Synthesis method of methyl hypophosphorous acid monoalkyl ester

Abstract

The invention provides a synthesis method of methyl hypophosphorous acid monoalkyl ester, which aims at solving the problems of high alcohol consumption, large byproduct chlorinated alkyl compounds, high product separation difficulty, large byproduct salt after an acid-binding agent is added, high process risk and the like in the existing synthesis process of methyl hypophosphorous acid monoalkyl ester, and belongs to the technical field of organic. Wherein one molecule of water is used for replacing one molecule of alcohol, while the methyl phosphorus dichloride and the alcohol are subjected to nucleophilic substitution reaction, the methyl phosphorus dichloride and the water are subjected to nucleophilic substitution reaction, and the methyl hypophosphorous acid monoalkyl ester and the byproduct bimolecular hydrogen chloride are directly obtained. Finally, on the premise of ensuring the reaction rate and the product yield, the amount of reaction byproducts is reduced, the separation difficulty is reduced, and the risk in the product separation and device operation process is reduced, so that the overall cost of synthesizing the methyl hypophosphorous acid monoalkyl ester is greatly reduced.

Description

Technical Field

[0001] The invention specifically relates to a method for synthesizing methyl hypophosphite monoalkyl ester, and belongs to the technical field of organic synthesis. Background Art

[0002] Methylphosphite is an important intermediate for the synthesis of glufosinate ammonium through the methane cracking-ACA method, and is also an important intermediate for high-end phosphorus flame retardants. With the gradual tightening of environmental protection policies, the market application of glufosinate ammonium and high-end phosphorus flame retardants has been greatly improved.

[0003] The synthesis process of methyl hypophosphite monoalkyl ester generally uses methyl phosphorus dichloride and alcohol as raw materials, and through reaction, obtains methyl hypophosphite monoalkyl ester and equivalent chloroalkane and hydrogen chloride of corresponding carbon number. Among them, one equivalent of methyl phosphorus dichloride first undergoes nucleophilic substitution reaction with two molecules of alcohol to obtain methyl dialkyl phosphite, and simultaneously produces two equivalents of hydrogen chloride as a by-product; then, one equivalent of methyl dialkyl phosphite and one equivalent of hydrogen chloride undergo nucleophilic substitution reaction again to obtain one equivalent of methyl hypophosphite monoalkyl ester and one equivalent of corresponding chloroalkane; The reaction mechanism involved is as follows: Among them, the reaction speed is fast and a large amount of heat is released at the same time. If an acid-binding agent is not added to eliminate the by-product of one equivalent of hydrogen chloride, it is necessary to control the reaction residence time and separate the methyl hypophosphite monoalkyl ester from the hydrogen chloride in time, otherwise the methyl hypophosphite monoalkyl ester will continue to react with the hydrogen chloride to finally generate methyl hypophosphite and the corresponding chloroalkane. The by-product chloroalkane needs to be separated separately and the subsequent application market is limited. At the same time, the flash point of the chloroalkane is low, and the risk in the process is relatively high. If an acid-binding agent is added, the post-processing process of the by-product salt is complicated. In addition, the alcohol consumption reaches more than two equivalents, and the cost of raw materials is high. In the synthesis process of methyl hypophosphite monoalkyl ester, methyl hypophosphite is first prepared, and then esterified with the corresponding alcohol to obtain methyl hypophosphite monoalkyl ester, such as the prior art "CN108752378A A method for synthesizing methyl hypophosphite monoalkyl ester". However, in the process of preparing methyl hypophosphite, phosphorus-containing toxic gas is mostly produced, and the process risk is high. At the same time, the process of reacting methyl hypophosphite with alcohol to obtain methyl hypophosphite monoalkyl ester is slow, the product purity is not high, and purification is difficult, etc. Summary of the invention

[0004] In view of the problems of high alcohol consumption, large amount of chloroalkanes as by-products, great difficulty in product separation, large amount of salt as by-products after adding acid-binding agents, and high process risks in the existing synthesis process of monoalkyl methyl hypophosphite, a method for synthesizing monoalkyl methyl hypophosphite is proposed. In this method, one molecule of alcohol is replaced by one molecule of water, and methyl phosphorus dichloride undergoes a nucleophilic substitution reaction with alcohol and water at the same time, directly obtaining monoalkyl methyl hypophosphite and producing two molecules of hydrogen chloride as by-products, thereby avoiding the process in which dialkyl methyl phosphite undergoes a substitution reaction with hydrogen chloride to generate monoalkyl methyl hypophosphite; Ultimately, under the premise of ensuring the reaction rate and product yield, the amount of reaction by-products is reduced, the separation difficulty is lowered, and the risks in the product separation and device operation process are reduced, so that the overall cost of synthesizing monoalkyl methyl hypophosphite is greatly reduced.

