Preparation method of methyl phosphine dichloride

Abstract

The invention relates to the field of chemical synthesis, in particular to a preparation method of methyl phosphine dichloride. The preparation method comprises the following specific steps: taking aluminum powder, chloromethane and iodomethane as raw materials, and carrying out a sesquialuminum reaction in a high-pressure reaction kettle to generate a sesquialuminum mixture of methyl aluminum dichloride and dimethyl aluminum chloride; dropwise adding the mixture into excessive phosphorus trichloride to carry out a phosphonation reaction to generate a complex (3CH3PC12. 2AlCl3, similarly hereinafter), standing and layering at a low temperature, continuously applying the mixture of phosphorus trichloride and a small amount of complex on the upper layer to a phosphonation reaction kettle, and obtaining a flocculent complex on the lower layer; and heating the flocculent complex, transferring the flocculent complex to a distillation kettle, and adding sodium chloride for decomplexing distillation to obtain methyl phosphine dichloride. After the method is adopted, the purity of the methylphosphonium dichloride is increased to 96% or above, the yield of the methylphosphonium dichloride is increased to 84% or above, the energy consumption of the distillation process is greatly reduced, the industrial operation process is simplified, the equipment failure rate is greatly reduced, and compared with the prior art, the method has remarkable progress and is suitable for industrial production of the methylphosphonium dichloride.

Description

Technical Field

[0001] The invention discloses a method for preparing methylphosphonic acid dichloride, belongs to the technical field of chemical production, and particularly relates to a method for synthesizing methylphosphonic acid dichloride through an aluminum process. Background Art

[0002] In recent years, with the development and promotion of new varieties of glufosinate-resistant transgenic crops, the increase of glyphosate-resistant weeds and the ban on paraquat, glufosinate or refined glufosinate has gained huge development space as a broad-spectrum, highly efficient non-selective herbicide. In 2022, its market size exceeded US$1 billion, and it has become the world's second largest herbicide and the most used hand-type herbicide. With the penetration of new generation transgenics, the ban on paraquat and the increase in compounding agents, the demand for glufosinate continues to increase, and its manufacturing technology continues to develop. Diethyl methylphosphite is one of the indispensable key intermediates for the synthesis of glufosinate or refined glufosinate, and it is also an important intermediate for the synthesis of organophosphorus flame retardants. The main steps of the synthesis of diethyl methylphosphite include the synthesis of methyl dichloride phosphorus and the synthesis of diethyl methylphosphite. Methyl dichloride phosphorus is divided into aluminum method, magnesium Grignard method, ternary complex method, etc. according to different raw materials, but the synthesis steps of diethyl methylphosphite basically adopt the methyl dichloride phosphorus esterification method, and the acid application agent adopts ammonia.

[0003] Patent CN109384812 discloses the use of aluminum method to synthesize diethyl methylphosphite (DEMP), firstly reacting methyl chloride and aluminum powder to obtain a mixture of methylaluminum dichloride and dimethylaluminum chloride; then adding the above mixture dropwise to excess phosphorus trichloride to carry out phosphination reaction to synthesize complex 3CH 3 PCl 2 ·2AlCl 3 , evaporating to remove excess phosphorus trichloride, adding sodium chloride to decomplex, and further evaporating to recover methyl dichlorophosphine; adding the methyl dichlorophosphine dropwise to a mixed solvent, introducing ammonia to generate diethyl methylphosphite and ammonium chloride solution, and obtaining diethyl methylphosphite through filtration and distillation. Patent CN110283204B discloses a system and method for preparing methylphosphite using methylaluminum chloride, wherein methylaluminum chloride is prepared in a fluidized bed reactor, and then methylaluminum chloride and phosphorus trichloride are reacted to generate a ligand 3CH 3 PCl 2 ·2AlCl 3 , and then react with an alkali metal halide to obtain methylphosphine chloride, and methylphosphine dichloride reacts with an alcohol to obtain a methylphosphite product.

[0004] Therefore, it can be seen from the above-mentioned prior art that the preparation of diethyl methylphosphite requires separation of phosphine trichloride and phosphinated ligand by distillation, which consumes a lot of energy. In addition, the viscosity of the materials changes dramatically during the distillation process, which easily leads to safety risks such as stirring kettle locking and mechanical seal leakage. It is necessary to develop a better separation method. Summary of the invention

[0005] Aiming at the problems that the prior art separates phosphorus trichloride and phosphinated ligands by a distillation method with large energy consumption, is prone to stirring lock, has low purity of methylphosphine dichloride, is prone to side reactions, etc., the present invention provides a method for preparing methylphosphine dichloride, optimizes the separation method by utilizing the principle of immiscible stratification of phosphorus trichloride and phosphine ligands, greatly reduces energy consumption, simplifies the operation process, and improves the purity of methylphosphine dichloride.

