Synthesis method of bis (1-methylheptyl) methylphosphonate

Abstract

The invention discloses a synthetic method of bis (1-methylheptyl) methylphosphonate, and belongs to the technical field of organic phosphorus compound preparation, and the synthetic method comprises the following specific steps: S1, adding phosphorus trichloride and a solvent into a reaction container, putting a reaction system into an ice-water bath, and dropwise adding sec-octanol into a phosphorus trichloride solution; after the reaction is finished, removing the solvent and unreacted sec-octanol through reduced pressure distillation to obtain an intermediate di (1-methylheptyl) phosphonite; s2, adding the di (1-methylheptyl) phosphonite obtained in the step S1 into an alkali solution, and putting a reaction system into an ice-water bath; after the reaction is completed, adding a methylation reagent into the system; and after the reaction is finished, washing the reaction liquid with water until the reaction liquid is neutral, and removing volatile components through reduced pressure distillation to obtain the target product methyl phosphonic acid di (1-methylheptyl) ester. The method provided by the invention has the advantages of high safety and strong process controllability, and is suitable for an alternative synthesis route of industrial production.

Description

Technical Field

[0001] This invention belongs to the field of organophosphorus compound preparation technology, specifically relating to a method for synthesizing di(1-methylheptyl) methylphosphonic acid. Background Technology

[0002] Di(1-methylheptyl) methylphosphonate (P350 extractant) is a highly efficient neutral organophosphorus extractant widely used in hydrometallurgy. It can be effectively used for the extraction, separation, and recovery of various rare earth and precious metals such as gallium, indium, scandium, thorium, uranium, cadmium, thallium, rhenium, and palladium. Its molecular structure is shown in the figure.

[0003]

[0004] The general synthetic method for di(1-methylheptyl) methylphosphonate is as follows: In a high-pressure reactor, chloromethane reacts with phosphorus trichloride under the catalysis of aluminum trichloride to generate methyl quaternary phosphine trichloride; subsequently, this intermediate reacts with 2-octanol to finally obtain the target product. The synthetic route is shown in the figure below.

[0005]

[0006] The key step in the above synthetic route is the preparation of methyl quaternary phosphine trichloride. However, the raw material chloromethane used in this process is gaseous at room temperature and pressure, and the reaction needs to be carried out at a relatively high temperature, resulting in a pressure inside the reactor that can reach as high as 50 kg / cm². 2 This not only poses significant safety risks in large-scale production but also makes the transportation and precise metering of chloromethane difficult. The synthesis method requires equipment with high pressure resistance and involves a complex production process.

[0007] Therefore, there is an urgent need to develop an alternative synthesis route that is highly safe, has strong process controllability, and is suitable for industrial production, in order to solve the problems of high safety hazards, high equipment requirements, and difficult measurement caused by the use of gaseous chloromethane in the existing technology. Summary of the Invention

[0008] In view of this, the present invention provides a method for synthesizing di(1-methylheptyl) methylphosphonic acid. This method has mild reaction conditions, does not require the use of a high-pressure reactor, avoids the safety hazards caused by high temperature and high pressure, and makes the reaction process safer and more controllable. At the same time, this process is simple to operate, has a high yield, and a simple post-processing procedure, which has good economic benefits and industrial application prospects, and is suitable for the large-scale production of di(1-methylheptyl) methylphosphonic acid.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a method for synthesizing di(1-methylheptyl) methylphosphonic acid, comprising the following steps:

[0011] S1. Synthesis of di(1-methylheptyl) phosphonite: Phosphorus trichloride (PCl3) and an appropriate amount of selected solvent were added to a reaction vessel, and the reaction system was placed in an ice-water bath. Under stirring, 2-octanol was slowly added dropwise to the phosphorus trichloride solution, and the reaction was carried out at 0-50℃ for 1 h. After the reaction was completed, the solvent and unreacted 2-octanol were removed by vacuum distillation to obtain the intermediate di(1-methylheptyl) phosphonite.

[0012] S2. Methylation reaction to generate the target product: Under stirring conditions, the di(1-methylheptyl) phosphonate obtained in step S1 was added to an alkaline solution, and the reaction system was also placed in an ice-water bath to remove the active hydrogen on the phosphorus atom. The temperature was controlled not to exceed 50°C during the reaction. After the deprotonation reaction was completed, a methylating agent was added to the system, and the reaction was continued to be stirred at room temperature for 1 to 5 hours. After the reaction was completed, the reaction solution was washed with water until neutral, and the volatile components were removed by vacuum distillation to obtain the target product di(1-methylheptyl) phosphonate.

[0013] Preferably, in step S1, the selected solvent is one of dichloromethane, 1,2-dichloroethane, chloroform, tetrahydrofuran, n-hexane, or petroleum ether.

[0014] Preferably, in step S1, the molar ratio of 2-octanol to phosphorus trichloride is (2.5-5):1.

