A continuous process for the preparation of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester

Abstract

The application discloses a continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, and belongs to the technical field of pesticide synthesis. The continuous preparation method is as follows: chloroacetic acid, isooctyl alcohol and a catalyst are mixed, and then are fed into a micro-channel esterification through a feeding pump; reaction liquid is collected, oil-water separation is performed on the reaction liquid, water is removed, and chloroacetic acid isooctyl ester is obtained; then o-cresol, a solvent, alkali and the chloroacetic acid isooctyl ester are respectively mixed, and then are fed into a continuous multi-stage stirring reactor for condensation reaction through a feeding pump; reaction liquid is collected, the alkali and the solvent are removed, and o-cresol phenoxyacetic acid isooctyl ester is obtained; finally, the o-cresol phenoxyacetic acid isooctyl ester is prepared into a 20% solution, and then is fed into a micro-channel reactor; after chlorination and removal of excessive chlorine and the solvent, 2-methyl-4-chlorophenoxyacetic acid isooctyl ester is obtained. The continuous preparation process is adopted, and the method has the advantages of short reaction time, high product purity, high yield, green environmental protection and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of pesticide synthesis, and particularly relates to a continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester. Background Art

[0002] While a wide variety of herbicides are currently commercially available, phenoxycarboxylic acid herbicides are the second most widely manufactured and used herbicide class globally, second only to glyphosate. Since the discovery and application of 2,4-D in 1942, phenoxycarboxylic acid compounds have experienced over 70 years of development as important herbicides. Their high selectivity and high spectral efficiency have earned them widespread acceptance, holding an irreplaceable position in today's market share. Phenoxycarboxylic acid herbicides are systemic, rapidly absorbed by plant roots and leaves and distributed throughout the plant. This leads to excessive concentrations of growth hormones within weeds, which in turn impacts plant cell growth and metabolism. These compounds can affect nearly every physiological process of plant growth, disrupting growth mechanisms and ultimately leading to weed death. In addition to their herbicidal properties, phenoxycarboxylic acid compounds also act as growth regulators, making them important intermediates in the synthesis of pesticides and pharmaceuticals. Different substituents and positions on the benzene ring, as well as the number of carbon atoms in the carboxylic acid, have led to the development of various phenoxycarboxylic acid herbicides, including 2-methyl-4-chlorophenoxyacetic acid; 2-methyl-4-chlorophenoxyacetic acid isooctyl ester; 2,4-dichlorophenoxyacetic acid; 2,4-dichlorophenoxyacetic acid butyl ester; 2,4-dichlorophenoxyacetic acid isooctyl ester; and 2,4-dibromophenoxyacetic acid. The selectivity, conductivity, and herbicidal activity exhibited by phenoxycarboxylic acid herbicides have ensured their continued importance as important herbicides to this day, forming the foundation for subsequent herbicide development and promoting the advancement of chemical weed control. Consequently, global research on phenoxycarboxylic acid herbicides continues to this day.

[0003] A search revealed a publicly available preparation process for 2-methyl-4-chlorophenoxyacetic acid, including CN 108774126 A. This process uses o-cresol, chloroacetic acid, and ethylene dichloride as raw materials, and proceeds through sodium chloride, condensation, chlorination, and salt formation to ultimately produce 2-methyl-4-chlorophenoxyacetic acid. This synthesis process suffers from high energy consumption and significant exhaust gas pollution from chlorination. Patent CN 101941903 A proposes reacting 2-methylphenoxyacetic acid with chlorine gas in a sodium hydroxide aqueous solution in the presence of catalysts such as dimethylaminopyridine and dimethylformamide to produce the finished product, 2-methyl-4-chlorophenoxyacetic acid. This process achieves a 95% yield and an active ingredient content exceeding 97%. However, the expensive raw material, 2-methylphenoxyacetic acid, leads to high production costs and produces significant exhaust gas pollution.