[0006] To achieve the above purpose, the present invention adopts the following process technology scheme: (1) Aluminum powder and methyl iodide are added to a high-pressure reactor, and methyl chloride is slowly introduced to carry out a sesquivalent reaction. The pressure and temperature are controlled to a certain level to generate a sesquivalent aluminum solution of methylaluminum chloride.

[0007] (2) Add a certain amount of phosphorus trichloride to the reactor, then slowly add methyl sesquialuminum solution, maintain a certain temperature for phosphination reaction, and generate methylphosphine dichloride and aluminum trichloride ligand (3CH 3 PCl 2 •2AlCl 3 The phosphination liquid is cooled and then separated into layers. The upper layer is a mixture of phosphorus trichloride and a small amount of ligands, which is further used in the phosphination reaction. The lower layer is mostly flocculent ligands.

[0008] (3) The lower layer of flocculent ligands is heated up and then transferred to a distillation kettle. The temperature in the kettle is controlled, solid sodium chloride is added, and methylphosphine dichloride is obtained by decomplexation and distillation.

[0009] In some embodiments, in step (1), the reaction temperature is 130-150° C., the reaction pressure is 0.2-0.8 MPa, and the reaction time is 5-8 h.

[0010] I suggest you tell me the dosage relationship between aluminum powder and methyl chloride. Methyl chloride is 2.5-3.0 wt% of aluminum powder, and methyl iodide is used as a catalyst, and the dosage is 0.5-5wt% of aluminum powder.

[0011] In step (2), the phosphorus trichloride is in excess of the mass of the methylaluminum chloride sesquiate, and the methylaluminum chloride sesquiate is added dropwise under the condition that the phosphorus trichloride is cooled to -10-15°C, and the dropping time is 6-10 hours.

[0012] As a preferred solution, the mass excess of phosphorus trichloride relative to methylaluminum chloride sesquihydrate in step (2) is 5-500%, and the excess is any value and any numerical range between 5-500%. When it exceeds 500%, although the technical effect of this case can be achieved, it will cause waste of raw materials and waste of post-processing recovery.

[0013] Further, when the phosphorus trichloride is cooled to 0-15°C, methylaluminum chloride sesquihydrate is added dropwise, and the adding time is 6-8 hours.

[0014] In the step (2), the phosphination reaction temperature is 50-70°C and the reaction time is 1-4h.

[0015] The phosphine solution obtained in step (2) is cooled to 30-40°C and allowed to stand and separate.

[0016] The upper layer obtained by layering in step (2) is a mixture containing phosphorus trichloride and a small amount of ligand, which can be recovered by distillation at 70-90° C. and -0.01 to -0.1 MPa to obtain phosphorus trichloride, which can be continuously used in the next batch of phosphination reactions.

[0017] In some embodiments, the amount of sodium chloride added in step (3) is 1.2-1.5 times the molar amount of aluminum powder; after adding sodium chloride, distillation is performed at 80-100° C. and -0.01 to -0.1 MPa to obtain methylphosphine dichloride.

[0018] The technical solution of the present invention has the following beneficial effects: (1) Compared with the prior art, the present technical solution is used to separate phosphorus trichloride and ligand (3CH 3 PCl 2 •2AlCl 3 ), which has the characteristics of low energy consumption, simple operation and complete separation of phosphorus trichloride.

[0019] (2) Compared with the prior art, the small amount of ligand separated by the present technical solution can further improve the activity of the phosphination reaction and improve the effect of the phosphination reaction.

[0020] (3) Compared with the prior art, the present technical solution increases the purity of methylphosphonic acid dichloride to more than 96%, and increases the yield of methylphosphonic acid dichloride to more than 86%, greatly reducing the equipment failure rate, which is a significant improvement over the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0022] The essential contents of the present invention are further illustrated by the embodiments of the present invention, but the present invention is not limited thereto: Example 1 280kg aluminum powder, 10kg methyl iodide, and 815kg methyl chloride were added into the autoclave in sequence. The reaction pressure was controlled at 0.4Mpa, the reaction temperature was 135°C, and the reaction time was 6h to generate sesquihydrate of methylaluminum chloride. Add 6543kg of phosphorus trichloride to the reactor and cool it to -5°C. Slowly add methylaluminum chloride to the reactor for phosphating reaction. Control the reaction temperature at 15°C. The reaction time is 8h. Then keep the temperature at 60°C for 2h to obtain the ligand (3CH 3 PCl 2 •2AlCl 3 ) Phosphating liquid.