[0015] Preferably, in step S1, the vacuum distillation is carried out at a distillation temperature of 40–80°C, a vacuum degree of 0.01–0.05 MPa, a condensation temperature of 0–10°C, and a distillation time of 30–90 min.

[0016] Preferably, in step S2, the alkali in the alkali solution is one of NaOH (sodium hydroxide), KOH (potassium hydroxide), NaH (sodium hydride), EtONa (sodium ethoxide), EtOK (potassium ethoxide), MeONa (sodium methoxide), MeOK (potassium methoxide), t-BuONa (sodium tert-butoxide), and t-BuOK (potassium tert-butoxide); the solvent in the alkali solution is one of diethyl ether, tetrahydrofuran, and 1,4-dioxane; and (0.04-0.05) mol of [a specific ingredient] is added to 100 mL of solvent in the alkali solution.

[0017] Preferably, in step S2, the molar ratio of the base to di(1-methylheptyl)phosphonate is (1-1.5):1; and the molar ratio of the base to the methylating agent is 1:1.

[0018] Preferably, in step S2, the methylating agent includes, but is not limited to, dimethyl sulfate (DMS) and dimethyl carbonate (DMC).

[0019] Preferably, in step S2, the vacuum distillation is carried out at a distillation temperature of 60–100°C, a vacuum degree of 0.01–0.05 MPa, a condensation temperature of 0–10°C, and a distillation time of 60–120 min.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] (1) This invention uses inexpensive and readily available phosphorus trichloride (PCl3) as a starting material. It first reacts with 2-octanol to generate the intermediate di(1-methylheptyl) phosphonite in near-equivalent yield, and the post-reaction processing is simple. Subsequently, the active hydrogen atoms in di(1-methylheptyl) phosphonite are removed under strongly alkaline conditions to generate the corresponding phosphonium anion. Then, the phosphonium anion directly undergoes an alkylation reaction with commonly used methylating agents (such as dimethyl sulfate or dimethyl carbonate) to finally synthesize the target product—di(1-methylheptyl) methylphosphonate—efficiently.

[0022] (2) This invention, by redesigning the synthetic route, successfully avoids the use of gaseous chloromethane in traditional processes, instead employing inexpensive and safe dimethyl sulfate or dimethyl carbonate as the methylating agent. The entire reaction process is carried out under normal pressure, with mild reaction conditions and high operational safety. Compared with existing technologies, this process eliminates the need for a high-pressure reactor, effectively solving the problems of difficult gaseous feedstock metering and the safety hazards caused by high temperature and pressure. Furthermore, this method has advantages such as low reaction temperature, short reaction time, high yield, and few byproducts, not only reducing energy consumption but also significantly improving feedstock utilization. High-purity products can be obtained with simple post-processing, which helps reduce production costs and equipment investment, and has good prospects for industrial application.

[0023] Therefore, the synthesis method of di(1-methylheptyl) methylphosphonic acid provided by the present invention has significant advantages in terms of process innovation and practical application. It can significantly improve its production efficiency and reduce manufacturing costs, and at the same time help to reduce the overall production cost of using it as an extractant in hydrometallurgical processes. Attached Figure Description

[0024] Figure 1 The NMR spectrum of the intermediate phosphonite di(1-methylheptyl) ester of this invention;

[0025] Figure 2 This is the NMR spectrum of the methylphosphonic acid di(1-methylheptyl) ester synthesized in this invention. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0028] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0029] The present invention provides a method for synthesizing di(1-methylheptyl) methylphosphonic acid, comprising the following steps:

[0030] S1. Synthesis of di(1-methylheptyl) phosphonite: Phosphorus trichloride (PCl3) and an appropriate amount of a selected solvent were added to a reaction vessel. The solvent was one of dichloromethane, 1,2-dichloroethane, chloroform, tetrahydrofuran, n-hexane, or petroleum ether. The reaction system was placed in an ice-water bath. Under stirring, 2-octanol and PCl3 were slowly added dropwise to the PCl3 solution at a molar ratio of (2.5–5):1, and the reaction was carried out at 0–50 °C for 1 h. After the reaction was completed, the solvent and unreacted 2-octanol were removed by vacuum distillation to obtain the intermediate di(1-methylheptyl) phosphonite. The vacuum distillation conditions were as follows: distillation temperature 40–80 °C, vacuum degree 0.01–0.05 MPa, condensation temperature 0–10 °C, and distillation time 30–90 min.

[0031] S2. Methylation reaction to generate the target product: Under stirring conditions, the di(1-methylheptyl) phosphonite obtained in step S1 is added to an alkaline solution, and the reaction system is also placed in an ice-water bath to remove the active hydrogen on the phosphorus atom; the alkaline is one of NaOH, KOH, NaH, EtONa, EtOK, MeONa, MeOK, t-BuONa or t-BuOK, and the solvent used is diethyl ether, tetrahydrofuran or 1,4-dioxane, and the amount of alkaline used is 1 to 1.5 times the molar amount of phosphonite; the temperature is controlled not to exceed 50°C during the reaction.

