Method for generating phenoxy carboxylic acid by utilizing acid exchange

Abstract

The invention discloses a method for generating phenoxy carboxylic acid by utilizing acid exchange, which belongs to the technical field of chemical industry and is a novel acid exchange reaction system taking water as a solvent, phenoxy carboxylic acid ester is taken as a raw material, a chlorinated acid aqueous solution is taken as both the raw material and the solvent, the phenoxy carboxylic acid is generated by reaction, the phenoxy carboxylic acid and chlorinated acid ester are directly obtained by one-step reaction, and the method is simple and convenient to operate. The method is high in conversion rate, short in flow, simple in process, simple in post-treatment mode, high in purity, capable of continuously returning a water phase to a system, greatly reduced in wastewater discharge amount, less in three wastes and environment-friendly.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and in particular to a method for generating phenoxycarboxylic acid by acid exchange. Background Art

[0002] Phenoxycarboxylic acid products are important pesticide products. Phenoxycarboxylic acid herbicides have the advantages of a wide weed control spectrum, good effect and low price. They are widely used in dry fields to control annual and perennial broad-leaved weeds and some weeds in the Cyperus family. Pre-emergence soil treatment also has a strong inhibitory effect on annual grass weeds and perennial weeds that propagate by seeds. Representative varieties of phenoxycarboxylic acid herbicides include 2,4-dichlorophenoxyacetic acid 2,4-D, 2,4-D ester, 2,4-D propionic acid, 2-methyl-4-chloropropionic acid, 2,4-D butyric acid, and 2-methyl-4-chloro, 4-chlorophenoxyacetic acid methyl ester.

[0003] At present, there are several main methods for synthesizing phenoxycarboxylic acid. Taking 2,4-D as an example, one process is to synthesize 2,4-dichlorophenol by chlorination reaction of phenol and chlorine, and then react 2,4-dichlorophenol sodium and sodium chloroacetate to generate 2,4-D sodium salt, and then acidify to generate 2,4-D; Patent CN100404491C uses phenol and liquid alkali to react to generate sodium phenol, sodium phenol and sodium chloroacetate to react to generate sodium phenoxyacetate, and then acidify sodium phenoxyacetate to generate phenoxyacetic acid, and then phenoxyacetic acid reacts with chlorine, etc. A chlorinating agent is used to react to generate 2,4-D; another process is for methyl chloroacetate to react with anhydrous sodium phenol to generate phenoxyacetate, methyl phenoxyacetate to react with a chlorinating agent to generate 2,4-D methyl ester, 2,4-D methyl ester is hydrolyzed under catalyst conditions to generate 2,4-D and methanol, and methanol is reacted with chloroacetic acid to generate methyl chloroacetate; these methods generally have some disadvantages: the first two process routes have a large amount of wastewater and a lot of waste salt, the third process route is long, the process is complicated, the equipment investment is large, and the investment payback period is long.

[0004] In view of the above reasons, it is necessary to develop a new method for synthesizing phenoxycarboxylic acid products. Summary of the invention

[0005] The purpose of the present application is to provide a method for producing phenoxycarboxylic acid by acid exchange, so as to solve the technical problems of cumbersome post-treatment, long synthesis route, and environmental pollution caused by large amount of wastewater and waste salt in the existing phenoxycarboxylic acid synthesis process.

[0006] To achieve the above purpose, the technical solution adopted in the present application is: to provide a method for generating phenoxycarboxylic acid by acid exchange, which specifically comprises the following steps: (i) Add phenoxycarboxylic acid ester and chlorinated acid aqueous solution into a reaction vessel, heat and premix, then add a catalyst, fill with inert gas, heat and reflux to obtain a mixed solution; (ii) The mixed liquid is transferred to a two-phase separation device for stratification to obtain a water phase and an oil phase. The water phase is recovered and returned to the system, and the oil phase is cooled and crystallized to obtain phenoxycarboxylic acid.

[0007] In one embodiment, The chlorinated acid content in the chlorinated acid aqueous solution in step (i) is 10-90%, preferably, the chlorinated acid content is 80%.

