CN113896653B

CN113896653B - Synthesis and purification method of 2-chloro-6-fluorobenzonitrile

Info

Publication number: CN113896653B
Application number: CN202111285442.1A
Authority: CN
Inventors: 王国平; 华慧梁; 徐旭辉; 张少美; 柯文健; 夏静; 范富良; 刘畅
Original assignee: ZHEJIANG DAYANG BIOTECH GROUP CO Ltd
Current assignee: ZHEJIANG DAYANG BIOTECH GROUP CO Ltd
Priority date: 2021-11-02
Filing date: 2021-11-02
Publication date: 2023-10-27
Anticipated expiration: 2041-11-02
Also published as: CN113896653A

Abstract

The invention discloses a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, which comprises the following steps: 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride are used as raw materials to react under the action of a catalyst, so that the product 2-chloro-6-fluorobenzonitrile and hydrogen chloride gas are obtained. Aiming at the characteristics of complex components and high impurity content of a product synthesized by taking byproduct 2-chloro-6-fluorotrichlorobenzyl as a raw material, the invention purifies the reaction product through a process route of rectification and mixed solvent recrystallization to obtain high-purity 2-chloro-6-fluorobenzonitrile. The 2-chloro-6-fluorobenzonitrile obtained by the method can be used for synthesizing 2, 6-difluorobenzonitrile, has simple process and mild reaction conditions, does not use dangerous chemicals with high toxicity and combustibility, can also remarkably reduce the production cost of the 2, 6-difluorobenzonitrile, and has good economic and social benefits.

Description

Synthesis and purification method of 2-chloro-6-fluorobenzonitrile

Technical Field

The invention belongs to the field of fine chemical industry, relates to a synthesis and purification technology of a fine medical intermediate, and particularly relates to a synthesis and purification method of 2-chloro-6-fluorobenzonitrile.

Background

2, 6-difluorobenzonitrile and 2, 6-difluorobenzamide and 2, 6-difluorobenzoic acid derived from the same are key intermediates for synthesizing a plurality of fluorobenzoyl urea pesticides such as hexaflumuron, chlorfluazuron, flufenoxuron and the like, can be used for synthesizing medicaments and liquid crystal materials, and has wide market prospect.

The main process flow of the 2, 6-difluorobenzonitrile at present comprises the following steps:

(1) Taking 2, 6-dichlorobenzonitrile as a raw material, adding potassium fluoride (high activity) into DMF solvent to perform fluorine substitution (halogen exchange reaction) at high temperature, filtering and rectifying to obtain 2, 6-difluorobenzonitrile, and selling the byproduct potassium chloride.

(2) 2, 6-dichlorobenzonitrile/potassium fluoride/organic solvent dmf=750/750/1000 (m/m), reaction temperature 90-130 ℃.

The main raw material 2, 6-dichlorobenzonitrile of 2, 6-difluorobenzonitrile is high-efficiency herbicide 'dixynitrile', is an excellent nitrile herbicide, has special inhibition effect on the germination of annual and perennial weed seeds, can be used for preventing and controlling overgrowth of various weeds, has very low toxicity to mammals, is not only an important intermediate of benzoyl urea green pesticides, but also widely used as intermediates and raw materials of various medicines, dyes, high polymer materials and the like.

The main process flow of the 2, 6-dichlorobenzonitrile comprises the following steps:

(1) Introducing chlorine into a catalyst (specifically unknown) by taking 6-chlorine-2-nitrotoluene as a raw material (3-chlorine-2-methylaniline intermediate), substituting nitro groups with chlorine (introducing chlorine for denitration reaction), rectifying to obtain 2, 6-dichlorotoluene, and obtaining hydrochloric acid containing nitric acid and nitrous acid as byproducts, and selling the hydrochloric acid as byproducts after treatment;

(2) Photo-chlorinating methyl on the side chain of the 2, 6-dichlorotoluene, rectifying to obtain 2, 6-dichlorotoluene, and simultaneously obtaining hydrochloric acid as a byproduct;

(3) Ammoniation is carried out on the 2, 6-dichloro methylene chloride to obtain the target product 2, 6-dichlorobenzonitrile and byproduct ammonium chloride, the unit consumption of liquid ammonia is very high, and the environmental protection pressure is high, so that the production cost and the environmental protection cost are high.

Because of environmental protection, safety control and other reasons, the market supply of the 2, 6-dichlorobenzonitrile is very tight, the price is increased, and the production of the downstream product 2, 6-difluorobenzonitrile is influenced.

2-chloro-6-fluorotrichlorobenzyl is a byproduct produced in the production of 2-chloro-6-fluorobenzaldehyde, the content is more than or equal to 95 percent, the content of 2-chloro-6-fluorodichlorobenzyl is less than or equal to 1.5 percent, the moisture is less than or equal to 0.05 percent, and the other maximum unknown single impurity is less than 2.0 percent; although 2-chloro-6-fluorotrichlorobenzyl can be used to prepare 2-chloro-6-fluorobenzoic acid, 2-chloro-6-fluorobenzoic acid has not yet been demanded in a large scale market, and is demanded in an amount of only several hundred kg worldwide a year. In addition, 2-chloro-6-fluorotrichlorobenzyl has not yet found other commercial uses, nor has it found related downstream products under development. Therefore, the storage can only be temporarily stored, and the warehouse of the company is occupied.

Disclosure of Invention

The invention aims to provide a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile.

In order to solve the technical problems, the invention provides a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, which comprises the following steps: 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride are used as raw materials to react under the action of a catalyst to obtain a product 2-chloro-6-fluorobenzonitrile and hydrogen chloride gas, wherein the reaction formula is as follows:

the method sequentially comprises the following steps of:

1) Heating 2-chloro-6-fluorotrichlorobenzyl (solid) to melt (about 80 ℃), and then putting into a reaction kettle;

2) Adding ammonium chloride, a catalyst and a polymerization inhibitor into the reaction kettle in the step 1), then heating to 200-240 ℃ for reaction, monitoring the reaction progress through gas chromatography, and stopping the reaction when the content of 2-chloro-6-fluorotrichlorobenzyl in the materials in the reaction kettle is less than or equal to 0.5%, so as to obtain reacted materials and hydrogen chloride gas;

2-chloro-6-fluorotrichlorobenzyl: ammonium chloride=1:2 to 3 molar ratio (preferably 1:2);

the catalyst is 0.47 to 1.0 percent of 2-chloro-6-fluorotrichlorobenzyl;

the polymerization inhibitor is 0.28 to 0.5 percent of 2-chloro-6-fluorotrichlorobenzyl;

the percentages are by weight;

3) Preparing hydrochloric acid (the concentration is controlled to be 30%) from the hydrogen chloride gas obtained in the step 2);

description: the preparation of hydrochloric acid from hydrogen chloride gas is a conventional technique, and the prepared hydrochloric acid is taken as a product for sale;

4) Cooling the reacted material obtained in the step 2) to 80+/-10 ℃ (namely, about 80 ℃), adding washing water into the cooled material for uniform stirring (stirring time is about 30-60 min), and preserving heat and standing at 60+/-10 ℃ until layering (obvious layering) occurs, and preserving heat and standing for about 1h, so that an organic phase I (positioned at the upper layer) and a water phase I (positioned at the lower layer) are separated;

the washing water is water (tap water) or water phase II obtained in the step 5) and water phase III obtained in the step 6);

the washing water is as follows: ammonium chloride=2±0.1:1 mass ratio of step 2);

description: for the first time, water is used as washing water; subsequently, water phase II obtained in the step 5) and water phase III obtained in the step 6) are used as washing water, and water is added for supplementing when the equivalent is insufficient;

5) Adding water (tap water) into the organic phase I obtained in the step 4), stirring and washing (stirring time is about 30-60 min), and preserving heat and standing at 60+/-10 ℃ until layering (obvious layering, preserving heat and standing time is about 1 h) occurs, so that an organic phase II and a water phase II are separated;

water: ammonium chloride=1±0.05:1 mass ratio of step 2);

6) Adding water (tap water) into the organic phase II obtained in the step 5) for stirring and washing (stirring time is about 30-60 min), and preserving heat and standing at 60+/-10 ℃ until layering (obvious layering, preserving heat and standing time is about 1 h) occurs, so that an organic phase III and a water phase III are separated;

Water: ammonium chloride=1±0.05:1 mass ratio of step 2);

7) Rectifying the organic phase III obtained in the step 6) under vacuum (the vacuum degree is-0.098 MPa) (the kettle temperature is controlled between 220 ℃ and 240 ℃ in the whole rectifying process), and collecting the organic phase III in sections through different rectifying kettle top temperatures; respectively obtaining a front cut, a middle cut and a rear cut;

when the top temperature of the rectifying still is between room temperature and 140 ℃, a front cut fraction (the content of 2-chloro-6-fluorobenzonitrile in the front cut fraction is less than or equal to 95 percent) is obtained;

when the top temperature of the rectifying still is higher than 140 ℃ and up to 160 ℃, a middle distillate (the condensate is colorless and becomes pale yellow at the moment, and the content of 2-chloro-6-fluorobenzonitrile in the middle distillate is more than or equal to 98 percent);

when the top temperature of the rectifying still is more than 160 ℃ until no fraction is generated (the rectifying is stopped after the top temperature is reduced to 100 ℃), obtaining a rear fraction (the content of 2-chloro-6-fluorobenzonitrile in the rear fraction is less than or equal to 95%);

