A method for dechlorination reduction of 2-chloro-6-fluorobenzyl trichloride

Abstract

The present invention provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, using 2-chloro-6-fluorobenzyl trichloride as a starting material, and carrying out a dechlorination reduction reaction with ethylenediaminetetraacetic acid disodium salt under the action of a solvent and a catalyst to obtain a reaction mixture; the reaction mixture is separated by distillation and rectification to obtain products 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl monochloride. The 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method of the present invention has the characteristics of simple process, high product yield and excellent quality, which not only solves the problem of by-product outlet, but also can significantly reduce the production cost of 2-chloro-6-fluorobenzyl monochloride or 2-chloro-6-fluorobenzyl dichloride, with good economic and social benefits. The present invention adds a synthetic route that reduces raw material costs and is more concise to the synthesis of 2-chloro-6-fluorobenzyl dichloride, and the resulting 2-chloro-6-fluorobenzyl dichloride can be used for the synthesis of 2-chloro-6-fluorobenzaldehyde in a conventional manner.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals and relates to a synthesis and purification technology of fine pharmaceutical intermediates, in particular to a dechlorination reduction method of 2-chloro-6-fluorobenzyltrichloride with simple process, high product yield and reduced cost. Background Art

[0002] 2-Chloro-6-fluorobenzaldehyde is a key intermediate of the human antibiotic flucloxacillin sodium, with an annual global demand of about 1,000 tons. There are two main production routes for 2-chloro-6-fluorobenzaldehyde. The first is to use 3-chloro-2-methylaniline as the raw material, through diazo and fluorination, to produce 2-chloro-6-fluorotoluene, and then through photochlorination, distillation and hydrolysis. The second is to use toluene as the raw material, through chlorination and distillation to produce 2,6-dichlorotoluene, and then through fluorination and distillation to obtain 2-chloro-6-fluorotoluene, and finally through photochlorination, distillation and hydrolysis.

[0003] The two process routes each have their own advantages, but due to the strict control of impurities in drugs, the impurities related to the second production route are difficult to control, and the conversion efficiency is also very low, and there is no practical industrial value. Currently, the first route is used for production both at home and abroad.

[0004] In the photochlorination process of 2-chloro-6-fluorotoluene, in order to control the conversion efficiency of chlorination and the energy consumption of distillation, about 3% of the raw materials are converted into 2-chloro-6-fluorobenzyl trichloride, resulting in raw material loss and a large amount of by-products that cannot be recycled and can only be disposed of as hazardous waste.

[0005] Of course, 2-chloro-6-fluorobenzoic acid can also be prepared by catalytic hydrolysis of 2-chloro-6-fluorobenzyl trichloride, but 2-chloro-6-fluorobenzoic acid is a pharmaceutical intermediate, and customers have strict requirements on product quality. The specific quality indicators are as follows: 2-chloro-6-fluorobenzoic acid content is greater than 99.5%, related single impurities are less than 0.2%, melting point is 156-158°C, and residue is less than 0.5%.

[0006] Since the isomer 5-chloro-2-methylaniline of the raw material 3-chloro-2-methylaniline for producing 2-chloro-6-fluorotoluene is difficult to be completely removed during the production process (currently, the process combining rectification and recrystallization can only control it to below 0.3%), the obtained 2-fluoro-6-fluorotoluene contains about 0.3% of 4-fluoro-2-fluorotoluene. However, since the steric hindrance of 4-fluoro-2-fluorotoluene is smaller than that of 2-fluoro-6-fluorotoluene, the methyl groups on the side chain are more easily chlorinated and all of them are converted into 4-chloro-2-fluorobenzyl trichloride (converted into 4-chloro-2-fluorobenzoic acid after hydrolysis), although it has no effect on the quality of 2-chloro-6-fluorobenzaldehyde, it directly affects the quality of the by-product 2-chloro-6-fluorobenzoic acid.

[0007] Due to the above reasons, the by-product acid impurity content in the production process of 2-chloro-6-fluorobenzaldehyde is high (the main impurities are 2-chloro-6-fluorobenzaldehyde, 4-chloro-2-fluorobenzoic acid, tar, sodium sulfate and sodium chloride, etc.). Due to the lack of suitable refining and purification methods before, it cannot be commercialized. A large amount of by-product acid can only be temporarily stored in warehouses or disposed of as hazardous waste, resulting in waste of resources and environmental pollution.

[0008] Previously, in order to solve the technical difficulties in the current prior art, the inventors have tried to purify 2-chloro-6-fluorobenzoic acid by using methods such as up-chemical method, macroporous resin adsorption method, acid-base recrystallization method, extraction method and methanol recrystallization method, but none of them were successful, either because of low yield, serious pollution or product quality that did not meet the requirements. At the same time, even if high-purity 2-chloro-6-fluorobenzoic acid is made, the market demand is very small.