[0008] In one embodiment, In step (i), the phenoxycarboxylic acid ester is one of methyl phenoxyacetate, methyl 2,4-dichlorophenoxyacetate, methyl 2-methyl-4-chlorophenoxyacetate, methyl o-methylphenoxyacetate, ethyl phenoxyacetate, ethyl 2,4-dichlorophenoxyacetate, ethyl 2-methyl-4-chlorophenoxyacetate or ethyl o-methylphenoxyacetate. Preferably, the phenoxycarboxylic acid ester is methyl phenoxyacetate.

[0009] In one embodiment, In step (i), the chlorinated acid is one of chloroacetic acid, 2-chloropropionic acid, 3-chloropropionic acid, 2-chlorobutyric acid or 4-chlorobutyric acid. Preferably, the chlorinated acid is chloroacetic acid; and the inert gas is nitrogen.

[0010] In one embodiment, The catalyst in step (i) is one of trifluoromethanesulfonic acid, p-toluenesulfonic acid, sulfuric acid or chlorinated acid autocatalysis, and the molar ratio of the phenoxycarboxylic acid ester to the catalyst is 1: 0.01-0.5; preferably, the catalyst is trifluoromethanesulfonic acid, and the molar ratio of the phenoxycarboxylic acid ester to the catalyst is 1: 0.05-0.1.

[0011] In one embodiment, In step (i), the molar ratio of the phenoxycarboxylic acid ester to the chlorinated acid is 1:0.9-1.1. Preferably, the molar ratio of the phenoxycarboxylic acid ester to the chlorinated acid is 1:1.

[0012] In one embodiment, The temperature of the premixed mixture in step (i) is 90-95°C, preferably 90°C.

[0013] In one embodiment, The temperature of the heating in step (i) is 90-130°C.

[0014] In one embodiment, The reaction time for preparing the mixed solution in step (i) is 2-10 h, preferably, the reaction time is 8 h.

[0015] In one embodiment, The temperature of the layering in step (ii) is 50-90°C.

[0016] The present application provides a method for generating phenoxycarboxylic acid by using acid exchange, which uses acid exchange as a reaction mechanism to replace the traditional chlorination reaction and acidification reaction to synthesize phenoxycarboxylic acid. The premise of acid exchange is that water must exist. The chlorinated acid aqueous solution is both a raw material and a solvent, which reduces the input amount of raw materials. In addition, in the presence of water in the acid exchange, the temperature for separating the by-product chloroester is low, which can make the purity and yield of the main product higher, and at the same time, the temperature of the reaction is reduced to solve the problem of poor high-temperature stability of the material. Secondly, in the presence of water in the acid exchange, the chloroester produced by the acid exchange and water can be azeotropically extracted from the top of the reactive distillation tower to promote the reaction. Thirdly, the azeotropic product of the chloroester and water extracted from the top of the tower can be directly separated, and the separated chloroacetic acid ester is returned to the condensation process, and the water is used to prepare the chloroacetic acid aqueous solution. Fourth, water exists in the acid exchange, and sodium chloride exists in a dissolved state, and the salting-out effect is more conducive to the subsequent phase separation of the product; in addition, the aqueous phase obtained by stratification can be recycled as a solvent. For example, when the concentration of the chlorinated acid is high, the high-concentration chlorinated acid is generally diluted to form a dilute chlorinated acid aqueous solution, and then the aqueous phase can be mixed with the concentrated chlorinated acid in proportion to form a dilute chlorinated acid aqueous solution for the next batch of synthetic reactions, and the aqueous phase can be continuously applied and applied many times; the oil phase can be directly cooled and crystallized to obtain a qualified solid product phenoxycarboxylic acid; the present application directly obtains phenoxycarboxylic acid and chlorinated acid esters in a one-step reaction, with high conversion rate, short process, simple process, simple post-treatment method, high purity, and the aqueous phase can be continuously returned to the system, which greatly reduces the amount of wastewater discharged, reduces the three wastes, is environmentally friendly, and is conducive to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0018] Figure 1 This is the HPLC spectrum of phenoxyacetic acid in Example 1; Figure 2 Schematic diagram of the synthesis reaction equation. DETAILED DESCRIPTION

