Method for preparing 2, 4-dichlorphenoxyacetic acid isooctyl ester

Abstract

The invention provides a method for preparing 2, 4-dichlorphenoxyacetic acid isooctyl ester, which comprises the following steps: carrying out heating reaction on 2, 4-dichlorphenoxyacetic acid and isooctanol under the action of strong acid cation exchange resin as a catalyst, carrying out suction filtration on the strong acid cation exchange resin when the reaction is finished, cooling the filtrate, neutralizing, extracting and desolventizing to obtain the product, and after it is judged that a reaction endpoint is reached through a TLC dot plate, carrying out post-treatment to obtain a 2, 4-D isooctyl ester product. The product prepared by the preparation method disclosed by the invention is high in yield, the yield can reach 98.0% or above, the purity is high, and the content of 2, 4-D isooctyl ester detected by HPLC (High Performance Liquid Chromatography) is 98.0% or above.

Description

Technical Field

[0001] The invention relates to the technical field of herbicide preparation, and specifically relates to a method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester. Background Art

[0002] 2,4-D 2-ethylhexyl ester is an important follow-up product of 2,4-D (full name 2,4-dichlorophenoxyacetic acid 2-ethylhexyl ester). Since 2,4-D butyl ester (full name 2,4-dichlorophenoxyacetic acid butyl ester) is highly volatile, it evaporates into gas when the temperature reaches 15°C. As a result, it is easy to cause drift when spraying the pesticide, causing serious damage to broad-leaved crops. In recent years, 2,4-D 2-ethylhexyl ester has been developed to replace 2,4-D butyl ester with much less drift damage.

[0003] At present, the industrial production method of 2,4-D isooctyl ester basically involves first preparing qualified 2,4-D (full name 2,4-dichlorophenoxyacetic acid) and then reacting it with isooctyl alcohol under the action of a catalyst for esterification. For example, Chinese patent CN103772200 uses concentrated sulfuric acid as a catalyst and toluene as a solvent for dehydration esterification under reflux. This method uses a large amount of toluene as a solvent, and removes the water generated during the esterification process by azeotropic reaction of toluene and water. However, toluene is a controlled chemical, volatile, and has a great impact on human health. The post-treatment reaction system uses 5% sodium hydroxide to adjust the pH to 10, which may cause the target product 2,4-D isooctyl ester to hydrolyze, reducing the yield of 2,4-D isooctyl ester and other disadvantages. Another example is Chinese patent CN114773190, the reaction temperature is high, the experimental risk factor is high; using concentrated hydrochloric acid with a mass concentration of 20% to 36.5% as a catalyst, concentrated hydrochloric acid is volatile, whether it is a laboratory test or an industrial scale-up test, it will cause harm to the health of on-site operators; in the post-treatment process, it is necessary to remove water by vacuum distillation and remove isooctyl alcohol by oil pump decompression, and isooctyl alcohol has a high boiling point, which makes the preparation process of 2,4-D isooctyl ester very energy-consuming, time-consuming, and increase production costs. Another example is Chinese patent CN114773190A, the consumption of isooctyl alcohol is relatively large, the reaction temperature is high, pressurization is required, and the laboratory risk factor is high; the catalyst is sodium bisulfate and hydrochloric acid, and the feeding method of adding sodium bisulfate first and then hydrochloric acid is adopted, and the reaction time is 1.8h and 3.5h respectively, which makes the preparation process of 2,4-D isooctyl ester increase production costs, time, increase in operating procedures, etc. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester with simple reaction and low energy consumption.

[0005] The specific process is that 2,4-dichlorophenoxyacetic acid and isooctyl alcohol are heated to 50°C~100°C under the action of a strong acidic cation exchange resin catalyst, and the end point of the reaction is determined by TLC spot plate, and then the 2,4-D isooctyl ester product is obtained by post-treatment. In some embodiments, the changes in the contents of 2,4-D and 2,4-D isooctyl ester are detected by TLC spot plate to determine whether the reaction has reached the end point.

[0006] The technical solution of the present invention also includes post-processing the product obtained after reaching the end point, wherein the post-processing comprises adding appropriate amounts of organic solvent and alkali solution respectively to make the pH value of the reaction system neutral (the neutral refers to a pH of 6.5-8.5), stirring for about 15 minutes, pouring into a separatory funnel, oscillating, standing, and layering, washing the organic phase with water for 2-3 times, drying with anhydrous magnesium sulfate, and filtering, and distilling the filtrate under reduced pressure until there is no effluent, thereby obtaining the 2,4-D isooctyl ester product.

