A production method of 2,6-dichloroquinoxaline

Abstract

The present invention belongs to the field of chemical engineering, and particularly relates to a production method of high-quality 2,6-dichloroquinoxaline. In order to improve the quality of 2,6-dichloroquinoxaline and reduce the sulfur residue therein, this method specifically utilizes the characteristics of good water solubility and fast reaction rate of the reaction product of sulfur and sodium hydroxide to separate the residual sulfur in 2,6-dichloroquinoxaline, and a tubular reactor is used in combination to slow down the rate of formation of bis(6-chloroquinoxalin-2-yl)sulfide impurities by the reaction of 2,6-dichloroquinoxaline and S during the desulfurization process, so that the qualified rate of this impurity in the subsequent intermediate and quizalofop-P-ethyl reaches 100%, and the quality competitiveness of quizalofop-P-ethyl is improved.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering, and specifically relates to a method for producing 2,6-dichloroquinoxaline. Background Art

[0002] p-Chloro-o-nitroacetoacetanilide cyclizes under strong alkaline conditions and is reduced to form 2-hydroxy-6-chloroquinoxaline. 2-Hydroxy-6-chloroquinoxaline undergoes a chlorination reaction to form 2,6-dichloroquinoxaline. Under strong alkaline conditions, 2,6-dichloroquinoxaline reacts with hydroquinone to form 4-(6-chloroquinoxalin-2-yloxy)phenol. 4-(6-Chloroquinoxalin-2-yloxy)phenol reacts with ethyl α-halopropionate or ethyl α-sulfonylpropionate under alkaline conditions to prepare quizalofop-p-ethyl.

[0003] As an export product, quizalofop-p-ethyl has increasingly high requirements not only for its content and optical properties, but also for its impurity control. Among them, bis(6-chloroquinoxalin-2-yl) sulfide is the main impurity to be controlled, and its index requirement is within 0.05% (by liquid chromatography normalization detection). This impurity is mainly generated during the subsequent reaction process of 2,6-dichloroquinoxaline and is formed by the reaction of 2,6-dichloroquinoxaline with sulfur under alkaline conditions. The reaction equation is as follows:

[0004] 。

[0005] To reduce the production cost of quizalofop-p-ethyl and enhance its cost competitiveness, sodium sulfide is selected as the reducing reagent during the preparation of 2-hydroxy-6-chloroquinoxaline. Therefore, elemental sulfur is generated during the reduction reaction and is carried into the chlorination reaction system along with 2-hydroxy-6-chloroquinoxaline, and then remains in 2,6-dichloroquinoxaline. A side reaction occurs in the reaction system of 2,6-dichloroquinoxaline and hydroquinone to form bis(6-chloroquinoxalin-2-yl) sulfide. To ensure that the impurity of bis(6-chloroquinoxalin-2-yl) sulfide in the quizalofop-p-ethyl product is below 0.05%, the sulfur residue in 2,6-dichloroquinoxaline is required to be below 0.01%. The conventional method for removing sulfur in 2,6-dichloroquinoxaline is through crystallization with organic solvents. To ensure the stable quality of 2,6-dichloroquinoxaline, the amount of organic solvents used needs to be increased, so the yield is affected. Therefore, the raw material cost for producing export-grade quizalofop-p-ethyl increases significantly. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a production method of 2,6-dichloroquinoxaline. In order to improve the quality of 2,6-dichloroquinoxaline and reduce the sulfur residue therein, the method specifically utilizes the characteristics of good water solubility and fast reaction rate of the reaction product of sulfur and sodium hydroxide to separate the residual sulfur in 2,6-dichloroquinoxaline, and uses a tubular reactor in combination to slow down the rate of formation of bis(6-chloroquinoxalin-2-yl) sulfide impurities by the reaction of 2,6-dichloroquinoxaline and S during the desulfurization process, so that the qualification rate of this impurity in the subsequent intermediate and quizalofop-p-ethyl reaches 100%, and the quality competitiveness of quizalofop-p-ethyl is improved.

[0007] The specific technical solution adopted by the present invention is as follows:

[0008] A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0009] (1) Prepare a toluene solution of 2,6-dichloroquinoxaline, wherein the mass concentration of 2,6-dichloroquinoxaline is 10-15%;

[0010] (2) Calculate the mass ratio of the sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline;

[0011] (3) Set the heating temperature of the first-stage tubular reactor at 60-80 °C. After the temperature is stable, start the feed pump of the toluene solution of 2,6-dichloroquinoxaline, with a feed rate of 50-100 ml / min. At the same time, start the feed pump of the sodium hydroxide solution, and set the feed rate according to the ratio calculated in step (2) for the sodium hydroxide solution and the toluene solution of 2,6-dichloroquinoxaline;

[0012] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected at the outlet end of the first-stage tubular reactor to maintain a pH of 10-11. After the liquid material comes out of the tubular reactor, it enters a separation and liquid separation device. The aqueous phase is separated, and the organic phase continues to enter the second-stage tubular reactor. At the same time, start the feed pump of dilute hydrochloric acid in the second-stage tubular reactor, and adjust the feed rate of dilute hydrochloric acid according to the pH of the second-stage tubular reactor to neutralize the sodium hydroxide in the liquid material and maintain a pH of 6-8 at the outlet end;

[0013] (5) After the liquid material comes out of the second-stage tubular reactor, it enters a separation and liquid separation device. The aqueous phase is separated, and the toluene phase is distilled, and 2,6-dichloroquinoxaline is obtained by cooling crystallization and filtration.