[0019] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0020] Example 1 (i) Add 167.7 g of 99% methyl phenoxyacetate and 118.2 g of 80% aqueous chloroacetic acid to a four-necked flask, heat to 90°C for premixing, add 15 g of trifluoromethanesulfonic acid after mixing evenly, fill with nitrogen, maintain the temperature between 90-130°C for reflux reaction for 8 h, and obtain a mixed solution; (ii) The mixed solution was transferred to a two-phase separation device for separation to obtain a water phase and an oil phase. The methyl chloroacetate generated by the reaction was continuously separated from the water phase. The separated water was continuously recovered and returned to step (i) to obtain about 173.2 g of a separated oil phase. At this time, the unconverted methyl phenoxyacetate was detected to be less than 0.1%. The material in the reaction flask was cooled to 80 ° C for separation, and 23 g of the upper water phase was separated. The lower layer obtained an oil phase, and the material phenoxyacetic acid was obtained by cooling and crystallization. 150.2 g of the material was obtained, and the detected content was 98.5%. The structural characterization is as follows Figure 1 The reaction equation is as shown Figure 2 As shown, wherein R1 is -CH2COOCH3, R2 is -CH2COOH, and R3 is -H; R1, R2, and R3 may also be other similar functional groups, see the following embodiments.

[0021] Example 2 (i) Add 237.5 g of 99% methyl 2,4-dichlorophenoxyacetate and 118.2 g of 80% aqueous chloroacetic acid solution to a four-necked flask, heat to 90°C for premixing, add 15 g of trifluoromethanesulfonic acid after mixing evenly, fill with nitrogen, maintain the temperature between 90-130°C for reflux reaction for 8 h, and obtain a mixed solution; (ii) The mixed solution was transferred to a two-phase separation device for stratification to obtain an aqueous phase and an oil phase. The methyl chloroacetate generated by the reaction was continuously separated from the aqueous phase, and the separated water was continuously recovered and returned to step (i) to obtain a separated oil phase of about 238.54 g. At this time, the unconverted 2,4-dichlorophenoxyacetic acid methyl ester was detected to be less than 0.1%. The material in the reaction flask was cooled to 80°C for stratification, and 19.32 g of the upper aqueous phase was separated, and the lower layer obtained an oil phase. The material 2,4-dichlorophenoxyacetic acid 219.22 g was obtained by cooling and crystallization, and the detected content was 98.59%.

[0022] Example 3 (i) Add 216.7 g of 99% 2-methyl-4-chlorophenoxyacetic acid methyl ester and 118.2 g of 80% chloroacetic acid aqueous solution into a four-necked flask, heat to 90°C for premixing, add 15 g of trifluoromethanesulfonic acid after mixing evenly, fill with nitrogen, maintain the temperature between 90-130°C for reflux reaction for 8 h, and obtain a mixed solution; (ii) The mixed solution was transferred to a two-phase separation device for stratification to obtain an aqueous phase and an oil phase. The methyl chloroacetate generated by the reaction was continuously separated from the aqueous phase, and the separated water was continuously recovered and returned to step (i) to obtain a separated oil phase of about 222.07 g. At this time, the unconverted 2-methyl-4-chlorophenoxyacetic acid methyl ester was detected to be less than 0.1%. The material in the reaction flask was cooled to 80°C for stratification, and 23.2 g of the upper aqueous phase was separated, and the lower layer obtained an oil phase. The material 2-methyl-4-chlorophenoxyacetic acid 198.87 g was obtained by cooling and crystallization, and the detected content was 98.62%.

[0023] Example 4 (i) Add 182 g of 99% methyl o-methylphenoxyacetate and 118.2 g of 80% chloroacetic acid aqueous solution into a four-necked flask, heat to 90°C for premixing, add 15 g of trifluoromethanesulfonic acid after mixing evenly, fill with nitrogen, maintain the temperature between 90-130°C for reflux reaction for 8 h, and obtain a mixed solution; (ii) The mixed solution was transferred to a two-phase separation device for stratification to obtain an aqueous phase and an oil phase. The methyl chloroacetate generated by the reaction was continuously separated from the aqueous phase, and the separated water was continuously recovered and returned to step (i) to obtain a separated oil phase of about 187.05 g. At this time, the unconverted methyl o-methylphenoxyacetate was detected to be less than 0.1%. The material in the reaction flask was cooled to 80°C for stratification, and 22.9 g of the upper aqueous phase was separated, and the lower layer obtained the oil phase. The solid material o-methylphenoxyacetic acid 164.15 g was obtained by cooling and crystallization, and the detected content was 98.77%.