[0007] As a preferred embodiment of the present invention, the molar ratio of the 2,4-dichlorophenoxyacetic acid to isooctyl alcohol is 1:1.0-3.0.

[0008] As a preferred embodiment of the present invention, the catalyst is PK228 (DIAION™ series, Mitsubishi Chemical Corporation), AmberLite HPR1200 H (DuPont), or D072 (Nankai University Chemical Plant).

[0009] As a preferred embodiment of the present invention, the added amount (mL) of the catalyst is 0.01% to 1% of the mass of 2,4-dichlorophenoxyacetic acid; preferably 0.01% to 0.5%; preferably 0.01% to 0.1%.

[0010] As a preferred embodiment of the present invention, the reaction time is 0.1-1h.

[0011] As a preferred embodiment of the present invention, the solvent added in the post-treatment is ethyl acetate, tetrahydrofuran, or N,N-dimethylformamide.

[0012] As a preferred embodiment of the present invention, the amount (mL) of the solvent added in the post-treatment is 1 to 10 times the mass of 2,4-dichlorophenoxyacetic acid.

[0013] As a preferred embodiment of the present invention, the alkali used in the post-treatment to adjust the pH is sodium bicarbonate, sodium carbonate or sodium hydroxide.

[0014] As a preferred embodiment of the present invention, the amount (mL) of the post-treatment alkali added is 1 to 10 times the mass of 2,4-dichlorophenoxyacetic acid.

[0015] Technical Effects (1) The preparation method of the present invention has good catalytic effect, the catalyst can be recycled and reused with good effect, the esterification reaction time is short, ethyl acetate is easy to recover, and the energy consumption is low.

[0016] (2) The preparation method of the present invention has simple procedures, is environmentally friendly, has low energy consumption, does not use any solvent in the reaction stage, and has a low cost for the post-treatment method. A strongly acidic cation exchange resin or the like is used as a catalyst. The changes in the contents of 2,4-D and 2,4-D isooctyl ester are detected by preliminary central control using a TLC spot plate, so that the experimental progress can be quickly and accurately grasped. A 5% sodium bicarbonate solution is used for post-treatment to adjust the pH to 7-8 to minimize the hydrolysis of the target product 2,4-D isooctyl ester. Ethyl acetate is added for post-treatment to dissolve the target product 2,4-D isooctyl ester therein. After separating the organic phase, it is found that washing with water 2-3 times can remove a small amount of isooctyl alcohol and salt in the system, and the target product 2,4-D isooctyl ester is obtained by removing the solvent.

[0017] (3) The product obtained by the preparation method of the present invention has a high yield, which can reach more than 95.0%, further can reach more than 97%, and further can reach more than 98%; the purity is high, and the content of 2,4-D isooctyl ester detected by HPLC is more than 98.0%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the liquid chromatogram of 2,4-dichlorophenoxyacetic acid isooctyl ester obtained in Example 1.

[0019] Figure 2 This is the H NMR spectrum of 2,4-dichlorophenoxyacetic acid isooctyl ester obtained in Example 1. DETAILED DESCRIPTION