8) And (3) main recrystallization:

taking the middle distillate obtained by the rectification in the step 7) as a main recrystallization starting material, or mixing the middle distillate obtained by the rectification in the step 7) with the crude product of the 2-chloro-6-fluorobenzonitrile obtained in the subsequent step 13) to be used as the main recrystallization starting material;

adding a main recrystallization starting material into a main recrystallization kettle, adding an organic solvent, heating to 50-60 ℃ (adding a reflux condenser tube to ensure that the organic solvent is not lost), stirring until the recrystallization starting material is dissolved (stirring time is about 30-60 minutes), finally dropwise adding pure water (water temperature is 50-60 ℃), and after the water dropwise adding is finished, starting to naturally cool down to precipitate crystals, and continuously cooling to room temperature to obtain a recrystallization slurry I;

The organic solvent: water= (3±0.1): the mass ratio of 1 is that of the components,

the (organic solvent+water): a mass ratio of main recrystallization starting material= (4±0.1): 5;

description: firstly, carrying out main recrystallization on the middle distillate obtained by rectifying in the step 7), and subsequently, mixing the middle distillate obtained by rectifying in the step 7) with the 2-chloro-6-fluorobenzonitrile crude product obtained in the step 13) to carry out main recrystallization;

9) Growing crystals of the recrystallized slurry I obtained in the step 8) for 12-24 hours at room temperature, and then performing centrifugal separation to obtain a wet 2-chloro-6-fluorobenzonitrile product with a drying weight loss of less than 3% (mass percent) and primary mother liquor;

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in vacuum (vacuum degree-0.095 Mpa) to obtain 2-chloro-6-fluorobenzonitrile (2-chloro-6-fluorobenzonitrile product);

11 Evaporating and concentrating the primary mother liquor obtained by the centrifugation in the step 9) under reduced pressure (the top temperature is 70-80 ℃ and the vacuum degree is-0.095 Mpa), so as to obtain an organic solvent aqueous solution and a kettle bottom liquid I respectively;

dehydrating the organic solvent aqueous solution (dehydrating through an inorganic vaporization permeable membrane), and returning the obtained anhydrous organic solvent to the step 8) or circularly using the anhydrous organic solvent in the step 12);

12 And (c) auxiliary recrystallization:

mixing the kettle bottom liquid I obtained in the step 11) and the front fraction and the rear fraction obtained in the step 7) after rectification, taking the mixture as an auxiliary recrystallization starting material, putting the mixture into an auxiliary recrystallization kettle, adding an organic solvent, heating the mixture to 50-60 ℃ (adding a reflux condenser tube to ensure that the organic solvent is not lost), stirring the mixture until the auxiliary recrystallization starting material is dissolved (stirring time is about 30-60 minutes), finally dropwise adding pure water (water temperature is 50-60 ℃), and starting to naturally cool and separate out crystals after the water dropwise adding is finished, and continuously cooling the mixture to room temperature to obtain a recrystallization slurry II;

the (organic solvent+water): auxiliary recrystallization starting material= (4±0.1): 5 mass ratio;

13 Crystal growth is carried out on the slurry II obtained in the step 12) for 12-24 hours at room temperature, centrifugal separation is carried out, and a 2-chloro-6-fluorobenzonitrile crude product with a drying weight loss of less than 3% (mass percent) and a secondary mother solution are obtained (the content of the 2-chloro-6-fluorobenzonitrile in the 2-chloro-6-fluorobenzonitrile crude product is more than or equal to 98 percent);

the 2-chloro-6-fluorobenzonitrile crude product returns to the step 8) for main recrystallization;

14 Step 14), concentrating the secondary mother liquor obtained by centrifugation under reduced pressure (the top temperature is 70-80 ℃ and the vacuum degree is-0.095 Mpa) to obtain an organic solvent aqueous solution and a kettle bottom liquid II;

the organic solvent aqueous solution is dehydrated (dehydrated through an inorganic vaporization impermeable membrane) to obtain anhydrous organic solvent, and the anhydrous organic solvent is returned to the step 8) or the step 12) for recycling.

Description: and taking the kettle bottom liquid II as a unit with qualification entrusted to residual liquid for innocent treatment.

As an improvement of the synthesis and purification method of the 2-chloro-6-fluorobenzonitrile of the present invention: the method also comprises the following steps:

15 Post-treatment of aqueous phase i):

and 4) removing impurities from the water phase I obtained by separating the liquid in the step 4) through resin adsorption, then, entering an ammonium chloride evaporation crystallizer for reduced pressure distillation and concentration, cooling a crystallized material, and performing centrifugal drying to obtain ammonium chloride, wherein mother liquor formed by the centrifugal drying returns to the ammonium chloride evaporation crystallizer for circulation concentration.

Description:

adsorbing the water phase I by using HYA115 macroporous resin to remove organic impurities therein, and removing impurities such as high-valence metal ions by using chelating resin HYC 500; after the organic matters and high-valence metal ions are removed by the water phase I through adsorption, the Total Organic Carbon (TOC) is less than 100ppm, and the zinc and iron ions are less than 0.001%.

After being dried, the ammonium chloride has a content of more than 99.5 percent and zinc and iron ions have a content of less than 0.001 percent, and the ammonium chloride returns to the step 1) for recycling or is used as a commodity sale (fertilizer).

As a further improvement of the method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile of the present invention, in the step 2):

the catalyst is zinc oxide (preferred) or ferric oxide;

the polymerization inhibitor is EDTA.

As a further improvement of the method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile of the present invention:

step 2) is to raise the temperature to 200 ℃ at a stage, then raise the temperature at a rate of 3-4 ℃/h, and not raise the temperature when the temperature reaches 240 ℃ (i.e. the highest reaction temperature does not exceed 240 ℃).

The reaction time of the whole step 2) is about 8 to 12 hours (from the temperature rise to 200 ℃).

The organic solvents in the step 8) and the step 12) are ethanol;

in the step 8), the dropping time of the pure water is 3 to 5 hours,

in step 12), the dropping time of the pure water is 3 to 5 hours.

Further improvements in the synthesis and purification of 2-chloro-6-fluorobenzonitrile as the subject invention

In the step 9), the centrifugal rotating speed is 800-1200 rpm, so that the drying weight loss of the 2-chloro-6-fluorobenzonitrile is ensured to be less than 3 percent (mass percent) by controlling the centrifugal time (the centrifugal time is about 15-30 minutes);

in the step 13), the centrifugal rotating speed is 800-1200 rpm, so that the drying weight loss of the 2-chloro-6-fluorobenzonitrile crude product is ensured to be less than 3 percent (mass percent) by controlling the centrifugal time (about 15-30 minutes).

As a further improvement of the method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile of the present invention, the step 10):

drying the wet 2-chloro-6-fluorobenzonitrile obtained in the step 9) in vacuum (the vacuum degree is-0.095 Mpa) at the drying temperature of 70-80 ℃ until the drying weight loss of the obtained 2-chloro-6-fluorobenzonitrile is less than 0.05%;

description: this step 10) is carried out in a vacuum oven, and the drying loss ratio of the obtained 2-chloro-6-fluorobenzonitrile is ensured by controlling the drying time.

As a further improvement of the method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile of the present invention, step 3) is: and (3) absorbing the hydrogen chloride gas obtained in the step (2) through a falling film and adsorbing the hydrogen chloride gas through resin to obtain byproduct hydrochloric acid (the mass concentration is 30%).

the 2-chloro-6-fluorotrichlorobenzyl in the step 1) is a byproduct of producing 2-chloro-6-fluorobenzaldehyde, and is purified by rectification, wherein the content is more than or equal to 95%, the content of 2-chloro-6-fluorodichlorobenzyl is less than or equal to 1.5%, the moisture is less than or equal to 0.05%, and the maximum unknown single impurity is less than 2.0%.

Aiming at the prior art, a new synthetic route is developed, and 2-chloro-6-fluorobenzyl chloride and ammonium chloride are used as raw materials to react under the action of a catalyst to prepare the 2-chloro-6-fluorobenzonitrile.

The 2-chloro-6-fluorobenzonitrile obtained by the method can be used for synthesizing 2, 6-difluorobenzonitrile, has simple process and mild reaction conditions, does not use dangerous chemicals with high toxicity and combustibility, can also remarkably reduce the production cost of the 2, 6-difluorobenzonitrile, and has good economic and social benefits. The current industrialized synthesis of 2, 6-difluorobenzonitrile takes 2, 6-dichloronitrile as raw material and is produced by fluorine-chlorine exchange. Thus, the invention adds a raw material and a simpler synthetic route to the synthesis of 2, 6-difluorobenzonitrile (one step can be reduced).

In the present invention, the weight loss on drying of 2-chloro-6-fluorobenzonitrile means the weight loss of 2-chloro-6-fluorobenzonitrile when dried under vacuum at 105℃until constant weight.

