A kind of synthetic method of S-2-chloropropionic acid methyl ester

Abstract

The invention discloses a synthetic method of S-2-chloropropionate, comprising the following steps: (1) D-methyl lactate and a phase transfer catalyst are uniformly mixed for standby use; (2) thionyl chloride is added to a chlorination container, a trapping device equipped with filler is installed at the feed port of the chlorination container, the trapping device and the chlorination container are raised to the reaction temperature, and then the mixture of step (1) is added to the chlorination container by the trapping device, and the reaction is continued after adding to generate S-2-chloropropionate; (3) the reaction solution after the reaction is post-processed to obtain S-2-chloropropionate. The synthetic method of the present invention has simple process operation, low equipment requirements, safe and easy-to-obtain raw materials, no high-risk substances are generated during the reaction, simple post-processing, green and environmentally friendly, high raw material conversion rate, and is conducive to industrial promotion and application.

Description

Technical Field

[0001] The invention relates to a method for synthesizing S-2-chloropropionic acid methyl ester, in particular to a method for synthesizing S-2-chloropropionic acid methyl ester which is green, environmentally friendly and has a high reaction conversion rate, and belongs to the technical field of pesticide synthesis. Background Art

[0002] Aryloxyphenoxypropionate herbicides are typical representatives of single isomers with high efficacy. They account for an increasing proportion of chiral pesticides. Due to their high efficiency, low toxicity, broad herbicidal spectrum, long application period, and safety for subsequent crops, they have been continuously developed and applied in recent years. S-2-chloropropionic acid methyl ester is an important intermediate for the synthesis of aryloxyphenoxypropionate herbicides such as oxadiazon, haloxyfop-butyl, cyhalofop-butyl, etc. Therefore, the synthesis of S-2-chloropropionic acid methyl ester is of great significance.

[0003] Patent CN102381969 discloses a method for synthesizing S-2-chloropropionic acid methyl ester, which mainly involves first preparing chiral hydrogen peroxide as a catalyst, and then using α-chloropropionic acid and methanol as raw materials to react and generate the target product. The technical route is mainly as follows: ① Preparation of catalyst hydrogen peroxide: neutralize the sodium peroxide aqueous solution with phosphoric acid or sodium dihydrogen phosphate to a pH value of 9.0-9.7 to generate sodium hydrogen phosphate and hydrogen peroxide, cool the sodium hydrogen phosphate and hydrogen peroxide aqueous solution to -5-5°C, and then separate the mixture containing sodium hydrogen phosphate and hydrogen peroxide aqueous solution in a centrifugal separator to obtain hydrogen peroxide; ② Preparation of S-2-chloropropionic acid methyl ester: measure α-chloropropionic acid and methanol in a molar ratio of 1:1 and add them to the reactor. Add the above catalyst hydrogen peroxide in an amount of 5-10% of the total raw materials, control the reaction temperature to 100-120°C, react for 8-10h, distill, and dry to obtain S-2-chloropropionic acid methyl ester.

[0004] Patent CN 103232344 discloses a method for synthesizing methyl S-2-chloropropionate, which is mainly synthesized by a Vilsemier reagent catalytic method. The technical route is mainly as follows: ① Preparation of Vilsemier reagent: Add a chlorinating agent to a reactor, and drop short-chain aliphatic substituted amide (such as DMF, DMAC) as a solvent, and stir the reaction to obtain a Vilsemier reagent solution; ② Synthesis of methyl S-2-chloropropionate: Add a small amount of solvent to the Vilsemier reagent obtained in the first step to obtain a mixed solution, drop R-methyl lactate into the mixed solution, and stir to obtain a product solution of the chlorination reaction, i.e., methyl S-2-chloropropionate solution; ③ Wash the methyl S-2-chloropropionate solution obtained in the second step with water, desolventize, and distill to obtain the product methyl S-2-chloropropionate, with a yield of 88%.

