Preparation method of 2, 6-dichloro-3-trichloromethylpyridine

Abstract

The invention discloses a preparation method of 2, 6-dichloro-3-trichloromethylpyridine, and belongs to the field of photochlorination reaction methods, the preparation method of 2, 6-dichloro-3-trichloromethylpyridine takes a compound shown as a formula # imgabs0 # as a raw material, and the 2, 6-dichloro-3-trichloromethylpyridine is synthesized by a photochlorination reaction one-step method; a chlorination reagent used in the photochlorination reaction is chlorine; the wavelength of a light source for the photochlorination reaction is 100-780 nm; wherein R is independently selected from methyl, monochloromethyl, dichloromethyl or trichloromethyl. According to the method, the target product can be obtained through a one-step method, and the conversion rate of the target product is high.

Description

Technical Field

[0001] The present invention relates to the field of photochlorination reaction methods, and more particularly to a method for preparing 2,6-dichloro-3-trichloromethylpyridine. Background Art

[0002] 2,6-Dichloro-3-trichloromethylpyridine can be used as an important intermediate for medicines, pesticides, etc., especially for the development of new compounds with herbicidal activity. The traditional method of introducing chlorine atoms on the pyridine ring is to carry out the reaction under the catalysis of metal chlorides such as WCl6, FeCl3 or SnCl4. However, the activity of these catalysts will gradually decrease as the reaction proceeds, thereby introducing impurities and reducing the purity of the product. According to the industrialized process, it is known that the main product obtained after catalytic chlorination of 2-chloro-5-trichloromethylpyridine is 2,3-dichloro-5-trichloromethylpyridine; as shown in the following equation, there will be no target compound in this reaction. In addition, the reaction also produces a small amount of by-product 2,3,6-trichloro-5-trichloromethylpyridine.

[0003]

[0004] Therefore, it is necessary to provide a method for preparing 2,6-dichloro-3-trichloromethylpyridine with low cost, high selectivity and high conversion rate. Summary of the Invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a method for preparing 2,6-dichloro-3-trichloromethylpyridine, which can prepare 2,6-dichloro-3-trichloromethylpyridine with high selectivity and high conversion rate.

[0006] To solve the above problems, the present invention adopts the following technical solutions.

[0007] A method for preparing 2,6-dichloro-3-trichloromethylpyridine, wherein the The compound shown is used as a raw material to synthesize 2,6-dichloro-3-trichloromethylpyridine in one step through a photochlorination reaction; the chlorination reagent used in the photochlorination reaction is chlorine gas; the wavelength of the light source for the photochlorination reaction is 100 to 780 nm;

[0008] Wherein, the R groups are independently selected from methyl, monochloromethyl, dichloromethyl or trichloromethyl.

[0009] Furthermore, the R group is methyl or monochloromethyl.

[0010] Furthermore, the wavelength of the light source is preferably 380-500 nm.

[0011] Furthermore, the reaction temperature during the photochlorination reaction is 70-160°C, preferably 100-130°C.

[0012] Furthermore, the photochlorination reaction is carried out in the presence of a solvent or in the absence of a solvent. In the presence of a solvent, the solvent is one or a mixture of two or more of monochlorobenzotrifluoride, dichlorobenzotrifluoride, trichlorobenzotrifluoride and dichlorobenzene.

[0013] Furthermore, the solvent is monochlorobenzotrifluoride or trichlorobenzotrifluoride; the monochlorobenzotrifluoride is o-chlorobenzotrifluoride, p-chlorobenzotrifluoride or m-chlorobenzotrifluoride.

[0014] Furthermore, when the preparation method is used in an industrial preparation process, it can be carried out in a batch reaction device of a kettle type or a tower type or a continuous reaction device of a kettle type or a tower type.

[0015] Furthermore, the preparation method also includes post-processing, wherein the post-processing comprises: removing the acid gas and the solvent from the product obtained by the photochlorination reaction, and then melting and crystallizing the product to obtain 2,6-dichloro-3-trichloromethylpyridine.