[0009] 2-Chloro-6-fluorobenzyltrichloride is a byproduct of the production of 2-chloro-6-fluorobenzaldehyde, with a general content of ≥90%, 2-chloro-6-fluorobenzyl dichloride content ≤5%, and the rest are other impurities. If 2-chloro-6-fluorobenzyltrichloride can be converted into 2-chloro-6-fluorobenzyl chloride or 2-chloro-6-fluorobenzyl dichloride by reduction dechlorination, it can be used as a resource, which not only reduces production costs, but also reduces the amount of three wastes. Summary of the invention

[0010] In order to solve the above problems, the present invention provides a dechlorination reduction method for 2-chloro-6-fluorobenzyltrichloride. The inventors have found through a large number of experimental studies that 2-chloro-6-fluorobenzyltrichloride can undergo a dechlorination reduction reaction with ethylenediaminetetraacetic acid disodium salt under the action of a solvent and a catalyst to obtain 2-chloro-6-fluorobenzyldichloride and 2-chloro-6-fluorobenzylmonochloride. The method has the characteristics of simple process, high product yield and excellent quality.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] The invention provides a 2-chloro-6-fluorobenzyltrichloride dechlorination reduction method. 2-chloro-6-fluorobenzyltrichloride is used as a starting material, and a dechlorination reduction reaction is carried out with ethylenediaminetetraacetic acid disodium salt under the action of a solvent and a catalyst to obtain a reaction mixture; the reaction mixture is separated by distillation and rectification to obtain products 2-chloro-6-fluorobenzyldichloride and 2-chloro-6-fluoromonochlorobenzyl.

[0013] As a preferred embodiment of the present invention, the 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method comprises the following steps:

[0014] 1) 2-chloro-6-fluorobenzyl trichloride as a starting material is heated until it melts, and then put into a reaction kettle;

[0015] 2) adding a solvent, a catalyst and ethylenediaminetetraacetic acid disodium salt into a reaction kettle, then heating to 190-200° C. for reaction, monitoring the reaction progress by gas chromatography, and stopping the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reaction kettle is ≤5.0% (excluding the solvent), thereby obtaining a reacted material I;

[0016] 3) The reaction material I obtained in step 2) is subjected to reduced pressure distillation to obtain a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle is disposed of as hazardous waste; the temperature of the reduced pressure distillation does not exceed 180°C.

[0017] 4) The mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochlorochloride, 2-chloro-6-fluorobenzyl dichlorochloride and 2-chloro-6-fluorobenzyl trichlorochloride obtained by distillation in step 3) is transferred into a distillation kettle for vacuum distillation, and the top fraction is collected to obtain 2-chloro-6-fluorobenzyl monochlorochloride and 2-chloro-6-fluorobenzyl dichlorochloride, respectively. The bottom residue is a mixture of 2-chloro-6-fluorobenzyl trichlorochloride and paraffin oil.

[0018] As a preferred embodiment of the present invention, in step 2), the solvent is paraffin oil.

[0019] As a preferred embodiment of the present invention, in step 2), the catalyst is ferric chloride.

[0020] As a preferred embodiment of the present invention, in step 2), the weight ratio of the solvent to the 2-chloro-6-fluorobenzyltrichloride is 0.5-1.0:1.

[0021] As a preferred embodiment of the present invention, in step 2), the weight ratio of the 2-chloro-6-fluorobenzyl trichloride to the disodium salt of ethylenediaminetetraacetic acid is 8-12:1.

[0022] As a preferred embodiment of the present invention, in step 3), the vacuum degree of the reduced pressure distillation is -0.090 MPa to -0.01 MPa, and when collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C, and the top temperature is 120-130°C; when collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C, and the top temperature is 130-134°C.

[0023] As a preferred embodiment of the present invention, when the 2-chloro-6-fluorobenzyl monochloroate obtained by distillation in step 4) is used to produce the pesticide flumetralin, the content of 2-chloro-6-fluorobenzyl monochloroate is greater than 99.5%, and the content of 2-chloro-6-fluorobenzyl dichloroate is less than 0.2%.

[0024] As a preferred embodiment of the present invention, when the 2-chloro-6-fluorobenzyl dichloride obtained by distillation in step 4) is used to produce 2-chloro-6-fluorobenzaldehyde through catalytic hydrolysis, the content of 2-chloro-6-fluorobenzyl monochloride is less than 0.1%, the content of 2-chloro-6-fluorobenzyl dichloride is greater than 99%, and the content of 2-chloro-6-fluorobenzyl trichloride is less than 1%.