The invention provides a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, which has high product yield, can realize circular economy and does not increase the discharge of three wastes. The method takes byproduct 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride as basic raw materials, and prepares the 2-chloro-6-fluorobenzonitrile through reaction under the action of a catalyst.

Aiming at the characteristics of complex components and high impurity content of a product synthesized by taking byproduct 2-chloro-6-fluorotrichlorobenzyl as a raw material, the invention purifies the reaction product through a process route of rectification and mixed solvent recrystallization to obtain high-purity 2-chloro-6-fluorobenzonitrile.

That is, in the main recrystallization in step 8) and the auxiliary recrystallization in step 12) of the present invention, the organic solvent (ethanol) and water are used as the mixed solvent.

Drawings

The following describes the embodiments of the present invention in further detail with reference to the accompanying drawings.

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

The invention will be further described with reference to specific examples, but the invention is not limited thereto, and the techniques described based on the invention are all part of the invention.

The raw materials of the invention are as follows:

ammonium chloride, industrial grade, 99.5% of water content, 0.06% of water, commercially available,

anhydrous zinc oxide, technical grade, 99.0% content, commercially available;

2-chloro-6-fluorotrichlorobenzyl, which is a byproduct of producing 2-chloro-6-fluorobenzaldehyde, is obtained by vacuum rectification;

absolute ethanol, technical grade, commercially available.

Room temperature generally means 15 to 25 ℃.

Example 1, a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, comprising the following steps in order:

1) 1020Kg of solid (4000 mol of 2-chloro-6-fluorotrichlorobenzyl containing 2-chloro-6-fluorotrichlorobenzyl) is heated to 80 ℃ to be melted and then put into a 2000L reaction kettle;

the 2-chloro-6-fluorotrichlorobenzyl in the step 1), wherein the content of the 2-chloro-6-fluorotrichlorobenzyl is 97.3 percent, the content of the 2-chloro-6-fluorodichlorobenzyl is 1.2 percent, the moisture is 0.05 percent, the maximum unknown single impurity is 1.2 percent, and the rest is other impurities.

2) 428Kg (8000 mol) of ammonium chloride, 5Kg of anhydrous zinc oxide as a catalyst and 3Kg of polymerization inhibitor (EDTA) are put into the reaction kettle in the step 1). Then carrying out stage heating reaction, wherein the initial reaction temperature is 200 ℃, then heating at the rate of 3-4 ℃ per hour, and the highest reaction temperature is not more than 240 ℃.

In the embodiment, the feeding mole ratio of the raw materials of 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride is 1:2; the feeding amount of the anhydrous zinc oxide catalyst is 0.5 percent (mass percent) of 2-chloro-6-fluorotrichlorobenzyl; the addition amount of the polymerization inhibitor (EDTA) is 0.3 percent (mass percent) of the 2-chloro-6-fluorotrichlorobenzyl.

After about 10 hours from the initial reaction temperature of 200 ℃, the progress of the reaction was monitored by gas chromatography, and the content of 2-chloro-6-fluorotrichlorobenzyl as a raw material in the reaction vessel was 0.42%, so that the reaction was stopped to obtain 878Kg of a reacted material.

3) The hydrogen chloride gas obtained in the step 2) is absorbed by a conventional falling film and adsorbed by resin (for example, refer to the patent of ZL201410439205.X, purification method of byproduct hydrochloric acid of 2-chloro-6-fluorobenzaldehyde or the like), 1927Kg of byproduct hydrochloric acid (the concentration is about 30%) is obtained and is used as a product for export.

4) Cooling 878Kg of the reacted material obtained in the step 2) to about 80 ℃, adding 856Kg of tap water into the cooled material, stirring the cooled material for 30 to 60 minutes, keeping the temperature at 60 ℃ and standing the cooled material for about 1 hour (obvious delamination exists), and separating an organic phase I (positioned at the upper layer) and a water phase I (positioned at the lower layer);

in this step, water: step 2) the mass ratio of ammonium chloride=2:1.

5) Adding 428Kg of tap water into the organic phase I obtained in the step 4) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating an organic phase II (positioned at the upper layer) and a water phase II (positioned at the lower layer);

in this step, water: step 2) the mass ratio of ammonium chloride=1:1.

6) Adding 428Kg of self-water into the organic phase II obtained in the step 5) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating an organic phase III (positioned at the upper layer) and a water phase III (positioned at the lower layer);

in this step, water: step 2) the ammonium chloride=1:1 mass ratio.

7) And step 6), rectifying 653Kg of organic phase III under vacuum (the vacuum degree is-0.098 MPa) (in the rectifying process, the kettle temperature can be controlled between 220 ℃ and 240 ℃ generally), and collecting the organic phase III in sections through different top temperatures to obtain a front fraction, a middle fraction and a rear fraction respectively. The different top temperature sectional collection control points are as follows:

a) Front cut: the top temperature is in the range of room temperature to 140 ℃, 18Kg of front cut fraction is obtained, wherein the content of 2-chloro-6-fluorobenzonitrile is 92.7 percent;

b) Middle distillate: the top temperature is in the range of more than 140 ℃ to 160 ℃ (condensate is colorless and turns into pale yellow), 565Kg of middle distillate is obtained, wherein the content of 2-chloro-6-fluorobenzonitrile is 98.3%;

c) Post-fraction: after a top temperature of more than 160℃until no fraction was present (distillation was stopped after the top temperature had fallen to 100 ℃) 45Kg of a post-fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 88.4%.

d) 25Kg of residual liquid at the bottom of the kettle.

8) Firstly throwing 565Kg of middle distillate obtained by rectifying in the step 7) into a main recrystallization kettle, then throwing 339Kg of absolute ethyl alcohol which is an organic solvent, heating to 50-60 ℃ (a reflux condenser tube is added to ensure that the organic solvent is not lost), stirring and dissolving, finally dropwise adding 113Kg of pure water (water temperature is 50-60 ℃), dropwise adding according to the average speed, dropwise adding water for 5 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and continuing cooling to room temperature to obtain 1017Kg of recrystallization slurry I.

In this step, the organic solvent is ethanol, ethanol/water=3/1 (m/m), and recrystallization is carried out in a ratio of solvent (ethanol and water)/crude product=4/5 (m/m).

9) Standing and crystallizing the recrystallized slurry I obtained in the step 8) for 12 hours at room temperature, and then carrying out centrifugal separation (separation for about 15 minutes at the rotation speed of 800-1200 rpm) to obtain 507Kg of 2-chloro-6-fluorobenzonitrile wet product (weight loss on drying of 2.1 percent, m/m) and 510Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ under the vacuum degree of-0.095 Mpa for 6 hours to obtain 497Kg of finished 2-chloro-6-fluorobenzonitrile with the content of 99.68 percent, 0.05 percent of 2-chloro-6-fluorobenzyl chloride, 0.04 percent of 2-chloro-6-fluorobenzyl chloride, 0.03 percent of drying loss, the maximum single impurity of other 0.12 percent and the balance of impurities.

11 And (3) concentrating the primary mother liquor obtained in the step (9) by vacuum evaporation (with the top temperature of 70-80 ℃ and the vacuum degree of-0.095 Mpa) by 510Kg, thereby obtaining 442Kg of ethanol aqueous solution (with the water content of 25.6%) and 68Kg of kettle bottom liquid I respectively.

The ethanol aqueous solution is dehydrated through a conventional inorganic vaporization osmotic membrane (for example, an inorganic vaporization osmotic membrane JTMZ7 of Jiangsu Jiutian Gaoke Co., ltd.) to obtain 320Kg of absolute ethanol, and the absolute ethanol is returned to the step 8) or the step 12) for recycling.

12 Mixing the 18Kg front fraction obtained in the step 11) with the 45Kg rear fraction obtained in the step 7), adding 78.6Kg of organic solvent (absolute ethyl alcohol), heating to 50-60 ℃ (adding a reflux condenser tube to ensure that the organic solvent is not lost), stirring for dissolving, finally dropwise adding 26.2Kg of pure water (water temperature 50-60 ℃), dropwise adding at an average speed for 3 hours until the water dropwise adding is finished, naturally cooling, precipitating crystals, and continuously cooling to room temperature to obtain 235.8Kg recrystallization slurry II.

13 And 12) standing and crystallizing the slurry II obtained in the step 12) at room temperature for 24 hours, and then carrying out centrifugal separation (separation for about 15 minutes at the rotating speed of 800-1200 r/min) to obtain 103Kg of crude 2-chloro-6-fluorobenzonitrile (content of 98.6 percent, weight loss on drying of 2.54 percent) and 132.8Kg of secondary mother liquor, and returning the crude 2-chloro-6-fluorobenzonitrile to the step 8) for recrystallization.

14 132.8Kg of secondary mother liquor obtained by centrifugation in the step 13) is evaporated and concentrated under reduced pressure (the top temperature is 70-80 ℃ and the vacuum degree is-0.095 Mpa) to respectively obtain 101.8Kg of ethanol water solution (the water content is 25.8%) and 31Kg of kettle bottom liquid II.