[0014] As a specific implementation manner: the inner diameter of the tubular reactor in step (3) is 5±0.2 mm, the liquid holdup is 450-500 ml, and the residence time of the liquid material in the tubular reactor is 5-10 min.

[0015] As a specific implementation manner: the preparation method of the toluene solution of 2,6-dichloroquinoxaline in step (1) is as follows:

[0016] 2-Hydroxy-6-chloroquinoxaline reacts with thionyl chloride in toluene solvent to form 2,6-dichloroquinoxaline. After the reaction is qualified, the remaining thionyl chloride is removed together with toluene, and then fresh toluene solvent is added to obtain a toluene solution of 2,6-dichloroquinoxaline, wherein the mass concentration of 2,6-dichloroquinoxaline is 10-15%.

[0017] As a specific embodiment: the specific steps for calculating the mass ratio of sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline in step (2) are as follows:

[0018] Prepare a sodium hydroxide solution with a mass concentration of 2-4%. First, heat a certain volume / certain mass of the toluene solution of 2,6-dichloroquinoxaline prepared in step (1) to 60-80 °C, dropwise add the prepared sodium hydroxide solution, stop dropping after detecting that the pH of the system is 10-11, calculate the consumption of the sodium hydroxide solution, and calculate the mass ratio of the sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline.

[0019] As a specific embodiment: the impurity of bis(6-chloroquinoxalin-2-yl)sulfide in the finally obtained 2,6-dichloroquinoxaline is below 0.02%, and the sulfur residue is below 0.01%.

[0020] Specifically: a production method of 2,6-dichloroquinoxaline, the steps are as follows:

[0021] (1) Prepare a toluene solution of 2,6-dichloroquinoxaline, wherein the mass concentration of 2,6-dichloroquinoxaline is 10-15%;

[0022] Preferably, the preparation method of the above toluene solution of 2,6-dichloroquinoxaline is as follows:

[0023] 2-Hydroxy-6-chloroquinoxaline reacts with thionyl chloride in toluene solvent to form 2,6-dichloroquinoxaline. After the reaction is qualified, the remaining thionyl chloride is removed together with toluene, and then fresh toluene solvent is added to obtain a toluene solution of 2,6-dichloroquinoxaline, wherein the concentration of 2,6-dichloroquinoxaline is 10-15%. This solution shows acidity due to the residual thionyl chloride; in addition, a toluene solution of 2,6-dichloroquinoxaline can also be prepared by using other existing chlorination processes, as long as the concentration of 2,6-dichloroquinoxaline therein is within the above range. At the same time, it is required that 2-hydroxy-6-chloroquinoxaline is produced by a process using sodium sulfide or sodium hydrosulfide as a reducing agent. Only the 2,6-dichloroquinoxaline prepared by the above process contains elemental sulfur and is suitable for the treatment method of this application.

[0024] (2) Calculate the mass ratio of sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0025] Prepare a sodium hydroxide solution with a mass concentration of 2-4%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline prepared in step (1), heat it to 60-80 °C, add dropwise the prepared sodium hydroxide solution, stop adding dropwise after detecting that the pH of the system is 10-11, calculate the consumption of the sodium hydroxide solution, and calculate the mass ratio of the sodium hydroxide solution to the 2,6-dichloroquinoxaline toluene solution;

[0026] The reason for setting the above steps is that there will be certain differences in the remaining amount of thionyl chloride in each batch, which makes the amount of alkali used in the subsequent process different. The inventor uses the above method to carry out quantitative titration first to confirm the proportion range of 2,6-dichloroquinoxaline and the alkali solution, so as to provide a reference for subsequent treatment.

[0027] (3) Set the heating temperature of the first-stage tubular reactor at 60-80 °C. After the temperature is stable, start the feed pump of the 2,6-dichloroquinoxaline toluene solution, with a feed rate of 50-100 ml / min. At the same time, start the feed pump of the sodium hydroxide solution, and set the feed rate according to the ratio calculated in step (2) of the sodium hydroxide solution and the 2,6-dichloroquinoxaline toluene solution;

[0028] The above-mentioned tubular reactor preferably has an inner diameter of 5 mm, a liquid holdup of 500 ml, and the residence time of the feed liquid in the tubular reactor is 5-10 min;

[0029] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected at the outlet end of the first-stage tubular reactor to maintain a pH of 10-11. After the feed liquid comes out of the tubular reactor, it enters a separation and liquid separator. The aqueous phase is separated and the organic phase continues to enter the second-stage tubular reactor. At the same time, start the dilute hydrochloric acid feed pump of the second-stage tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the second-stage tubular reactor to neutralize the sodium hydroxide in the feed liquid and maintain a pH of 6-8 at the outlet end;

[0030] (5) After the feed liquid comes out of the second-stage tubular reactor, it enters a separation and liquid separator. The aqueous phase is separated and the toluene phase is distilled. 2,6-Dichloroquinoxaline is obtained by cooling crystallization and filtration, with a quantitative content of more than 99%, a yield of more than 96%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is less than 0.02%, and the sulfur residue is less than 0.01%.