[0020] Example 1 In a 250mL three-necked flask, add 20g 2,4-D, 14.14g isooctyl alcohol, and 0.01g catalyst (PK228), insert a thermometer, stir, and heat in an oil bath to 70°C. Preliminary central control detection of 2,4-D and 2,4-D isooctyl ester content changes (based on the change in the concentration of the TLC plate points) was performed by TLC spot plate. Samples were taken at intervals of 10 minutes for observation. When the central control showed that the reaction lasted for 40 minutes, the reaction time was further extended. The concentration of the 2,4-D point no longer changed, that is, the reaction reached the end point after 40 minutes. Then the reaction solution was filtered out of the strong acid cation exchange resin while hot, and an appropriate amount of 5% sodium bicarbonate solution was added to the filtrate to make the pH value of the reaction system neutral, stirred for 15 minutes, and then an appropriate amount of ethyl acetate was added. After stirring evenly, it was poured into a separatory funnel, shaken, allowed to stand, and layered. The organic phase was washed with water 2 to 3 times, and then dried with anhydrous magnesium sulfate and filtered. The filtrate was decompressed and distilled until there was no effluent, that is, 28.82g of 2,4-D isooctyl ester product, with a light yellow transparent liquid appearance and a yield of 98.93%. The content of 2,4-D isooctyl ester detected by HPLC was 98.91%, the free acid was 0.006%, the water was 0.042%, the free phenol was not detected, and the acetone insoluble matter was not detected. The hydrogen spectrum detector of 2,4-dichlorophenoxyacetic acid isooctyl ester is a 400MHz nuclear magnetic spectrometer, 3.31ppm is the solvent peak of deuterated MeOH, and 4.87ppm is the water peak. 1H NMR (400 MHz, MeOH) δ 7.35 (d, J = 2.6 Hz, 1H), 7.17 (dd, J = 8.9, 2.6 Hz, 1H), 6.92 (t, J = 7.8 Hz, 1H), 4.75 (d, J = 22.7 Hz, 2 H), 4.13 – 4.02 (m, 2H),1.50 (dt, J = 17.7, 8.9 Hz, 1H), 1.34 – 1.19 (m, 8H), 0.87 (ddd, J = 15.0,9.4, 6.1 Hz, 6H). Example 2 In a 250mL three-necked flask, add 20g 2,4-D, 14.14g isooctyl alcohol, and 0.05g catalyst (AmberLite HPR1200 H), insert a thermometer, stir, and heat to 70°C in an oil bath. Preliminary central control detection of 2,4-D and 2,4-D isooctyl ester content changes (based on the change in the concentration of the TLC plate points) was performed by TLC spot plate. Samples were taken at intervals of 10 minutes for observation. When the central control showed that the reaction lasted for 50 minutes, the reaction time was further extended. The concentration of the 2,4-D point no longer changed, that is, the reaction reached the end point after 50 minutes of reaction. Then, the reaction solution was filtered out while hot to remove the strongly acidic cation exchange resin, and an appropriate amount of 5% sodium bicarbonate solution was added to the filtrate to make the pH value of the reaction system neutral, and the mixture was stirred for 15 minutes. An appropriate amount of ethyl acetate was then added, and the mixture was evenly stirred and poured into a separatory funnel. The mixture was shaken, allowed to stand, and separated into layers. The organic phase was washed with water for 2 to 3 times, and then dried over anhydrous magnesium sulfate and filtered. The filtrate was distilled under reduced pressure until there was no effluent, i.e., 29.02 g of 2,4-D isooctyl ester product was obtained, and the product was a light yellow transparent liquid with a yield of 96.25%. The content of 2,4-D isooctyl ester was 98.85% as determined by HPLC, the free acid was 0.008%, the water content was 0.051%, free phenol was not detected, and acetone insoluble matter was not detected.

[0021] Example 3 In a 250mL three-necked flask, add 20g 2,4-D, 14.14g isooctyl alcohol, and 0.1g catalyst (D072), insert a thermometer, stir, and heat in an oil bath to 70°C. Preliminary central control detection of 2,4-D and 2,4-D isooctyl ester content changes through TLC spot plate (judged by the change in density of TLC plate points), sampling spot plate observation at intervals of 10 minutes, when the central control shows that the reaction has reached 30 minutes, continue to extend the reaction time, the density of 2,4-D point no longer changes, that is, the reaction reaches the end point after 30 minutes. Then, the reaction solution was filtered out while hot to remove the strongly acidic cation exchange resin, and an appropriate amount of 5% sodium bicarbonate solution was added to the filtrate to make the pH value of the reaction system neutral, and stirred for 15 minutes. Then, an appropriate amount of ethyl acetate was added, stirred evenly, and poured into a separatory funnel, shaken, allowed to stand, and layered. The organic phase was washed with water 2 to 3 times, and then dried with anhydrous magnesium sulfate and filtered. The filtrate was distilled under reduced pressure until there was no effluent, that is, 29.41 g of 2,4-D isooctyl ester product, with a light yellow transparent liquid appearance and a yield of 97.55%. The content of 2,4-D isooctyl ester detected by HPLC was 98.70%, the free acid was 0.007%, the water was 0.049%, free phenol was not detected, and acetone insoluble matter was not detected.

[0022] Example 4 In a 1000mL three-necked flask, add 110.5g 2,4-D, 1.5g concentrated sulfuric acid, 65.7g isooctyl alcohol, and 300mL toluene. Reflux dehydration, liquid phase sampling tracking and analysis, the reaction end point is reached in about 3h, and the 2,4-D (normalized) content is controlled to be ≤2wt%. Cool to 60℃, adjust pH=10 with 5% sodium hydroxide, and separate into layers. Wash the organic layer with water until neutral, distill under normal pressure to remove solvent, and distill under reduced pressure after most of the solvent is distilled out until there is no distillate. 158g of product is obtained with a purity of 97% (normalized). The weight yield is 95%.