The ethanol water solution is dehydrated through a conventional inorganic vaporization permeable membrane, 73Kg of ethanol is obtained and returned to the step 8) or the step 12) for recycling.

And taking the kettle bottom liquid II as a unit with qualification entrusted to residual liquid for innocent treatment.

15 1065Kg of aqueous phase I (ammonium chloride concentration 21.1%) obtained by separating in step 4) are reacted according to 2m ³ The flow rate/h was measured by passing through a bed of HYA115 macroporous resin (resin bed diameter 1.0m, height 6m, resin loading 4 m) ³ ) Adsorbing to remove organic impurities, and adding 3-5m ³ The flow rate/h was controlled by a chelating resin HYC500 (loading 5m ³ ) Removing impurities such as high-valence metal ions, and then taking the impurities as evaporation raw materials to enter an ammonium chloride evaporation crystallizer for reduced pressure evaporation concentration, cooling the obtained crystallization material, and performing centrifugal drying to obtain an ammonium chloride wet product, wherein mother liquor formed by the centrifugal drying is returned to the ammonium chloride evaporation crystallizer as the evaporation raw materials for circulation concentration.

After removing organic matters and high-valence metal ions by adsorption, the Total Organic Carbon (TOC) of the aqueous phase I is 60ppm, and zinc and iron ions are less than 0.001%, so that the aqueous phase I is used as evaporation raw materials for reduced pressure distillation and concentration.

Evaporating the obtained ammonium chloride, wherein the content of the ammonium chloride is 99.62%, the content of zinc chloride is 0.0002%, the Total Organic Carbon (TOC) is 39ppm, the moisture is 0.05%, and the method meets the requirement of the step 1).

Example 2, a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, the ammonium chloride feeding amount of the step 2) of the example 1 is increased from 428Kg (8000 mol) to 642Kg (12000 mol), tap water used in the step 5) is changed into an aqueous phase II obtained in the step 5) of the example 1 and an aqueous phase III obtained in the step 6), and the rest part is complemented by tap water; the remainder was identical to example 1. The method comprises the following steps:

2-chloro-6-fluorotrichlorobenzyl is the same as in example 1.

2) 642Kg (12000 mol) of ammonium chloride, 5Kg of anhydrous zinc oxide as a catalyst and 3Kg of polymerization inhibitor (EDTA) are put into the reaction kettle in the step 1). Then carrying out stage heating to react, wherein the initial reaction temperature is 200 ℃, then heating at the rate of 3-4 ℃ per hour, and the highest reaction temperature is not more than 240 ℃.

In the embodiment, the feeding mole ratio of the raw materials of 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride is 1:3; the anhydrous zinc oxide of the catalyst is 0.5 percent of the 2-chloro-6-fluorotrichlorobenzyl; the addition amount of the polymerization inhibitor (EDTA) is 0.3 percent of the 2-chloro-6-fluorotrichlorobenzyl.

After about 8 hours from the initial reaction temperature of 200 ℃, monitoring the reaction progress by gas chromatography, wherein the content of the raw material 2-chloro-6-fluorotrichlorobenzyl in the material in the reaction kettle is 0.39%, and stopping the reaction to obtain 1090Kg of reacted material.

3) And step 2), the hydrogen chloride gas obtained by the reaction is absorbed by a conventional falling film and adsorbed by resin, so that 1930Kg of byproduct hydrochloric acid (the concentration is about 30%) is obtained and is taken as a product for sale.

4) Cooling 1090Kg of the reacted material obtained in the step 2) to about 80 ℃, adding 872Kg of a mixed solution (the volume ratio of the mixed solution is about 1:1) of the water phase II obtained in the step 5) of the example 1 and the water phase III obtained in the step 6) into the cooled material, adding 412Kg of tap water into the mixed solution, stirring the mixed solution for 30-60 min, keeping the temperature at 60 ℃ and standing the mixed solution for about 1h (obvious delamination exists), and separating an organic phase II and a water phase II;

The total water consumption of the implementation is 1284Kg, and the mass ratio of the total water consumption to the ammonium chloride added in the step 2) is 2:1.

5) Adding 642Kg of tap water into the organic phase I obtained in the step 4) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating an organic phase II and a water phase II;

the addition amount of water in the embodiment is controlled by the ammonium chloride in the step 2), and the mass ratio of the water to the ammonium chloride is 1:1.

6) Adding 642Kg of self-water into the organic phase II obtained in the step 5) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating out an organic phase III and a water phase III;

the addition amount of the water in the embodiment is controlled by the ammonium chloride added in the step 2), and the mass ratio of the water to the ammonium chloride is 1:1.

7) And 658Kg of the organic phase III obtained in the step 6) is rectified under vacuum, and the front fraction, the middle fraction and the rear fraction are obtained by carrying out sectional collection through different top temperatures. The different top temperature sectional collection control points are as follows:

a) Front cut: the top temperature is in the range of room temperature to 140 ℃, 20Kg of front cut fraction is obtained, wherein the content of 2-chloro-6-fluorobenzonitrile is 92.4 percent;

b) Middle distillate: the top temperature is in the range of more than 140 ℃ to 160 ℃, 567Kg of middle distillate is obtained, wherein the content of 2-chloro-6-fluorobenzonitrile is 98.2%;

c) Post-fraction: after a top temperature of more than 160℃until no fraction was present, 45Kg of a post fraction was obtained, the content of 2-chloro-6-fluorobenzonitrile being 89.3%.

d) 26Kg of residual liquid at the bottom of the kettle.

8) Firstly putting 567Kg of the middle distillate obtained in the step 7) into a main crystallization kettle, then putting 340.2Kg of an organic solvent, namely absolute ethyl alcohol, heating to 50-60 ℃, stirring for dissolution, finally dripping 113.4Kg of pure water (the water temperature is 50-60 ℃) according to the average speed, dripping the water for 5 hours until the water dripping is finished, starting to naturally cool, precipitating crystals, and continuing cooling to room temperature to obtain 1020.6Kg of recrystallized slurry I.

9) And 8) standing and crystallizing the slurry I obtained in the step 8) at room temperature for 12 hours, and then performing centrifugal separation to obtain 509Kg of wet 2-chloro-6-fluorobenzonitrile (weight loss on drying of 2.2%, m/m) and 511.6Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ and under the vacuum degree of-0.095 Mpa for 6 hours to obtain 498Kg of finished 2-chloro-6-fluorobenzonitrile product, wherein the content of the finished 2-chloro-6-fluorobenzonitrile product is 99.71%, the content of 2-chloro-6-fluorobenzyl chloride is 0.05%, the content of 2-chloro-6-fluorobenzyl chloride is 0.04%, the drying loss is 0.03%, the maximum single impurity is 0.13%, and the balance is impurities.

11 511.6Kg of the primary mother liquor obtained by the centrifugation in the step 9) was evaporated and concentrated under reduced pressure to obtain 442.6Kg of an aqueous ethanol solution (water content: 25.4%) and 69Kg of a tank bottoms I, respectively.

The ethanol water solution is dehydrated through an inorganic vaporization osmotic membrane, so that 321Kg of anhydrous organic solvent is returned to the step 8) or the step 12) for recycling.

12 And (3) mixing the 69Kg kettle bottom liquid I obtained in the step (11), the 20Kg front fraction obtained in the step (7) and the 45Kg rear fraction (134 Kg total), adding 80.4Kg absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolving, finally dropwise adding 26.8Kg pure water (water temperature 50-60 ℃), dropwise adding according to an average speed, wherein the water dropwise adding time is 3 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and continuously cooling to room temperature to obtain 241.2Kg recrystallization slurry II.

13 And 12) standing and crystallizing the slurry II obtained in the step 12) at room temperature for 24 hours, and then carrying out centrifugal separation to obtain 105.3Kg of crude 2-chloro-6-fluorobenzonitrile (content 98.4%, drying weight loss 2.48%) and 135.9Kg of secondary mother liquor, and returning the crude 2-chloro-6-fluorobenzonitrile to the step 8) for recrystallization.

14 And step 13), carrying out reduced pressure evaporation concentration on 135.9Kg of secondary mother liquor obtained by centrifugation, thereby obtaining 104.6Kg of ethanol water solution (the water content is 25.3%) and 31.3Kg of kettle bottom liquid II.

The ethanol water solution is dehydrated through an inorganic vaporization osmotic membrane, and 74Kg of ethanol is obtained and returned to the step 8) or the step 12) for recycling.

15 1698Kg of aqueous phase I (ammonium chloride concentration 25.32%) obtained in step 4) were treated as in step 15) of example 1;

after the organic matters and high-valence metal ions are removed by the water phase I through adsorption, the Total Organic Carbon (TOC) is 58ppm, and the zinc and iron ions are less than 0.001%.

The ammonium chloride obtained by the evaporation is dried to obtain 411Kg of ammonium chloride, wherein the content of the ammonium chloride is 99.53%, the content of zinc chloride is 0.0003%, the Total Organic Carbon (TOC) is 47ppm, the moisture is 0.05%, and the requirements of the step 1) are met. Returning to the step 1) for recycling or serving as a commodity export (fertilizer).