[0031] Compared with the prior art, the beneficial effects of this application are:

[0032] (1) The inventor controls the removal of sulfur on the premise of controlling the impurity of bis(6-chloroquinoxalin-2-yl)sulfide by studying the difference between the generation conditions of bis(6-chloroquinoxalin-2-yl)sulfide impurities and the reaction conditions of sulfur with strong alkali;

[0033] (2) Combining the advantages of the tubular reactor, namely the continuous feeding, discharging, and separation methods, by controlling the feeding rate, the contact time between 2,6-dichloroquinoxaline and the lye at high temperature is shortened, effectively controlling the increase of bis(6-chloroquinoxalin-2-yl)sulfide impurities. Finally, the content and yield of 2,6-dichloroquinoxaline obtained are improved compared with the prior art, indicating that the method provided by the present invention does not cause other adverse effects on the preparation of 2,6-dichloroquinoxaline;

[0034] (3) By combining two-stage tubular reactors, sulfur is removed in the first-stage tubular reactor, the pH of the system is adjusted in the second-stage tubular reactor, and at the same time, the system is adjusted to neutral, and at the same time, the inorganic salts generated by the reaction of sulfur and sodium hydroxide are further removed, avoiding the hydrolysis of 2,6-dichloroquinoxaline into 2-hydroxy-6-chloroquinoxaline in the subsequent treatment process;

[0035] (4) Through the above treatment, the sulfur content in 2,6-dichloroquinoxaline is reduced to less than 0.01%. In the subsequent reaction, bis(6-chloroquinoxalin-2-yl)sulfide impurities are effectively controlled, and the qualification rate of this impurity in quizalofop-p-ethyl reaches 100%, improving the quality competitiveness of quizalofop-p-ethyl. Description of the Drawings

[0036] Figure 1 It is the high-performance liquid chromatography (HPLC) diagram of the toluene solution of 2,6-dichloroquinoxaline obtained in step (1) of Example 1.

[0037] In the figure, 2-hydroxy-6-chloroquinoxaline is at 3.646 min, the toluene solvent is around 6.2 min, 2,6-dichloroquinoxaline is at 6.785 min, bis(6-chloroquinoxalin-2-yl)sulfide impurity is at 16.85 min, and sulfur is at 30.213 min; after the chlorination reaction, the sulfur in the system is relatively large and the bis(6-chloroquinoxalin-2-yl)sulfide impurity is very small;

[0038] Figure 2 It is the high-performance liquid chromatography (HPLC) diagram of 2,6-dichloroquinoxaline obtained after final drying in Example 1.

[0039] In the figure, 2,6-dichloroquinoxaline is at 6.590 min, bis(6-chloroquinoxalin-2-yl)sulfide impurity is at 16.347 min, and sulfur is at 29.943 min; after treatment, the residual sulfur is very small and the bis(6-chloroquinoxalin-2-yl)sulfide impurity increases slightly; compared Figure 1 , the chromatographic peak position moves forward slightly; another impurity in this chlorination reaction is at 10.411 min, and under this detection condition, the absorption of this impurity peak is strong, and its quantitative content is about 20% of the normalized detection content;

[0040] Figure 3 It is the high-performance liquid chromatography (HPLC) diagram of 2,6-dichloroquinoxaline obtained after final drying in Comparative Example 2.

[0041] In the figure, 6.756 min is 2,6-dichloroquinoxaline, 16.704 min is bis(6-chloroquinoxalin-2-yl) sulfide impurity, and 30.401 min is sulfur;

[0042] Figure 4 It is the high performance liquid chromatography (HPLC) chart of 4-(6-chloroquinoxalin-2-yloxy)phenol obtained in Application Example 1.

[0043] In the figure, 3.447 min is 4-(6-chloroquinoxalin-2-yloxy)phenol, 4.720 min is 2,6-dichloroquinoxaline, and 11.260 min is bis(6-chloroquinoxalin-2-yl) sulfide impurity;

[0044] Figure 5 It is the high performance liquid chromatography (HPLC) chart of 4-(6-chloroquinoxalin-2-yloxy)phenol obtained in Application Example 2.

[0045] In the figure, 3.473 min is 4-(6-chloroquinoxalin-2-yloxy)phenol, 4.790 min is 2,6-dichloroquinoxaline, and 11.451 min is bis(6-chloroquinoxalin-2-yl) sulfide impurity. Detailed implementation mode

[0046] The above content of the present invention will be further described in detail below in the form of specific examples in conjunction with the accompanying drawings. However, it should not be understood that the scope of the above subject matter of the present invention is limited to the following examples. All technologies implemented based on the above content of the present invention belong to the scope of the present invention. Unless otherwise specified, the raw materials used in the following examples are commercially available products. Unless otherwise specified, the concentrations mentioned in this application are mass concentrations.

[0047] In the following examples, the quantitative content of 2,6-dichloroquinoxaline is detected by the external standard method of high performance liquid chromatography:

[0048] (1) Mobile phase: acetonitrile: 0.8% acetic acid aqueous solution = 70:30;

[0049] (2) Column temperature: 40 °C, flow rate: 1 ml / min, absorption wavelength: 254 nm;

[0050] (3) Chromatographic column: Shimadzu VP-ODS 4.6*150 mm, particle size 5 μm

[0051] The impurities in 2,6-dichloroquinoxaline are detected by the gradient normalization method of high performance liquid chromatography:

[0052] (1) Mobile phase: acetonitrile: 0.8% acetic acid aqueous solution;

[0053] (2) Column temperature: 40 °C, flow rate: 1 ml / min, absorption wavelength: 254 nm;

[0054] (3)Mobile phase setting:

[0055]

[0056] In the following examples, the impurity contents of sulfur and bis(6-chloroquinoxalin-2-yl)sulfide are the normal contents in liquid chromatography.

