Continuous flow preparation method of clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one

Abstract

This invention belongs to the field of organic chemical engineering technology, specifically a continuous flow preparation method for the clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. The invention includes: mixing 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one with a toluene solution of triethylamine and a toluene solution of propionyl chloride, and feeding the mixture into a multi-stage oscillating reactor for acylation to obtain a preliminary 5-[(2-ethylthio)propyl]-3-one-1-cyclohexen-1-propionate product and a suspension of triethylamine hydrochloride; separating the triethylamine hydrochloride and the reaction solution through a storage tank; then mixing the mixture with a toluene solution of DMAP (4-dimethylaminopyridine) and feeding it into a microchannel reactor for Fries rearrangement to obtain the final product 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. The method of this invention has high time and space productivity, high degree of automation, good safety performance, low energy consumption and easy industrial scale-up application.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical engineering technology, and specifically relates to a method for preparing the clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one. Background Technology

[0002] 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one is an important intermediate in cyclohexenone herbicides. These herbicides exhibit excellent selectivity, strong killing effect on grass weeds, and are safe for dicotyledonous crops. They are mainly used to control annual and perennial grass weeds and free-growing cereal crops in broadleaf fields, thus showing broad application prospects in the pesticide field. The structural formula of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one is shown in formula (1):

[0003]

[0004] Currently, the industrial synthesis method for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one mainly involves adding triethylamine dropwise to a reactor containing 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one, raising the temperature and controlling it between 48-50°C, then adding propionyl chloride dropwise while controlling the dropping rate. After the propionyl chloride is added, steam is introduced to raise the temperature to 90-95°C, and the reaction is maintained at this temperature for 2 hours. Subsequently, the steam is turned off, the temperature is lowered to 50°C, and PDM is added to the reactor. The reaction is then carried out at a temperature controlled at 50±1°C for 6 hours. This method has a long reaction time, strict temperature requirements, significant safety risks, and high energy consumption. In the laboratory, there is also a method using aluminum trichloride as a catalyst, dissolving 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one in dichloromethane, adding propionyl chloride dropwise, then adding aluminum trichloride, reacting under ice bath conditions for 4 hours, and then refluxing for 12 hours. However, this method requires post-processing, is cumbersome, involves high reaction temperatures, and is inefficient, making it unsuitable for industrial production. Summary of the Invention

[0005] To overcome the shortcomings of traditional batch reactor synthesis methods, such as long reaction time, significant safety hazards, high energy consumption, and low efficiency, as well as the stringent requirements for industrial production conditions, this invention provides a continuous flow preparation method for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. This method offers relatively mild reaction conditions, significantly shortens reaction time, substantially improves the automation and efficiency of the process, greatly reduces energy consumption, significantly enhances safety, and is easily applicable to industrial applications.

[0006] The continuous flow preparation method of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one provided by this invention uses a continuous system consisting of multiple sequentially connected microchannel mixers, a multi-stage oscillating reactor, a filter storage tank with a sand core filter layer, and a microchannel reactor. The specific steps are as follows:

[0007] (1) The mixture containing 5-[2-(2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one and triethylamine and the reaction solution containing propionyl chloride are respectively fed into the first micro mixer for mixing, and then enter the multi-stage oscillating reactor for acylation reaction to obtain a suspension of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate and triethylamine hydrochloride;

[0008] (2) The suspension of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate and triethylamine hydrochloride obtained from the multi-stage oscillating reactor in step (1) was adjusted to pH and then entered into a filter storage tank with a sand core filter layer to separate the reaction solution of triethylamine hydrochloride and 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate.

[0009] (3) In step (2), the 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate reaction solution flows out from the filter storage tank with the sand core filter layer and is mixed with the reaction solution of the catalyst in the second micro mixer. Then, it enters the microchannel reactor for Fries rearrangement reaction to obtain the final product 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one.

[0010] Its chemical reaction formula is:

[0011]

[0012] Preferably, the reaction solution in step (1) is an organic solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one and triethylamine and an organic solution of propionyl chloride; the organic solvent in the organic solution is any one of toluene, xylene, dichloromethane, acetone and tetrahydrofuran, preferably toluene or dichloromethane;

[0013] Preferably, in step (1), the flow rate ratio of the organic solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one and triethylamine to the organic solution of propionyl chloride is controlled such that the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one to triethylamine is in the range of 1:(1.0 to 1.5). More preferably, the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy The molar ratio of 2-cyclohexen-1-one to triethylamine is in the range of 1:(1.1 to 1.2); the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one to propionyl chloride is controlled in the range of 1:(1.0 to 1.5), more preferably the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one to propionyl chloride is in the range of 1:(1.0 to 1.2).