From the comparison of example 2 and example 1, the yield and quality of the 2-chloro-6-fluorobenzonitrile product obtained in step 10) are hardly different, which means that there is no practical significance in increasing the amount of ammonium chloride added in step 2), but rather in increasing the energy consumption and processing cost of the subsequent evaporation of ammonium chloride.

Example 3, a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, the catalyst addition amount of step 2) of example 1 was increased from 5Kg to 10Kg, the polymerization inhibitor addition amount was increased from 3Kg to 5Kg, and the remainder was identical to example 1. The method comprises the following steps:

2-chloro-6-fluorotrichlorobenzyl is the same as in example 1.

2) 428Kg (8000 mol) of ammonium chloride, 10Kg of anhydrous zinc oxide as a catalyst and 5Kg of polymerization inhibitor (EDTA) are put into the reaction kettle in the step 1). Then the reaction is carried out by stage heating, the initial reaction temperature is 200 ℃, then the temperature is raised at the rate of 3-4 ℃ per hour, and the highest reaction temperature is not more than 240 ℃.

In the embodiment, the feeding mole ratio of the raw materials of 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride is 1:2; the feeding amount of the anhydrous zinc oxide catalyst is 1.0% of that of 2-chloro-6-fluorotrichlorobenzyl; the addition amount of the polymerization inhibitor (EDTA) is 0.5 percent of the 2-chloro-6-fluorotrichlorobenzyl.

Monitoring the reaction progress by gas chromatography after about 10 hours from the initial reaction temperature of 200 ℃, stopping the reaction until the content of the raw material 2-chloro-6-fluorotrichlorobenzyl is 0.42%, and obtaining 885Kg of reacted material;

3) The hydrogen chloride gas obtained by the reaction in the step 2) is absorbed by a conventional falling film and adsorbed by resin, 1928Kg of byproduct hydrochloric acid (the concentration is about 30%) is obtained and is taken as a product for sale;

4) Cooling 885Kg of the reacted material obtained in the step 2) to about 80 ℃, adding 856Kg of tap water into the cooled material, stirring the mixture for 30 to 60 minutes, keeping the temperature at 60 ℃ and standing the mixture for about 1 hour (obvious layering exists), and separating an organic phase I and a water phase I;

In the step, the mass ratio of the added water amount to the ammonium chloride added in the step 2) is 2:1.

5) Adding 428Kg of tap water into the organic phase I obtained in the step 4) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating an organic phase II and a water phase II;

in the step, the addition amount of water is controlled by ammonium chloride added in the step 2), and the mass ratio of the water to the ammonium chloride is 1:1.

6) Adding 428Kg of self-water into the organic phase II obtained in the step 5) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating out an organic phase III and a water phase III;

7) And step 6), rectifying 656Kg of the organic phase III obtained in the step under a vacuum state, and carrying out sectional collection through different top temperatures to obtain a front fraction, a middle fraction and a rear fraction. Different top temperature staging collection control points, example 1.

20Kg of a front-end fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 92.9%;

565Kg of a middle fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 98.4%;

46Kg of a post-fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 88.2%;

25Kg of residual liquid at the bottom of the kettle.

8) Firstly, throwing 565Kg of medium fraction obtained by rectifying in the step 7) into a main recrystallization kettle, then throwing 339Kg of absolute ethyl alcohol which is an organic solvent, heating to 50-60 ℃, stirring for dissolution, finally, dropwise adding 113Kg of pure water (water temperature is 50-60 ℃) according to an average speed, dropwise adding water for 5 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and continuing cooling to room temperature to obtain 1017Kg of recrystallization slurry I.

9) And 8) standing and crystallizing the slurry I obtained in the step 8) at room temperature for 12 hours, and then performing centrifugal separation to obtain 506Kg of 2-chloro-6-fluorobenzonitrile wet product (weight loss on drying is 2.2%, m/m) and 511Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ and under the vacuum degree of-0.095 Mpa for 6 hours to obtain 496Kg of finished 2-chloro-6-fluorobenzonitrile product, wherein the content is 99.63%, 2-chloro-6-fluorobenzyl chloride is 0.05%, 2-chloro-6-fluorobenzyl chloride is 0.04%, the drying loss is 0.03%, the maximum single impurity is 0.14%, and the balance is impurities.

11 511Kg of the primary mother liquor obtained by the centrifugation in the step 9) was evaporated and concentrated under reduced pressure to obtain 442Kg of an aqueous ethanol solution (water content: 25.5%) and 69Kg of a tank bottoms I, respectively.

The ethanol water solution is dehydrated through an inorganic vaporization osmotic membrane, and 320Kg of absolute ethanol is obtained and returned to the step 8) or the step 12) for recycling.

12 And (3) mixing the 69Kg kettle bottom liquid I obtained in the step (11), the 20Kg front fraction obtained in the rectification of the step (7) and the 46Kg rear fraction (135 Kg total), adding 81Kg of absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolving, finally dropwise adding 27Kg of pure water (water temperature 50-60 ℃), dropwise adding at an average speed for 3 hours until the water dropwise adding is finished, naturally cooling, precipitating crystals, and continuously cooling to room temperature to obtain 243Kg of recrystallized slurry II.

13 And 12) standing and crystallizing the slurry II obtained in the step 12) at room temperature for 24 hours, and then carrying out centrifugal separation to obtain 105Kg of crude 2-chloro-6-fluorobenzonitrile (content 98.4%, drying weight loss 2.36%) and 138Kg of secondary mother liquor, and returning the crude 2-chloro-6-fluorobenzonitrile to the step 8) for recrystallization.

14 And step 13), carrying out reduced pressure evaporation concentration on 138Kg of secondary mother liquor obtained by centrifugation to obtain 106Kg of ethanol water solution (water content 25.1%) and 32Kg of kettle bottom liquid II respectively.

The ethanol water solution is dehydrated through an inorganic vaporization permeable membrane, 72Kg of ethanol is obtained and returned to the step 8) or the step 12) for recycling.

15 Equivalent to step 15) of example 1), approximately 208Kg of dried ammonium chloride is obtained, the ammonium chloride content being 99.58%, the zinc chloride being 0.0007%, the Total Organic Carbon (TOC) being 52ppm, the moisture being 0.05%, according to the requirements of step 1). Returning to the step 1) for recycling or serving as a commodity export (fertilizer).

Example 3 has no practical significance in that it does not significantly improve the product yield or product quality, but increases the material consumption and the amount of contaminants, although the amounts of catalyst and polymerization inhibitor are increased, compared with example 1.

Example 4, a method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile, the raw materials used in step 1) of example 1 were exchanged, mainly the content of 2-chloro-6-fluorotrichlorobenzyl as the raw material was reduced from 97.3% to 95.0%, otherwise equivalent to example 1. The method comprises the following steps:

1) 1044Kg (4000 mol of 2-chloro-6-fluorotrichlorobenzyl containing 2-chloro-6-fluorotrichlorobenzyl) of solid was heated to 80℃to melt, and then put into a 2000L reaction kettle;

2-chloro-6-fluorotrichlorobenzyl described in the step 1), wherein the content of 2-chloro-6-fluorotrichlorobenzyl is 95.0%, the content of 2-chloro-6-fluorodichlorobenzyl is 1.5%, the moisture is 0.05%, the maximum unknown single impurity is 2.0%, and the rest is other impurities.

2) 428Kg (8000 mol) of ammonium chloride, 5Kg of anhydrous zinc oxide as a catalyst and 3Kg of polymerization inhibitor (EDTA) are put into the reaction kettle in the step 1). Then the reaction is carried out by stage heating, the initial reaction temperature is 200 ℃, then the temperature is raised at the rate of 3-4 ℃ per hour, and the highest reaction temperature is not more than 240 ℃.

In the embodiment, the feeding mole ratio of the raw materials of 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride is 1:2; the feeding amount of the anhydrous zinc oxide serving as the catalyst is about 0.5 percent (mass percent) of 2-chloro-6-fluorotrichlorobenzyl; the amount of the polymerization inhibitor (EDTA) to be fed was about 0.3% by mass of 2-chloro-6-fluorotrichlorobenzyl.

After about 12 hours from the initial reaction temperature of 200 ℃, monitoring the reaction progress by gas chromatography, wherein the content of the raw material 2-chloro-6-fluorotrichlorobenzyl in the material in the reaction kettle is 0.42%, and stopping the reaction to obtain 914Kg of reacted material.

3) The hydrogen chloride gas obtained by the reaction in the step 2) is absorbed by a conventional falling film and is absorbed by resin, so that 1888Kg of byproduct hydrochloric acid (the concentration is about 30%) is obtained and is taken as a product for sale;

4) Cooling 914Kg of the reacted material obtained in the step 2) to about 80 ℃, adding 856Kg of tap water into the cooled material, stirring the mixture for 30 to 60 minutes, keeping the temperature at 60 ℃ and standing the mixture for about 1 hour (obvious delamination exists), and separating an organic phase I and a water phase I;

In this step, the mass ratio of the water addition amount to the ammonium chloride added in step 2) was 2:1.