[0004] Patent CN113173844A primarily involves the following steps: A) adding o-cresol and chloroacetic acid to a composite organic solvent, cooling the system to 10-20°C, and then adding a solid base to initiate a salt-forming reaction; B) after the salt-forming reaction, adding trimethylamine hydrochloride as a catalyst, and raising the temperature to 100-130°C for a condensation reaction; C) after the condensation reaction, cooling the system to 25-35°C, and adding sodium hypochlorite to initiate a hypochlorination reaction to produce sodium 2-methyl-4-chlorophenoxyacetate; D) after the hypochlorination reaction, controlling the temperature to 50-80°C, and adding hydrochloric acid for acidification to obtain 2-methyl-4-chlorophenoxyacetic acid. This invention achieves a yield of 94% and a content of 97%. However, this invention consumes a lot of energy, and the use of sodium hypochlorite as a chlorinating agent poses significant safety risks. Furthermore, according to the examples described in the document, there are uncertainties in the production process, posing significant risks.

[0005] Patent CN101921190A proposes the production of 2-methylphenoxyacetic acid by introducing chlorine into an alcoholic solvent (corresponding to the alcohol portion of the target ester) in the presence of phenothiazine and dimethylaminopyridine as catalysts to produce esters of 2-methyl-4-chlorophenoxyacetic acid. The total yield of 2-methyl-4-chlorophenoxyacetic acid esters is increased to over 92%, and the active ingredient content is increased to over 93%. However, this technology utilizes expensive o-methylphenoxyacetic acid, resulting in high production costs.

[0006] Patent CN111646879A uses sodium o-methylphenolate as a reactant and an organic phase methyl chloroacetate solution as a reaction solvent in the condensation reaction. Chlorine is then introduced into the condensed reaction solution for chlorination. After completion, the solution is transferred to a hydrolysis reactor to obtain a sodium salt solution of 2-methyl-4-chloro-2-one. Hydrochloric acid is added to the solution for hydrolysis to obtain 2-methyl-4-chloro-2-one. Although this technology can produce both 2-methyl-4-chloro-2-one sodium salt and 2-methyl-4-chloro-2-one, the chlorine reacts with methanol during the chlorination reaction, resulting in side reactions and reducing reaction efficiency.

[0007] 2-Methyl-4-chloropropane is mainly used for the following crops: winter wheat fields, summer corn fields, wheat fields, spring wheat fields, spring corn fields, citrus orchards, paddy field borders, rice transplanting fields, rice fields, rice fields (direct seeding), rice transplanting fields, corn fields, sugarcane fields, transplanted rice fields, apple orchards, millet fields, and non-arable land. 2-Methyl-4-chloropropane is usually used in the form of its sodium salt, and can also be made into its isooctyl ester, which has the characteristics of high efficiency and low toxicity. 2-Methyl-4-chloropropane sodium salt is basically obtained by hydrolysis of 2-Methyl-4-chloropropane, and its synthesis process is based on 2-Methyl-4-chloropropane. 2-Methyl-4-chloropropane sodium salt is mainly used for the following crops: winter wheat fields, summer corn fields, wheat, wheat fields, spring wheat fields, eucalyptus forests, rice, dry direct seeding rice fields, rice fields (direct seeding), rice transplanting fields, corn, corn fields, sugarcane fields, transplanted rice fields, apple orchards, non-arable land, sorghum, and tall fescue lawns. 2-Methyl-4-chlorophenoxyacetic acid 2-ethylhexyl ester is mainly used in the following crops: winter wheat fields, soybean fields, wheat fields, spring wheat fields, spring corn fields, rice fields (direct seeding), rice transplanting fields, corn fields, millet fields, and sorghum fields. Among them, 2-methyl-4-chlorophenoxyacetic acid 2-ethylhexyl ester is more active than 2-methyl-4-chlorophenoxyacetic acid sodium (2-methyl-4-chlorophenoxyacetic acid sodium), has better effects on resistant weeds, and is safer. For example, for resistant cruciferous weeds, 2-methyl-4-chlorophenoxyacetic acid sodium (2-methyl-4-chlorophenoxyacetic acid sodium) has poor low temperature resistance and is prone to phytotoxicity at low temperatures, while 2-methyl-4-chlorophenoxyacetic acid 2-ethylhexyl ester is resistant to low temperatures and is safer to use at low temperatures than 2-methyl-4-chlorophenoxyacetic acid sodium (2-methyl-4-chlorophenoxyacetic acid sodium). When used under the same low temperature conditions, the phytotoxicity is much lower than that of 2-methyl-4-chlorophenoxyacetic acid sodium.