[0005] Patent CN 102775303 discloses a method for synthesizing methyl S-2-chloropropionate, which mainly involves dropping methyl D-lactate into thionyl chloride, and standing and stratifying after the reaction is completed to obtain methyl S-2-chloropropionate. The technical route is mainly as follows: ① Prepare 429 parts by weight of methyl D-lactate and 534 parts by weight of thionyl chloride; ② Add 534 parts by weight of thionyl chloride into a reactor, and after the addition, the reactor is at a normal pressure of 70°C, and then slowly drop 429 parts by weight of methyl lactate into the reactor again to generate a mixed gas of methyl S-2-chloropropionate, hydrochloric acid and sulfur dioxide, and stand and stratify to obtain methyl S-2-chloropropionate, with a yield of 90%.

[0006] Among the above-mentioned prior arts, the phosphoric acid used in patent CN 102381969 is highly corrosive to equipment and has high requirements for equipment, and the hydrogen peroxide used is an explosive and dangerous chemical, which is very dangerous to store and use. In patent CN103232344, the wastewater treatment method generated by DMF is relatively complicated, and DMF is easily hydrolyzed under strong acid, and the hydrolysis product further decomposes to release non-condensable gases, including carbon monoxide, carbon dioxide and hydrogen, which is relatively dangerous, and the yield is low, only 88%. In addition, the Vilsmeier reagent is easy to absorb water and deliquescence, is not easy to preserve, has high requirements for experimental operation and conditions, and increases the operation steps. In patent CN 102775303, it is difficult to separate methyl S-2-chloropropionate from water, which can easily cause product loss. In addition, after simple separation, a large amount of hydrogen chloride and sulfur dioxide exist in the oil phase. Under strong acidic conditions, methyl S-2-chloropropionate is easily hydrolyzed, which affects the yield. The yield of this patent is only 90%. No good treatment method for tail gas hydrochloric acid and sulfur dioxide is disclosed, which is not conducive to industrialization. Summary of the invention

[0007] In view of the deficiencies in the prior art, the present invention provides a method for synthesizing S-2-chloropropionic acid methyl ester. The method has simple process operation, low equipment requirements, safe and easily available raw materials, no highly dangerous substances are generated during the reaction, post-treatment is simple, green and environmentally friendly, and the raw material conversion rate is high, which is conducive to industrial promotion and application.

[0008] The specific technical solutions of the present invention are as follows:

[0009] A method for synthesizing S-2-chloropropionic acid methyl ester comprises the following steps:

[0010] (1) Mix D-methyl lactate and a phase transfer catalyst evenly and set aside;

[0011] (2) adding thionyl chloride into a chlorination container, installing a collecting device equipped with fillers at the feed inlet of the chlorination container, raising the collecting device and the chlorination container to the reaction temperature, and then adding the mixture of step (1) into the chlorination container through the collecting device. After the addition is complete, continuing the reaction to generate S-2-chloropropionic acid methyl ester;

[0012] (3) The reaction solution is post-treated to obtain S-2-chloropropionic acid methyl ester.

[0013] Furthermore, the present invention uses a phase transfer catalyst to increase the chlorination reaction rate. The phase transfer catalyst is pyridine. Preferably, the amount of the phase transfer catalyst is 3-6% of the mass of D-methyl lactate.

[0014] Furthermore, the molar ratio of D-methyl lactate to thionyl chloride is 1:1.05-1.3.

[0015] Further, D-methyl lactate and thionyl chloride are subjected to chlorination reaction in a chlorination container, and no solvent is involved in the chlorination reaction process. The main reaction equation is:

[0016]

[0017] Furthermore, in step (2), the chlorination container can be a simple reaction container, which can be a reactor in industrialization or a flask, a conical flask, etc. in the laboratory. The chlorination container has at least one feed inlet, and a capture device filled with fillers is installed on one of the feed inlets.