[0023] Example 5 In a 250mL four-necked flask equipped with a thermometer, 2,4-D (82.70g, 0.37mol), isooctyl alcohol (57.82g, 0.444mol), and catalyst 20% hydrochloric acid (0.68g, 0.0037mol) were added, and a vacuum distillation apparatus was set up. The oil bath was heated to 140°C, stirring was started at 700r / min, and the negative pressure was reduced to about -0.02MPa. The vacuum distillation reaction for dehydration was started for 3h. The LC central control detected the 2,4-D content (liquid phase internal standard method) and found that there was 2.81wt% left. The oil pump was changed for desolventization. The oil pump was depressurized to 10KPa for desolventization until no isooctyl alcohol was evaporated, which took about 1.5h. Then, the reaction solution was cooled to about 120°C, 2.0g of activated carbon was added, and stirred for 0.5h. The reaction solution was cooled to 80°C and filtered to obtain the isooctyl ester product, which was weighed and sampled for analysis. 119.71 g of 2,4-D isooctyl ester product was obtained, which was a colorless to light yellow transparent liquid in appearance, with a yield of 97.09%. The purity tested by gas chromatography internal standard method was 98.62%, the free acid was 0.59%, the water content was 0.14%, the free phenol was not detected, and the acetone insoluble matter was not detected.

[0024] Example 6 2,4-D isooctyl ester is produced by reacting 2,4-D acid and isooctyl alcohol under catalyst conditions, the molar ratio of 2,4-D acid to isooctyl alcohol is 1:1.35, the reaction temperature is 150°C, the reaction time is 11 hours, nitrogen is introduced to make the vacuum degree reach 0.095~0.1Mpa, and it is maintained for 1 hour to obtain 2,4-D isooctyl ester; the catalyst is sodium bisulfate and hydrochloric acid, and the order of adding sodium bisulfate and hydrochloric acid is to add sodium bisulfate first, carry out catalytic reaction, and then add hydrochloric acid for catalytic reaction. The mass of sodium bisulfate added accounts for 0.1% of the total mass of isooctyl alcohol; the mass of hydrochloric acid added accounts for 1% of the total mass of isooctyl alcohol. The catalytic reaction time of sodium bisulfate is 1.8h; the catalytic reaction time of hydrochloric acid is 3.5h. The 2,4-D isooctyl ester prepared by the method is tested for relevant indicators, and the content is 98.40%, the acidity is 0.23%, and the appearance is a light yellow liquid.

[0025] Comparative Example 1 In a 250mL three-necked flask, add 20g 2,4-D, 14.14g isooctyl alcohol, and 0.1g anion resin catalyst (D201), insert a thermometer, stir, and heat in an oil bath to 70°C. Preliminary central control detection of 2,4-D and 2,4-D isooctyl ester content changes through TLC spot plate (judged by the change in density of TLC plate points), sampling spot plate observation at intervals of 10 minutes, when the central control shows that the reaction has reached 60 minutes, continue to extend the reaction time, the density of 2,4-D point no longer changes, that is, the reaction reaches the end point after 60 minutes. Then, the reaction solution was filtered out while hot to remove the anion exchange resin, and an appropriate amount of 5% hydrochloric acid was added to the filtrate to make the pH value of the reaction system neutral, and the mixture was stirred for 15 minutes. Then, an appropriate amount of ethyl acetate was added, and the mixture was evenly stirred and poured into a separatory funnel. The mixture was shaken, allowed to stand, and separated into layers. The organic phase was washed with water for 2 to 3 times, and then dried over anhydrous magnesium sulfate and filtered. The filtrate was distilled under reduced pressure until no effluent was obtained, i.e., 25.77 g of 2,4-D isooctyl ester product was obtained, and the product was a light yellow transparent liquid with a yield of 85.47%. The content of 2,4-D isooctyl ester was 97.98% as determined by HPLC, the free acid was 0.007%, the water content was 0.05%, free phenol was not detected, and acetone insoluble matter was not detected.