[0025] As a preferred embodiment of the present invention, the bottom liquid mixture obtained by distillation in step 4) is returned to step 2) to replace the solvent.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method of the present invention has the characteristics of simple process, high product yield and excellent quality, which not only solves the problem of by-product outlet, but also can significantly reduce the production cost of 2-chloro-6-fluorobenzyl monochloride or 2-chloro-6-fluorobenzyl dichloride, and has good economic and social benefits. Therefore, the present invention adds a synthetic route that reduces raw material costs and is more concise to the synthesis of 2-chloro-6-fluorobenzyl dichloride. The 2-chloro-6-fluorobenzyl dichloride obtained by the present invention can be used for the synthesis of 2-chloro-6-fluorobenzaldehyde in a conventional manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0029] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The raw material of the present invention: 2-chloro-6-fluorobenzyl trichloride is a by-product of producing 2-chloro-6-fluorobenzaldehyde and is obtained by vacuum distillation; the content is 90%.

[0032] Paraffin oil, technical grade, commercially available.

[0033] Ethylenediaminetetraacetic acid disodium salt, technical grade, commercially available.

[0034] Catalyst (ferric chloride), technical grade, commercially available.

[0035] See also Figure 1 The present invention provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, comprising the following steps:

[0036] 1) 2-chloro-6-fluorobenzyl trichloride as a starting material is heated until it melts, and then put into a reaction kettle;

[0037] 2) adding a solvent, a catalyst and ethylenediaminetetraacetic acid disodium salt into a reaction kettle, then heating to 190-200° C. for reaction, monitoring the reaction progress by gas chromatography, and stopping the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reaction kettle is ≤5.0% (excluding the solvent), thereby obtaining a reacted material I;

[0038] 3) The reaction material I obtained in step 2) is subjected to reduced pressure distillation to obtain a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle is disposed of as hazardous waste; the temperature of the reduced pressure distillation does not exceed 180°C.

[0039] 4) The mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochlorochloride, 2-chloro-6-fluorobenzyl dichlorochloride and 2-chloro-6-fluorobenzyl trichlorochloride obtained by distillation in step 3) is transferred into a distillation kettle for vacuum distillation, and the top fraction is collected to obtain 2-chloro-6-fluorobenzyl monochlorochloride and 2-chloro-6-fluorobenzyl dichlorochloride, respectively. The bottom residue is a mixture of 2-chloro-6-fluorobenzyl trichlorochloride and paraffin oil.

[0040] Example 1

[0041] See also Figure 1 This embodiment provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, which comprises the following steps in sequence:

[0042] The following steps are included in sequence:

[0043] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0044] 2) Add 500 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor reaches 4.0-5.0% (excluding the solvent) to obtain the reacted material I;

[0045] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0046] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0047] The reaction time is 2.5h.

[0048] After the reaction, the content of 2-chloro-6-fluorobenzyl trichloride in material I was 4.12% (excluding the solvent).

[0049] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1174 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0050] The temperature of the reduced pressure distillation does not exceed 180°C.

[0051] The mixture obtained by vacuum distillation contained 32.53% paraffin oil, 5.54% 2-chloro-6-fluorobenzyl monochloride, 56.05% 2-chloro-6-fluorobenzyl dichloride and 3.83% 2-chloro-6-fluorobenzyl trichloride, and 2.04% impurities.

[0052] 4) Transfer 1174 kg of the mixture obtained by distillation in step 3) into a distillation kettle for vacuum distillation, collect the top fraction, and obtain 65 kg of 2-chloro-6-fluorobenzyl chloride, 664 kg of 2-chloro-6-fluorobenzyl dichloride, and 445 kg of bottom residue;

[0053] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0054] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0055] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0056] The distillation yielded 65 kg of 2-chloro-6-fluorobenzyl monochlorochloride, of which the main content was 99.58%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.18%, and the rest was impurities.

[0057] The distillation yielded 664 kg of 2-chloro-6-fluorobenzyl dichloride, of which the main content was 99.12%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.13%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.53%, and the rest were impurities.

[0058] 445 kg of the residual liquid at the bottom of the distillation kettle mainly contains 2-chloro-6-fluorobenzyl trichloride and paraffin oil, of which the content of 2-chloro-6-fluorobenzyl trichloride is 9.21%, the content of paraffin oil is 85.84%, and the rest is other impurities, which can be returned to step 1) to replace paraffin oil and part of the raw materials.

[0059] 5) The 664 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 99.82%, the content of 2-chloro-6-fluorobenzyl monochloride is 0.08%, and the content of 2-chloro-6-fluorobenzoic acid is 0.06%.

[0060] Example 2

[0061] The residual amount of 2-chloro-6-fluorobenzyltrichloride in the material after the reaction in step 2) of Example 1 was increased from 4.12% to 4.98%, and the rest was the same as Example 1.