[0005] Among them, the overall reaction equation involved is: The partial reaction equations involved are: In order to achieve the above technical objectives, the following technical solutions are proposed: The first purpose of the technical solution is to provide: a method for synthesizing monoalkyl methyl phosphite, comprising the following steps: S1 pretreatment: nitrogen is used to replace the gas in the reactor, and the temperature in the reactor is controlled to be 100-200°C and the pressure to be -0.098--0.05MPa; Among them, for the reactor, an intermittent reactor or a continuous reactor is used, and a continuous reactor is preferred. Nitrogen replacement is to maintain an inert gas environment in the reactor. For example, if there is oxygen in the reactor, there will be safety risks (methyl phosphorus dichloride reacts violently with oxygen and may explode), and more impurities will be produced. In addition, the temperature and pressure control involved must first make the reactor reach the predetermined temperature and pressure and stabilize before adding the material to avoid the material failing to reach the required physical state after entering the reactor and failing to react as required; S2 feeding: alcohol at a temperature of 50-180°C, water at a temperature of 60-120°C and methyl phosphorus dichloride at a temperature of 70-100°C are sequentially introduced into the reactor; The alcohol can be a mixture of monohydric alcohol and / or dihydric alcohol. In actual production, monohydric alcohols of C1 to C8 are preferred to avoid more impurities during the reaction. The alcohol purity is ≥98%, anhydrous (if there is water, the proportion of water as a reaction raw material will be recalculated); the raw water is deionized water; the purity of methyl phosphorus dichloride is ≥95%; The feed ratio of alcohol, water and methyl phosphorus dichloride is controlled to be 1.0-2.5:0.01-1.0:1, and the total molar amount of alcohol and water is 2.0-3.5 times the molar amount of methyl phosphorus dichloride; S3 reaction: nucleophilic substitution reaction (the reaction speed is fast, the heat release is large, and under continuous reaction conditions, the reaction residence time is 0.1 to 1.5 seconds) to obtain a crude monoalkyl methyl hypophosphite; After the gas discharged from the reactor (hydrogen chloride, unconsumed alcohol and a small amount of chloroalkanes) is cooled, the hydrogen chloride and the liquid phase are separated. After the hydrogen chloride is absorbed by the tail gas treatment system, hydrochloric acid of different concentrations can be obtained. The liquid phase enters the low-boiling separation tower to separate the alcohol and the corresponding chloroalkanes. S4 post-treatment: The crude methyl hypophosphite monoalkyl ester obtained in step S3 is subjected to distillation separation and purification to obtain methyl hypophosphite monoalkyl ester.

[0006] The second object of the technical solution is to provide: a synthesis system of methyl hypophosphite monoalkyl ester, comprising an alcohol storage tank, a water storage tank, a methyl phosphorus dichloride storage tank and a reactor; Alcohol storage tank: connected to the reactor through an alcohol feed pipe, on which an alcohol vaporizer, an alcohol delivery pump, an alcohol flow meter and an alcohol feed regulating valve are arranged, and the alcohol flow meter and the alcohol feed regulating valve are connected through an electrical signal; Water storage tank: connected to the reactor through a water feed pipe, on which a water vaporizer, a water delivery pump, a water flow meter and a water feed regulating valve are provided, and the water flow meter and the water feed regulating valve are connected through an electrical signal; Methyl phosphorus dichloride storage tank: connected to the reactor through a methyl phosphorus dichloride feed pipe, on which a methyl phosphorus dichloride vaporizer, a methyl phosphorus dichloride delivery pump, a methyl phosphorus dichloride flowmeter and a methyl phosphorus dichloride feed regulating valve are provided, and the methyl phosphorus dichloride meter is connected to the methyl phosphorus dichloride feed regulating valve through an electrical signal; Reactor: It is also connected with a nitrogen inlet pipe, a temperature control system and a negative pressure system, wherein the temperature control system includes a steam inlet pipe and a boiler, etc., and steam is provided on the steam inlet pipe; the negative pressure system includes a vacuum pump, etc.; and the reactor is provided with a temperature detector and a pressure detector.