[0018] Furthermore, in step (2), the capture device has the following two functions: 1. Capture thionyl chloride and D-methyl lactate in the by-product tail gas to prevent the raw materials from being discharged with the tail gas, thereby avoiding the loss of raw materials; 2. During the process of adding the raw materials or the reaction, the raw materials thionyl chloride and D-methyl lactate will contact in the capture device, thereby reacting, reducing the reaction time of the materials in the chlorination container and improving the overall reaction rate. The capture device includes a capture body, the interior of the capture body is a cavity, a feed inlet at the top, a discharge port at the bottom, an air outlet on the side wall, and the collector is filled with fillers. The capture body is vertical, vertically mounted on the chlorination container, or connected to the chlorination container through a pipeline or the like. In the laboratory process, a cylindrical tube can be used as the capture body, and fillers can be filled in it as a capture device. In large-scale industrial production, a conventional packed tower can be used as a capture device. The filler is used to achieve effective distribution of D-methyl lactate, and the filler can be made of ceramic or glass structured fillers, irregular fillers, etc.

[0019] Furthermore, in step (2), the reaction temperature of the capture device and the chlorination container is controlled at 55-65°C, and then the mixture of step (1) is added, and the reaction is continued after the addition is completed. Preferably, the mixture of step (1) is first heated to 55-65°C, the chlorination container is heated to 55-65°C, the capture device is heated to 55-65°C, and then the mixture of step (1) is dripped into the thionyl chloride at 55-65°C through the capture device, and the temperature is controlled at 55-65°C during the entire dripping process and the subsequent insulation process.

[0020] Furthermore, in step (2), the mixture of step (1) is added dropwise for 1.5-3 hours. Because the addition is done dropwise, D-lactate methyl ester and the phase transfer catalyst are added to the excess thionyl chloride, and the excess thionyl chloride can be used as both a reactant and a solvent, thereby avoiding the use of a solvent. In addition, the dropwise addition method and the presence of the phase transfer catalyst greatly improve the phase contact of the reactants, effectively improve the selectivity of the reaction, and reduce the occurrence of side reactions.

[0021] Furthermore, the capture device is also connected to a gas recovery device, and the gas recovery device includes a water absorption device and an alkali absorption device connected in sequence, wherein the water absorption device is connected to the gas outlet of the capture device. The water absorption device is filled with water, and the alkali absorption device is filled with a sodium hydroxide solution. The hydrogen chloride and sulfur dioxide tail gas formed by the reaction enter the gas absorption device through the capture device, and the capture device intercepts the thionyl chloride and D-methyl lactate overflowing with the tail gas to prevent the loss of raw materials. At the same time, the thionyl chloride and D-methyl lactate continue to react in the capture device, and the remaining tail gas enters the gas absorption device for absorption and is converted into hydrochloric acid and sodium sulfite. The hydrochloric acid contains a small amount of sulfur dioxide, and the hydrochloric acid solution can be directly sold as a by-product or used as a downstream product. The sodium sulfite solution can be recovered to obtain sodium sulfite after cooling and crystallization.

[0022] Furthermore, in step (2), after the mixture of step (1) is added dropwise, nitrogen is introduced into the chlorination container to accelerate the discharge of by-product gas and reduce the amount of subsequent washing water and alkaline washing water. The nitrogen introduction time is 0.5-1h.

[0023] Furthermore, in step (3), the post-treatment includes the steps of washing the reaction liquid with water, washing with alkali, distilling and rectifying. Washing with water refers to dropping the reaction liquid into water, then adding dichloromethane for extraction to obtain an oil phase. Alkaline washing refers to washing the oil phase with sodium carbonate solution at a pH of 6-7, and then washing with water to neutrality. Distillation refers to removing dichloromethane from the oil phase after alkali washing by distillation.

[0024] Furthermore, the temperature of water washing and alkali washing is controlled at 0-30°C.