[0057] Example 1 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0058] (1)Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 2.28 kg of toluene solvent, add 315 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.5%. Cool down to below 40 °C and start vacuum distillation to recover 1.8 kg of toluene solvent with thionyl chloride. Add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline; after detection, the sulfur residue is 1.6%, and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.012%; its high-performance liquid chromatography diagram is as Figure 1 shown;

[0059] (2)Prepare a sodium hydroxide solution with a mass concentration of 4%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline prepared in step (1), heat up to 80 °C, dropwise add the prepared 4% sodium hydroxide solution, stop dropping after detecting that the pH of the system is 10 - 11. It can be calculated that 9.3 ml of 4% sodium hydroxide solution is consumed (when calculating the theoretical yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0060] (3)Set the heating temperature of the first-stage tubular reactor to 80 °C. After the temperature is stable, turn on the feed pump for the toluene solution of 2,6-dichloroquinoxaline, with a feed rate of 50 ml / min. At the same time, turn on the feed pump for the sodium hydroxide solution, and according to the sodium hydroxide dosage converted in step (2), control the feed rate to be 4.7 ml / min;

[0061] (4)Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected in the first-stage tubular reactor to keep the pH at 10 - 11. After the liquid material comes out of the tubular reactor, it enters the stratification and separation device. The temperature of the stratification and separation device is kept at 75 - 80 °C. The aqueous phase is separated, and the organic phase continues to enter the second-stage tubular reactor with a heating temperature of 80 °C. At the same time, turn on the feed pump for 0.5% dilute hydrochloric acid in the second-stage tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the second-stage tubular reactor to keep the pH at the outlet of the second-stage tubular reactor at 6 - 8;

[0062] (5) After the feed liquid comes out of the secondary tubular reactor, it enters the stratifying and separating device. The aqueous phase is separated, and the toluene phase is collected. After the feeding of the tubular reactor is completed, 3.2 kg of toluene is recovered by distillation. 385.5 g of 2,6-dichloroquinoxaline (theoretical yield: 390 g) is obtained by cooling crystallization, filtration, and drying. The quantitative content is 99.4%, the yield is 98.2%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.015%, and the sulfur residue is 0.004%. The high-performance liquid chromatography diagram is as Figure 2 shown.

[0063] Example 2 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0064] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 1, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, and heat up to 90-92 °C for 8 h. After detecting that the residue of 2-hydroxy-6-chloroquinoxaline is 0.4%, start vacuum desolvation when the temperature is lowered to below 40 °C, recover 1.8 kg of toluene solvent with thionyl chloride, add 2.3 kg of fresh toluene, add 20 g of activated carbon, heat up to 75-80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.7% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.013%;

[0065] (2) Prepare a sodium hydroxide solution with a mass concentration of 4%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline in step (1), heat up to 80 °C, dropwise add the prepared 4% sodium hydroxide solution, and stop dropping after detecting that the pH of the system is 10-11. It can be calculated that 13.8 ml of 4% sodium hydroxide solution is consumed (when calculating the theoretical yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0066] (3) Set the heating temperature of the primary tubular reactor to 80 °C. After the temperature is stable, start the feed pump of the 2,6-dichloroquinoxaline toluene solution, with a feed rate of 50 ml / min. At the same time, start the feed pump of the sodium hydroxide solution, and control the feed rate to 7.9 ml / min according to the sodium hydroxide dosage converted in step (2);

[0067] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected in the primary tubular reactor to keep the pH at 10-11. After the feed liquid comes out of the tubular reactor, it enters the stratifying and separating device. The temperature of the stratifying and separating device is kept at 75-80 °C. The aqueous phase is separated, and the organic phase continues to enter the secondary tubular reactor with a heating temperature of 80 °C. At the same time, start the feed pump of 0.5% dilute hydrochloric acid in the secondary tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the secondary tubular reactor to keep the pH at the outlet of the secondary tubular reactor at 6-8;

[0068] (5) After the feed liquid comes out of the secondary tubular reactor, it enters the stratifying and separating device. The aqueous phase is separated and the toluene phase is collected. After the feeding of the tubular inductor is completed, 1.9 kg of toluene is recovered by distillation uniformly. 372.7 g of 2,6-dichloroquinoxaline (theoretical yield 385 g) is obtained by means of cooling crystallization, filtration and drying. The quantitative content is 99.1%, the yield is 96.0%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.020%, and the sulfur residue is 0.008%.