[0008] 2-Methyl-4-chlorophenoxyacetic acid 2-ethylhexyl ester, also known as 2-methyl-4-chloro-2-ethylhexyl ester, is a phenoxycarboxylic acid herbicide characterized by high efficacy, low toxicity, low residue, no weed resistance, and environmental friendliness. It is widely used to control annual and perennial broadleaf weeds in paddy fields, wheat fields, corn, sugarcane, and other grass crops. With the emergence of 2-methyl-4-chloro-2-ethylhexyl ester, it is expected to increasingly replace 2-methyl-4-chloro-2-ethylhexyl ester in the future. A search revealed a publicly available preparation process for 2-methyl-4-chloro-2-ethylhexyl ester in the literature by Yan Chuanming et al. from the Jiangsu Pesticide Research Institute. The main process involves esterification using 2-methyl-4-chloro-2-ethylhexyl ester with isooctyl alcohol under hydrochloric acid catalysis to produce 2-methyl-4-chloro-2-ethylhexyl ester with a product content of 90.2% and an overall yield of ≥95%. (Chemical Industry Times, November 2000). This process uses hydrochloric acid as a catalyst, and the product content and overall yield could be further improved.

[0009] Patent CN102295561A proposes a process using o-cresol as a raw material, which reacts with caustic soda to produce sodium o-cresol. Chloroacetic acid reacts with caustic soda to produce sodium chloroacetate, which is then added dropwise to the sodium o-cresol to produce sodium 2-methylphenoxyacetate. Hydrochloric acid is then added to produce 2-methylphenoxyacetic acid, followed by chlorination with chlorine to produce 2-methyl-4-chlorophenoxyacetic acid, which is then esterified with isooctyl ester to produce 2-methyl-4-chloroisooctyl ester. Currently disclosed 2-methyl-4-chloroisooctyl ester is obtained through the esterification of 2-methyl-4-chloroisooctyl ester, which has a long and complex process and a low overall yield, resulting in increased production costs. Summary of the Invention

[0010] In view of the above problems existing in the prior art, the technical problem to be solved by the present invention is to provide a green, efficient and continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, which has the advantages of short reaction time and high conversion rate.

[0011] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0012] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester comprises the following steps:

[0013] (1) Esterifying chloroacetic acid and isooctyl alcohol under acid catalysis, controlling the temperature and reaction time, and performing gas phase detection, and completing the reaction to obtain isooctyl chloroacetate; the reaction formula is as follows:

[0014]

[0015] (2) o-cresol, solvent, alkali, and isooctyl chloroacetate are added to a reactor, and the temperature is controlled to condense to produce o-cresol phenoxyacetic acid isooctyl ester; the reaction formula is as follows:

[0016]

[0017] (3) o-cresol phenoxyacetic acid 2-ethylhexyl ester is prepared into a solution, chlorinated by a microchannel reactor, and then transferred to a concentration kettle to remove chlorine and solvent to obtain 2-methyl-4-chlorophenoxyacetic acid 2-ethylhexyl ester; the reaction formula is as follows:

[0018]

[0019] In step 1), the reaction temperature is 80-90° C. and the reaction time is 8 h.

[0020] In step (2), the solvent is selected from N,N-dimethylformamide, acetonitrile, acetone, and dichloroethane.

[0021] In step (2), the base is selected from sodium carbonate, potassium carbonate, cesium carbonate, sodium methoxide, and sodium ethoxide.

[0022] In step (2), the condensation reaction temperature is 80° C. and the reaction time is 8-12 h.

[0023] In step (3), the reaction temperature is 80-90°C and the reaction time is 40-60s.

[0024] A continuous preparation method for 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, comprising the following steps:

[0025] 1) dissolving chloroacetic acid in isooctyl alcohol to prepare a mixed solution A, adding concentrated sulfuric acid to the isooctyl alcohol to prepare a solution B, respectively feeding A and B into a microchannel reactor through two feed pumps for reaction, temperature-controlled esterification reaction, and performing oil-water separation on the reaction solution, whereby the oil phase is isooctyl chloroacetate;

[0026] 2) o-cresol and the isooctyl chloroacetate prepared in step 1) are dissolved in dichloroethane to form a solution C, potassium carbonate is dissolved in dichloroethane to form a turbid solution D, and C and D are respectively fed into a continuous multi-stage stirred reactor using two feed pumps, and the reaction is temperature-controlled. After completion, the filtrate is a solution of isooctyl o-methylphenoxyacetate, and the solvent is removed to obtain isooctyl o-methylphenoxyacetate;

[0027] 3) The o-methylphenoxyethyl ester prepared in step 2) is prepared into a solution, fed into a microchannel by a feed pump, and subjected to a chlorination reaction under temperature control. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 2-methyl-4-chloroethyl ester.