[0025] Further, in a specific embodiment of the present invention, a specific method for synthesizing S-2-chloropropionic acid methyl ester is provided, comprising the following steps:

[0026] 1. Preparation of methyl lactate mixed solution

[0027] Mix 1 molar equivalent of D-methyl lactate and 5% by mass of D-methyl lactate in a phase transfer catalyst pyridine at room temperature, stir for 30 minutes, and set aside;

[0028] 2. Chlorination reaction

[0029] 1.05-1.3 molar equivalents of chlorinating agent thionyl chloride is added into a chlorination container, and the temperature is slowly raised to 55-65°C; a capture device is installed vertically on the chlorination container, and the temperature of the capture device is controlled to be 55-65°C. The D-methyl lactate mixed solution begins to drip slowly into the chlorination container through the capture device, and the dripping time is controlled to be 1.5-3h. After the dripping is completed, nitrogen is added into the system to accelerate the discharge of hydrogen chloride and sulfur dioxide gas in the system, and a chlorinated liquid is obtained after the reaction is completed.

[0030] , post-processing

[0031] 3.1 Washing

[0032] The chlorinated liquid is cooled to below 50°C, and the chlorinated liquid is dripped into water with a temperature below 20°C, and the temperature is controlled at 0-30°C during the dripping. After the dripping is completed, dichloromethane is added as an extractant, and the temperature is kept at 0-30°C for washing and extraction for 30min-1h, and the mixture is allowed to stand for 30min-1h to separate layers; the amount of water used is 0.3-0.4 times the mass of D-methyl lactate, and the amount of dichloromethane used is 0.3-0.4 times the mass of D-methyl lactate;

[0033] 3.2 Alkaline washing

[0034] The oil phase after water washing is added with 8-12wt% sodium carbonate aqueous solution for alkali washing, the pH value of alkali washing is controlled at 6-7, and the temperature is controlled at 0-30°C. After the alkali washing is completed, the oil phase is further washed with water at room temperature;

[0035] 3.3 Distillation

[0036] The alkali-washed oil phase enters the distillation tower to remove the solvent dichloromethane, which is then recycled to the water-washing stage;

[0037] 3.4 Distillation;

[0038] S-2-chloropropionic acid methyl ester enters the distillation tower, and S-2-chloropropionic acid methyl ester with a content of 99% is taken out from the top of the tower, and the kettle residue is taken out from the bottom of the tower;

[0039] 3.5 Exhaust gas treatment

[0040] The hydrogen chloride and sulfur dioxide generated by chlorination are absorbed by water and diluted alkali to prepare HCL aqueous solution and sodium sulfite aqueous solution respectively, wherein the hydrochloric acid solution contains a small amount of sulfur dioxide, which can be sold as a by-product or used as a downstream product, and the sodium sulfite aqueous solution is cooled and crystallized to obtain a sodium sulfite product, which can be sold. The diluted alkali is preferably a sodium hydroxide solution with a concentration of 5-20wt%.

[0041] The present invention has the following beneficial effects:

[0042] 1. The present invention uses D-lactate methyl ester and thionyl chloride as raw materials and pyridine as phase transfer catalyst, does not require additional solvents, and each raw material is easy to obtain and has high safety. The reaction is carried out at an optimal temperature of 55°C-65°C, the reaction temperature is relatively milder, the side reactions are less, and it is easier to control. The raw material conversion rate can reach up to 100%, and the selectivity can reach up to 99%.

[0043] 2. A capture device is installed on the chlorination container, which can prevent the raw materials D-methyl lactate and thionyl chloride from being discharged from the kettle along with the tail gas, thereby avoiding the loss of raw materials and improving the conversion rate of raw materials. The temperature of the capture device is controlled at 55°C-65°C. The thionyl chloride entrained in the tail gas and D-methyl lactate are premixed and reacted in the capture device, thereby reducing the reaction time of the materials in the chlorination container and improving the overall reaction rate.