[0026] Comparative Example 2 In a 250mL three-necked flask, add 20.0g 2,4-D and 14.14g isooctyl alcohol, insert a thermometer, heat in an oil bath to 100℃, stir for about 30min, the system becomes clear and transparent, start to drop 0.5mL phosphoric acid as a catalyst, and use TLC spot plate to preliminarily detect the changes in the contents of 2,4-D and 2,4-D isooctyl ester (based on the changes in the density of the TLC plate spots). Take samples at intervals of 1h for spot plate observation. When the central control shows that the reaction has lasted for 7h, continue to extend the reaction time, and the density of the 2,4-D spot no longer changes, that is, the reaction reaches the end point after 7h. Then the reaction solution was cooled to room temperature (25°C), an appropriate amount of 5% sodium bicarbonate solution was added to make the pH value of the reaction system neutral, and the mixture was stirred for 15 minutes. An appropriate amount of ethyl acetate was then added and stirred evenly. The mixture was poured into a separatory funnel, shaken, allowed to stand, and separated into layers. The organic phase was washed with water for 2 to 3 times, dried over anhydrous magnesium sulfate, and filtered. The filtrate was distilled under reduced pressure until no effluent was found, i.e., 27.13 g of 2,4-D isooctyl ester product was obtained. The product was a light yellow transparent liquid with a yield of 89.98%. The content of 2,4-D isooctyl ester was 97.91% as determined by HPLC. The free acid was 0.72%, the water content was 0.20%, the free phenol was 0.005%, and no acetone insoluble matter was detected.

[0027] From the above test results, it can be seen that the catalyst is a strong acid cation exchange resin, and the yield and purity of the target product 2,4-D isooctyl ester are higher than those of Comparative Example 1 and Comparative Example 2. Other detection control indicators are far lower than the mass concentration content required by the industry standard (the group standard issued by the China Pesticide Industry Association); in Comparative Example 1 and Comparative Example 2, anionic resin and phosphoric acid are used as catalysts, respectively, and the obtained 2,4-D isooctyl ester products have low yields and low purity. Using a strong acid cation exchange resin as a catalyst, the changes in the content of 2,4-D and 2,4-D isooctyl ester can be detected by preliminary central control using a TLC spot plate, and the progress of the experiment can be quickly and accurately grasped. The post-treatment uses a 5% sodium bicarbonate solution to adjust the pH value to neutral, and the hydrolysis of the target product 2,4-D isooctyl ester is minimized. Ethyl acetate is added to the post-treatment to dissolve the target product 2,4-D isooctyl ester therein. After separating the organic phase, the experiment found that washing with water 2 to 3 times can remove a small amount of isooctyl alcohol and salt in the system, and the solvent is removed to obtain the target product 2,4-D isooctyl ester. The method of the invention has good catalytic effect, the catalyst can be recycled and reused with good effect, the esterification reaction time is short, ethyl acetate is easy to recover, the energy consumption is low, and the product yield and purity are high.

Claims

1. A method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester, characterized in that: 2,4-dichlorophenoxyacetic acid and isooctyl alcohol are subjected to a temperature-raising reaction under the action of a strongly acidic cation exchange resin as a catalyst. After the reaction is completed, the strongly acidic cation exchange resin is filtered out while hot, and the filtrate is cooled and subjected to neutralization, extraction, and desolventization to obtain the product; after reaching the reaction endpoint through TLC spot plate, the 2,4-D isooctyl ester product is obtained through post-treatment.

2. The method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester according to claim 1, characterized in that: The molar ratio of the 2,4-dichlorophenoxyacetic acid to isooctyl alcohol is 1:1.0-3.

0.

3. The method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester according to claim 1, characterized in that: The catalyst is any one of PK228, AmberLite HPR1200 H, and D072.

4. The method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester according to claim 1, characterized in that: The added amount of the catalyst is 0.01% to 1% of the mass of 2,4-dichlorophenoxyacetic acid.

5. The method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester according to claim 1, characterized in that: The catalytic reaction temperature is 50°C-100°C, and the reaction time is 0.1-1h.

6. The method for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester according to claim 1, characterized in that: The post-treatment step is to filter out the product at the end point of the reaction while hot from the strongly acidic cation exchange resin, adjust the pH value of the filtrate to neutral with a 5-10% sodium bicarbonate solution, stand for stratification after stirring, and wash, dry, filter, and distill under reduced pressure the aqueous phase after stratification to obtain the product 2,4-D isooctyl ester.

7. The method for preparing isooctyl 2,4-dichlorophenoxyacetate according to claim 6, characterized in that: The organic solvent added in the post-treatment is ethyl acetate, tetrahydrofuran, and N,N-dimethylformamide.

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