[0062] See also Figure 1 This embodiment provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, which comprises the following steps in sequence: 1) heating 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then putting it into a reaction kettle;

[0063] 2) Add 500 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor reaches 4.0-5.0% (excluding the solvent) to obtain the reacted material I;

[0064] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0065] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0066] The reaction time is 2.5h.

[0067] After the reaction, the content of 2-chloro-6-fluorobenzyl trichloride in material I is 4.98% (excluding the solvent).

[0068] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1182 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0069] The temperature of the reduced pressure distillation does not exceed 180°C.

[0070] The mixture obtained by vacuum distillation contained 32.32% paraffin oil, 1.10% 2-chloro-6-fluorobenzyl monochloride, 60.32% 2-chloro-6-fluorobenzyl dichloride and 4.57% 2-chloro-6-fluorobenzyl trichloride, and the rest were impurities.

[0071] 4) Transfer 1182 kg of the mixture obtained by distillation in step 3) into a distillation kettle for vacuum distillation, collect the top fraction, and obtain 13 kg of 2-chloro-6-fluorobenzyl chloride, 718 kg of 2-chloro-6-fluorobenzyl dichloride, and 451 kg of bottom liquid;

[0072] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0073] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0074] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0075] 13 kg of 2-chloro-6-fluorobenzyl monochloride was obtained by distillation, of which the main content was 99.63%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.12%, and the rest were impurities.

[0076] The distillation yielded 718 kg of 2-chloro-6-fluorobenzyl dichloride, of which the main content was 99.26%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.11%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.53%, and the rest were impurities.

[0077] 451 kg of the residual liquid at the bottom of the distillation kettle mainly contains 2-chloro-6-fluorobenzyl trichloride and paraffin oil, of which the content of 2-chloro-6-fluorobenzyl trichloride is 11.09%, the content of paraffin oil is 84.7%, and the rest is other impurities, which can be returned to step 1) to replace paraffin oil and part of the raw materials.

[0078] 5) 718 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 99.74%, the content of 2-chloro-6-fluorobenzyl monochloride is 0.07%, and the content of 2-chloro-6-fluorobenzoic acid is 0.11%.

[0079] Example 3

[0080] In this embodiment, the paraffin oil in step 2) of embodiment 1 is increased from 500 kg to 1000 kg, and the solvent: 2-chloro-6-fluorobenzyl trichloride = 1:1 (weight ratio). The other steps are the same as those of embodiment 1.

[0081] See also Figure 1 This embodiment provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, which comprises the following steps in sequence: 1) heating 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then putting it into a reaction kettle;

[0082] 2) Add 1000 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor reaches 4.0-5.0% (excluding the solvent) to obtain the reacted material I;

[0083] Solvent: 2-chloro-6-fluorobenzyl trichloride = 1:1 (weight ratio);

[0084] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0085] The reaction time is 3.0h.

[0086] After the reaction, the content of 2-chloro-6-fluorobenzyltrichloride in material I was 4.52% (excluding the solvent).

[0087] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1683.2 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0088] The temperature of the reduced pressure distillation does not exceed 180°C.

[0089] The mixture obtained by vacuum distillation contained 52.34% paraffin oil, 61.35% 2-chloro-6-fluorobenzyl monochloride, 41.88% 2-chloro-6-fluorobenzyl dichloride and 2.94% 2-chloro-6-fluorobenzyl trichloride, and the rest were impurities.

[0090] 4) The 1683.2 kg mixture obtained by distillation in step 3) was transferred into a distillation kettle for vacuum distillation, and the top fraction was collected to obtain 22.5 kg of 2-chloro-6-fluorobenzyl chloride, 710 kg of 2-chloro-6-fluorobenzyl dichloride, and 950.7 kg of bottom liquid;

[0091] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0092] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0093] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0094] The distillation yielded 22.5 kg of 2-chloro-6-fluorobenzyl monochlorochloride, of which the main content was 99.56%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.14%, and the rest was impurities.

[0095] 710 kg of 2-chloro-6-fluorobenzyl dichloride was obtained by distillation, of which the main content was 99.16%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.15%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.61%, and the rest were impurities.

[0096] The residual liquid at the bottom of the distillation kettle is 950.7 kg, which mainly contains 2-chloro-6-fluorobenzyl trichloride and paraffin oil, of which the content of 2-chloro-6-fluorobenzyl trichloride is 4.73% (45 kg), the content of paraffin oil is 92.67% (881 kg), and the rest is other impurities, which can be returned to step 1) to replace paraffin oil and part of the raw materials.

[0097] 5) 710 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 99.78%, the content of 2-chloro-6-fluorobenzyl monochloride is 0.07%, and the content of 2-chloro-6-fluorobenzoic acid is 0.13%.