[0007] Furthermore, the reactor is a batch reactor or a continuous reactor.

[0008] Furthermore, the reactor discharge port is connected to a crude liquid storage tank for methyl hypophosphite monoalkyl ester, and the crude liquid storage tank for methyl hypophosphite monoalkyl ester is connected to a post-processing system.

[0009] Furthermore, the reactor gas outlet is connected to a reaction gas phase condenser, the gas phase outlet of the reaction gas phase condenser is connected to a tail gas treatment system, the tail gas treatment system includes a hydrogen chloride absorption tower, and the tail gas treatment system is connected to a hydrochloric acid collection tank; The reaction low-boiling-point outlet on the reaction gas phase condenser is connected with a reaction low-boiling-point collecting tank, the reaction low-boiling-point collecting tank is connected with a low-boiling-point separation tower, the alcohol outlet on the low-boiling-point separation tower is connected with a heat exchanger, the heat exchanger is connected with the alcohol collecting tank; the chloroalkane outlet on the low-boiling-point separation tower is connected with a chloroalkane condenser, the chloroalkane condenser discharge port is connected with a chloroalkane collecting tank; the chloroalkane condenser discharge port is also connected with the low-boiling-point separation tower through a reflux pipe.

[0010] The positional relationships such as “on” and “between” in this technical solution are defined according to the conditions under actual use. They are conventional terms in this technical field and are also conventional terms used by technical personnel in this field in actual use.

[0011] The beneficial technical effects brought about by adopting this technical solution are: 1. In the present invention, alcohol, water and methyl phosphorus dichloride are used as raw materials, wherein one molecule of alcohol is replaced by one molecule of water, and methyl phosphorus dichloride undergoes a nucleophilic substitution reaction with alcohol and water at the same time, directly obtaining methyl hypophosphite monoalkyl ester, and producing two molecules of hydrogen chloride as by-products, thereby avoiding the process in which methyl diphosphite and hydrogen chloride undergo a substitution reaction to generate methyl hypophosphite monoalkyl ester; Ultimately, under the premise of ensuring the reaction rate and product yield, the amount of reaction by-products is reduced, the difficulty of separation is reduced, and the risks in the product separation and device operation process are reduced, so that the overall cost of synthesizing monoalkyl methyl hypophosphite is greatly reduced; 2. The present invention ensures the orderliness, controllability and sustainability of the reaction system by adopting a reactor, an alcohol flowmeter and an alcohol feed regulating valve connected by electrical signals, a water flowmeter and a water feed regulating valve connected by electrical signals, and a methyl phosphorus dichloride meter and a methyl phosphorus dichloride feed regulating valve connected by electrical signals, thereby promoting the stable synthesis of monoalkyl methyl hypophosphite, improving the yield and reducing the amount of by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the working principle of the present invention; Figure 2 It is a device connection diagram involved in the present invention; Figure 3 Is the gas chromatogram of the product in Example 1; Figure 4 is the gas chromatogram of the product in Example 2; Figure 5 is the gas chromatogram of the chloroalkane in Comparative Example 1; Figure 6 This is a physical picture of the monoalkyl methyl hypophosphite involved in the present invention; Among them, in the figure: 1, methyl phosphorus dichloride storage tank, 2, alcohol storage tank, 3, water storage tank, 4, reactor, 5, alcohol feed pipe, 6, alcohol vaporizer, 7, alcohol delivery pump, 8, alcohol flow meter, 9, alcohol feed regulating valve, 10, water vaporizer, 11, water delivery pump, 12, water flow meter, 13, water feed regulating valve, 14, water feed pipe, 15, methyl phosphorus dichloride feed pipe, 16, methyl phosphorus dichloride vaporizer, 17, methyl phosphorus dichloride delivery pump, 18, methyl phosphorus dichloride flow meter, 19, methyl Phosphorus chloride feed regulating valve, 20. Nitrogen inlet pipe, 21. Temperature control system, 22. Negative pressure system, 23. Temperature detector, 24. Pressure detector, 25. Post-processing system, 26. Methyl hypophosphite monoalkyl ester crude liquid storage tank, 27. Reaction gas phase condenser, 28. Hydrogen chloride absorption tower, 29. Hydrochloric acid collection tank, 30. Low boiling point separation tower, 31. Chloroalkane collection tank, 32. Reaction low boiling point collection tank, 33. Heat exchanger, 34. Alcohol collection tank, 35. Chloroalkane condenser, 36. Reflux pipe. DETAILED DESCRIPTION