[0028] In step 1), the temperature was controlled at 90° C. and the reaction was carried out for 2 min.

[0029] In step 2), the temperature was controlled at 80° C. and the reaction was carried out for 5 h.

[0030] In step 3), the temperature was controlled at 80° C. and the reaction was carried out for 60 seconds.

[0031] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0032] (1) The present invention provides a continuous preparation method for 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, comprising esterifying chloroacetic acid with isooctyl alcohol to obtain isooctyl chloroacetate, then directly condensing isooctyl chloroacetate with o-cresol to prepare isooctyl o-cresol phenoxyacetic acid, and then chlorinating the isooctyl o-cresol phenoxyacetic acid to obtain isooctyl 2-methyl-4-chlorophenoxyacetic acid. The preparation process is simple, time consumption is greatly reduced, and production efficiency is improved.

[0033] (2) This method can be produced continuously. Compared with the existing public technology, the reaction process is clean, the wastewater output is small, the product purity is as high as 92.5% or more, the conversion rate and yield are high, and the yield reaches more than 94.5%. The solvent can be recycled.

[0034] (3) The present invention uses a microchannel reactor for chlorination, which shortens the chlorination process time, greatly improves operational safety, and reduces the probability of side reactions. Compared with traditional kettle reactors, it greatly reduces labor costs and improves work efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flow chart of the preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester of Example 1-5;

[0036] Figure 2 This is a flow chart of the continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester of Example 6-10. DETAILED DESCRIPTION

[0037] The present invention will be further described below with reference to specific examples. The following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. All raw materials used can be obtained from public commercial sources unless otherwise specified.

[0038] The purity of the raw materials used in the following examples are: chloroacetic acid purity 98%, isooctyl alcohol purity 98%, and o-cresol purity 98%.

[0039] In the following examples, the product purity was determined by the area normalization method; the product yield was calculated using the formula:

[0040]

[0041]

[0042]

[0043] Example 1

[0044] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 1 The specific steps are as follows:

[0045] 1) 4000g of chloroacetic acid was added to a reactor (synthesis reactor), 3812g of isooctyl alcohol was added, 200g of concentrated sulfuric acid was added dropwise, and the reaction was carried out at 90°C for 8h. The gas phase was controlled and the reaction endpoint was when the isooctyl alcohol content was less than 0.5%. After the reaction was completed, water was removed to obtain 5984g of isooctyl chloroacetate with a purity of 98% and a yield of 98.9%.

[0046] 2) 500 g of o-cresol was added to a reaction kettle (condensation kettle), 3000 mL of N,N-dimethylformamide was added, 1917 g of potassium carbonate was added, and 956 g of isooctyl chloroacetate prepared in step 1) was added. The mixture was reacted at 80° C. for 12 h, and the liquid phase was controlled. After the o-cresol was completely reacted (or the concentration was <0.5%), the mixture was filtered and the solvent was removed. The solvent was recovered and reused in the above-mentioned reaction kettle to obtain 1248 g of isooctyl o-methylphenoxyacetate with a purity of 95% and a yield of 97.3%.

[0047] 3) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 2) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentration vessel to remove excess chlorine and solvent (for recycling), yielding 1067 g of 2-methyl-4-chloroisooctyl ester with a purity of 90% and a yield of 94.6%.

[0048] Example 2

[0049] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 1 The specific steps are as follows:

[0050] 1) adding 500 g of o-cresol to a reactor, adding 3000 mL of N,N-dimethylformamide, adding 2260 g of cesium carbonate, adding 960 g of isooctyl chloroacetate prepared in Example 1), reacting at 80° C. for 12 h, controlling the liquid phase, filtering after the o-cresol is completely reacted (or <0.5%), removing the solvent, and recycling the solvent to the above reactor for reuse, to obtain 1261 g of isooctyl o-methylphenoxyacetate with a purity of 97% and a yield of 98.3%;

[0051] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 1) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentrator to remove excess chlorine and solvent, thereby obtaining 1067 g of 2-methyl-4-chloroisooctyl ester with a purity of 92% and a yield of 94.6%.