[0098] Example 4

[0099] 445 kg of the bottom liquid obtained by distillation in step 4) of Example 1 and 451 kg of the bottom liquid obtained by distillation in step 4) of Example 2 were mixed to obtain a total of 892 kg (including 91 kg of 2-chloro-6-fluorobenzyl trichloride, 764 kg of paraffin oil, and 37 kg of other impurities) to replace paraffin oil and part of 2-chloro-6-fluorobenzyl trichloride. The other steps were the same as in Example 1.

[0100] See also Figure 1 This embodiment provides a 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method, which comprises the following steps in sequence: 1) heating 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then putting it into a reaction kettle;

[0101] 2) Add 441 kg of the bottom residue obtained by distillation in step 4) of Example 1 and 451 kg of the bottom residue obtained by distillation in step 4) of Example 2 (a total of 892 kg, including 91 kg of 2-chloro-6-fluorobenzyl trichloride, 764 kg of paraffin oil and 37 kg of other impurities), 0.5 kg of ferric chloride and 100 kg of disodium ethylenediaminetetraacetic acid into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the materials in the reactor is 4.0-5.0% (excluding the solvent), and obtain the reacted material I;

[0102] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.7:1 (weight ratio);

[0103] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10.9:1 (weight ratio)

[0104] The reaction time is 3.0h.

[0105] After the reaction, the content of 2-chloro-6-fluorobenzyl trichloride in material I is 4.99% (excluding the solvent).

[0106] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1533.5 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0107] The temperature of the reduced pressure distillation does not exceed 180°C.

[0108] The mixture obtained by vacuum distillation contained 42.13% paraffin oil, 0.92% 2-chloro-6-fluorobenzyl monochloride, 51.19% 2-chloro-6-fluorobenzyl dichloride, 3.88% 2-chloro-6-fluorobenzyl trichloride, and 1.89% impurities.

[0109] 4) The 1533.5 kg mixture obtained by distillation in step 3) was transferred into a distillation kettle for vacuum distillation, and the top fraction was collected to obtain 14 kg of 2-chloro-6-fluorobenzyl chloride, 791 kg of 2-chloro-6-fluorobenzyl dichloride, and 728.5 kg of bottom residue;

[0110] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0111] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0112] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0113] 14 kg of 2-chloro-6-fluorobenzyl monochlorochloride was obtained by distillation, of which the main content was 99.51%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.18%, and the rest was impurities.

[0114] The distillation yielded 791 kg of 2-chloro-6-fluorobenzyl dichloride, of which the main content was 99.19%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.15%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.49%, and the rest were impurities.

[0115] The residual liquid at the bottom of the distillation kettle is 728.5 kg, which mainly contains 2-chloro-6-fluorobenzyl trichloride and paraffin oil, of which the content of 2-chloro-6-fluorobenzyl trichloride is 7.62%, the content of paraffin oil is 88.68%, and the rest is other impurities, which can be returned to step 1) to replace paraffin oil and part of the raw materials.

[0116] 5) 791 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 99.76%, the content of 2-chloro-6-fluorobenzyl monochloride is 0.08%, and the content of 2-chloro-6-fluorobenzoic acid is 0.11%.

[0117] Comparative Example 1

[0118] Eliminate the solvent (paraffin oil) in step 2) of Example 1, and the rest is equivalent to step 4) of Example 1; the following steps are included in sequence:

[0119] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0120] 2) Add 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor reaches 4.0-5.0% (excluding the solvent), to obtain the reacted material I;

[0121] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0122] From the comparative experimental results, the reaction temperature is very difficult to control, and the temperature fluctuates between 190-220°C. During the reaction, the temperature rises from 190°C to 220°C and repeats in this temperature range. The color of the reaction solution gradually deepens and turns black, and a large amount of unidentified solids are generated, which obviously indicates polymerization. In the absence of a reaction solvent as a medium, the heat transfer is poor, and the reaction exotherm causes the temperature to rise too quickly.

[0123] The reaction time is 2.5h.

[0124] After the reaction, the content of 2-chloro-6-fluorobenzyltrichloride in material I was 2.04% (excluding the solvent).

[0125] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 442 kg of a mixture of 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the bottom liquid was disposed of as hazardous waste (the bottom liquid was a coke-like solid, which was difficult to release from the reactor and could only be cleaned by manually opening the reactor cover);

[0126] The temperature of the reduced pressure distillation does not exceed 180°C.

[0127] The mixture obtained by vacuum distillation contained 2.77% of 2-chloro-6-fluorobenzyl monochloride, 59.37% of 2-chloro-6-fluorobenzyl dichloride and 3.83% of 2-chloro-6-fluorobenzyl trichloride, and the rest was 1.49% of impurities.