[0024] Example 5 The difference between this embodiment and embodiment 1 is that the content of chloroacetic acid in the chloroacid aqueous solution is 10%, the mass of the chloroacetic acid aqueous solution is 1040 g, and the other operations are the same. After layered cooling and crystallization, 150.6 g of phenoxyacetic acid is obtained, and the detected content is 98.29%.

[0025] Example 6 The difference between this embodiment and embodiment 1 is that the content of chloroacetic acid in the chloroacid aqueous solution is 30%, the mass of the chloroacetic acid aqueous solution is 316 g, and the other operations are the same. After layered cooling and crystallization, 149.89 g of phenoxyacetic acid is obtained, and the detected content is 98.11%.

[0026] Example 7 The difference between this embodiment and embodiment 1 is that the content of chloroacetic acid in the chloroacid aqueous solution is 50%, the mass of the chloroacetic acid aqueous solution is 171 g, and the other operations are the same. After layered cooling and crystallization, 135.39 g of phenoxyacetic acid is obtained, and the detected content is 98.61%.

[0027] Example 8 The difference between this embodiment and embodiment 1 is that the content of chloroacetic acid in the chloroacid aqueous solution is 90%, the mass of the chloroacetic acid aqueous solution is 106 g, and the other operations are the same. After layered cooling and crystallization, 151.2 g of phenoxyacetic acid is obtained, and the detected content is 98.76%.

[0028] Example 9 The difference between this embodiment and embodiment 1 is that methyl phenoxyacetate is replaced with ethyl phenoxyacetate, the added mass of ethyl phenoxyacetate is 182 g, the added mass of 90% chloroacetic acid aqueous solution is 105.1 g, and the other operations are the same, and 150.15 g of phenoxyacetic acid is obtained, the detected content is 98.64%, and the by-product is ethyl chloroacetate.

[0029] Example 10 The difference between this embodiment and embodiment 9 is that ethyl phenoxyacetate is replaced with ethyl 2,4-dichlorophenoxyacetate, the added mass of ethyl 2,4-dichlorophenoxyacetate is 252 g, the added mass of 90% chloroacetic acid aqueous solution is 105.1 g, and the other operations are the same, and 219.7 g of 2,4-dichlorophenoxyacetic acid is obtained, and the detected content is 98.11%.

[0030] Embodiment 11 The difference between this embodiment and embodiment 9 is that ethyl phenoxyacetate is replaced with ethyl 2-methyl-4-chlorophenoxyacetate, the added mass of ethyl 2-methyl-4-chlorophenoxyacetate is 231 g, the added mass of 90% chloroacetic acid aqueous solution is 105.1 g, and the other operations are the same, and 197.99 g of 2-methyl-4-chlorophenoxyacetic acid is obtained, and the detected content is 98.33%.

[0031] Example 12 The difference between this embodiment and embodiment 9 is that ethyl phenoxyacetate is replaced with ethyl o-methylphenoxyacetate, the added mass of ethyl o-methylphenoxyacetate is 196 g, the added mass of 90% chloroacetic acid aqueous solution is 105 g, and the other operations are the same. The mass of the obtained o-methylphenoxyacetic acid is 163.5 g, and the detected content is 98.88%.

[0032] Example 13 The difference between this embodiment and embodiment 1 is that chloroacetic acid is replaced by 2-chloropropionic acid, and the added mass of 80% 2-chloropropionic acid aqueous solution is 135.5 g. The other operations are the same, and the mass of the obtained 2-phenoxypropionic acid is 150.03 g, and the detected content is 98.66%.