[0023] The phosphination liquid was cooled to 40°C and then separated into layers. The upper layer was a mixture of phosphorus trichloride and a small amount of ligands, and the lower layer was mostly flocculent ligands. The upper layer was distilled at 70°C and -0.05Mpa to obtain recovered phosphorus trichloride. PCl in phosphorus trichloride was recovered by gas chromatography. 3 content; 700 kg of sodium chloride was added to the lower layer, and methylphosphine dichloride was recovered by distillation at 80° C. and −0.08 MPa. The main content of methylphosphine dichloride was analyzed by gas chromatography, and the product yield was calculated based on aluminum powder.

[0024] The above recovered phosphorus trichloride set was used for the second, third, fourth and fifth batches, and fresh phosphorus trichloride was used to make up to 6543 kg. Other conditions remained unchanged. The comparative data are as follows:

[0025] Example 2 Add 280kg aluminum powder and 10kg iodomethane into a high-pressure reactor, and then introduce 815kg methyl chloride to carry out a sesquivalent reaction. The reaction pressure is controlled at 0.4Mpa, the reaction temperature is 135°C, and the reaction time is 6h to generate a sesquivalent of methylaluminum chloride. Add 6543kg of phosphorus trichloride to the reactor and cool it to -5°C. Then slowly add methyl sesquialuminum solution to carry out phosphating reaction. Control the reaction temperature at 15°C for 8 hours. Then keep the temperature at 60°C for 2 hours to generate methyl dichlorophosphine and aluminum trichloride ligand (3CH 3 PCl 2 •2AlCl 3 ); The phosphination liquid is cooled to 25°C and statically separated to obtain a mixture of phosphorus trichloride and a small amount of ligand in the upper layer, and the main content of phosphorus trichloride is analyzed by gas chromatography; the upper layer liquid is heated to 70°C, and distilled and recovered at -0.05Mpa to obtain phosphorus trichloride, and the main content of phosphorus trichloride is analyzed by gas chromatography; 700 kg of sodium chloride was added to the lower layer, and methylphosphine dichloride was recovered by distillation at 80° C. and −0.08 MPa. The main content of methylphosphine dichloride was analyzed by gas chromatography, and the product yield was calculated based on aluminum powder.

[0026] The above recovered phosphorus trichloride set was used for the second, third, fourth and fifth batches, and fresh phosphorus trichloride was used to make up to 6543 kg. Other conditions remained unchanged. The comparative data are as follows:

Claims

1. A method for preparing methylphosphonic acid dichloride, characterized in that: The steps include: (1) Adding methyl chloride to a mixture of aluminum powder and methyl iodide to carry out a sesquivalent reaction to produce methylaluminum chloride sesquivalent; (2) Slowly add methylaluminum chloride sesquihydrate dropwise into phosphorus trichloride to carry out phosphination reaction to generate phosphination solution of methylphosphine dichloride and aluminum trichloride ligand 3CH3PCl2•2AlCl3, cool the phosphination solution and then allow it to stand for stratification; (3) The flocculent ligand in the lower layer is heated, solid sodium chloride is added, and methylphosphine dichloride is obtained by decomplexation and distillation.

2. The method for preparing methylphosphonic acid dichloride according to claim 1, wherein In step (1), the reaction temperature is 130-150° C., the reaction pressure is 0.2-0.8 MPa, and the reaction time is 5-8 h.

3. The preparation method of methylphosphonic acid dichloride according to claim 1, characterized in that, In step (2), the phosphorus trichloride is in excess of the mass of the methylaluminum chloride sesquiate, and the methylaluminum chloride sesquiate is added dropwise under the condition that the phosphorus trichloride is cooled to -10-15°C, and the dropping time is 6-10 hours.

4. The method for preparing methylphosphonic acid dichloride according to claim 3, characterized in that: In step (2), the mass excess of phosphorus trichloride relative to methylaluminum chloride sesquiate is 5-500%, and methylaluminum chloride sesquiate is added dropwise under the condition that the phosphorus trichloride is cooled to 0-15°C, and the dropping time is 6-8h.

5. The method for preparing methylphosphonic acid dichloride according to claim 4, characterized in that: In step (2), the phosphination reaction temperature is 50-70° C. and the reaction time is 1-4 h.

6. The method for preparing methylphosphonic acid dichloride according to claim 5, characterized in that: The phosphine solution obtained in step (2) is cooled to 30-40°C and allowed to stand and separate into layers.

7. The method for preparing methylphosphonic acid dichloride according to claim 1, characterized in that: The upper layer obtained by layering in step (2) is a mixture containing phosphorus trichloride and a small amount of ligand, which is distilled and recovered at 70-90° C. and -0.01 to -0.1 MPa to obtain phosphorus trichloride.

8. The method for preparing methylphosphonic acid dichloride according to claim 1, characterized in that: In step (3), the amount of sodium chloride added is 1.2-1.5 times the molar amount of aluminum powder; after adding sodium chloride, distillation is performed at 80-100° C. and -0.01 to -0.1 MPa to obtain methylphosphine dichloride.

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