[0044] 3. The D-methyl lactate and the phase transfer catalyst of the present invention are added dropwise to the chlorination container through a capture device, which greatly improves the phase contact of the reactants, effectively improves the selectivity of the reaction, and reduces the occurrence of side reactions.

[0045] 4. The present invention collects the generated hydrogen chloride and sulfur dioxide, and converts the tail gas into hydrochloric acid solution and sodium sulfite solution by water absorption and alkali absorption, thereby realizing the comprehensive utilization of the tail gas, avoiding the emission of waste gas, and being more environmentally friendly.

[0046] 5. Since the density of S-2-chloropropionic acid methyl ester and water are similar, dichloromethane is added as an extractant to increase the density difference between the oil phase and the water phase, reduce material loss, and thus improve the product yield. Low-temperature water washing and low-temperature alkali washing are used to greatly reduce the hydrolysis of the product and improve the product yield. DETAILED DESCRIPTION

[0047] The present invention is further explained and illustrated by specific embodiments below. The following description is only exemplary and does not limit its content.

[0048] Example 1

[0049] 1) 3.2 mol of thionyl chloride is put into a chlorination flask and the temperature is raised to 60°C. A collecting tube is installed on the chlorination flask. The collecting tube is a vertical glass tube with upper and lower openings. A glass filler is installed in the glass tube. The side wall of the glass tube has an opening, which is connected to a water absorption bottle, and the water absorption bottle is connected to a 20% liquid alkali absorption bottle;

[0050] 2) Add 2.83 mol of D-methyl lactate and 0.19 mol of pyridine into the preparation flask, stir and heat to 60°C;

[0051] 3) Slowly drip the D-methyl lactate pyridine solution into the chlorination flask through the capture tube, control the dripping speed to ensure that the dripping time is 1.5 hours, and keep the temperature of the capture tube and the chlorination flask at 60-65°C during this period;

[0052] 4) After the addition is completed, nitrogen is introduced under the chlorination flask liquid, and the stripping is carried out for 30 minutes. Samples are taken to detect the content of D-methyl lactate ≤ 0.1%, and the reaction is completed;

[0053] 5) Cool the chlorinated solution in the chlorination flask to 40°C, add it to 100g of 15°C water, add 1.2mol of dichloromethane, stir for 30min, and let stand for 30min;

[0054] 6) Take the lower oil phase, add 200g 10wt% sodium carbonate aqueous solution for washing, and control the pH value to 7 and the temperature to 15℃;

[0055] 7) Add 100g water to the oil phase and wash until it becomes neutral and then separate the layers;

[0056] 8) The oil phase is distilled under normal pressure, and the content of dichloromethane in the oil phase is controlled to be 0.1% to be qualified;

[0057] 9) Oil phase distillation, reflux ratio 2:1, extracting S-2-chloropropionic acid methyl ester with content > 99%, and discharging the kettle residue;

[0058] 10) The hydrogen chloride and sulfur dioxide gases formed by the reaction are absorbed by a water absorption bottle and a 20% liquid alkali absorption bottle. When the hydrogen chloride content in the water absorption bottle reaches 30wt%, the water is replaced. When the liquid alkali content in the liquid alkali absorption bottle is lower than 1wt%, the liquid alkali is replaced.

[0059] After testing, the effective content of the product was 99.1%, 2.69 mol of S-2-chloropropionic acid methyl ester was produced, and the yield was 95%.