[0033] Embodiment 14 The difference between this embodiment and embodiment 1 is that chloroacetic acid is replaced by 3-chloropropionic acid, and the added mass of 80% 3-chloropropionic acid aqueous solution is 135.5 g. The other operations are the same, and the mass of the obtained phenoxypropionic acid is 148.44 g, and the detected content is 98.27%.

[0034] Embodiment 15 The difference between this embodiment and embodiment 1 is that chloroacetic acid is replaced by 2-chlorobutyric acid, and the added mass of 80% 2-chlorobutyric acid aqueous solution is 153 g. The other operations are the same, and the mass of the obtained 2-phenoxyvaleric acid is 149.00 g, and the detected content is 98.34%.

[0035] Example 16 The difference between this embodiment and embodiment 1 is that chloroacetic acid is replaced by 4-chlorobutyric acid, and the added mass of 80% 4-chlorobutyric acid aqueous solution is 153 g. The other operations are the same, and the mass of phenoxybutyric acid obtained is 148.36 g, and the detected content is 98.11%.

[0036] Embodiment 17 The difference between this embodiment and embodiment 1 is that trifluoromethanesulfonic acid is replaced by p-toluenesulfonic acid, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 148.88 g, and the detected content is 98.17%.

[0037] Embodiment 18 The difference between this embodiment and embodiment 1 is that trifluoromethanesulfonic acid is replaced by sulfuric acid, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 148.31 g, and the detected content is 97.89%.

[0038] Embodiment 19 The difference between this embodiment and embodiment 1 is that no additional catalyst is added, and chloroacetic acid is used for self-catalysis. The other operations are the same, and the mass of the obtained phenoxyacetic acid is 146.31 g, and the detected content is 96.89%.

[0039] Embodiment 20 The difference between this embodiment and embodiment 1 is that the premixing temperature is 95° C., and the other operations are the same. The mass of the obtained phenoxyacetic acid is 149.13 g, and the detected content is 98.77%.

[0040] Embodiment 21 The difference between this embodiment and embodiment 1 is that the reaction time of step (I) is 2 h, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 135.12 g, and the detected content is 97.33%.

[0041] Embodiment 22 The difference between this embodiment and embodiment 1 is that the reaction time of step (I) is 5 h, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 139.00 g, and the detected content is 97.54%.

[0042] Embodiment 23 The difference between this embodiment and embodiment 1 is that the reaction time of step (I) is 10 h, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 150.13 g, and the detected content is 98.67%.

[0043] Embodiment 24 The difference between this embodiment and embodiment 1 is that the temperature of layering in step (ii) is 50°C, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 150.73 g, and the detected content is 98.55%.

[0044] Embodiment 25 The difference between this embodiment and embodiment 1 is that the temperature of layering in step (ii) is 90° C., and the other operations are the same. The mass of the obtained phenoxyacetic acid is 149.49 g, and the detected content is 98.43%.

[0045] Embodiment 26 The difference between this embodiment and embodiment 1 is that the molar ratio of methyl phenoxyacetate to trifluoromethanesulfonic acid in step (i) is changed from 1:0.1 to 1:0.05, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 149.49 g, and the detected content is 97.15%.

[0046] Embodiment 27 The difference between this embodiment and embodiment 1 is that the molar ratio of methyl phenoxyacetate to trifluoromethanesulfonic acid in step (i) is changed from 1:0.1 to 1:0.01, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 148.32 g, and the detected content is 97.17%.

[0047] Embodiment 28 The difference between this embodiment and embodiment 1 is that the molar ratio of methyl phenoxyacetate to trifluoromethanesulfonic acid in step (i) is changed from 1:0.1 to 1:0.5, and the other operations are the same. The mass of the obtained phenoxyacetic acid is 149.98 g, and the detected content is 97.65%.