[0128] 4) Transfer 442 kg of the mixture obtained by distillation in step 3) into a distillation kettle for vacuum distillation, collect the top fraction, and obtain 96 kg of 2-chloro-6-fluorobenzyl chloride, 278 kg of 2-chloro-6-fluorobenzyl dichloride, and 68 kg of bottom residue;

[0129] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0130] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0131] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0132] 96 kg of 2-chloro-6-fluorobenzyl monochlorochloride was obtained by distillation, of which the main content was 98.53%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.18%, the content of newly added unknown single impurity was 0.62%, and the rest were impurities, which did not meet the quality requirements for the production of the pesticide flumetralin.

[0133] 278 kg of 2-chloro-6-fluorobenzyl dichloride was obtained by distillation, of which the main content was 97.82%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.16%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.53%, and two unknown impurities were added (the content was as high as 1.86% and 0.93%), and the others were impurities.

[0134] 5) The 278 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 98.12%, which does not meet the downstream demand.

[0135] Compared with Example 1, the total yield of 2-chloro-6-fluorobenzyl monochloride and 2-chloro-6-fluorobenzyl dichloride decreased from 729 Kg to 374 Kg, a decrease of 48.70%, and the quality did not meet the specified requirements.

[0136] Comparative Example 2

[0137] The reaction temperature of step 2) of Example 1 was lowered to 180° C. The other steps were the same as those of Example 1, and the following steps were sequentially included:

[0138] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0139] 2) Add 500 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of disodium ethylenediaminetetraacetic acid into the reactor, and then heat it to 180°C for reaction.

[0140] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0141] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0142] The reaction time is 2.5h, 5.0h, 10h, 15h, 24h and 48h, and samples are taken respectively. The reaction progress is monitored by gas chromatography. When the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor is 4.0-5.0% (excluding the solvent), the reaction is stopped to obtain the reaction material I;

[0143] Results From the gas chromatography test results, after 48 hours of reaction, the raw material 2-chloro-6-fluorobenzyl trichloride had basically no reaction.

[0144] It can be seen from Comparative Example 2 that the reaction temperature cannot be lower than 190°C.

[0145] Comparative Example 3

[0146] The 2-chloro-6-fluorobenzyl trichloride content in the material after the reaction in step 2) of Example 1 was reduced from 4.0% (excluding the solvent) to 2% (excluding the solvent) and then the reaction was stopped. The rest was the same as in Example 1, and the following steps were sequentially included:

[0147] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0148] 2) Add 500 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor reaches 2% (excluding the solvent), and obtain the reacted material I;

[0149] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0150] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0151] The reaction time is 6.0h.

[0152] After the reaction, the content of 2-chloro-6-fluorobenzyl trichloride in material I was 2.01% (excluding the solvent).

[0153] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1104.5 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0154] The temperature of the reduced pressure distillation does not exceed 180°C.

[0155] The mixture obtained by vacuum distillation contained 34.59% paraffin oil, 32.05% 2-chloro-6-fluorobenzyl monochloride, 28.07% 2-chloro-6-fluorobenzyl dichloride and 1.99% 2-chloro-6-fluorobenzyl trichloride, and the rest was 3.30% impurities.

[0156] 4) Transfer 1104.5 kg of the mixture obtained by distillation in step 3) into a distillation kettle for vacuum distillation, collect the top fraction, and obtain 359 kg of 2-chloro-6-fluorobenzyl chloride, 317 kg of 2-chloro-6-fluorobenzyl dichloride, and 428.5 kg of the bottom residue;

[0157] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0158] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0159] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0160] 359 kg of 2-chloro-6-fluorobenzyl monochlorochloride was obtained by distillation, of which the main content was 98.6%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.18%, two new uncontaminated single impurities were added (the contents of the two unknown single impurities were 0.82% and 0.42% respectively), and the rest were impurities.

[0161] 317 kg of 2-chloro-6-fluorobenzyl dichloride was obtained by distillation, of which the main content was 97.79%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.19%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.41%, and two new uncontaminated single impurities (the contents of the two unknown single impurities were 0.94% and 0.62% respectively) were added, and the rest were impurities.

[0162] 5) 317 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 98.42%, which does not meet the downstream demand.

[0163] Comparing Comparative Example 3 with Example 1, the quality of the obtained 2-chloro-6-fluorobenzyl monochloride and 2-chloro-6-fluorobenzyl dichloride did not meet the specified requirements.