[0013] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0014] The synthesis reaction involved in the present invention is an exothermic reaction with a fast reaction speed and a large amount of heat release. In view of the characteristics of the synthesis reaction, the present invention reduces the amount of reaction by-products, reduces the difficulty of separation, and reduces the risks in the process of product separation and device operation while ensuring the reaction rate and product yield through specific process condition control and material ratio relationship, a suitable synthesis system and feed control, so as to greatly reduce the overall cost of synthesizing methyl hypophosphite monoalkyl ester and ensure the stability and sustainability of the synthesis reaction.

[0015] This is illustrated by the following examples.

[0016] Embodiment 1: 1. After replacing the air in the reactor with nitrogen, turn on the temperature control system of the reactor to raise the temperature in the reactor to 100°C; turn on the negative pressure system of the reactor to make the negative pressure reach -0.098MPa; 2. After the temperature and pressure in the reactor reach the requirements and stabilize, n-butanol is introduced into the reactor, and its feed flow rate is adjusted to 0.5 mol / min, and the corresponding alcohol vaporizer heating temperature is controlled to 60°C; 3. First, water was introduced into the reactor, and its feed flow rate was adjusted to 0.2 mol / min, and the corresponding water vaporizer heating temperature was controlled to 50°C; 4. After the above two materials are fed stably, methyl phosphorus dichloride is introduced into the reactor, and its feed flow rate is adjusted to 0.2 mol / min, and the corresponding methyl phosphorus dichloride vaporizer heating temperature is controlled to 70°C; 5. After the methyl phosphorus dichloride is introduced, the reaction temperature is controlled to be maintained at 120-130°C when the reaction starts; 6. After the temperature, pressure and feed rate in the reactor are stable, start taking the feed data and discharge data within 20 minutes. The results are shown in Table 1.

[0017] 549.58 g of material was obtained from the discharge port at the bottom of the reactor. Analysis showed that the main content of mono-n-butyl methylphosphinate in the product was 96.8%. After the reaction low-boiling products were treated in a low-boiling product separation tower, 19.79 g of n-butyl chloride was obtained, and the gas phase detection content was 99.2%; the calculated yield of methyl hypophosphite was 97.7%.

[0018] Embodiment 2: 1. After replacing the air in the reactor with nitrogen, turn on the temperature control system of the reactor to raise the temperature in the reactor to 100°C; turn on the negative pressure system of the reactor to make the negative pressure reach -0.096MPa; 2. After the temperature and pressure in the reactor reach the requirements and stabilize, ethanol is introduced into the reactor, and its feed flow rate is adjusted to 0.3 mol / min, and the corresponding alcohol vaporizer heating temperature is controlled to 60°C; 3. First, water was introduced into the reactor, and its feed flow rate was adjusted to 0.2 mol / min, and the corresponding water vaporizer heating temperature was controlled to 50°C; 4. After the above two materials are fed stably, methyl phosphorus dichloride is introduced into the reactor, and its feed flow rate is adjusted to 0.2 mol / min, and the corresponding methyl phosphorus dichloride vaporizer heating temperature is controlled to 70°C; 5. After the methyl phosphorus dichloride is introduced, the reaction temperature is controlled to be maintained at 110-120°C when the reaction starts; 6. After the temperature, pressure and feed rate in the reactor are stable, start taking the feed data and discharge data within 20 minutes. The results are shown in Table 1.