[0052] Example 3

[0053] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 1 The specific steps are as follows:

[0054] 1) 500 g of o-cresol was added to a reactor, 4000 mL of acetonitrile was added, 1000 g of sodium carbonate was added, and 960 g of isooctyl chloroacetate prepared in Example 1) was added. The mixture was reacted at 80° C. for 12 h. The liquid phase was controlled. After the o-cresol was completely reacted (or the concentration was <0.5%), the mixture was filtered and the solvent was removed. The solvent was recovered and reused in the reactor to obtain 1262 g of isooctyl o-methylphenoxyacetate with a purity of 97.2% and a yield of 98.4%.

[0055] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 1) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentrator to remove excess chlorine and solvent, thereby obtaining 1067 g of 2-methyl-4-chloroisooctyl ester with a purity of 92.5% and a yield of 94.6%.

[0056] Example 4

[0057] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 1 The specific steps are as follows:

[0058] 1) 500 g of o-cresol was added to a reactor, 5000 mL of acetone was added, 945 g of sodium ethoxide was added, 960 g of isooctyl chloroacetate prepared in Example 1) was added, and the mixture was reacted at 80 ° C for 12 h. The liquid phase was controlled. After the o-cresol was completely reacted, the mixture was filtered and the solvent was removed. The solvent was recovered and reused in the above reactor to obtain 1261 g of isooctyl o-methylphenoxyacetate with a purity of 82.5% and a yield of 98.3%.

[0059] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 1) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentrator to remove excess chlorine and solvent, thereby obtaining 1011 g of 2-methyl-4-chloroisooctyl ester with a purity of 76.5% and a yield of 89.6%.

[0060] Example 5

[0061] A method for preparing 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 1 The specific steps are as follows:

[0062] 1) 500 g of o-cresol was added to a reactor, 3000 mL of dichloroethane was added, 750 g of sodium methoxide was added, 960 g of isooctyl chloroacetate prepared in Example 1) was added, and the mixture was reacted at 80° C. for 12 h. The liquid phase was controlled. After the o-cresol was completely reacted, the mixture was filtered and the solvent was removed. The solvent was recovered and reused in the above reactor to obtain 1158 g of isooctyl o-methylphenoxyacetate with a purity of 74.5% and a yield of 90.3%;

[0063] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 1) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentration kettle to remove excess chlorine and solvent, thereby obtaining 1011 g of 2-methyl-4-chloroisooctyl ester with a purity of 73% and a yield of 90%.

[0064] Example 6

[0065] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0066] 1) 8000g of chloroacetic acid is dissolved in 7500g of isooctyl alcohol to form a mixed solution A, 400g of concentrated sulfuric acid is added to 2500g of isooctyl alcohol to form solution B, and A and B are respectively introduced into a microchannel reactor by two feed pumps for reaction (A, B flow ratio is chloroacetic acid: isooctyl alcohol=1.1:1 in molar ratio), and the reaction is carried out at 90°C with a residence time of about 2min. The discharge port is transferred to a separating kettle, and the reaction solution is subjected to oil-water separation. The oil phase is isooctyl chloroacetate, and 15750g of isooctyl chloroacetate is obtained with a purity of 98.5% and a yield of 99.2%.

[0067] 2) 1000g of o-cresol and 1920g of isooctyl chloroacetate prepared in step 1) were dissolved in 2000mL of ethylene dichloride to form solution C, 3835g of potassium carbonate was dissolved in 4000mL of ethylene dichloride to form turbid solution D, and C and D were respectively introduced into a continuous multi-stage stirred reactor using two feed pumps (the flow ratio of C and D was o-cresol: isooctyl chloroacetate: potassium carbonate by molar ratio = 1:1.1:3), and the reaction was carried out at 80°C for about 5h. The reaction solution was discharged into a filter tank through a discharge port. The filtrate obtained was a solution of isooctyl o-methylphenoxyacetic acid, and the solvent was removed (recycled) to obtain 2522g of isooctyl o-methylphenoxyacetic acid with a purity of 96% and a yield of 97.9%.

[0068] 3) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 2) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentration kettle to remove excess chlorine and the solvent was recycled to obtain 1068 g of 2-methyl-4-chloroisooctyl ester with a purity of 92.5% and a yield of 94.7%.