[0060] Example 2

[0061] 1) 3.4 mol of thionyl chloride is put into a chlorination flask and the temperature is raised to 55°C. A collecting tube is installed on the chlorination flask. The collecting tube is a vertical glass tube with upper and lower openings. A glass filler is installed in the glass tube. The side wall of the glass tube has an opening, which is connected to a water absorption bottle, and the water absorption bottle is connected to a 20% liquid alkali absorption bottle;

[0062] 2) Add 2.8 mol of D-methyl lactate and 0.19 mol of pyridine into the preparation flask, stir and heat to 55°C;

[0063] 3) Slowly drip the D-methyl lactate pyridine solution into the chlorination flask through the trap tube, control the dripping speed to ensure that the dripping time is 3 hours, and keep the temperature at 65°C during this period;

[0064] 4) After the addition is completed, nitrogen is introduced under the chlorination flask liquid, and the stripping is performed for 1 hour. Samples are taken to detect the content of D-methyl lactate ≤ 0.1%, and the reaction is completed;

[0065] 5) Cool the chlorinated liquid to 50°C, add it to 100g of 20°C water, add 1.18mol of dichloromethane, stir for 30min, and let stand for 30min;

[0066] 6) Take the lower oil phase and add 200g 10% sodium carbonate aqueous solution for washing, control the pH value to 6.5 and the temperature to 20℃;

[0067] 7) Add 100g water to the oil phase and wash until it becomes neutral and then separate the layers;

[0068] 8) The oil phase is distilled under normal pressure, and the content of dichloromethane in the oil phase is controlled to be 0.1% to be qualified;

[0069] 9) Oil phase distillation, reflux ratio 2:1, extracting S-2-chloropropionic acid methyl ester with content > 99%, and discharging the kettle residue;

[0070] 10) The hydrogen chloride and sulfur dioxide gases formed by the reaction are absorbed by a water absorption bottle and a 20% liquid alkali absorption bottle. When the hydrogen chloride content in the water absorption bottle is 30-32wt%, the water is replaced. When the liquid alkali content in the liquid alkali absorption bottle is lower than 1wt%, the liquid alkali is replaced.

[0071] After testing, the effective content of the product was 99.2%, and 2.685 mol of S-2-chloropropionic acid methyl ester was produced with a yield of 95.9%.

[0072] Comparative Example 1

[0073] S-2-chloropropionic acid methyl ester was prepared according to the method of Example 2, except that the input amount of thionyl chloride was 2.8 mol. After testing, the effective content of the obtained product was 99.2%, and 2.2 mol of S-2-chloropropionic acid methyl ester was produced, with a yield of 78.6%.

[0074] Comparative Example 2

[0075] 1) 3.4 mol of thionyl chloride is put into a chlorination flask and the temperature is raised to 40°C. A collecting tube is installed on the chlorination flask. The collecting tube is a vertical glass tube with upper and lower openings. A glass filler is installed in the glass tube. The side wall of the glass tube has an opening, which is connected to a water absorption bottle, and the water absorption bottle is connected to a 20% liquid alkali absorption bottle;

[0076] 2) Add 2.8 mol of D-methyl lactate and 0.19 mol of pyridine into the preparation flask, stir and heat to 40°C;

[0077] 3) Slowly drip the D-methyl lactate pyridine solution into the chlorination flask through the trap tube, control the dripping speed to ensure that the dripping time is 3 hours, and keep the temperature at 40-45°C during this period;

[0078] 4) After the addition is completed, nitrogen is introduced under the chlorination flask liquid, and the stripping is performed for 1 hour. Samples are taken to detect the content of D-methyl lactate ≤ 0.1%, and the reaction is completed;

[0079] 5) Cool the chlorinated liquid to 50°C, add it to 100g of 20°C water, add 1.18mol of dichloromethane, stir for 30min, and let stand for 30min;

[0080] 6) Take the lower oil phase and add 200g 10% sodium carbonate aqueous solution for washing, control the pH value to 6.5 and the temperature to 20℃;

[0081] 7) Add 100g water to the oil phase and wash until it becomes neutral and then separate the layers;

[0082] 8) The oil phase is distilled under normal pressure, and the content of dichloromethane in the oil phase is controlled to be 0.1% to be qualified;

[0083] 9) Oil phase distillation, reflux ratio 2:1, extracting S-2-chloropropionic acid methyl ester with content > 99%, and discharging the kettle residue;

[0084] 10) The hydrogen chloride and sulfur dioxide gases formed by the reaction are absorbed by a water absorption bottle and a 20% liquid alkali absorption bottle. When the hydrogen chloride content in the water absorption bottle is 30-32wt%, the water is replaced. When the liquid alkali content in the liquid alkali absorption bottle is lower than 1wt%, the liquid alkali is replaced.

