Method for refining imazethapyr intermediate

Abstract

The invention discloses a refining method of an imazethapyr intermediate, which comprises the following steps: adding an organic solvent and a 5-ethylpyridine-2, 3-dicarboxylate crude product into a refining reaction kettle, and stirring until the solution is clear; adding a sulfuric acid aqueous solution with the concentration of 60-80%, fully stirring, and standing for layering; transferring the sulfuric acid aqueous solution layer into another reaction kettle, adding water to dilute and reduce the concentration of the sulfuric acid aqueous solution to 10-30%, then adding an organic solvent, fully stirring, and standing for layering; transferring the organic layer into another reaction kettle, adding water, fully stirring, and standing for layering; transferring an organic layer into a distillation kettle, and removing the organic solvent under reduced pressure to obtain a 5-ethyl pyridine-2, 3-dicarboxylate refined product. The purity of the crude product can be improved from 85-90% to 97% or above by utilizing different solubility of the 5-ethylpyridine-2, 3-dicarboxylate in sulfuric acid aqueous solutions with different concentrations, and the method is low in raw material loss, simple to operate and suitable for industrial mass production.

Description

Technical Field

[0001] The invention belongs to the technical field of compound refining, and specifically relates to a method for refining an imidazolin intermediate. Background Art

[0002] Imidazolinone is an imidazolinone herbicide developed by the American Cyanamid Company. Its trade names are Pusaite, Imazethapyr, and Pusaite. Due to its wide weed control spectrum, high activity, and strong selectivity, it is widely used in the prevention and control of annual grass crabgrass, perennial grass white grass, and broad-leaved Xanthium in peanut fields, soybean fields, and woodlands.

[0003] In the prior art, the synthetic route of imidazoline is as follows: .

[0004] Among them, 5-ethylpyridine-2,3-dicarboxylate (including 5-ethylpyridine-2,3-dicarboxylic acid dimethyl ester and 5-ethylpyridine-2,3-dicarboxylic acid diethyl ester) is the key intermediate for the synthesis of imidazolin.

[0005] In the prior art, the synthetic route of 5-ethylpyridine-2,3-dicarboxylate is as follows: .

[0006] This synthetic route will inevitably generate impurities 1 to 7; among them, impurities 1 and 2 are the main impurities, with a total content of nearly 10%; impurities 1 to 7 are difficult to remove by conventional purification methods, resulting in a low purity of 5-ethylpyridine-2,3-dicarboxylate, usually only 85 to 90%.

[0007] The structures of impurities 1 to 7 are as follows: . Summary of the invention

[0008] The object of the present invention is to solve the above problems and provide a method for refining an imidazolin intermediate which has not only good refining effect and high purity of the refined product, but also simple operation and is suitable for large-scale industrial production.

[0009] The technical solution for achieving the purpose of the present invention is: a method for refining an imidazolin intermediate, comprising the following steps: ① Add organic solvent and crude 5-ethylpyridine-2,3-dicarboxylate to the refining reaction kettle and stir until dissolved; ② Add 60-80% sulfuric acid aqueous solution to the refining reactor, stir thoroughly, and let stand to separate layers; ③ Transfer the lower sulfuric acid aqueous solution layer into another reaction kettle, add water to dilute the sulfuric acid aqueous solution to 10-30%, then add organic solvent, stir thoroughly, and let stand to separate; ④ Transfer the upper organic layer into another reactor, add water, stir thoroughly, and let stand to separate the layers; ⑤ Transfer the upper organic layer into a distillation kettle and remove the organic solvent under reduced pressure to obtain 5-ethylpyridine-2,3-dicarboxylate.

[0010] In the above steps ① and ③, the organic solvent is one of toluene, dichloromethane and dichloroethane, preferably toluene.

[0011] In the above step ②, the weight of sulfuric acid in the aqueous sulfuric acid solution is 1 to 2 times the weight of the crude 5-ethylpyridine-2,3-dicarboxylate.

[0012] In the above step ②, the concentration of the aqueous sulfuric acid solution is preferably 60-65%, more preferably 62.5%.