[0016] Furthermore, there is no clear requirement for the flow rate of chlorine, but it will affect the speed of the reaction. The distribution and flow rate of chlorine can be adjusted and optimized accordingly according to the scale of the reaction and actual requirements. The adjustment and optimization of the distribution and flow rate of chlorine will not affect the conversion rate and selectivity of the reaction itself; the reaction process can be tracked and detected by GC (gas chromatography).

[0017] Furthermore, the principle of the present invention is as follows (taking the compound 2-chloro-5-methylpyridine as an example of a starting material):

[0018]

[0019] The process of the photochlorination reaction is carried out step by step, and a monochloro substituted product as shown in Formula II, a dichloro substituted product as shown in Formula III, a trichloro substituted product as shown in Formula IV, and a tetrachloro substituted product as shown in Formula V are generated in sequence; the above intermediate products will coexist during the reaction process. For example, in the initial stage of the reaction, 2-chloro-5-methylpyridine shown in Formula I, a monochloro substituted product as shown in Formula II, a dichloro substituted product as shown in Formula III, and a trichloro substituted product as shown in Formula IV will coexist in the system. As the reaction proceeds, the raw materials are gradually consumed, and the monochloro substituted product as shown in Formula II, the dichloro substituted product as shown in Formula III, and the trichloro substituted product as shown in Formula IV will coexist in the system. When the monochloro substituted product as shown in Formula II is almost consumed, the product as shown in Formula V begins to appear in the system. Because of this, the monochloro substituent shown in Formula II, the dichloro substituent shown in Formula III, and the trichloro substituent shown in Formula IV appear in the system as intermediates. Therefore, the monochloro substituent shown in Formula II, the dichloro substituent shown in Formula III, and the trichloro substituent shown in Formula IV can also be used as starting materials to carry out photochlorination reaction to generate a tetrachloro substituent shown in Formula V, i.e., 2,6-dichloro-3-trichloromethylpyridine.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] This plan is based on The compound shown is used as a raw material, preferably the R group is methyl or monochloromethyl, that is, the preferred compound 2-chloro-5-methylpyridine or 2-chloro-5-chloromethylpyridine is used as the raw material, and the target compound 2,6-dichloro-3-trichloromethylpyridine is synthesized in a one-step method under the condition of a light source wavelength of 100 to 780 nm through a photochlorination reaction. This method has high selectivity and high conversion rate, and is not prone to the production of the by-product 2,3,6-trichloro-5-trichloromethylpyridine. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a GC chromatogram of a sample taken when the reaction was carried out for 2 hours in Example 1;

[0023] Figure 2 This is a GC chromatogram of a sample taken for 12 hours after the reaction in Example 1;

[0024] Figure 3 The GC chromatogram of the purchased compound of formula VI is used for comparative analysis;

[0025] Figure 4 This is the mass spectrum of the final product 2,6-dichloro-3-trichloromethylpyridine in Example 1.

[0026] Wherein, I, II, III, IV, V and VI represent the compound of formula I, the compound of formula II, the compound of formula III, the compound of formula IV, the compound of formula V and the compound of formula VI, respectively. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described below in conjunction with the accompanying drawings. Without additional explanation, the raw materials used in the following examples are all industrial grade and are used directly without purification. The GC conditions are: column oven 180°C, carrier gas flow rate 0.5mL / min. The detector is FID, the chromatographic column model is HT-5, and the gas chromatograph instrument model is GC99 (purchased from Hangzhou Haohai Scientific Instrument Co., Ltd.); the peak times of the compounds represented by Formula I to Formula VI in the GC chromatogram are 5.6min, 7.2min, 8.9min, 10.5min, 19.0min and 14.9min, respectively. The chemical structural formulas of the compounds represented by Formula I to Formula VI are as follows:

[0028]

[0029] The compound represented by Formula VI was purchased from commercial sources, and its peak time was compared with that of the compound represented by Formula V.

