximately 1 minute of aeration, a significant temperature rise is observed in the flask. Cool using an ice-water bath, maintaining the reaction temperature at 50°C. Samples are taken periodically during the reaction and monitored using GC. When the o-cresol conversion rate is ≥99%, aeration is stopped. A total of 27 minutes of aeration is completed, followed by a 15-minute incubation period to obtain the chlorinated reaction solution. Samples of the chlorinated reaction solution are then analyzed by GC, and the selectivity of 4-chloro-o-cresol is calculated.

[0055] The chlorination reaction solution was post-processed according to the method in Example 1 to obtain 4-chloro-o-cresol product. Quantitative analysis was performed using HPLC to obtain the content and yield.

[0056] 4-Chloro-o-cresol was prepared according to the conditions in Table 3, and the results are shown in Table 4.

[0057]

[0058]

[0059] Comparative Example 1

[0060] 4-Chloro-o-cresol was prepared according to the method in Example 1, except that 4,4'-bipyridine was not added, and 1.1 g of copper chloride was replaced with 1.6 g of copper chloride. The results showed that the product contained 91.4% 4-chloro-o-cresol, and the yield was 89.8% based on o-cresol.

[0061] Comparative Example 2

[0062] 4-Chloro-o-cresol was prepared according to the method in Example 1, except that copper chloride was not added, and 0.5 g of 4,4'-bipyridine was replaced with 1.6 g of 4,4'-bipyridine. The results showed that the product contained 78.7% 4-chloro-o-cresol, and the yield was 76.5% based on o-cresol.

[0063] Comparative Example 3

[0064] 4-Chloro-o-cresol was prepared according to the method in Example 1, except that 1.1 g of copper chloride was replaced with 1.1 g of copper sulfate. The results showed that the product contained 84.1% 4-chloro-o-cresol, and the yield based on o-cresol was 82.1%.

[0065] Comparative Example 4

[0066] 4-Chloro-o-cresol was prepared according to the method in Example 1, except that 0.5 g of 4,4'-bipyridine was replaced with 0.5 g of pyridine. The results showed that the product contained 92.2% 4-chloro-o-cresol, and the yield (based on o-cresol) was 90.3%.

[0067] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principle of the present invention. For example, chlorophenols in the chlorination reaction solution can also be separated by extraction + distillation or extraction + back-extraction, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for the catalytic chlorination synthesis of chlorophenols, characterized in that: The method includes the step of reacting phenol in water with a mixture of chlorine and air in the presence of a catalyst to obtain a chlorinated reaction solution; the catalyst is a mixture of a first catalyst and a second catalyst, wherein the first catalyst is one or both of copper chloride and cuprous chloride, and the second catalyst is one or both of 2,2'-bipyridine and 4,4'-bipyridine; the phenol is one of phenol, 2-chlorophenol, 4-chlorophenol, and o-cresol; when the phenol is phenol, the main chlorination product is 2,4-dichlorophenol or 4-chlorophenol; when the phenol is 2-chlorophenol, the main chlorination product is 2,4-dichlorophenol; when the phenol is 4-chlorophenol, the main chlorination product is 2,4-dichlorophenol; when the phenol is o-cresol, the main chlorination product is 4-chloro-o-cresol.

2. The preparation method according to claim 1, characterized in that: The amount of the first catalyst is 1% to 5% of the weight of phenol, and the amount of the second catalyst is 0.5% to 2.5% of the weight of phenol.

3. The preparation method according to claim 1, characterized in that: The volume ratio of air to chlorine is 1.25 to 1.5:

1.

4. The preparation method according to claim 1, characterized in that: The reaction temperature is 50–80℃.

5. The preparation method according to claim 1, characterized in that: The amount of water used is 1 to 5 times the mass of phenol.

6. The preparation method according to claim 1, characterized in that: It also includes the step of separating the chlorination reaction solution and dehydrating the crude chlorophenol obtained from the separation to obtain the chlorophenol product.

7. The preparation method according to claim 6, characterized in that: The separation temperature is 50–60℃.

8. The preparation method according to claim 6, characterized in that: Dehydration is achieved by distillation at a temperature of 80–100°C.

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