[0019] 431.11 g of material was obtained from the discharge port at the bottom of the reactor. Analysis showed that the main content of methylphosphinate in the product was 97.4%. After the reaction low-boiling products were treated in a low-boiling product separation tower, a total of 9.89 g of ethyl chloride was obtained, and the gas phase detection content was 99.1%; the calculated yield of methyl phosphite was 97.2%.

[0020] Embodiment 3: 1. After replacing the air in the reactor with nitrogen, turn on the temperature control system of the reactor to raise the temperature in the reactor to 150°C; turn on the negative pressure system of the reactor to make the negative pressure reach -0.05MPa; 2. After the temperature and pressure in the reactor reach the requirements and stabilize, n-butanol is introduced into the reactor, and its feed flow rate is adjusted to 0.24 mol / min, and the corresponding alcohol vaporizer heating temperature is controlled to 120°C; 3. First, water was introduced into the reactor, and its feed flow rate was adjusted to 0.2 mol / min, and the corresponding water vaporizer heating temperature was controlled to 100°C; 4. After the above two materials are fed stably, methyl phosphorus dichloride is introduced into the reactor, and its feed flow rate is adjusted to 0.2 mol / min, and the corresponding methyl phosphorus dichloride vaporizer heating temperature is controlled to 100°C; 5. After the methyl phosphorus dichloride is introduced, the reaction temperature is controlled to be maintained at 140-150°C when the reaction starts; 6. After the temperature, pressure and feed rate in the reactor are stable, start taking the feed data and discharge data within 20 minutes. The results are shown in Table 1.

[0021] 538.38 g of material was obtained from the discharge port at the bottom of the reactor. Analysis showed that the main content of mono-n-butyl methylphosphinate in the product was 97.6%.

[0022] After the reaction low-boiling products were treated in a low-boiling product separation tower, 13.8 g of n-butyl chloride was obtained, and the gas phase detection content was 99.3%; the calculated yield of methyl hypophosphite was 96.5%.

[0023] Embodiment 4-8: On the basis of Example 1, Examples 4-8 respectively adopted the material proportions and reaction conditions described in Table 1 below, and the obtained results are respectively shown in Table 1 below.

[0024] Embodiment 9: On the basis of Examples 1-8, this example provides: a synthesis system of methyl hypophosphite monoalkyl ester, comprising an alcohol storage tank 2, a water storage tank 3, a methyl phosphorus dichloride storage tank 1 and a reactor 4; Alcohol storage tank 2: connected to reactor 4 via alcohol feed pipe 5, on which alcohol vaporizer 6, alcohol delivery pump 7, alcohol flow meter 8 and alcohol feed regulating valve 9 are arranged, and alcohol flow meter 8 and alcohol feed regulating valve 9 are connected via electrical signals; Water storage tank 3: connected to reactor 4 through water feed pipe 14, on which water vaporizer 10, water delivery pump 11, water flow meter 12 and water feed regulating valve 13 are arranged, and water flow meter 12 and water feed regulating valve 13 are connected through electrical signals; Methyl phosphorus dichloride storage tank 1: connected to reactor 4 through methyl phosphorus dichloride feed pipe 15, on which methyl phosphorus dichloride feed pipe 15 is provided methyl phosphorus dichloride vaporizer 16, methyl phosphorus dichloride delivery pump 17, methyl phosphorus dichloride flowmeter 18 and methyl phosphorus dichloride feed regulating valve 19, and the methyl phosphorus dichloride meter is connected to the methyl phosphorus dichloride feed regulating valve 19 through an electrical signal; Reactor 4: It is also connected with a nitrogen inlet pipe 20, a temperature control system 21 and a negative pressure system 22, wherein the temperature control system 21 includes a steam inlet pipe and a boiler, etc., and steam is provided on the steam inlet pipe; the negative pressure system 22 includes a vacuum pump, etc.; the reactor is provided with a temperature detector 23 and a pressure detector 24.

[0025] Among them, the reactor 4 is a microchannel reactor.

[0026] In addition, the discharge port of the reactor 4 is connected to a crude liquid storage tank 26 for methyl hypophosphite, and the crude liquid storage tank 26 for methyl hypophosphite is connected to a post-processing system 25 .