7) And (3) rectifying 686Kg of organic phase III obtained in the step (6) under a vacuum state, and carrying out sectional collection through different top temperatures to obtain a front fraction, a middle fraction and a rear fraction. Different top temperature staging collection control points example 1:

22Kg of a front-end fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 91.8%;

560Kg of a middle distillate was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 98.0%;

49Kg of a rear fraction was obtained, the content of 2-chloro-6-fluorobenzonitrile being 89.1%.

55Kg of residual liquid at the bottom of the kettle.

8) Firstly, putting 560Kg of middle distillate obtained by rectifying in the step 7) into a main recrystallization kettle, then putting 336Kg of absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolution, finally, dropwise adding 112Kg of pure water (water temperature is 50-60 ℃) according to an average speed, dropwise adding water for 5 hours until the water dropwise adding is finished, starting natural cooling, precipitating crystals, and then continuously cooling to room temperature to obtain 1008Kg of recrystallization slurry I.

The organic solvent is ethanol, ethanol/water=3/1 (m/m), and the recrystallization is carried out according to the proportion of solvent (ethanol and water)/crude product=4/5 (m/m).

9) And 8) standing and crystallizing the slurry I obtained in the step 8) at room temperature for 12 hours, and then performing centrifugal separation to obtain 495Kg of 2-chloro-6-fluorobenzonitrile wet product (weight loss on drying is 2.51%, m/m) and 513Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ and under the vacuum degree of-0.095 Mpa for 6 hours to obtain 482Kg of finished 2-chloro-6-fluorobenzonitrile product, wherein the content is 99.51 percent, the 2-chloro-6-fluorobenzyl chloride is 0.09 percent, the 2-chloro-6-fluorobenzyl chloride is 0.08 percent, the drying loss is 0.05 percent, the maximum single impurity is 0.18 percent, and the balance is impurities.

11 513Kg of primary mother liquor obtained by centrifugation in the step 9) is evaporated and concentrated under reduced pressure to obtain 435Kg of ethanol water solution (water content 25.1%) and 78Kg of kettle bottom liquid I respectively.

The ethanol aqueous solution is dehydrated through an inorganic vaporization osmotic membrane, and 316Kg of absolute ethanol is returned to the step 8) or the step 12) for recycling.

12 Mixing the 78Kg kettle bottom solution I obtained in the step 11), the 22Kg front fraction obtained in the rectification of the step 7) and the 49Kg rear fraction (total 149 Kg), adding 89.4Kg absolute ethyl alcohol which is an organic solvent, heating to 50-60 ℃, stirring for dissolving, finally dropwise adding 29.8Kg pure water (water temperature 50-60 ℃), dropwise adding according to an average speed, wherein the water dropwise adding time is 3 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and continuously cooling to room temperature to obtain 268.2Kg recrystallization slurry II.

13 And 12) standing and crystallizing the slurry II obtained in the step 12) at room temperature for 24 hours, and then carrying out centrifugal separation to obtain 114Kg of 2-chloro-6-fluorobenzonitrile crude product (content 98.1 percent, drying weight loss 2.48 percent) and 154.2Kg of secondary mother liquor, and returning the 2-chloro-6-fluorobenzonitrile crude product to the step 8) for recrystallization.

14 And step 13), carrying out reduced pressure evaporation concentration on 154.2Kg of secondary mother liquor obtained by centrifugation to obtain 117.2Kg of ethanol water solution (the water content is 25.3%) and 37Kg of kettle bottom liquid II respectively.

The ethanol water solution is dehydrated through an inorganic vaporization permeable membrane, and 78Kg of ethanol is obtained and returned to the step 8) or the step 12) for recycling.

15 Step 15) equivalent to example 1);

211Kg of dried ammonium chloride with the content of 99.59 percent, 0.0007 percent of zinc chloride and 59ppm of Total Organic Carbon (TOC) and the moisture content of 0.05 percent are obtained, which meets the requirements of the step 1). Returning to the step 1) for recycling or serving as a commodity export (fertilizer).

As can be seen from example 4, the content of the raw material 2-chloro-6-fluorotrichlorobenzyl in the step 1) is reduced from 97.3% to 95.0%, and according to the operation of the embodiment 1 of the present invention, the qualified product 2-chloro-6-fluorobenzonitrile can be produced, and the product yield and quality are slightly reduced compared with the embodiment 1.

Comparative example 1 the ammonium chloride charge of example 1, step 2), was reduced from 428Kg to 321Kg, otherwise identical to example 1. The method comprises the following steps:

1) Step 1) is equivalent to step 1) of example 1.

2) 321Kg (6000 mol) of ammonium chloride was charged into the reaction vessel described in step 1), otherwise identical to step 1) of example 1.

In the comparative example 1, the feeding mole ratio of the raw materials of 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride is 1:1.5; the feeding amount of the anhydrous zinc oxide catalyst is 0.5 percent (mass percent) of 2-chloro-6-fluorotrichlorobenzyl; the addition amount of the polymerization inhibitor (EDTA) is 0.3 percent (mass percent) of the 2-chloro-6-fluorotrichlorobenzyl.

The reaction progress was monitored by gas chromatography, and since the conversion of the starting material had not reached the design requirement (less than 0.5%), after 48 hours from the initial reaction temperature of 200 ℃, the content of 2-chloro-6-fluorotrichlorobenzyl as the starting material remained 19.46%, and the reaction was stopped to obtain 901Kg of reacted material.

3) And (2) absorbing hydrogen chloride gas obtained in the step (2) through a conventional falling film and adsorbing with resin to obtain 1557Kg of byproduct hydrochloric acid (the concentration is about 30%), and taking the byproduct hydrochloric acid as a product for export.

4) Cooling the 901Kg reacted material obtained in the step 2) to about 80 ℃, adding 642Kg tap water into the cooled material, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious layering exists), and separating an organic phase I and a water phase I;

in this step, the mass ratio of water to ammonium chloride added in step 2) was 2:1.

5) Adding 321Kg of tap water into the organic phase I obtained in the step 4) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating an organic phase II and a water phase II;

6) Adding 321Kg of self-water into the organic phase II obtained in the step 5) again for washing, stirring for 30-60 min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating out an organic phase III and a water phase III;

7) And (3) rectifying 750Kg of organic phase III obtained in the step (6) under a vacuum state, and carrying out sectional collection through different top temperatures to obtain a front fraction, a middle fraction and a rear fraction. Different top temperature staging collection control points example 1:

24Kg of a front-end fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 91.6%;

398Kg of a middle fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 96.3%;

296Kg of a post-fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 30.8%;

the residual liquid at the bottom of the kettle is 32Kg.

8) Firstly, putting 398Kg of medium fraction obtained by rectifying in the step 7) into a main recrystallization kettle, then putting 238.8Kg of absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolution, finally, dropwise adding 79.6Kg of pure water (the water temperature is 50-60 ℃) according to an average speed, dropwise adding the water for 5 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and then continuously cooling to room temperature to obtain 716.4Kg of recrystallization slurry I.

9) And 8) recrystallizing the obtained slurry I, growing the crystals for 12 hours, and performing centrifugal separation to obtain 359Kg of wet 2-chloro-6-fluorobenzonitrile (weight loss on drying of 2.52 percent, m/m) and 357.4Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ under the vacuum degree of-0.095 Mpa for 6 hours to obtain 350Kg of finished 2-chloro-6-fluorobenzonitrile with the content of 99.08 percent, 0.12 percent of 2-chloro-6-fluorobenzyl chloride, 0.59 percent of 2-chloro-6-fluorobenzyl chloride, 0.03 percent of drying loss, the maximum single impurity of other 0.12 percent and the balance of impurities.

11 357.4Kg of the primary mother liquor obtained by the centrifugation in the step 9) is evaporated and concentrated under reduced pressure to obtain 309.4Kg of ethanol water solution (water content 25.1%) and 48Kg of kettle bottom liquid I respectively.

The ethanol water solution is dehydrated through an inorganic vaporization osmotic membrane, and 219Kg of ethanol is obtained and returned to the step 8) or the step 12) for recycling.

12 Mixing the 24Kg front fraction obtained by rectifying the 48Kg kettle bottom liquid I obtained by the step 11) and the 296Kg rear fraction (total 368 Kg), adding 220.8Kg of absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolving, finally dropwise adding 73.6Kg of pure water (the water temperature is 50-60 ℃), dropwise adding according to the average speed, and the water dropwise adding time is 3 hours until the water dropwise adding is finished, starting to naturally cool, precipitating crystals, and continuously cooling to room temperature to obtain 662.4Kg of recrystallization slurry II.

13 And 12) recrystallizing the obtained slurry II, growing the crystals for 24 hours, and then carrying out centrifugal separation to obtain 89.3Kg of crude 2-chloro-6-fluorobenzonitrile (content 93.7 percent, drying weight loss 2.54 percent) and 573.1Kg of secondary mother liquor, and returning the crude 2-chloro-6-fluorobenzonitrile to the step 8) for recrystallization.

14 573.1Kg of secondary mother liquor obtained by centrifugation in the step 13) is evaporated and concentrated under reduced pressure to obtain 294.4Kg of ethanol water solution (the water content is 24.9%) and 278.7Kg of kettle bottom liquid II respectively.