[0069] Example 3 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0070] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 2, add 0.5 kg of fresh toluene solvent, add thionyl chloride 255 g, and heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.4%. Start vacuum desolvation after cooling to below 40 °C, recover 1.8 kg of toluene solvent with thionyl chloride, add 3 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain the toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.6% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.011%;

[0071] (2) Prepare a sodium hydroxide solution with a concentration of 4%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline in step (1), heat up to 80 °C, dropwise add the prepared 4% sodium hydroxide solution, and stop dropping after detecting that the pH of the system is 10 - 11. It can be calculated that 10.6 ml of 4% sodium hydroxide solution is consumed (when calculating the theoretical yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0072] (3) Set the heating temperature of the primary tubular reactor to 80 °C. After the temperature is stable, start the feed pump of the 2,6-dichloroquinoxaline toluene solution, with a feed rate of 50 ml / min. At the same time, start the feed pump of the sodium hydroxide solution, and control the feed rate to 5.3 ml / min according to the converted sodium hydroxide dosage in step (2);

[0073] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected in the primary tubular reactor to keep the pH at 10 - 11. After the feed liquid comes out of the tubular reactor, it enters the stratifying and separating device. The temperature of the stratifying and separating device is kept at 75 - 80 °C. The aqueous phase is separated and the organic phase continues to enter the secondary tubular reactor with a heating temperature of 80 °C. At the same time, start the feed pump of 0.5% dilute hydrochloric acid in the secondary tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the secondary tubular reactor to keep the pH at the outlet of the secondary tubular reactor at 6 - 8;

[0074] (5) After the feed liquid comes out of the secondary tubular reactor, it enters the stratifying and separating device. The aqueous phase is separated, and the toluene phase is collected. After the feeding of the tubular inductor is completed, 2.7 kg of toluene is recovered by distillation uniformly. 377 g of 2,6-dichloroquinoxaline (theoretical yield: 388 g) is obtained by cooling crystallization, filtration, and drying. The quantitative content is 99.2%, the yield is 96.4%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.018%, and the sulfur residue is 0.006%.

[0075] Example 4 A production method of 2,6-dichloroquinoxaline, and its specific steps are as follows:

[0076] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 3, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.5%. Start vacuum desolvation after cooling to below 40 °C, recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain the toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.5% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.012%;

[0077] (2) Prepare a sodium hydroxide solution with a concentration of 4%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline in step (1), heat up to 80 °C, dropwise add the prepared 4% sodium hydroxide solution, and stop dropping after detecting that the pH of the system is 10 - 11. It can be calculated that 9.3 ml of the 4% sodium hydroxide solution is consumed (when calculating the theoretical yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0078] (3) Set the heating temperature of the primary tubular reactor to 80 °C. After the temperature is stable, start the feeding pump of the 2,6-dichloroquinoxaline toluene solution, with a feeding speed of 100 ml / min. At the same time, start the feeding pump of the sodium hydroxide solution, and control the feeding speed to 9.3 ml / min according to the converted sodium hydroxide dosage in step (2);

[0079] (4) Fine-tune the feeding speed of the sodium hydroxide solution according to the pH detected in the primary tubular reactor to keep the pH at 10 - 11. After the feed liquid comes out of the tubular reactor, it enters the stratifying and separating device. The temperature of the stratifying and separating device is kept at 75 - 80 °C. The aqueous phase is separated, and the organic phase continues to enter the secondary tubular reactor with a heating temperature of 80 °C. At the same time, start the feeding pump of 0.5% dilute hydrochloric acid in the secondary tubular reactor, and adjust the feeding speed of the dilute hydrochloric acid according to the pH of the secondary tubular reactor to keep the pH at the outlet of the secondary tubular reactor at 6 - 8;

[0080] (5) After the feed liquid comes out of the secondary tubular reactor, it enters the stratifying and separating device. The aqueous phase is separated, and the toluene phase is collected. After the feeding of the tubular inductor is completed, toluene is recovered by distillation in a unified manner, 3.2 kg of toluene is recovered, and 383 g of 2,6-dichloroquinoxaline (theoretical yield: 389 g) is obtained by cooling crystallization, filtration, and drying. The quantitative content is 99.2%, the yield is 97.7%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.017%, and the sulfur residue is 0.005%.

[0081] Example 5 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0082] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 4, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.3%. Start vacuum desolvation after cooling to below 40 °C, recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.6% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.012%;

[0083] (2) Prepare a sodium hydroxide solution with a concentration of 2%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline in step (1), heat up to 80 °C, dropwise add the prepared 2% sodium hydroxide solution, stop dropping after detecting that the pH of the system is 10 - 11. It can be calculated that 20 ml of the 2% sodium hydroxide solution is consumed (when calculating the theoretical yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0084] (3) Set the heating temperature of the primary tubular reactor to 80 °C. After the temperature is stable, start the feed pump for the toluene solution of 2,6-dichloroquinoxaline, with a feed rate of 100 ml / min. At the same time, start the feed pump for the sodium hydroxide solution, and control the feed rate to 20 ml / min according to the sodium hydroxide dosage converted in step (2);

[0085] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected in the primary tubular reactor to keep the pH at 10 - 11. After the feed liquid comes out of the tubular reactor, it enters the stratifying and separating device. The temperature of the stratifying and separating device is kept at 75 - 80 °C. The aqueous phase is separated, and the organic phase continues to enter the secondary tubular reactor with a heating temperature of 80 °C. At the same time, start the feed pump for 0.5% dilute hydrochloric acid in the secondary tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the secondary tubular reactor to keep the pH at the outlet of the secondary tubular reactor at 6 - 8;

[0086] (5) After the feed liquid comes out of the secondary tubular reactor, it enters the stratifying and separating device. The aqueous phase is separated and the toluene phase is collected. After the feeding of the tubular inductor is completed, 3.2 kg of toluene is recovered by distillation. 385 g of 2,6-dichloroquinoxaline (theoretical yield: 389 g) is obtained by cooling crystallization, filtration and drying. The quantitative content is 99.0%, the yield is 98.0%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.015%, and the sulfur residue is 0.004%.