[0164] Comparative Example 4

[0165] The amount of disodium ethylenediaminetetraacetic acid added in step 2) of Example 1 was increased from 100 kg to 200 kg, and the other steps were the same as those of Example 1, and the following steps were sequentially included:

[0166] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0167] 2) Add 500 kg of paraffin oil, 0.5 kg of ferric chloride and 200 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor is 4-5% (excluding the solvent), and obtain the reacted material I;

[0168] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0169] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 5:1 (weight ratio)

[0170] The reaction time is 2.5h.

[0171] After the reaction, the content of 2-chloro-6-fluorobenzyl trichloride in material I was 2.01% (excluding the solvent).

[0172] 3) The reaction material I obtained in step 2) was distilled under reduced pressure (pressure of about -0.095 MPa) to obtain 1061.5 kg of a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and the residual liquid at the bottom of the kettle was disposed of as hazardous waste;

[0173] The temperature of the reduced pressure distillation does not exceed 180°C.

[0174] The mixture obtained by vacuum distillation contained 35.99% paraffin oil, 36.36% 2-chloro-6-fluorobenzyl monochloride, 21.86% 2-chloro-6-fluorobenzyl dichloride and 2.07% 2-chloro-6-fluorobenzyl trichloride, and 3.72% impurities.

[0175] 4) Transfer 1061.5 kg of the mixture obtained by distillation in step 3) into a distillation kettle for vacuum distillation, collect the top fraction, and obtain 389 kg of 2-chloro-6-fluorobenzyl chloride, 234 kg of 2-chloro-6-fluorobenzyl dichloride, and 436.5 kg of the bottom residue;

[0176] During the distillation process, the vacuum degree is -0.095MPa and the bottom temperature of the kettle is 120-180℃;

[0177] When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C;

[0178] When collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C;

[0179] 389 kg of 2-chloro-6-fluorobenzyl monochlorochloride was obtained by distillation, of which the main content was 99.23%, the content of 2-chloro-6-fluorobenzyl dichloride was 0.18%, and the rest was impurities.

[0180] 236 kg of 2-chloro-6-fluorobenzyl dichloride was obtained by distillation, of which the main content was 99.15%, the content of 2-chloro-6-fluorobenzyl monochloride was 0.16%, the content of 2-chloro-6-fluorobenzyl trichloride was 0.22%, and the rest were impurities.

[0181] 5) The 236 kg of 2-chloro-6-fluorobenzyl dichloride obtained in step 4) is hydrolyzed with sulfuric acid as a catalyst, and then washed with alkali and distilled to obtain 2-chloro-6-fluorobenzaldehyde. The content of the obtained 2-chloro-6-fluorobenzaldehyde is 99.53%, which meets the downstream demand.

[0182] Compared with Example 1, the quality of the obtained 2-chloro-6-fluorobenzyl monochloride and 2-chloro-6-fluorobenzyl dichloride both meet the specified requirements, but the amount of 2-chloro-6-fluorobenzyl dichloride is less (from 664Kg to 236Kg), and the consumption of the raw material ethylenediaminetetraacetic acid disodium salt is significantly increased.

[0183] Comparative Example 5

[0184] The amount of solvent added in step 2) of Example 1 is increased from 500Kg to 2000Kg, and the rest is the same as Example 1, and the following steps are sequentially included:

[0185] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0186] 2) Add 2000 kg of paraffin oil, 0.5 kg of ferric chloride and 100 kg of ethylenediaminetetraacetic acid disodium salt into the reactor, then heat to 190-200 ° C for reaction, monitor the reaction progress by gas chromatography, and stop the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor is 4-5% (excluding the solvent), and obtain the reacted material I;

[0187] Solvent: 2-chloro-6-fluorobenzyl trichloride = 2:1 (weight ratio);

[0188] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 5:1 (weight ratio)

[0189] The reaction time was 2.5h, 5.0h, 10h, 15h and 24h, and samples were taken respectively. The reaction progress was monitored by gas chromatography. When the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor was 4.0-5.0% (excluding the solvent), the reaction was stopped (see Table 1), and the reaction material I was obtained;

[0190] Table 1. 2-Chloro-6-fluorobenzyl trichloride content

[0191] Reaction time / h 2-Chloro-6-fluorobenzyl trichloride content / % (excluding solvent) 2.5 67.3％ 5 51.6％ 10 24.9％ 15 11.3％ 24 5.21％

[0192] From the above results, it can be seen that if the solvent: 2-chloro-6-fluorobenzyl trichloride = 2:1 (weight ratio), the reaction time will be prolonged and the energy consumption will increase. Therefore, the appropriate solvent ratio must be strictly controlled.

[0193] Comparative Example 6

[0194] The catalyst in step 2) of Example 1 is eliminated, and the rest is the same as Example 1, and the following steps are sequentially included:

[0195] 1) Heat 1000 kg of raw material 2-chloro-6-fluorobenzyl trichloride until it melts, and then put it into a reaction kettle;

[0196] 2) Add 500 kg of paraffin oil and 100 kg of disodium ethylenediaminetetraacetic acid into the reactor, and then heat it to 180°C for reaction.