The ethanol water solution is dehydrated through an inorganic vaporization osmotic membrane, and 210Kg of anhydrous organic solvent is returned to the step 8) or the step 12) for recycling.

15 Step 15) of example 1).

Compared with the example 1, the conversion rate of the raw material 2-chloro-6-fluorotrichlorobenzyl is obviously reduced due to the reduction of the feed ratio of ammonium chloride, the quality of the subsequent rectifying and recrystallization products is also influenced, and the obtained product 2-chloro-6-fluorobenzonitrile does not meet the specified requirement due to the higher impurity 2-chloro-6-fluorotrichlorobenzyl, and the main content is also lower than 99.5 percent of standard.

Comparative example 2,

The polymerization inhibitor (EDTA) of example 1, step 2) was omitted, otherwise identical to example 1, and the following were specified:

1) Step 1) is equivalent to step 1) of example 1.

2) 428Kg (8000 mol) of ammonium chloride and 5Kg of anhydrous zinc oxide as a catalyst were put into the reaction vessel described in the step 1). Other operations are equivalent to step 2 of example 1

The reaction progress was monitored by gas chromatography, and the reaction time was 10.68% of the starting material remaining after 12h of detection, starting from 200℃at the initial reaction temperature, while the material viscosity was very high, with significant polymer and tar formation. Continuing the reaction until 24 hours, wherein the content of the raw material 2-chloro-6-fluorotrichlorobenzyl is 8.47%, and stopping the reaction to obtain 986Kg of reacted material;

3) Enabling the hydrogen chloride gas obtained in the step 2) to be absorbed through a conventional falling film and absorbed through resin, so as to obtain 1558Kg byproduct hydrochloric acid (the concentration is about 30%), and using the byproduct hydrochloric acid as a product for export;

4) Cooling 986Kg of the reacted material obtained in the step 2) to about 80 ℃, adding 856Kg of tap water into the cooled material, stirring the mixture for 30 to 60 minutes, keeping the temperature at 60 ℃ and standing the mixture for about 1 hour (obvious layering exists), and separating an organic phase I and a water phase I;

in this step, the mass ratio of water to ammonium chloride added in step 2) is 2:1.

5) Adding 428Kg of tap water into the organic phase I obtained in the step 4) again for washing, stirring for 30-60min, keeping the temperature at 60 ℃ and standing for about 1h (after obvious layering), and separating an organic phase II and a water phase II;

6) Adding 428Kg of self-water into the organic phase II obtained in the step 5) again for washing, stirring for 30-60min, keeping the temperature at 60 ℃ and standing for about 1h (obvious delamination exists), and separating out an organic phase III and a water phase III;

7) Rectifying 815Kg of organic phase III obtained in the step 6) under vacuum, and collecting the organic phase III in sections through different top temperatures to obtain a front fraction, a middle fraction and a rear fraction. Different top temperature staging collection control points example 1:

28Kg of a front-end fraction was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 93.9%;

327Kg of middle distillate was obtained, in which the content of 2-chloro-6-fluorobenzonitrile was 95.8%;

98Kg of a rear fraction was obtained, the content of 2-chloro-6-fluorobenzonitrile being 32.6%.

362Kg of residual liquid at the bottom of the kettle.

8) Firstly, throwing 327Kg of middle distillate obtained by rectification in the step 7) into a main recrystallization kettle, then throwing 196.2Kg of absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolution, finally, dripping 65.4Kg of pure water (the water temperature is 50-60 ℃) according to the average speed, dripping the water for 5 hours until the water dripping is finished, starting to naturally cool, precipitating crystals, and continuing cooling to room temperature to obtain 588.6Kg of recrystallization slurry I.

9) And 8) recrystallizing the obtained slurry I, growing the crystals for 12 hours, and performing centrifugal separation to obtain 253Kg of wet 2-chloro-6-fluorobenzonitrile (weight loss on drying of 2.47%, m/m) and 335.6Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ under the vacuum degree of-0.095 Mpa for 6 hours to obtain 246Kg of finished 2-chloro-6-fluorobenzonitrile with the content of 98.72 percent, 0.11 percent of 2-chloro-6-fluorobenzyl chloride, 0.47 percent of 2-chloro-6-fluorobenzyl chloride, 0.04 percent of dry weight loss, the maximum single impurity of 0.58 percent of other impurities and the balance of impurities.

The subsequent steps are not performed.

The content of the 2-chloro-6-fluorobenzonitrile of the product obtained in the comparative example 2 is less than 99.5%, and the product is high in single impurity and does not meet the specified quality requirement. Meanwhile, the reaction produces a large amount of polymer and tar, the product yield is obviously reduced, 362Kg of kettle bottom residual liquid is produced by rectification in the step 7), more than 337Kg of kettle bottom residual liquid is produced in comparison with the method in the embodiment 1, the disposal cost is high, and the raw material utilization rate is low.

Comparative example 3, the recrystallization solvent of example 1, step 8) and step 12) was changed from ethanol/water=3/1 (m/m) to absolute ethanol, otherwise identical to example 1, comprising the following steps in order:

Steps 1-7) are equivalent to steps 1-7) of example 1.

8) Firstly, throwing 565Kg of middle distillate obtained by rectifying in the step 7) into a main recrystallization kettle, then throwing 452Kg of absolute ethyl alcohol which is an organic solvent, heating to 50-60 ℃, stirring for dissolution, preserving heat for 5 hours at 50-60 ℃, starting natural cooling, continuously cooling to room temperature after crystal precipitation, and obtaining 1017Kg of recrystallization slurry I.

In this step, the organic solvent is absolute ethanol, and the recrystallization is carried out by feeding in the ratio of solvent absolute ethanol/crude product=4/5 (m/m).

9) And 8) standing and crystallizing the slurry I obtained in the step 8) at room temperature for 12 hours, and then performing centrifugal separation to obtain 229Kg of wet 2-chloro-6-fluorobenzonitrile (1.98% of dry weight loss, m/m) and 788Kg of primary mother liquor.

10 Drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) in a vacuum oven at 70-80 ℃ under the vacuum degree of-0.095 Mpa for 6 hours to obtain 224.5Kg of finished 2-chloro-6-fluorobenzonitrile product, wherein the content is 99.21 percent, the content of 2-chloro-6-fluorobenzyl chloride is 0.09 percent, the content of 2-chloro-6-fluorobenzyl chloride is 0.26 percent, the drying loss is 0.03 percent, the maximum single impurity is 0.32 percent, and the balance is impurities.

11 788Kg of primary mother liquor obtained by centrifugation in the step 9) is evaporated and concentrated under reduced pressure to obtain 447.5Kg of organic solvent ethanol and 340.5Kg of kettle bottom liquid I respectively.

And (5) returning 447.5Kg of organic solvent ethanol obtained in the above to the step 8) or the step 12) for recycling.

12 Mixing the 340.5Kg kettle bottom liquid I obtained in the step 11), the 18Kg front fraction obtained in the rectification of the step 7) and the 45Kg rear fraction (total 403.5 Kg), adding 394.5Kg absolute ethyl alcohol serving as an organic solvent, heating to 50-60 ℃, stirring for dissolving, preserving the heat at 50-60 ℃ for 3 hours, starting natural cooling, precipitating crystals, and continuing cooling to room temperature to obtain 798Kg recrystallization slurry II.

13 And 12) recrystallizing the obtained slurry II, growing the crystals for 24 hours, and then carrying out centrifugal separation to obtain 167Kg of crude 2-chloro-6-fluorobenzonitrile (content is 97.6 percent, drying weight loss is 2.04 percent) and 631Kg of secondary mother liquor, and returning the crude 2-chloro-6-fluorobenzonitrile to the step 8) for recrystallization.

14 631Kg of secondary mother liquor obtained by centrifugation in the step 13) is evaporated and concentrated under reduced pressure to obtain 387Kg of organic solvent ethanol and 244Kg of kettle bottom liquid II.

The organic solvent returns to the step 8) or the step 12) for cyclic application.

15 Step 15) equivalent to example 1).

Comparative example 3 has a lower yield and a lower quality than example 1, indicating that the use of absolute ethanol alone as a solvent is not suitable for recrystallization, and that the effect is less than ethanol/water=3/1 (m/m).

Comparative example 4, eliminating step 15) of example 1) the removal of impurities such as high-valence metal ions by chelating resin HYC500, otherwise identical to example 1, comprises the following steps in order:

steps 1) to 14) are equivalent to steps 1) to 14) of example 1.

15 1065Kg of aqueous phase I (ammonium chloride concentration 21.1%) obtained by separating in step 4) are reacted according to 2m ³ The flow rate/h was measured by passing through a bed of HYA115 macroporous resin (resin bed diameter 1.0m, height 6m, resin loading 4 m) ³ ) Adsorbing, removing organic impurities, concentrating under reduced pressure, cooling the crystallized material, centrifuging, and concentrating mother liquor in an ammonium chloride evaporating crystallizer.