[0085] After testing, the effective content of the product was 99.2%, 0.5 mol of S-2-chloropropionic acid methyl ester was produced, and the yield was 17.9%.

[0086] Comparative Example 3

[0087] 1) 3.4 mol of thionyl chloride is put into a chlorination flask and the temperature is raised to 55-65°C. A collecting tube is installed on the chlorination flask. The collecting tube is a vertical glass tube with upper and lower openings. A glass filler is installed in the glass tube. The side wall of the glass tube has an opening, which is connected to a water absorption bottle, and the water absorption bottle is connected to a 20% liquid alkali absorption bottle;

[0088] 2) Add 2.8 mol of D-methyl lactate and 0.19 mol of pyridine into the preparation flask, stir and heat to 55-60°C;

[0089] 3) Slowly drip the D-methyl lactate pyridine solution directly into the chlorination flask without passing through the trap tube, and control the dripping speed to ensure that the dripping time is 3 hours, and keep the temperature at 65°C during this period;

[0090] 4) After the addition is completed, nitrogen is introduced under the chlorination flask liquid, and the stripping is performed for 1 hour. Samples are taken to detect the content of D-methyl lactate ≤ 0.1%, and the reaction is completed;

[0091] 5) Cool the chlorinated liquid to 50°C, add it to 100g of 20°C water, add 1.18mol of dichloromethane, stir for 30min, and let stand for 30min;

[0092] 6) Take the lower oil phase and add 200g 10% sodium carbonate aqueous solution for washing, control the pH value to 6.5 and the temperature to 20℃;

[0093] 7) Add 100g water to the oil phase and wash until it becomes neutral and then separate the layers;

[0094] 8) The oil phase is distilled under normal pressure, and the content of dichloromethane in the oil phase is controlled to be 0.1% to be qualified;

[0095] 9) Oil phase distillation, reflux ratio 2:1, extracting S-2-chloropropionic acid methyl ester with content > 99%, and discharging the kettle residue;

[0096] 10) The hydrogen chloride and sulfur dioxide gases formed by the reaction are absorbed by a water absorption bottle and a 20% liquid alkali absorption bottle. When the hydrogen chloride content in the water absorption bottle is 30-32wt%, the water is replaced. When the liquid alkali content in the liquid alkali absorption bottle is lower than 1wt%, the liquid alkali is replaced.

[0097] After testing, the effective content of the product was 99.2%, 2.1 mol of S-2-chloropropionic acid methyl ester was produced, and the yield was 75%.

[0098] Comparative Example 4

[0099] 1) 3.4 mol of thionyl chloride is put into a chlorination flask and the temperature is raised to 70-75°C. A collecting tube is installed on the chlorination flask. The collecting tube is a vertical glass tube with upper and lower openings. A glass filler is installed in the glass tube. The side wall of the glass tube has an opening, which is connected to a water absorption bottle, and the water absorption bottle is connected to a 20% liquid alkali absorption bottle;

[0100] 2) Add 2.8 mol of D-methyl lactate and 0.19 mol of pyridine into the preparation flask, stir and heat to 70-75°C;

[0101] 3) Slowly drip the D-methyl lactate pyridine solution into the chlorination flask through the trap tube, control the dripping speed to ensure that the dripping time is 3 hours, and maintain the temperature at 70-75°C during this period;

[0102] 4) After the addition is completed, nitrogen is introduced under the chlorination flask liquid, and the stripping is performed for 1 hour. Samples are taken to detect the content of D-methyl lactate ≤ 0.1%, and the reaction is completed;