[0014] Preferably, the temperature in the multi-stage oscillating reactor described in step (1) is controlled at 20–120°C, more preferably at 60–100°C. The residence time of the mixed reactants in the multi-stage continuous oscillating reactor is controlled at 2–10 minutes, more preferably 2–5 minutes.

[0015] Preferably, the reaction solution obtained in step (1) and the controlled delivery to the microchannel reactor in step (3) are mixed with acid to adjust the pH value to 4-7, more preferably between 5-6.

[0016] Preferably, in step (3), the flow rate ratio of the organic solution of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate to the organic solution of the catalyst is controlled such that the molar ratio of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one to the catalyst is in the range of 1:(0.1 to 0.5). More preferably, the molar ratio of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one to the catalyst is within the range of 1:(0.1 to 0.5). The molar ratio of the ketone compound to the catalyst is in the range of 1:(0.3 to 0.5); the temperature in the micromixer and microchannel reactor is controlled within the range of 30 to 90°C, more preferably within the range of 40 to 70°C; the residence time of the mixed reactants in the microchannel reactor is controlled within the range of 1 to 20 minutes, more preferably within the range of 5 to 10 minutes; the back pressure during the reaction is controlled within the range of 0.1 to 2.0 MPa, more preferably within the range of 0.5 to 1.0 MPa.

[0017] Preferably, in step (3), the catalyst used is any one of DMAP, PDM, N-fluoropyridine trifluoromethanesulfonate, and 1-fluoro-2,4,6-trimethylpyridine trifluoromethanesulfonate. More preferably, the catalyst is DMAP or PDM.

[0018] Preferably, the micromixer described in steps (1), (2), (3), and (5) is any one of a static mixer, a T-type micromixer, a Y-type micromixer, a cross-shaped mixer, a coaxial flow micromixer, and a flow-focusing micromixer. More preferably, any one of a cross-shaped mixer, a coaxial flow micromixer, and a flow-focusing micromixer is used.

[0019] Preferably, the microchannel reactor described in steps (1), (2), (3) and (5) is a tubular microchannel reactor, a plate microchannel reactor, or other types of microchannel reactors available on the market.

[0020] Preferably, the inner diameter of the tubular microchannel reactor in steps (1), (2), (3) and (5) is 50 micrometers to 10 millimeters, more preferably, the inner diameter is 100 micrometers to 5 millimeters; the volume of the multi-stage oscillating reactor is 50 milliliters to 90 milliliters, more preferably, the volume is 48 milliliters.

[0021] The present invention provides a method for the continuous preparation of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one (1) using a continuous chemical reaction system. This method can be conveniently used to achieve large-scale industrial production of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one (1) through a multi-channel parallel amplification strategy.

[0022] Beneficial effects

[0023] The method for preparing 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one proposed in this invention, employing a continuous system consisting of multiple sequentially connected micromixers, multi-stage continuous oscillators, a filter storage tank with a sand core filter layer, and a microchannel reactor, has the following advantages compared to the traditional batch reactor synthesis method:

[0024] 1. The continuous flow microchannel reaction system has excellent mass transfer, heat transfer and material molecule mixing performance, which greatly shortens the reaction time and greatly improves the reaction efficiency. The total synthesis of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one can be completed within 10-30 minutes, which is shortened from several days in the traditional batch reactor reaction.

[0025] 2. The method for preparing 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one of the present invention has many advantages over previously reported routes, such as shorter synthetic route, simpler process, milder conditions and lower energy consumption.

[0026] 3. It enables continuous synthesis from raw materials to finished products, with the process proceeding continuously and without interruption. It is highly automated, requires no external intervention, has high time and space efficiency, significantly reduces the number of operators and labor intensity, and significantly reduces production costs.

[0027] 4. The use of a microchannel reactor allows for convenient industrial scale-up of the synthesis method of this invention through a multi-channel parallel amplification strategy, enabling rapid industrial production. Attached Figure Description

[0028] Figure 1 This is a flow chart of the continuous flow preparation process of the clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one of the present invention. Detailed Implementation

[0029] To illustrate the technical content, structural features, objectives, and effects of the technical solution in detail, the following description, in conjunction with specific embodiments and accompanying drawings, provides further explanation. This embodiment is implemented based on the technical solution of this invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of this invention is not limited to the following embodiments.