[0087] Example 6 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0088] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 5, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.4%. Start vacuum desolvation after cooling to below 40 °C, recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain the toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.5% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.014%;

[0089] (2) Prepare a sodium hydroxide solution with a concentration of 2%. First, use a four-necked flask to hold 100 ml of the toluene solution of 2,6-dichloroquinoxaline in step (1), heat up to 80 °C, dropwise add the prepared 2% sodium hydroxide solution, stop dropping after detecting that the pH of the system is 10 - 11. It can be calculated that 20 ml of the 2% sodium hydroxide solution is consumed (when calculating the yield later, subtract the toluene solution of 2,6-dichloroquinoxaline consumed in this step);

[0090] (3) Set the heating temperature of the primary tubular reactor to 70 °C. After the temperature is stable, start the feed pump of the 2,6-dichloroquinoxaline toluene solution, with a feed rate of 100 ml / min. At the same time, start the feed pump of the sodium hydroxide solution, and control the feed rate to 20 ml / min according to the amount of sodium hydroxide converted in step (2);

[0091] (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected in the primary tubular reactor to keep the pH at 10 - 11. After the feed liquid comes out of the tubular reactor, it enters the stratifying and separating device. The temperature of the stratifying and separating device is kept at 75 - 80 °C. The aqueous phase is separated and the organic phase continues to enter the secondary tubular reactor with a heating temperature of 70 °C. At the same time, start the feed pump of 0.5% dilute hydrochloric acid in the secondary tubular reactor, and adjust the feed rate of the dilute hydrochloric acid according to the pH of the secondary tubular reactor to keep the pH at the outlet of the secondary tubular reactor at 6 - 8;

[0092] After the feed liquid comes out of the secondary tubular reactor, it enters a stratifying and separating device. The aqueous phase is separated, and the toluene phase is collected. After the feeding of the tubular inductor is completed, 3.2 kg of toluene is recovered by distillation. 2,6-dichloroquinoxaline (theoretical yield: 389 g) is obtained by cooling crystallization, filtration and drying. The quantitative content is 99.0%, the yield is 97.7%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.020%, and the sulfur residue is 0.008%.

[0093] In the 2,6-dichloroquinoxaline finally prepared in the above example, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide, although seemingly increased compared with the sulfide impurity in step (1), the increase is limited and generally still controlled below 0.05%. Moreover, the sulfur residue is greatly reduced, further ensuring the quality of the quizalofop-p-ethyl product.

[0094] Application Example 1 Preparation of 4-(6-chloroquinoxalin-2-yloxy)phenol

[0095] Using 40.2 g of 2,6-dichloroquinoxaline, 26.7 g of hydroquinone, 9 g of sodium hydroxide, and 162.8 g of water obtained in Example 6, the temperature is raised to 98 - 100 °C and reacted for 10 h. After detecting that the residue of 2,6-dichloroquinoxaline is less than 0.5%, the temperature is lowered to 80 °C for filtration. The filter cake is washed with water until the filtrate is neutral and colorless, and then dried to obtain 53.8 g of 4-(6-chloroquinoxalin-2-yloxy)phenol. The quantitative content is 95.5%, the yield is 94.2%, and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.020%. Its high performance liquid chromatography diagram is as Figure 4 shown.

[0096] Since the sulfur residue in the 2,6-dichloroquinoxaline obtained in Example 6 is very low, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide remains unchanged during the subsequent preparation of 4-(6-chloroquinoxalin-2-yloxy)phenol.

[0097] Comparative Example 1 A production method of 2,6-dichloroquinoxaline, the specific steps are as follows:

[0098] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Example 6, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.3%. Cool down to below 40 °C and start vacuum distillation to remove the solvent. Recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.5% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.014%;

[0099] (2) Prepare a 2% sodium hydroxide solution. While maintaining at about 80 °C, slowly add the prepared 2% sodium hydroxide solution dropwise to the solution in step (1). Stop adding when the pH of the system is detected to be 10 - 11. 950 g of the 2% sodium hydroxide solution is consumed. After the addition is completed, stir for 0.5 h, let it stand for liquid separation, and separate out the aqueous phase;

[0100] (3) Adjust the organic phase to pH 6 - 78 with 0.15% hydrochloric acid, consume 85 g of hydrochloric acid, stir for 0.5 h, let it stand for liquid separation, and separate out the aqueous phase;

[0101] (4) Distill the toluene phase to recover 3.2 kg of toluene. Obtain 385 g of 2,6-dichloroquinoxaline (theoretical yield: 398 g) by cooling crystallization, filtration, and drying. The quantitative content is 98.5%, the yield is 95.3%, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.45%, and the sulfur residue is 0.55%.

[0102] Compared with Example 5, in this comparative example, a reaction flask is used instead of a tubular reactor, and sulfur cannot be removed well. Moreover, due to the long contact time with the sodium hydroxide solution, the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is relatively large.