After the organic matters are removed by adsorption, the Total Organic Carbon (TOC) of the aqueous phase I is 69ppm, and the zinc ions are 0.23%.

The ammonium chloride obtained by evaporation has an ammonium chloride content of 99.32%, zinc chloride of 0.62%, a Total Organic Carbon (TOC) of 67ppm and a moisture of 0.03%, which does not meet the requirements of step 1).

The process of eliminating chelating resin HYC500 to remove high-valence metal ions and other impurities in comparative example 4 is illustrated, the metal ions of the obtained ammonium chloride are out of standard, and the ammonium chloride content is low.

Finally, it should also be noted that the above list is merely a few specific embodiments of the present invention. Obviously, the invention is not limited to the above embodiments, but many variations are possible. All modifications directly derived or suggested to one skilled in the art from the present disclosure should be considered as being within the scope of the present invention.

Claims

The synthesis and purification method of the 2-chloro-6-fluorobenzonitrile is characterized by comprising the following steps: 2-chloro-6-fluorotrichlorobenzyl and ammonium chloride are used as raw materials to react under the action of a catalyst to obtain 2-chloro-6-fluorobenzonitrile and hydrogen chloride gas;

the method sequentially comprises the following steps of:

1) Heating 2-chloro-6-fluorotrichlorobenzyl to be molten, and then putting the molten 2-chloro-6-fluorotrichlorobenzyl into a reaction kettle;

2-chloro-6-fluorotrichlorobenzyl is a byproduct of producing 2-chloro-6-fluorobenzaldehyde, the content is more than or equal to 95 percent through rectification and purification, the content of 2-chloro-6-fluorodichlorobenzyl is less than or equal to 1.5 percent, the moisture is less than or equal to 0.05 percent, and the other maximum unknown single impurity is less than 2.0 percent;

2) Adding ammonium chloride, a catalyst and a polymerization inhibitor into the reaction kettle in the step 1), then heating to 200-240 ℃ for reaction, monitoring the reaction progress through gas chromatography, and stopping the reaction when the content of 2-chloro-6-fluorotrichlorobenzyl in the materials in the reaction kettle is less than or equal to 0.5%, so as to obtain reacted materials and hydrogen chloride gas;

2-chloro-6-fluorotrichlorobenzyl: ammonium chloride = 1:2 to 3 molar ratio;

the catalyst is 0.47 to 1.0 percent of 2-chloro-6-fluorotrichlorobenzyl;

the polymerization inhibitor is 0.28 to 0.5 percent of 2-chloro-6-fluorotrichlorobenzyl;

the percentages are by weight;

the catalyst is anhydrous zinc oxide;

the polymerization inhibitor is EDTA;

3) Preparing hydrochloric acid from the hydrogen chloride gas obtained in the step 2);

4) Cooling the reacted material obtained in the step 2) to 80+/-10 ℃, adding washing water into the cooled material, stirring the mixture, and keeping the temperature at 60+/-10 ℃ and standing until layering occurs, thereby separating an organic phase I and a water phase I;

the washing water is water or water phase II obtained in the step 5) and water phase III obtained in the step 6);

the washing water is as follows: ammonium chloride=2±0.1:1 mass ratio of step 2);

5) Adding water into the organic phase I obtained in the step 4), stirring and washing, and preserving heat and standing at 60+/-10 ℃ until layering occurs, so as to separate an organic phase II and a water phase II;

water: ammonium chloride=1±0.05:1 mass ratio of step 2);

6) Adding water into the organic phase II obtained in the step 5), stirring and washing, and preserving heat and standing at 60+/-10 ℃ until layering occurs, so as to separate an organic phase III and a water phase III;

water: ammonium chloride=1±0.05:1 mass ratio of step 2);

7) Rectifying the organic phase III obtained in the step 6) in a vacuum state, and collecting the organic phase III in sections through different top temperatures of a rectifying kettle; respectively obtaining a front cut, a middle cut and a rear cut;

when the top temperature of the rectifying still is between room temperature and 140 ℃, obtaining a front fraction;

when the top temperature of the rectifying still is more than 140 ℃ and up to 160 ℃, a middle fraction is obtained;

When the top temperature of the rectifying still is more than 160 ℃ until no fraction is generated, obtaining a post fraction;

8) And (3) main recrystallization:

taking the middle distillate obtained by the rectification in the step 7) as a main recrystallization starting material, or mixing the middle distillate obtained by the rectification in the step 7) with the crude product of the 2-chloro-6-fluorobenzonitrile obtained in the subsequent step 13) to be used as the main recrystallization starting material;

adding a main recrystallization starting material into a main recrystallization kettle, adding an organic solvent, heating to 50-60 ℃, stirring until the recrystallization starting material is dissolved, finally dripping pure water, starting natural cooling after the dripping of the water is finished, and continuously cooling to room temperature to obtain recrystallization slurry I;

the organic solvent: water= (3±0.1): the mass ratio of 1 is that of the components,

the (organic solvent+water): a mass ratio of main recrystallization starting material= (4±0.1): 5;

9) Growing crystals of the recrystallized slurry I obtained in the step 8) for 12-24 hours at room temperature, and then performing centrifugal separation to obtain a wet 2-chloro-6-fluorobenzonitrile product with a drying weight loss of less than 3% and primary mother liquor;

10 Vacuum drying the wet 2-chloro-6-fluorobenzonitrile product obtained in the step 9) to obtain 2-chloro-6-fluorobenzonitrile;

11 Concentrating the primary mother liquor obtained by the centrifugation in the step 9) by reduced pressure evaporation, thereby respectively obtaining an organic solvent aqueous solution and a kettle bottom liquid I;

Dehydrating the organic solvent aqueous solution, and returning the obtained anhydrous organic solvent to the step 8) or circularly applying the anhydrous organic solvent to the step 12);

12 And (c) auxiliary recrystallization:

mixing the kettle bottom liquid I obtained in the step 11) and the front fraction and the rear fraction obtained in the step 7) after rectification, taking the mixture as an auxiliary recrystallization starting material, putting the mixture into an auxiliary recrystallization kettle, adding an organic solvent, heating to 50-60 ℃, stirring until the auxiliary recrystallization starting material is dissolved, finally dropwise adding pure water, and after the water is dropwise added, starting to naturally cool and separate out crystals, and continuously cooling to room temperature to obtain a recrystallization slurry II;

the organic solvent: water= (3±0.1): the mass ratio of 1 is that of the components,

the (organic solvent+water): auxiliary recrystallization starting material= (4±0.1): 5 mass ratio;

13 Step 12), growing crystals of the slurry II obtained by recrystallization at room temperature for 12-24 hours, and then performing centrifugal separation to obtain a 2-chloro-6-fluorobenzonitrile crude product with a drying weight loss of less than 3% and a secondary mother solution;

the 2-chloro-6-fluorobenzonitrile crude product returns to the step 8) for main recrystallization;

14 Step 14), concentrating the secondary mother liquor obtained by centrifugation by reduced pressure evaporation to obtain an organic solvent aqueous solution and a kettle bottom liquid II;

the organic solvent aqueous solution is dehydrated to obtain anhydrous organic solvent, and the anhydrous organic solvent is returned to the step 8) or the step 12) for recycling.
2. The method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 1, further comprising the steps of:

15 Post-treatment of aqueous phase i):

and 4) separating the liquid to obtain a water phase I, removing impurities through adsorption of HYA115 macroporous resin, then, entering an ammonium chloride evaporation crystallizer for reduced pressure distillation and concentration, cooling a crystallized material, centrifuging and spin-drying to obtain ammonium chloride, and returning a mother solution formed by centrifuging and spin-drying to the ammonium chloride evaporation crystallizer for circulation concentration.
3. The method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 1 or 2, wherein:

step 2) is to raise the temperature to 200 ℃ at a stage, then raise the temperature at a rate of 3-4 ℃/h, and not raise the temperature when the temperature reaches 240 ℃.
4. A method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 3, wherein:

the organic solvents in the step 8) and the step 12) are ethanol;

in the step 8), the dropping time of the pure water is 3 to 5 hours,

in step 12), the dropping time of the pure water is 3 to 5 hours.
5. The method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 4, wherein:

in the step 9), the centrifugal rotating speed is 800-1200 r/min, so that the drying weight loss of the 2-chloro-6-fluorobenzonitrile is ensured to be less than 3% by controlling the centrifugal time;

In the step 13), the centrifugal rotating speed is 800-1200 r/min, so that the drying weight loss of the 2-chloro-6-fluorobenzonitrile crude product is ensured to be less than 3% by controlling the centrifugal time.
6. The method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 5, wherein the step 10):

and (3) carrying out vacuum drying on the wet 2-chloro-6-fluorobenzonitrile obtained in the step 9) at the drying temperature of 70-80 ℃ until the drying weight loss of the obtained 2-chloro-6-fluorobenzonitrile is less than 0.05%.
7. The method for synthesizing and purifying 2-chloro-6-fluorobenzonitrile according to claim 6, wherein the step 3) is as follows: and (3) absorbing the hydrogen chloride gas obtained in the step (2) through a falling film and adsorbing the hydrogen chloride gas through resin to obtain byproduct hydrochloric acid.