[0030] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0031] Example 1

[0032] Using 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one (purity: 95.4%) and propionyl chloride (purity: 99.1%) as raw materials, and toluene as solvent, a toluene solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one and triethylamine was prepared by dissolving 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one with a content of 15.01 wt% and triethylamine with a content of 8.5 wt% in toluene. A 22.07 wt% propionyl chloride toluene solution was prepared by dissolving propionyl chloride in toluene, and a 17.98 wt% DMAP toluene solution was prepared by dissolving DMAP in toluene. A toluene solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one and a toluene solution of propionyl chloride were fed at flow rates of 12 mL / min and 4 mL / min, respectively, over a feeding time of 20 min. The feed amounts were 250.88 g (0.194 mol) of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one, 89.52 g (0.213 mol) of propionyl chloride, and 23.51 g (0.2328 mol) of triethylamine. The molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one, triethylamine, and propionyl chloride was 1:1.2:1.1. The two feed streams were vigorously mixed and reacted in a multi-stage oscillating reactor with a holding volume of 48 mL. The residence time of the reactants in the multi-stage oscillating reactor was 3 minutes. Simultaneously, the reaction temperature of the multi-stage oscillating reactor was controlled at 70℃. The product entered a filter storage tank with a sand core filter layer, and hydrogen chloride gas was introduced to adjust the pH value to ensure complete removal of triethylamine. After separating triethylamine hydrochloride and the reaction solution, the resulting reaction solution and DMAP toluene solution were pumped into a tubular microchannel reactor. The flow rate of the DMAP toluene solution was 0.447 mL / min, the feed time was 20 min, the DMAP feed amount was 7.8 g, and the molar ratio of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate to DMAP was 1:0.3. The residence time of the reaction solution and DMAP in the tubular microchannel reactor with a holding volume of 100 mL was 6.08 min. The temperature of the tubular microchannel reactor was controlled at 70℃, and the back pressure was 1 MPa. After post-processing, the product was obtained by rotary evaporation, yielding 51.85 g of product. The product content was determined by liquid chromatography using a C-18 column. Analysis showed that the purity of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one was 99%.

[0033] Yield = (Total product mass × Product purity / 270) / (Mass of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one / 214) × 100%. Yield of 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one = (51.85 g × 99% / 270) / (41.516 / 214) × 100% = 97.99%.

[0034] Examples 2-5

[0035] The same continuous synthesis system for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one as in Example 1 was used, with the following differences: the feed molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one, triethylamine, and propionyl chloride was 1:1.2:1.15; the flow rates of the toluene solutions of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one and triethylamine, and the toluene solution of propionyl chloride were 6 mL / min and 2 mL / min, respectively; and the residence time of the materials in the multistage shaking reactor was 2 minutes. The reaction conditions in the Fries rearranged microchannel reactor were the same, with reaction temperatures controlled at 30°C, 70°C, 90°C, and 110°C in Examples 2-5, respectively. The product results are shown in Table 1.

[0036] Table 1. Effect of different temperatures on acylation reaction

[0037] test Reaction temperature / °C purity / % Yield / % Example 2 30 87.6 85.2 Example 3 70 96.7 93.8 Example 4 90 95.3 92.1 Example 5 110 85.1 84.9

[0038] The data in the table above shows that appropriately increasing the reaction temperature can accelerate the mixing and mass transfer rate between materials, increase the reaction rate, and improve the conversion rate and product yield. However, when the temperature exceeds a certain threshold, increasing the reaction temperature can cause side reactions in the reaction system, which is not conducive to the reaction process.

[0039] Examples 6-8

[0040] The same continuous synthesis system as in Example 1 was used for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. The difference was that the molar ratio of the three materials was controlled, and the product results are shown in Table 2.

[0041] Table 2. Effect of different molar ratios of materials on the reaction

[0042]

[0043] As can be seen from the data in the table above, appropriately increasing the amounts of propionyl chloride and triethylamine can improve the conversion rate of raw materials and the yield of products, which is beneficial to the reaction.

[0044] Examples 9-12

[0045] The same continuous synthesis system as in Example 1 was used for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. The differences from Example 1 were: the reaction temperature in the multi-stage oscillating reactor was controlled at 90°C; the DMAP flow rate in the tubular microchannel reactor of the Fries rearrangement was 1 mL / min; the back pressure was 0.5 MPa; and the residence time of the Fries rearrangement reaction was changed to 5 minutes. In Examples 9-12, the residence time of the acylation reaction was controlled at 30°C, 70°C, 90°C, and 110°C, respectively; the product results are shown in Table 3.

[0046] Table 3. Effect of different acylation reaction residence times on the reaction

[0047] test Dwell time / minute purity / % Yield / % Experimental Example 9 2 81.3 76.4 Experimental Example 10 4 94.2 93.0 Experimental Example 11 7 85.1 85.1 Experimental Example 12 10 82.7 80.3

[0048] As can be seen from the data in the table above, too short a residence time in the acylation reaction will lead to incomplete reaction between reactants, resulting in a decrease in the conversion rate of raw materials; however, too long a residence time in the acylation reaction will cause the product to remain in the reaction system for too long, which may lead to side reactions between the product and the raw materials in addition to the main reaction, reducing the yield and purity of the target product. Therefore, the residence time of the acylation reaction needs to be kept within a suitable range.