[0030] Example 1:

[0031] 135g 2-chloro-5-methylpyridine and 240g parachlorotrifluorobenzol were added to a four-necked flask equipped with mechanical stirring, a thermometer, and a condenser tube. An LED blue light (wavelength of 420-450nm) was turned on and irradiated. The reaction was heated to 105°C and chlorine was introduced. The flow rate was maintained at about 0.4L / min and the temperature was 100-120°C. The initial heat release was significant. Samples were taken for GC detection at 1h, 2h, 3h, 4h, 6h, 8h, 10h, and 12h. The reaction conversion rate was shown in the table below. When the compound content of Formula IV was ≤5.0%, the product was collected and subjected to melt crystallization after deacidification and precipitation to obtain the target product 2,6-dichloro-3-trichloromethylpyridine.

[0032] Table 1 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0033] I II III IV V 1h 13.1％ 58.5％ 26.2％ 1.8％ 0 2h 12.3％ 2.5％ 50.4％ 34.7％ 0 3h 0 1.4％ 2.2％ 95.5％ 0 4h 0 0 0.4％ 94.6％ 5.0％ 6h 0 0 0 74.5％ 24.6％ 8h 0 0 0 46.6％ 52.5％ 10h 0 0 0 22.3％ 76.7％ 12h 0 0 0 3.8％ 95.4％

[0034] Depend on Figure 1-Figure 3It can be seen that after 2 hours of reaction, the compound represented by formula I, the compound represented by formula II, the compound represented by formula III and the compound represented by formula IV will exist simultaneously in the reaction solution; after 12 hours of reaction, the compound represented by formula I and the compound represented by formula II in the reaction solution will be completely converted into the compound represented by formula IV and the compound represented by formula V, and the compound represented by formula VI will not be generated.

[0035] The final product was tested by GC-MS, and the mass spectrum was as follows: Figure 4 shown.

[0036] Example 2:

[0037] In the four-hole bottle that mechanical stirring, thermometer, condenser pipe are housed, add 135g 2-chloro-5-picoline and 240g parachlorobenzotrifluoride, open LED ultraviolet lamp (wavelength is 100~380nm) irradiation, heat temperature raising to 105 ℃, begin to feed chlorine, keeping flow to be about 0.4L / min, temperature is 100~120 ℃, initial stage heat release is obvious, sampling GC detection respectively during 1h, 2h, 3h, 4h, 8h, 12h, 16h, 20h and 24h.Reaction conversion is as shown in the table below, and as can be seen, compared with embodiment 1, speed of reaction obviously reduces.After compound content≤5.0% shown in formula IV, collect rear resultant and it is carried out deacidification, precipitation back melt crystallization obtains target product 2,6-dichloro-3-trichloromethyl pyridine.

[0038] Table 2 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0039] I II III IV V 1h 20.1％ 61.5％ 17.2％ 0.8％ 0 2h 8.3％ 11.5％ 44.4％ 32.7％ 0 3h 3.3％ 7.4％ 12.2％ 75.5％ 0 4h 0 0 4.6％ 92.9％ 1.8％ 8h 0 0 0 84.5％ 14.6％ 12h 0 0 0 66.6％ 32.5％ 16h 0 0 0 42.3％ 56.7％ 20h 0 0 0 18.8％ 80.4％ 24h 0 0 0 4.5％ 94.1％

[0040] Example 3:

[0041] 135g of 2-chloro-5-methylpyridine and 240g of parachlorotrifluorobenzol were added to a four-necked flask equipped with a mechanical stirrer, a thermometer, and a condenser. The LED red light (wavelength of 500-780nm) was turned on and irradiated. The temperature was raised to 105°C and chlorine gas was introduced, maintaining a flow rate of about 0.4L / min and a temperature of 100-120°C. An exothermic reaction was observed in the initial stage. Samples were taken for GC analysis at 1h, 2h, 3h, 4h, 8h, 12h, 16h, and 20h. The reaction conversion rate is shown in the table below. It can be seen that the reaction rate was significantly reduced compared to Example 1. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected and subjected to deacidification, desolvation, and melt crystallization to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0042] Table 3 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0043]

[0044]

[0045] Example 4:

[0046] This embodiment differs from embodiment 1 in that light sources of different wavelengths (380-420 nm and 450-500 nm) are used, while other reaction conditions remain unchanged. The conversion rates of the final products are shown in the following table (to clearly observe the effects of light sources of different wavelengths on the reaction, the data of embodiments 1-3 are also supplemented in the table, and the reaction time is unified as 12 h):