[0027] The gas outlet of the reactor 4 is connected to a reaction gas phase condenser 27, and the gas phase outlet of the reaction gas phase condenser 27 is connected to a tail gas treatment system, the tail gas treatment system includes a hydrogen chloride absorption tower 28, and the tail gas treatment system is connected to a hydrochloric acid collection tank 29; The reaction low-boiling-point outlet of the reaction gas phase condenser 27 is connected to a reaction low-boiling-point collecting tank 32, and the reaction low-boiling-point collecting tank 32 is connected to a low-boiling-point separation tower 30. The alcohol outlet of the low-boiling-point separation tower 30 is connected to a heat exchanger 33, and the heat exchanger 33 is connected to an alcohol collecting tank 34; the chloroalkane outlet of the low-boiling-point separation tower 30 is connected to a chloroalkane condenser 35, and the discharge port of the chloroalkane condenser 35 is connected to a chloroalkane collecting tank 31; the discharge port of the chloroalkane condenser 35 is also connected to the low-boiling-point separation tower 30 through a reflux pipe 36.

[0028] Comparative Example 1: 1. After replacing the air in the reactor with nitrogen, turn on the temperature control system of the reactor to raise the temperature in the reactor to 100°C; turn on the negative pressure system of the reactor to make the negative pressure reach -0.098MPa; 2. After the temperature and pressure in the reactor reach the requirements and stabilize, n-butanol is introduced into the reactor, and its feed flow rate is adjusted to 0.7 mol / min, and the corresponding alcohol vaporizer heating temperature is controlled to 60°C; 3. After the above-mentioned material feed is stable, methyl phosphorus dichloride is introduced into the reactor, and its feed flow rate is adjusted to 0.2 mol / min, and the corresponding methyl phosphorus dichloride vaporizer heating temperature is controlled to 70°C; 4. After the methyl phosphorus dichloride is introduced, the reaction temperature is controlled to be maintained at 120-130°C when the reaction begins.

[0029] 5. After all parameters in the reactor are stable, start collecting the feed and discharge data within 20 minutes.

[0030] 533.68 g of material was obtained from the discharge port at the bottom of the reactor. Analysis showed that the main content of mono-n-butyl methylphosphinate in the product was 95.4%. After the reaction low-boiling products were treated in a low-boiling product separation tower, a total of 407.22 g of n-butyl chloride was obtained, and the gas phase detection content was 99.6%; the calculated yield of methyl hypophosphite was 93.5%.

[0031] Table 1 From Table 1, we can see that: 1. After using water to replace alcohol, the by-product of chloroalkanes in the reaction system can be significantly reduced; and, as the amount of water added increases, the consumption of alcohol can be significantly reduced; Second, when the reaction device remains unchanged, the yield is higher when using alcohols with 4 carbon atoms or less than alcohols with 6 carbon atoms or more; 3. By adjusting the reaction temperature and the corresponding reaction pressure, the reaction yield can be maintained at ≥96%.

Claims

1. A method for synthesizing monoalkyl methylphosphinate, characterized in that: The steps include: S1 pretreatment: nitrogen is used to replace the gas in the reactor, and the temperature in the reactor is controlled to be 100-200°C and the pressure to be -0.098--0.05MPa; S2 feeding: alcohol at a temperature of 50-180°C, water at a temperature of 60-120°C and methyl phosphorus dichloride at a temperature of 70-100°C are sequentially introduced into the reactor; The feed ratio of alcohol, water and methyl phosphorus dichloride is controlled to be 1.0-2.5:0.01-1.0:1, and the total molar amount of alcohol and water is 2.0-3.5 times the molar amount of methyl phosphorus dichloride; S3 reaction: nucleophilic substitution reaction is carried out to obtain a crude product of monoalkyl methyl hypophosphite; S4 post-treatment: The crude methyl hypophosphite monoalkyl ester obtained in step S3 is subjected to distillation separation and purification to obtain methyl hypophosphite monoalkyl ester.

2. The method for synthesizing monoalkyl methyl phosphinate according to claim 1, characterized in that: In step S2, the alcohol is a C1-C8 monohydric alcohol and / or a dihydric alcohol.