[0069] Example 7

[0070] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0071] 1) 1000g of o-cresol and 1920g of isooctyl chloroacetate prepared in step 1) were dissolved in 2000mL of dichloroethane to form solution C, 1890g of sodium ethoxide was dissolved in 2000mL of dichloroethane to form turbid solution D, and C and D were respectively fed into a continuous multi-stage stirred reactor using two feed pumps (the flow ratio of C to D was o-cresol: isooctyl chloroacetate: sodium ethoxide = 1:1.1:3 by molar ratio), and the reaction was carried out at 80°C for about 5h. The reaction solution was discharged into a filter tank through a discharge port. The filtrate obtained was a solution of isooctyl o-methylphenoxyacetic acid. The solvent was removed to obtain 2530g of isooctyl o-methylphenoxyacetic acid with a purity of 84% and a yield of 98.3%.

[0072] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 2) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of 60 s. The discharge port was transferred to a concentration kettle to remove excess chlorine and solvent, thereby obtaining 1069 g of 2-methyl-4-chloroisooctyl ester with a purity of 79% and a yield of 94.8%.

[0073] Example 8

[0074] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0075] 1) 1000g of o-cresol and 1920g of isooctyl chloroacetate prepared in Example 6) were dissolved in 2000mL of ethylene dichloride to form a solution C, and 2940g of sodium carbonate was dissolved in 2000mL of ethylene dichloride to form a turbid solution D. C and D were respectively introduced into a continuous multi-stage stirred reactor using two feed pumps (the flow ratio of C to D was o-cresol: isooctyl chloroacetate: sodium carbonate by molar ratio = 1:1.1:3). The reaction was carried out at 80°C for about 5h. The reaction solution was discharged into a filter tank through a discharge port. The filtrate obtained was a solution of isooctyl o-methylphenoxyacetic acid. The solvent was removed to obtain 2533g of isooctyl o-methylphenoxyacetic acid with a purity of 97.4% and a yield of 98.4%.

[0076] 2) 1000 g of the isooctyl o-methylphenoxyacetate prepared in step 2) was prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination. The reaction was carried out at 80° C. with a residence time of approximately 60 s. The discharge port was transferred to a concentration kettle to remove excess chlorine and solvent, thereby obtaining 1068 g of 2-methyl-4-chloroisooctyl ester with a purity of 92.7% and a yield of 94.7%.

[0077] Example 9

[0078] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0079] 1) 1000 g of o-cresol and 1920 g of isooctyl chloroacetate were dissolved in 2000 mL of ethylene dichloride to form solution C, and 4520 g of cesium carbonate was dissolved in 4000 mL of ethylene dichloride to form turbid solution D. C and D were respectively fed into a continuous multi-stage stirred reactor using two feed pumps (the flow ratio of C to D was o-cresol: isooctyl chloroacetate: cesium carbonate = 1:1.1:3 by molar ratio). The reaction was carried out at 80° C. for about 5 h. The reaction solution was discharged into a filter tank through a discharge port. The filtrate obtained was a solution of isooctyl o-methylphenoxyacetic acid. The solvent was removed to obtain 2526 g of isooctyl o-methylphenoxyacetic acid with a purity of 98.4% and a yield of 98.5%.

[0080] 2) 1000 g of 2-ethylhexyl methylphenoxyacetic acid is prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination reaction at 80° C. with a residence time of approximately 60 s. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 1070 g of 2-methyl-4-chloro-2-ethylhexyl methyl ester with a purity of 93.6% and a yield of 94.9%.

[0081] Example 10

[0082] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0083] 1) 1000 g of o-cresol and 1920 g of isooctyl chloroacetate were dissolved in 2000 mL of ethylene dichloride to form solution C, and 1500 g of sodium methoxide was dissolved in 2000 mL of ethylene dichloride to form turbid solution D. C and D were respectively fed into a continuous multi-stage stirred reactor using two feed pumps (the flow ratio of C to D was o-cresol: isooctyl chloroacetate: cesium carbonate = 1:1.1:3 by molar ratio). The reaction was carried out at 80° C. for about 5 h. The reaction solution was discharged into a filter tank through a discharge port. The filtrate obtained was a solution of isooctyl o-methylphenoxyacetic acid. The solvent was removed to obtain 2532 g of isooctyl o-methylphenoxyacetic acid with a purity of 80.2% and a yield of 98.7%.