[0197] Solvent: 2-chloro-6-fluorobenzyl trichloride = 0.5:1 (weight ratio);

[0198] 2-Chloro-6-fluorobenzyl trichloride: disodium ethylenediaminetetraacetic acid = 10:1 (weight ratio)

[0199] The reaction time is 2.5h, 5.0h, 10h, 15h, 24h and 48h, and samples are taken respectively. The reaction progress is monitored by gas chromatography. When the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reactor is 4.0-5.0% (excluding the solvent), the reaction is stopped to obtain the reaction material I;

[0200] Results From the gas chromatography test results, after 48 hours of reaction, the residual amount of the raw material 2-chloro-6-fluorobenzyl trichloride was still 86.23%.

[0201] It can be seen from Comparative Example 6 that it is difficult to react without a catalyst.

[0202] It can be seen that the present invention adds a synthetic route to the synthesis of 2-chloro-6-fluorobenzyl dichloride, which reduces the cost of raw materials and is more concise. The 2-chloro-6-fluorobenzyl dichloride obtained by the present invention can be subsequently used for the synthesis of 2-chloro-6-fluorobenzaldehyde in a conventional manner.

[0203] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for dechlorinating and reducing 2-chloro-6-fluorobenzyl trichloride, characterized in that: The following steps are involved: 1) 2-chloro-6-fluorobenzyl trichloride as a starting material is heated until it melts, and then put into a reaction kettle; 2) adding a solvent, a catalyst and ethylenediaminetetraacetic acid disodium salt into a reaction kettle, then heating to 190-200° C. for reaction, monitoring the reaction progress by gas chromatography, and stopping the reaction when the content of 2-chloro-6-fluorobenzyl trichloride in the material in the reaction kettle is ≤5.0%, thereby obtaining a reacted material I; the solvent is paraffin oil, the catalyst is ferric chloride, the weight ratio of the solvent to the 2-chloro-6-fluorobenzyl trichloride is 0.5-1.0:1; the weight ratio of the 2-chloro-6-fluorobenzyl trichloride to the ethylenediaminetetraacetic acid disodium salt is 8-12:1; 3) subjecting the reaction material I obtained in step 2) to vacuum distillation to obtain a mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochloride, 2-chloro-6-fluorobenzyl dichloride and 2-chloro-6-fluorobenzyl trichloride, and disposing the bottom residue as hazardous waste; the temperature of the vacuum distillation shall not exceed 180° C.; 4) The mixture of paraffin oil, 2-chloro-6-fluorobenzyl monochlorochloride, 2-chloro-6-fluorobenzyl dichlorochloride and 2-chloro-6-fluorobenzyl trichlorochloride obtained by distillation in step 3) is transferred into a distillation kettle for vacuum distillation, and the top fraction is collected to obtain 2-chloro-6-fluorobenzyl monochlorochloride and 2-chloro-6-fluorobenzyl dichlorochloride, respectively. The bottom residue is a mixture of 2-chloro-6-fluorobenzyl trichlorochloride and paraffin oil.

2. A 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method according to claim 1, characterized in that: In step 4), the vacuum degree of the reduced pressure distillation is -0.095 MPa. When collecting 2-chloro-6-fluorobenzyl chloride, the kettle temperature is 145-146°C and the top temperature is 120-130°C; when collecting 2-chloro-6-fluorobenzyl dichloride, the kettle temperature is 146-150°C and the top temperature is 130-134°C.

3. A 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method according to claim 1, characterized in that: Step 4) When the 2-chloro-6-fluorobenzyl monochloride obtained by distillation is used to produce the pesticide flumetralin, the content of 2-chloro-6-fluorobenzyl monochloride is greater than 99.5%, and the content of 2-chloro-6-fluorobenzyl dichloride is less than 0.2%.

4. A 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method according to claim 1, characterized in that: Step 4) When the 2-chloro-6-fluorobenzyl dichloride obtained by distillation is used for producing 2-chloro-6-fluorobenzaldehyde through catalytic hydrolysis, the content of 2-chloro-6-fluorobenzyl monochloride is less than 0.1%, the content of 2-chloro-6-fluorobenzyl dichloride is greater than 99%, and the content of 2-chloro-6-fluorobenzyl trichloride is less than 1%.

5. A 2-chloro-6-fluorobenzyl trichloride dechlorination reduction method according to claim 1, characterized in that: Step 4) The bottom residual liquid mixture obtained by distillation is returned to step 2) to replace the solvent and part of the raw material 2-chloro-6-fluorobenzyl trichloride.

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