[0103] Comparative Example 2 A production method of 2,6-dichloroquinoxaline, and its specific steps are as follows:

[0104] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered in Comparative Example 1, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.4%. Cool down to below 40 °C and start vacuum distillation to remove the solvent. Recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.6% and the impurity of bis(6-chloroquinoxalin-2-yl)sulfide is 0.013%;

[0105] (2) Prepare a 4% sodium hydroxide solution. While maintaining the temperature at around 80 °C, add the prepared 4% sodium hydroxide solution dropwise to the solution in step (1). Stop adding when the pH of the system reaches 10 - 11. 500 g of the 4% sodium hydroxide solution is consumed. After the addition is complete, stir for 0.5 h, let it stand for liquid separation, and separate out the aqueous phase;

[0106] (3) Adjust the organic phase to pH 6 - 78 with 0.15% hydrochloric acid, consume 100 g of hydrochloric acid, stir for 0.5 h, let it stand for liquid separation, and separate out the aqueous phase;

[0107] (4) Distill and recover 3.2 kg of toluene from the toluene phase. Obtain 383 g of 2,6 - dichloroquinoxaline (theoretical yield: 398 g) by means of cooling crystallization, filtration, and drying. The quantitative content is 98.3%, the yield is 94.6%, the impurity of bis(6 - chloroquinoxalin - 2 - yl) sulfide is 0.77%, and the sulfur residue is 0.09%. The high - performance liquid chromatography diagram is as Figure 3 shown.

[0108] Based on Comparative Example 1, increasing the mass concentration of sodium hydroxide and using a reaction flask instead of a tubular reactor results in a relatively better sulfur removal effect compared to Comparative Example 1, but the impurity of bis(6 - chloroquinoxalin - 2 - yl) sulfide also continues to increase.

[0109] Comparative Example 3 A method for producing 2,6 - dichloroquinoxaline, the specific steps are as follows:

[0110] (1) Weigh 380 g of 2 - hydroxy - 6 - chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered from Comparative Example 2, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2 - hydroxy - 6 - chloroquinoxaline is 0.4%. Cool down to below 40 °C and start vacuum desolvation to recover 1.8 kg of toluene solvent with thionyl chloride. Add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6 - dichloroquinoxaline, in which the sulfur residue is 1.5% and the impurity of bis(6 - chloroquinoxalin - 2 - yl) sulfide is 0.013%;

[0111] (2) Prepare a 2% sodium hydroxide solution. While maintaining the temperature at around 80 °C, add the prepared 2% sodium hydroxide solution dropwise to the solution in step (1). Stop adding when the pH of the system reaches 10 - 11. 960 g of the 2% sodium hydroxide solution is consumed. After the addition is complete, stir for 1 h, let it stand for liquid separation, and separate out the aqueous phase;

[0112] (3) Adjust the organic phase to pH 6 - 78 with 0.5% hydrochloric acid, consume 100 g of hydrochloric acid, stir for 0.5 h, let it stand for liquid separation, and separate out the aqueous phase;

[0113] (4) 3.2 kg of toluene was recovered by distillation from the toluene phase, and 384.8 g of 2,6-dichloroquinoxaline (theoretical yield: 398 g) was obtained by cooling crystallization, filtration, and drying. The quantitative content was 98.7%, the yield was 95.4%, the impurity of bis(6-chloroquinoxalin-2-yl) sulfide was 0.45%, and the sulfur residue was 0.34%.

[0114] Based on Comparative Example 1, the amount of sodium hydroxide was increased, and a reaction flask was used instead of a tubular reactor. The sulfur removal effect was improved compared with Comparative Example 1, but the impurity of bis(6-chloroquinoxalin-2-yl) sulfide still exceeded the specified requirements.

[0115] Comparative Example 4 A method for producing 2,6-dichloroquinoxaline, the specific steps are as follows:

[0116] (1) Weigh 380 g of 2-hydroxy-6-chloroquinoxaline with a content of 95%, add 1.8 kg of toluene containing thionyl chloride recovered from Comparative Example 3, add 0.5 kg of fresh toluene solvent, add 255 g of thionyl chloride, heat up to 90 - 92 °C in 2 h and react for 8 h. Detect that the residue of 2-hydroxy-6-chloroquinoxaline is 0.4%. Start vacuum distillation below 40 °C to recover 1.8 kg of toluene solvent with thionyl chloride, add 3.5 kg of fresh toluene, add 20 g of activated carbon, heat up to 75 - 80 °C for decolorization for 0.5 h, and filter to obtain a toluene solution of 2,6-dichloroquinoxaline, in which the sulfur residue is 1.7% and the impurity of bis(6-chloroquinoxalin-2-yl) sulfide is 0.014%;

[0117] (2) 3.2 kg of toluene was recovered by distillation from the toluene phase, and 396 g of 2,6-dichloroquinoxaline (theoretical yield: 398 g) was obtained by cooling crystallization, filtration, and drying. The quantitative content was 98.2%, the yield was 97.7%, the impurity of bis(6-chloroquinoxalin-2-yl) sulfide was 0.005%, and the sulfur residue was 1.2%.