[0084] 2) 1000 g of 2-ethylhexyl methylphenoxyacetic acid is prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination reaction at 80° C. with a residence time of approximately 60 s. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 1068 g of 2-methyl-4-chloro-2-ethylhexyl methyl ester with a purity of 82% and a yield of 94.7%.

[0085] Example 11

[0086] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0087] 1) The operation was the same as in Example 9, except that the reaction temperature was set to 60° C. and the residence time was 10 h. Finally, 2515 g of isooctyl o-methylphenoxyacetate was obtained with a purity of 97.2% and a yield of 98.1%.

[0088] 2) 1000 g of 2-ethylhexyl methylphenoxyacetic acid is prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination reaction at 80° C. with a residence time of approximately 60 s. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 1070 g of 2-methyl-4-chloro-2-ethylhexyl methyl ester with a purity of 92.1% and a yield of 94.9%.

[0089] Example 12

[0090] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0091] 1) The operation was the same as in Example 9, except that the reaction temperature was set to 70° C. and the residence time was 8 h. Finally, 2519 g of isooctyl o-methylphenoxyacetate was obtained with a purity of 97.8% and a yield of 98.2%.

[0092] 2) 1000 g of 2-ethylhexyl methylphenoxyacetic acid is prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination reaction at 80° C. with a residence time of approximately 60 s. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 1070 g of 2-methyl-4-chloro-2-ethylhexyl methyl ester with a purity of 92.7% and a yield of 94.9%.

[0093] Example 13

[0094] A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, the process flow is as follows Figure 2 The specific steps are as follows:

[0095] 1) The operation was the same as in Example 9, except that the reaction temperature was set to 90° C. and the residence time was 8 h. Finally, 2519 g of isooctyl o-methylphenoxyacetate was obtained with a purity of 97.2% and a yield of 98.2%.

[0096] 2) 1000 g of 2-ethylhexyl methylphenoxyacetic acid is prepared into a 20% solution and fed into a microchannel via a feed pump for chlorination reaction at 80° C. with a residence time of approximately 60 s. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 1070 g of 2-methyl-4-chloro-2-ethylhexyl methyl ester with a purity of 92.4% and a yield of 94.9%.

[0097] Comparing Examples 1 and 6, 2 and 9, 3 and 8, 4 and 10, and 5 and 7, it was found that the continuous flow reaction had obvious advantages over the traditional kettle reaction. Under the same experimental conditions, the continuous flow reaction time was shorter, the conversion rate was higher, the possibility of side reactions was greatly reduced, and the final product purity was higher.

[0098] Comparing Examples 9, 11, 12 and 13, it can be found that for the same continuous reaction, as the reaction temperature increases to 80°C, the conversion rate is the highest, the required reaction time is relatively reduced, and the purity of the product is relatively improved.

Claims

1. A continuous preparation method of 2-methyl-4-chlorophenoxyacetic acid isooctyl ester, characterized in that: The specific steps are as follows: 1) Dissolve chloroacetic acid in isooctyl alcohol to prepare a mixed solution A, add concentrated sulfuric acid to isooctyl alcohol to prepare solution B, and feed A and B into a microchannel reactor through two feed pumps respectively for reaction. Control the temperature for esterification reaction, separate the oil and water from the reaction liquid, and the oil phase is isooctyl chloroacetate; control the temperature at 90°C and react for 2 minutes; 2) o-cresol and the isooctyl chloroacetate prepared in step 1) are dissolved in dichloroethane to form solution C, potassium carbonate is dissolved in dichloroethane to form turbid solution D, C and D are respectively fed into a continuous multi-stage stirred reactor using two feed pumps, the reaction is temperature-controlled, and after completion, the filtrate is a solution of isooctyl o-methylphenoxyacetate, and the solvent is removed to obtain isooctyl o-methylphenoxyacetate; the temperature is controlled at 80° C. and the reaction is carried out for 5 hours; 3) The isooctyl o-methylphenoxyacetic acid prepared in step 2) is prepared into a solution, fed into a microchannel using a feed pump, and subjected to a chlorination reaction under temperature control. The discharge port is transferred to a concentration kettle to remove excess chlorine and solvent to obtain 2-methyl-4-chloroisooctyl ester; the temperature is controlled at 80° C. and the reaction is carried out for 60 seconds.

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