[0047] Table 4 Effect of different wavelength light sources on final product conversion rate

[0048] Light source wavelength (nm) Conversion rate of final product (%) 100～380 32.5％ 380～420 86.5％ 420～450 95.4％ 450～500 88.6％ 500～780 62.5％

[0049] It can be seen from Examples 1 to 4 that when the light source is blue light with a wavelength of 380 to 500 nm, the time for generating the final product can be accelerated, so that the target product 2,6-dichloro-3-trichloromethylpyridine with a high conversion rate can be obtained within 12 hours. Therefore, the light source is preferably blue light with a wavelength of 380 to 500 nm.

[0050] Example 5:

[0051] 135g 2-chloro-5-picoline and 240g o-chlorotrifluorobenzol are added to a four-necked flask equipped with mechanical stirring, thermometer, and condenser tube, LED blue light (wavelength is 420-450nm) is turned on and irradiated, and heat temperature raising is to 105 ℃, and chlorine is started to be fed, and flow rate is kept to be about 0.4L / min, and temperature is 100-120 ℃, and initial stage heat release is obvious, and sampling GC detection is respectively carried out at 1h, 2h, 3h, 4h, 6h, 8h, 10h and 12h. Reaction conversion is as shown in the table below. When compound content shown in formula IV is less than or equal to 5.0%, resultant is collected and subjected to deacidification, precipitation and rear melt crystallization to obtain target product 2,6-dichloro-3-trichloromethyl pyridine.

[0052] Table 5 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0053] I II III IV V 1h 14.1％ 63.5％ 21.2％ 0.8％ 0 2h 2.3％ 12.5％ 60.4％ 24.7％ 0 3h 0 0.6％ 7.2％ 91.5％ 0 4h 0 0 0.4％ 83.7％ 15.1％ 6h 0 0 0 62.6％ 26.6％ 8h 0 0 0 42.4％ 56.8％ 10h 0 0 0 18.3％ 80.8％ 12h 0 0 0 2.9％ 96.4％

[0054] Example 6:

[0055] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, 135g of 2-chloro-5-methylpyridine and 240g of m-chlorotrifluorobenzol were added. Irradiation was performed using an LED blue light (wavelength 420-450nm). The temperature was raised to 105°C, and chlorine gas was introduced at a flow rate of approximately 0.4 L / min and a temperature of 100-120°C. A significant exotherm was observed during the initial stage. Samples were collected for GC analysis at 1, 2, 3, 4, 6, 8, 10, and 12 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected, deaerated, desolvated, and then melt crystallized to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0056] Table 6 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0057]

[0058]

[0059] Example 7:

[0060] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, 135g of 2-chloro-5-methylpyridine and 240g of dichlorobenzene were added. An LED blue light (wavelength 420-450nm) was used for irradiation. The temperature was raised to 105°C, and chlorine gas was introduced, maintaining a flow rate of approximately 0.4L / min and a temperature of 100-120°C. A significant exotherm was observed in the initial stage. Samples were taken for GC analysis at 1, 2, 3, 4, 6, 8, 10, and 12 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the reaction was stopped. As can be seen in the table, the content of the target product was significantly reduced compared to Example 1. GCMS analysis suggested that the solvent dichlorobenzene underwent a chlorination reaction. After deaeration and desolvation, the target product, 2,6-dichloro-3-trichloromethylpyridine, was obtained by melt crystallization.