[0049] Examples 13-16

[0050] The same continuous synthesis system as in Example 1 was used for 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one. The differences from Example 1 were: the reaction temperature in the multi-stage oscillating reactor was controlled at 90°C; the DMAP flow rate in the tubular microchannel reactor of the Fries rearrangement was 1 mL / min; the back pressure was 0.5 MPa; and the residence time of the acylation reaction was changed to 5 minutes. The catalyst used was also different. The product results are shown in Table 4.

[0051] Table 4. Effects of different catalysts on the reaction

[0052] test Catalyst types purity / % Yield / % Experimental Example 13 DMAP 97.2 95.8 Experimental Example 14 PDM 94.2 92.1 Experimental Example 15 N-Fluoropyridine Trifluoromethanesulfonate 87.6 83.9 Experimental Example 16 1-Fluoro-2,4,6-Trimethylpyridine trifluoromethanesulfonate 82.7 77.3

[0053] As can be seen from the data in the table above, all three catalysts can effectively convert the Fries rearrangement reaction of the product intermediate. However, among the three catalysts, DMAP has the highest conversion efficiency and the best catalytic efficiency.

Claims

1. A continuous flow process for the preparation of an enoxamide intermediate, 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-l-one, characterized in that, A continuous system consisting of multiple sequentially connected micromixers, multi-stage oscillating reactors, a filter storage tank with a sand core filter layer, and a microchannel reactor is used. The specific steps are as follows: (1) The mixture containing 5-[2-(2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one and triethylamine and the reaction solution containing propionyl chloride are respectively fed into the first micro mixer for mixing, and then enter the multi-stage oscillating reactor for acylation reaction to obtain a suspension of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate and triethylamine hydrochloride; (2) The suspension of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate and triethylamine hydrochloride obtained from the multi-stage oscillating reactor in step (1) was adjusted to pH and then entered into a filter storage tank with a sand core filter layer to separate the reaction solution of triethylamine hydrochloride and 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate. (3) The 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate reaction solution flowing out of the filter storage tank with sand core filter layer in step (2) and the reaction solution of the catalyst are respectively introduced into the second micro mixer for mixing, and then into the microchannel reactor for Fries rearrangement reaction to obtain the final product 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexene-1-one; In step (1), the flow rate ratio of the organic solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one and triethylamine to the organic solution of propionyl chloride is controlled so that the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one to triethylamine is in the range of 1: (1.0~1.5); and the molar ratio of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one to propionyl chloride is in the range of 1: (1.0~1.5). In step (3), the flow rate ratio of the organic solution of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate to the organic solution of the catalyst is controlled so that the molar ratio of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate to the catalyst is in the range of 1:(0.1~0.5); the temperature in the second micro-mixer and the microchannel reactor is controlled in the range of 30~90 ℃; the residence time of the mixed reactants in the microchannel reactor is 1~20 minutes; and the back pressure during the reaction is 0.1~2.0 MPa.

2. The continuous flow preparation method of clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 1, characterized in that, The reaction solution in step (1) is an organic solution of 5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one and triethylamine and an organic solution of propionyl chloride; the organic solvent in the organic solution is any one of toluene, xylene, dichloromethane, acetone and tetrahydrofuran.

3. The continuous flow preparation method of clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 1, characterized in that, In step (1), the temperature inside the multi-stage oscillating reactor is controlled at 20~120℃; the residence time of the mixed reactants in the multi-stage oscillating reactor is 2~10 minutes.

4. The continuous flow preparation method of the clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 1, characterized in that, In step (2), the pH of the reaction solution obtained in step (1) is adjusted to 4-7 and then fed into the microchannel reactor. After entering the filter storage tank with a sand core filter layer, triethylamine hydrochloride is separated. After removing the salt, an organic solution of 5-[(2-ethylthio)propyl]-3-one-1-cyclohexene-1-propionate is obtained.

5. The continuous flow preparation method of the clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 1, characterized in that, In step (3), the catalyst used is any one of DMAP, PDM (N,N-m-phenylenebismaleimide), N-fluoropyridine trifluoromethanesulfonate, and 1-fluoro-2,4,6-trimethylpyridine trifluoromethanesulfonate.

6. The continuous flow preparation method of clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 1, characterized in that, The micromixer is any one of a static mixer, a T-type micromixer, a Y-type micromixer, a cross-type mixer, a coaxial flow micromixer, and a flow focusing micromixer; the microchannel reactor is a tubular microchannel reactor or a plate microchannel reactor.

7. The continuous flow preparation method of clethodim intermediate 5-[2-(ethylthio)propyl]-2-propionyl-3-hydroxy-2-cyclohexen-1-one according to claim 6, characterized in that, The tubular microchannel reactor has an inner diameter of 50 micrometers to 10 millimeters; the multi-stage oscillating reactor has a volume of 50 milliliters to 90 milliliters.

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