[0103] 5) Cool the chlorinated liquid to 50°C, add it to 100g of 20°C water, add 1.18mol of dichloromethane, stir for 30min, and let stand for 30min;

[0104] 6) Take the lower oil phase and add 200g 10% sodium carbonate aqueous solution for washing, control the pH value to 6.5 and the temperature to 20℃;

[0105] 7) Add 100g water to the oil phase and wash until it becomes neutral and then separate the layers;

[0106] 8) The oil phase is distilled under normal pressure, and the content of dichloromethane in the oil phase is controlled to be 0.1% to be qualified;

[0107] 9) Oil phase distillation, reflux ratio 2:1, extracting S-2-chloropropionic acid methyl ester with content > 99%, and discharging the kettle residue;

[0108] 10) The hydrogen chloride and sulfur dioxide gases formed by the reaction are absorbed by a water absorption bottle and a 20% liquid alkali absorption bottle. When the hydrogen chloride content in the water absorption bottle is 30-32wt%, the water is replaced. When the liquid alkali content in the liquid alkali absorption bottle is lower than 1wt%, the liquid alkali is replaced.

[0109] After testing, the effective content of the product was 99.2%, 2.5 mol of S-2-chloropropionic acid methyl ester was produced, and the yield was 89.3%.

Claims

1. A method for synthesizing S-2-chloropropionic acid methyl ester, characterized in that The following steps are involved: (1) Mix D-methyl lactate and a phase transfer catalyst evenly and set aside; (2) adding thionyl chloride into a chlorination container, installing a collecting device equipped with fillers at the feed inlet of the chlorination container, raising the collecting device and the chlorination container to the reaction temperature, and then adding the mixture of step (1) into the chlorination container through the collecting device. After the addition is complete, continuing the reaction to generate S-2-chloropropionic acid methyl ester; (3) post-treating the reaction solution to obtain S-2-chloropropionic acid methyl ester; The phase transfer catalyst is pyridine; the molar ratio of D-methyl lactate to thionyl chloride is 1:1.05-1.3; In step (2), the reaction temperature of the capture device and the chlorination container is controlled at 55-65°C, and then the mixture of step (1) is added, and after the addition is completed, the reaction is continued at a temperature-keeping temperature.

2. The synthesis method according to claim 1, characterized in that: The amount of phase transfer catalyst used is 3-6% of the mass of D-methyl lactate.

3. The synthesis method according to claim 1, characterized in that: In step (2), the mixture of step (1) is added dropwise for 1.5-3 hours.

4. The synthesis method according to claim 1 or 3, characterized in that: The filler in the capture device is glass filler or ceramic filler.

5. The synthesis method according to claim 1, characterized in that: The capture device is also connected to the gas recovery device, which includes a water absorption device and an alkali absorption device connected in sequence, wherein the water absorption device is connected to the capture device.

6. The synthesis method according to claim 5, characterized in that: The water absorption device is filled with water, and the alkali absorption device is filled with sodium hydroxide solution.

7. The synthesis method according to claim 1, characterized in that: In step (2), after the mixture of step (1) is added, nitrogen is introduced into the chlorination container to accelerate the discharge of by-product gas.

8. The synthesis method according to claim 7, characterized in that: In step (2), the nitrogen is introduced for 0.5-1 h.

9. The synthesis method according to claim 1, characterized in that: In step (3), the post-treatment includes the steps of washing the reaction liquid with water, washing with alkali, distilling and rectifying. Washing with water refers to dropping the reaction liquid into water, then adding dichloromethane for extraction to obtain an oil phase. Alkaline washing refers to washing the oil phase with sodium carbonate solution at a pH of 6-7, and then washing with water to neutrality. Distillation refers to removing dichloromethane from the oil phase after alkali washing by distillation.

10. The synthesis method according to claim 9, characterized in that: In step (3), the temperature of water washing and alkali washing is 0-30°C.

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