[0061] Table 7 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0062]

[0063]

[0064] Example 8:

[0065] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, 135g of 2-chloro-5-methylpyridine and 240g of trichlorobenzotrifluoride were added. Irradiation was performed using an LED blue light (wavelength 420-450nm). The temperature was raised to 105°C, and chlorine gas was introduced at a flow rate of approximately 0.4 L / min and a temperature of 100-120°C. A significant exotherm was observed during the initial stage. Samples were collected for GC analysis at 1, 2, 3, 4, 6, 8, 10, and 12 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected, deaerated, desolvated, and then melt-crystallized to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0066] Table 8 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0067] I II III IV V 1h 14.9％ 56.3％ 25.2％ 2.8％ 0 2h 0％ 2.8％ 61.8％ 34.2％ 0 3h 0 0％ 34.2％ 64.6％ 0 4h 0 0 0.9％ 91.6％ 6.6％ 6h 0 0 0 66.5％ 32.1％ 8h 0 0 0 43.9％ 55.4％ 10h 0 0 0 20.8％ 78.7％ 12h 0 0 0 1.8％ 97.4％

[0068] Example 9:

[0069] 340g of molten 2-chloro-5-methylpyridine (mp.16-18°C) was added to a four-necked flask equipped with mechanical stirring, a thermometer, and a condenser tube. The mixture was irradiated with an LED blue light (wavelength of 420-450nm), heated to 105°C, and chlorine was introduced. The flow rate was maintained at about 1.0L / min and the temperature was 100-120°C. The initial heat release was obvious, and samples were taken for GC detection at 1h, 2h, 3h, 4h, 5h, 7h, 9h, and 11h. The reaction conversion rate is shown in the table below. When the content of the compound shown in Formula IV was ≤5.0%, the product was collected and subjected to deacidification and desolvation followed by melt crystallization to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0070] Table 9 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0071] I II III IV V 1h 24.6％ 58.4％ 16.0％ 0 0 2h 0.5％ 25.1％ 66.2％ 25.2％ 0 3h 0 0％ 43.8％ 55.5％ 0 4h 0 0 0.2％ 92.0％ 6.1％ 5h 0 0 0 86.0％ 13.6％ 7h 0 0 0 46.6％ 52.5％ 9h 0 0 0 22.3％ 76.7％ 11h 0 0 0 2.9％ 96.5％

[0072] As can be seen from Examples 1 and 5 to 9, when dichlorobenzene is used as the solvent, the purity of the obtained product is low. When no solvent is added or when monochlorobenzotrifluoride or trichlorobenzotrifluoride is used as the solvent, a higher conversion rate can be obtained in about 12 hours.

[0073] Example 10:

[0074] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, 171g of 2-chloro-5-chloromethylpyridine and 240g of para-chlorobenzotrifluoride were added. Irradiation was performed using an LED blue light (wavelength 420-450nm). The temperature was raised to 110°C and chlorine gas was introduced, maintaining a flow rate of approximately 0.4 L / min and a temperature of 110-130°C. A significant exotherm was observed during the initial stage. Samples were collected for GC analysis at 1, 2, 3, 5, 7, and 9 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected and subjected to deaeration, desolvation, and melt crystallization to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0075] Table 10 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0076] I II III IV V 1h 0 18.7％ 63.2％ 17.7％ 0 2h 0 1.5％ 23.1％ 74.2％ 0 3h 0 0 0.3％ 96.8％ 1.9％ 5h 0 0 0 64.7％ 34.4％ 7h 0 0 0 32.8％ 67.0％ 9h 0 0 0 3.7％ 96.1％

[0077] Example 11:

[0078] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, add 244g of 2-chloro-5-trichloromethylpyridine and 240g of para-chlorobenzotrifluoride. Irradiate with an LED blue light (wavelength 420-450nm), heat to 120°C, and begin introducing chlorine gas at a flow rate of approximately 0.4L / min at a temperature of 115-135°C. Samples were taken for GC analysis after 2, 4, 8, and 10 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected, deaerated, desolvated, and then melt crystallized to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0079] Table 11 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0080] I II III IV V 2h 0 0 0 73.9％ 25.6％ 4h 0 0 0 53.1％ 46.4％ 8h 0 0 0 25.8％ 73.3％ 10h 0 0 0 3.1％ 96.2％

[0081] Example 12:

[0082] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, add 208g of 2-chloro-5-dichloromethylpyridine and 240g of para-chlorobenzotrifluoride. Irradiate with an LED blue light (wavelength 420-450nm), heat to 120°C, and begin introducing chlorine gas at a flow rate of approximately 0.4 L / min at a temperature of 115-135°C. Samples were taken for GC analysis at 1, 2, 3, 4, 6, 8, 10, and 11 hours. The reaction conversion rates are shown in the table below. When the content of the compound represented by Formula IV was ≤5.0%, the product was collected, deaerated, desolvated, and then melt crystallized to obtain the target product, 2,6-dichloro-3-trichloromethylpyridine.