[0013] In the above step ③, the concentration of the aqueous sulfuric acid solution after adding water is preferably 25 to 30%, more preferably 26.5%.

[0014] The present invention has positive effects: through a large number of experiments, the present invention finds that the solubility of 5-ethylpyridine-2,3-dicarboxylate is different in sulfuric acid aqueous solutions of different concentrations. By utilizing the different solubilities of 5-ethylpyridine-2,3-dicarboxylate in sulfuric acid aqueous solutions of different concentrations, the purity of the crude product can be increased from 85-90% to more than 97%, and the raw material loss is small, the operation is simple, and the process is suitable for large-scale industrial production. DETAILED DESCRIPTION

[0015] (Example 1) The purification method of the imidazoline intermediate of the present embodiment comprises the following steps: ① Add 800L of toluene to the refining reactor, add 450kg of crude 5-ethylpyridine-2,3-dicarboxylic acid diethyl ester with a purity of 87% under stirring, and stir until dissolved.

[0016] ② Add 960 kg of 62.5% sulfuric acid aqueous solution into the refining reactor, stir for 30 minutes, let stand for 30 minutes, and separate the layers. At this time, impurities 1 and 2 and other fat-soluble impurities remain in the toluene layer, while 5-ethylpyridine-2,3-dicarboxylic acid diethyl ester and other water-soluble impurities are dissolved in the lower sulfuric acid aqueous solution layer.

[0017] ③ Transfer the lower sulfuric acid aqueous solution layer to another reactor, first add 1300kg of water, at this time the concentration of sulfuric acid aqueous solution drops to 26.5%, then add 800L of toluene, stir for 30min, let stand for 30min, and separate the layers. At this time, other water-soluble impurities remain in the sulfuric acid aqueous solution layer, while 5-ethylpyridine-2,3-dicarboxylic acid diethyl ester is dissolved in the upper toluene layer.

[0018] ④ Transfer the upper toluene layer into another reactor, add 500 kg of water, stir for 30 minutes, let stand for 30 minutes, separate the layers, and further remove residual sulfuric acid and water-soluble impurities.

[0019] ⑤ Transfer the upper toluene layer into a distillation kettle, first distill at normal pressure, then distill at reduced pressure, with the temperature not exceeding 120°C. After the toluene is evaporated to dryness, 375.8 kg of refined 5-ethylpyridine-2,3-dicarboxylic acid diethyl ester is obtained with a purity of 97.6% and a refined yield of 93.7%.

[0020] (Example 2 to Example 5) The preparation methods of each embodiment are basically the same as that of embodiment 1, and the differences are shown in Table 1.

[0021] Table 1 Weight and concentration of sulfuric acid aqueous solution added in step ② Step ③ Water added and concentration after dilution Refined product weight Purity of refined products Refining yield Example 1 960kg, 62.5% 1300kg, 26.5% 375.8kg 97.6% 93.7% Example 2 960kg, 62.5% 1040kg, 30.0% 375.2kg 97.7% 93.6% Example 3 960kg, 62.5% 2040kg, 20.0% 374.5kg 97.3% 93.1% Example 4 960kg, 60.0% 1213kg, 26.5% 375.4kg 97.5% 93.5% Example 5 960kg, 70.0% 1575kg, 26.5% 373.8kg 97.4% 93.0%

[0022] (Example 6) The purification method of the imidazoline intermediate of the present embodiment comprises the following steps: ① Add 540L of toluene to the refining reactor, add 300kg of crude 5-ethylpyridine-2,3-dicarboxylic acid dimethyl ester with a purity of 85% under stirring, and stir until dissolved.

[0023] ② Add 640 kg of 62.5% sulfuric acid aqueous solution into the refining reactor, stir for 30 minutes, let stand for 30 minutes, and separate the layers. At this time, impurities 1 and 2 and other fat-soluble impurities remain in the toluene layer, while 5-ethylpyridine-2,3-dicarboxylic acid dimethyl ester and other water-soluble impurities are dissolved in the lower sulfuric acid aqueous solution layer.