3. The method for synthesizing monoalkyl methyl phosphinate according to claim 1, characterized in that: In step S2, the purity of alcohol is ≥98% and does not contain water; the water is deionized water; and the purity of methyl phosphorus dichloride is ≥95%.

4. The method for synthesizing monoalkyl methyl phosphinate according to claim 1, characterized in that: The reaction gas phase obtained in step S3 is condensed to obtain hydrogen chloride gas and reaction low-boiling products, and the hydrogen chloride gas is treated in a hydrogen chloride absorption tower to obtain hydrochloric acid, which is recycled and reused; The reaction low-boiling products are separated to obtain by-product chloroalkane and unreacted alcohol, and the by-product chloroalkane is condensed and collected; The unreacted C1-C8 monohydric alcohols are condensed and directly reused as raw materials.

5. A synthesis system for monoalkyl methyl hypophosphite, characterized in that: A synthesis system used in the synthesis method according to any one of claims 1 to 4, the synthesis system comprising an alcohol storage tank (2), a water storage tank (3), a methyl phosphorus dichloride storage tank (1) and a reactor (4); The alcohol storage tank (2) is connected to the reactor (4) via an alcohol feed pipe (5); an alcohol vaporizer (6), an alcohol delivery pump (7), an alcohol flow meter (8) and an alcohol feed regulating valve (9) are provided on the alcohol feed pipe (5); the alcohol flow meter (8) and the alcohol feed regulating valve (9) are connected via an electrical signal; The water storage tank (3) is connected to the reactor (4) via a water feed pipe (14); a water vaporizer (10), a water delivery pump (11), a water flow meter (12) and a water feed regulating valve (13) are provided on the water feed pipe (14); the water flow meter (12) and the water feed regulating valve (13) are connected via an electrical signal; The methyl phosphorus dichloride storage tank (1) is connected to the reactor (4) via a methyl phosphorus dichloride feed pipe (15); the methyl phosphorus dichloride feed pipe (15) is provided with a methyl phosphorus dichloride vaporizer (16), a methyl phosphorus dichloride delivery pump (17), a methyl phosphorus dichloride flow meter (18) and a methyl phosphorus dichloride feed regulating valve (19); the methyl phosphorus dichloride meter and the methyl phosphorus dichloride feed regulating valve (19) are connected via an electrical signal; The reactor (4) is also connected to a nitrogen inlet pipe (20), a temperature control system (21) and a negative pressure system (22), and a temperature detector (23) and a pressure detector (24) are provided on the reactor.

6. The synthesis system of monoalkyl methyl hypophosphite according to claim 5, characterized in that: The reactor (4) includes a batch reactor or a continuous reactor.

7. The synthesis system of monoalkyl methyl phosphinate according to claim 5, characterized in that: The discharge port of the reactor (4) is connected to a crude liquid storage tank (26) of methyl hypophosphite monoalkyl ester, and the crude liquid storage tank (26) of methyl hypophosphite monoalkyl ester is connected to a post-processing system (25).

8. The synthesis system of monoalkyl methyl phosphinate according to claim 5, characterized in that: The reactor (4) is connected to a reaction gas phase condenser (27) at its gas outlet, and an upper gas phase outlet of the reaction gas phase condenser (27) is connected to a tail gas treatment system, the tail gas treatment system comprising a hydrogen chloride absorption tower (28), and the tail gas treatment system is connected to a hydrochloric acid collection tank (29); The reaction low boiling point outlet of the reaction gas phase condenser (27) is connected to a reaction low boiling point collecting tank (32), the reaction low boiling point collecting tank (32) is connected to a low boiling point separation tower (30), the alcohol outlet of the low boiling point separation tower (30) is connected to a heat exchanger (33), and the heat exchanger (33) is connected to the alcohol collecting tank (34); the chloroalkane outlet of the low boiling point separation tower (30) is connected to a chloroalkane condenser (35), and the discharge port of the chloroalkane condenser (35) is connected to the chloroalkane collecting tank (31); the discharge port of the chloroalkane condenser (35) is also connected to the low boiling point separation tower (30) via a reflux pipe (36).

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