[0048] Table 1 Yield table of some examples

[0049] The present application provides a method for generating phenoxycarboxylic acid by using acid exchange, which specifically comprises the following steps: adding phenoxycarboxylic acid ester and chlorinated acid aqueous solution into a reaction container, heating and premixing, then adding a catalyst, charging inert gas to raise the temperature, and obtaining a mixed solution; transferring the mixed solution to a two-phase separation device for stratification to obtain an aqueous phase and an oil phase, recycling the aqueous phase back into the system, cooling and crystallizing the oil phase, and obtaining phenoxycarboxylic acid; the present application uses acid exchange as a reaction mechanism, replacing the traditional chlorination reaction and acidification reaction to synthesize phenoxycarboxylic acid, the premise of acid exchange must be the presence of water, the chlorinated acid aqueous solution is both a raw material and a solvent, and the amount of raw material input is reduced; and in the presence of water in the acid exchange, the temperature of separating the by-product chlorinated acid ester is low, so that the purity and yield of the main product can be higher, and at the same time, the reaction temperature is reduced to solve the problem of poor high-temperature stability of the material; secondly, in the presence of water in the acid exchange, the chlorinated acid ester and water produced by the acid exchange can be azeotropically extracted from the top of the reactive distillation tower, promoting the reaction; Thirdly, the azeotrope of chloroacid ester and water taken out from the top of the tower can be directly separated, and the separated methyl chloroacetate is returned to the condensation process, and the water is used to prepare the chloroacetic acid aqueous solution, which greatly saves the production cost; fourthly, water exists in the acid exchange, and sodium chloride exists in a dissolved state, and the salting-out effect is more conducive to the subsequent phase separation of the product; in addition, the aqueous phase obtained by stratification can be recycled as a solvent. For example, when the concentration of the chloroacid is high, the high-concentration chloroacid is generally diluted to prepare a dilute chloroacid aqueous solution, and then the aqueous phase can be mixed with the concentrated chloroacid in proportion to prepare a dilute chloroacid aqueous solution for the next batch of synthetic reactions, and the aqueous phase can be continuously applied, and the application number is large; the oil phase can be directly cooled and crystallized to obtain a qualified solid product phenoxycarboxylic acid; the present application directly obtains phenoxycarboxylic acid and chloroacid ester in a one-step reaction, with high conversion rate, short process, simple process, simple post-treatment method, high purity, and the aqueous phase can be continuously returned to the system, so that the wastewater discharge is greatly reduced, the three wastes are reduced, and it is environmentally friendly.

[0050] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0051] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for producing phenoxycarboxylic acid by acid exchange, characterized in that: The specific steps include: (i) Add phenoxycarboxylic acid ester and chlorinated acid aqueous solution into a reaction vessel, heat and premix, then add a catalyst, fill with inert gas, heat and reflux to obtain a mixed solution; (ii) The mixed liquid is transferred to a two-phase separation device for stratification to obtain a water phase and an oil phase. The water phase is recovered and returned to the system, and the oil phase is cooled and crystallized to obtain phenoxycarboxylic acid.

2. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The content of chlorinated acid in the chlorinated acid aqueous solution in step (1) is 10-90%.

3. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The phenoxycarboxylic acid ester in step (i) is one of methyl phenoxyacetate, methyl 2,4-dichlorophenoxyacetate, methyl 2-methyl-4-chlorophenoxyacetate, methyl o-methylphenoxyacetate, ethyl phenoxyacetate, ethyl 2,4-dichlorophenoxyacetate, ethyl 2-methyl-4-chlorophenoxyacetate or ethyl o-methylphenoxyacetate.

4. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: In step (i), the chlorinated acid is one of chloroacetic acid, 2-chloropropionic acid, 3-chloropropionic acid, 2-chlorobutyric acid or 4-chlorobutyric acid, and the inert gas is nitrogen.

5. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The catalyst in step (i) is one of trifluoromethanesulfonic acid, p-toluenesulfonic acid, sulfuric acid or chlorinated acid autocatalysis; the molar ratio of the phenoxycarboxylic acid ester to the catalyst is 1:0.01-0.

5.

6. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: In step (i), the molar ratio of the phenoxycarboxylic acid ester to the chlorinated acid is 1:0.9-1.

1.

7. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The temperature of the heated premix in step (i) is 90-95°C.

8. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The temperature of the heating in step (i) is 90-130°C.

9. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The reaction time for preparing the mixed solution in step (i) is 2-10 h.

10. The method for producing phenoxycarboxylic acid by acid exchange according to claim 1, characterized in that: The temperature of the layering in step (ii) is 50-90°C.

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