[0083] Table 12 Content of the compound represented by formula I to the compound represented by formula V in the four-necked bottle at different times

[0084] I II III IV V 1h 0 0 5.9％ 93.2％ 0 2h 0 0 0 93.4％ 5.6％ 3h 0 0 0 84.4％ 14.6％ 4h 0 0 0 73.3％ 25.7％ 6h 0 0 0 46.7％ 52.2％ 8h 0 0 0 20.6％ 78.1％ 10h 0 0 0 6.9％ 91.8％ 11h 0 0 0 2.4％ 95.7％

[0085] Comparative Example 1:

[0086] To a four-necked flask equipped with a mechanical stirrer, thermometer, and condenser, add 488 g of molten 2-chloro-5-trichloromethylpyridine (mp. 53-55°C) and 1.2 g of WCl6. Heat to 170°C and begin introducing chlorine gas at a flow rate of approximately 0.6 L / min at a temperature of 160-180°C. Samples are collected for GC analysis at 10, 20, 30, and 40 hours. The reaction conversion is shown in the table below.

[0087] Table 11 Content of the compound represented by formula I to the compound represented by formula VI in the four-necked bottle at different times

[0088] I II III IV V VI 10h 0 0 0 53.8％ 0 45.6％ 20h 0 0 0 13.1％ 0 86.2％ 30h 0 0 0 0.6％ 0 93.3％ 40h 0 0 0 0.1％ 0 91.1％

[0089] In the comparative example, the raw materials used contained 0.5% 2,6-dichloro-3-trichloromethylpyridine. Experiments revealed that 2,6-dichloro-3-trichloromethylpyridine was converted into a byproduct, 2,3,6-trichloro-5-trichloromethylpyridine (not shown in the table). As the reaction progressed, the content of the main product, the compound represented by Formula VI, decreased, indicating that some of the byproduct, 2,3,6-trichloro-5-trichloromethylpyridine, was also converted.

[0090] It should be noted that in the tables of Examples 1 to 12 and Comparative Example 1, some impurities were not counted.

Claims

1. A method for preparing 2,6-dichloro-3-trichloromethylpyridine, characterized in that: In the form The compound shown is used as a raw material to synthesize 2,6-dichloro-3-trichloromethylpyridine in one step through a photochlorination reaction; the chlorination reagent used in the photochlorination reaction is chlorine gas; the wavelength of the light source for the photochlorination reaction is 100 to 780 nm; Wherein, the R groups are independently selected from methyl, monochloromethyl, dichloromethyl or trichloromethyl.

2. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 1, characterized in that: The R group is methyl or monochloromethyl.

3. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 1, characterized in that: The wavelength of the light source is 380-500 nm.

4. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 1, characterized in that: The reaction temperature during the photochlorination reaction is 70-160°C.

5. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 1, characterized in that: The photochlorination reaction is carried out in the presence of a solvent or in the absence of a solvent. In the presence of a solvent, the solvent is one or a mixture of two or more of monochlorobenzotrifluoride, dichlorobenzotrifluoride, trichlorobenzotrifluoride and dichlorobenzene.

6. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 5, characterized in that: The solvent is monochlorobenzotrifluoride or trichlorobenzotrifluoride; the monochlorobenzotrifluoride is o-chlorobenzotrifluoride, p-chlorobenzotrifluoride or m-chlorobenzotrifluoride.

7. A method for preparing 2,6-dichloro-3-trichloromethylpyridine according to claim 1, characterized in that: The preparation method further comprises post-processing, wherein the post-processing method comprises: removing acid gas and solvent from the product obtained by the photochlorination reaction, and then melting and crystallizing the product to obtain 2,6-dichloro-3-trichloromethylpyridine.

Images