[0118] If the sulfur in the toluene solution of 2,6-dichloroquinoxaline is not removed, and only the sulfur residue is reduced by crystallization in this Comparative Example 4, although the impurity of bis(6-chloroquinoxalin-2-yl) sulfide can be reduced to 0.005%, but in the subsequent reaction for preparing the intermediate of quizalofop-P-ethyl, 2,6-dichloroquinoxaline and sulfur will continue to react to form the impurity of bis(6-chloroquinoxalin-2-yl) sulfide and far exceed the specified requirements, which is specifically reflected in the following application comparative examples:

[0119] Application Example 2 Preparation of 4-(6-chloroquinoxalin-2-yloxy)phenol

[0120] Using 40.7 g of 2,6-dichloroquinoxaline, 26.7 g of hydroquinone, 9 g of sodium hydroxide, and 162.8 g of water obtained from Comparative Example 4, the temperature was raised to 98 - 100 °C and reacted for 10 h. After detecting that the residual amount of 2,6-dichloroquinoxaline was less than 0.5%, the temperature was lowered to 80 °C for filtration. The filter cake was washed with water until the pH of the filtrate was neutral and colorless, and then dried to obtain 53.1 g of 4-(6-chloroquinoxalin-2-yloxy)phenol, with a quantitative content of 94.5%, a yield of 92.0%, and 1.23% of bis(6-chloroquinoxalin-2-yl) sulfide impurity. Its high-performance liquid chromatography diagram is as Figure 5 shown.

[0121] Due to the high sulfur residue in the 2,6-dichloroquinoxaline obtained from Comparative Example 4, during the subsequent preparation of 4-(6-chloroquinoxalin-2-yloxy)phenol, since the system is strongly alkaline, the impurity of bis(6-chloroquinoxalin-2-yl) sulfide increases and far exceeds the control index. Moreover, because this impurity is basically insoluble in water and has poor solubility in conventional organic solvents such as toluene or ethanol, its removal effect is very poor during the subsequent preparation of quizalofop-p-ethyl, and high-quality quizalofop-p-ethyl cannot be obtained.

[0122] By comparing the application examples and application comparative examples, it can be seen that by using the production method provided in the present application, the sulfur content in 2,6-dichloroquinoxaline is reduced to less than 0.01%. In the subsequent reaction, the impurity of bis(6-chloroquinoxalin-2-yl) sulfide can be effectively controlled, so that the qualified rate of this impurity in quizalofop-p-ethyl reaches 100%, improving the quality competitiveness of quizalofop-p-ethyl.

[0123] For those of ordinary skill in the art, the specific embodiments only exemplarily describe the present invention. Obviously, the specific implementation of the present invention is not limited by the above methods. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A production method of 2,6-dichloroquinoxaline, characterized in that, The specific steps are as follows: (1) Prepare a toluene solution of 2,6-dichloroquinoxaline, where the mass concentration of 2,6-dichloroquinoxaline is 10-15%; (2) Calculate the mass ratio of the sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline. The specific steps are as follows: Prepare a sodium hydroxide solution with a mass concentration of 2-4%. First, heat a certain volume of the toluene solution of 2,6-dichloroquinoxaline prepared in step (1) to 60-80 °C, dropwise add the prepared sodium hydroxide solution, stop dropping when the pH of the system is detected to be 10-11, calculate the consumption of the sodium hydroxide solution, and calculate the mass ratio of the sodium hydroxide solution to the toluene solution of 2,6-dichloroquinoxaline; (3) Set the heating temperature of the first-stage tubular reactor to 60-80 °C. After the temperature stabilizes, start the feed pump for the toluene solution of 2,6-dichloroquinoxaline, with a feed rate of 50-100 ml / min. At the same time, start the feed pump for the sodium hydroxide solution, and set the feed rate according to the ratio calculated in step (2) for the sodium hydroxide solution and the toluene solution of 2,6-dichloroquinoxaline; the inner diameter of the tubular reactor is 5±0.2 mm, the liquid holdup is 450-500 ml, and the residence time of the liquid in the tubular reactor is 5-10 min; (4) Fine-tune the feed rate of the sodium hydroxide solution according to the pH detected at the outlet end of the first-stage tubular reactor to maintain a pH of 10-11. After the liquid leaves the tubular reactor, it enters a liquid-liquid separator. The aqueous phase is separated, and the organic phase continues to enter the second-stage tubular reactor. At the same time, start the feed pump for dilute hydrochloric acid in the second-stage tubular reactor, and adjust the feed rate of dilute hydrochloric acid according to the pH of the second-stage tubular reactor to neutralize the sodium hydroxide in the liquid, and maintain a pH of 6-8 at the outlet end; (5) After the liquid leaves the second-stage tubular reactor, it enters a liquid-liquid separator. The aqueous phase is separated, and the toluene phase is distilled. 2,6-dichloroquinoxaline is obtained by cooling crystallization and filtration.

2. The production method of 2,6-dichloroquinoxaline according to claim 1, characterized in that: The preparation method of the toluene solution of 2,6-dichloroquinoxaline in step (1) is as follows: 2-Hydroxy-6-chloroquinoxaline reacts with thionyl chloride in a toluene solvent to form 2,6-dichloroquinoxaline. After the reaction is qualified, the remaining thionyl chloride is removed together with toluene, and then fresh toluene solvent is added to obtain a toluene solution of 2,6-dichloroquinoxaline, where the mass concentration of 2,6-dichloroquinoxaline is 10-15%.

3. The production method of 2,6-dichloroquinoxaline according to claim 1, characterized in that: The impurity of bis(6-chloroquinoxalin-2-yl) sulfide in the finally obtained 2,6-dichloroquinoxaline is below 0.02%, and the sulfur residue is below 0.01%.

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