[0024] ③ Transfer the lower sulfuric acid aqueous solution layer to another reactor, first add 866 kg of water, at this time the concentration of the sulfuric acid aqueous solution drops to 26.5%, then add 540 L of toluene, stir for 30 minutes, let stand for 30 minutes, and separate the layers. At this time, other water-soluble impurities remain in the sulfuric acid aqueous solution layer, while 5-ethylpyridine-2,3-dicarboxylic acid dimethyl ester is dissolved in the upper toluene layer.

[0025] ④ Transfer the upper toluene layer into another reactor, add 333 kg of water, stir for 30 minutes, let stand for 30 minutes, separate the layers, and further remove residual sulfuric acid and water-soluble impurities.

[0026] ⑤ Transfer the upper toluene layer into a distillation kettle, first distill at normal pressure, then distill at reduced pressure, with the temperature not exceeding 120°C. After the toluene is evaporated to dryness, 243.5 kg of refined 5-ethylpyridine-2,3-dicarboxylic acid dimethyl ester is obtained with a purity of 98.1% and a refined yield of 93.7%.

[0027] (Example 7 to Example 10) The preparation methods of each embodiment are basically the same as that of embodiment 6, and the differences are shown in Table 2.

[0028] Table 2 Weight and concentration of sulfuric acid aqueous solution added in step ② Step ③ Water added and concentration after dilution Refined product weight Purity of refined products Refining yield Example 6 640kg, 62.5% 866kg, 26.5% 243.5kg 98.1% 93.7% Example 7 640kg, 62.5% 960kg, 25.0% 243.0kg 98.0% 93.4% Example 8 640kg, 62.5% 1860kg, 16.0% 238.2kg 97.8% 91.3% Example 9 640kg, 65.0% 930kg, 26.5% 243.1kg 97.9% 93.3% Example 10 640kg, 75.0% 1170kg, 26.5% 240.0kg 97.9% 92.1%

Claims

1. A method for refining an imidazolin intermediate, comprising the following steps: ① Add organic solvent and crude 5-ethylpyridine-2,3-dicarboxylate to the refining reaction kettle and stir until dissolved; ② Add 60-80% sulfuric acid aqueous solution to the refining reactor, stir thoroughly, and let stand to separate layers; ③ Transfer the lower sulfuric acid aqueous solution layer into another reaction kettle, add water to dilute the sulfuric acid aqueous solution to 10-30%, then add organic solvent, stir thoroughly, and let stand to separate; ④ Transfer the upper organic layer into another reactor, add water, stir thoroughly, and let stand to separate the layers; ⑤ Transfer the upper organic layer into a distillation kettle and remove the organic solvent under reduced pressure to obtain 5-ethylpyridine-2,3-dicarboxylate.

2. The method for refining the imazethapyr intermediate according to claim 1, characterized in that: In the above steps ① and ③, the organic solvent is one of toluene, dichloromethane and dichloroethane.

3. The method for refining the imazethapyr intermediate according to claim 2, characterized in that: In the above steps ① and ③, the organic solvent is toluene.

4. The method for refining the imazethapyr intermediate according to claim 1, characterized in that: In the above step ②, the weight of sulfuric acid in the aqueous sulfuric acid solution is 1 to 2 times the weight of the crude 5-ethylpyridine-2,3-dicarboxylate.

5. The method for refining the imazethapyr intermediate according to claim 1, characterized in that: In the above step ②, the concentration of the aqueous sulfuric acid solution is 60-65%.

6. The method for refining the imazethapyr intermediate according to claim 5, characterized in that: In the above step ②, the concentration of the aqueous sulfuric acid solution is 62.5%.

7. The method for refining the imazethapyr intermediate according to claim 1, characterized in that: In the above step ③, the concentration of the aqueous sulfuric acid solution after adding water is 25-30%.

8. The method for refining the imazethapyr intermediate according to claim 7, characterized in that: In the above step ③, the concentration of the aqueous sulfuric acid solution after adding water is 26.5%.