[0032] After the deprotonation reaction is complete, a methylating agent (dimethyl sulfate or dimethyl carbonate) is added to the system in the same molar amount as the added base. The reaction is continued with stirring at room temperature for 1–5 hours. After the reaction is complete, the reaction solution is washed with water until neutral, and volatile components are removed by vacuum distillation to obtain the target product, di(1-methylheptyl) methylphosphonate. The vacuum distillation conditions are as follows: distillation temperature 60–100 °C, vacuum degree 0.01–0.05 MPa, condensation temperature 0–10 °C, and distillation time 60–120 min.

[0033] The synthetic principle of the methylphosphonic acid di(1-methylheptyl) ester of this invention is as follows:

[0034]

[0035] The synthesis method provided by this invention uses phosphorus trichloride (PCl3) and 2-octanol to generate di(1-methylheptyl) phosphonite, followed by the introduction of a methyl group under alkaline conditions via a pH bond. This method not only avoids the use of chloromethane gas and solves the problem of difficult raw material metering, but also eliminates the safety hazards associated with using high-pressure reactors and high reaction temperatures. The specific process is as follows:

[0036] Step 1: Generate di(1-methylheptyl) phosphonite

[0037] Phosphorus trichloride (PCl3) reacts with 2-octanol to almost quantitatively convert into di(1-methylheptyl) phosphonite. This reaction is a nucleophilic substitution reaction, in which 2-octanol acts as a nucleophile to attack the phosphorus atom in the phosphorus trichloride molecule, releasing HCl in the process. Specifically: PCl3 + 2-octanol → di(1-methylheptyl) phosphonite + 3HCl.

[0038] Step 2: Dehydrogenation to generate phosphine anions under alkaline conditions.

[0039] Di(1-methylheptyl) phosphonite loses a proton (H) under the action of a strong base such as sodium tert-butoxide (t-BuONa) to form the corresponding phosphine anion.

[0040] Step 3: Introducing methyl groups into dimethyl sulfate

[0041] The generated phosphoanion reacts with dimethyl sulfate (Me₂SO₄) to introduce a methyl group onto the phosphorus atom, thereby generating the target product—di(1-methylheptyl) methylphosphonate. This reaction is an electrophilic substitution reaction, in which dimethyl sulfate acts as the methyl source. That is: di(1-methylheptyl) phosphonite. - +Me2SO4→Di(1-methylheptyl)methylphosphonic acid +byproduct.

[0042] This invention avoids the direct use of toxic and difficult-to-measure chloromethane gas, reduces the need for high-pressure equipment and the risks associated with high-temperature operation, and provides a safer, more efficient, and easier-to-control production method for preparing di(1-methylheptyl) methylphosphonate. This method offers a more environmentally friendly and safer option for industrial production.

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0044] Example 1

[0045] This embodiment describes a method for synthesizing di(1-methylheptyl) methylphosphonic acid ester, and the specific steps are as follows:

[0046] Synthesis of S1. Di(1-methylheptyl) phosphonite:

[0047] In a 2.5L two-necked reaction flask, one neck is connected to a dropping funnel, and the other neck is connected to a tail gas absorption device. Add 0.5L of 1,2-dichloroethane and 1 mol of phosphorus trichloride (PCl3) to the reaction flask, and cool the reaction system in an ice-water bath. Dissolve 3 mol of 2-octanol in 0.5L... After adding 1,2-dichloroethane, it was slowly added dropwise to the phosphorus trichloride solution through a dropping funnel, controlling the dropping rate to keep the reaction temperature below 20°C. After the addition was complete, the reaction was stirred for 1 hour in an ice-water bath. After the reaction was completed, the solvent and unreacted 2-octanol were removed using a rotary evaporator at 30°C and a vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Subsequently, vacuum distillation was carried out for 90 minutes at 40°C, a vacuum of 0.01 MPa (absolute pressure ≤ 0.01 MPa, i.e., approximately 1 kPa), and a condensation temperature of 2°C to further remove the byproduct 2-chlorooctane. The residue in the reaction flask was the target intermediate—di(1-methylheptyl)phosphonite—with a yield exceeding 98%.

[0048] S2. Methylation reaction generates the target product:

[0049] Add 100 mL of anhydrous tetrahydrofuran (THF) to a 250 mL two-necked reaction flask and cool the reaction system in an ice-water bath. Then add 46 mmol of sodium tert-butoxide and stir until it is completely dissolved. Next, slowly add 40 mmol of di(1-methylheptyl) phosphonite through a dropping funnel. After the solution has been added, slowly add 46 mmol of dimethyl sulfate under ice-water bath conditions. After the addition is complete, remove the ice-water bath and let the reaction system continue to be stirred at room temperature for 1 h.

[0050] After the reaction was completed, the solvent and the generated tert-butanol were removed from the reaction system using a rotary evaporator at 30°C and a vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Subsequently, 50 mL of water and 20 mL of ethyl acetate were added to the residue, and the aqueous phase was extracted three times with ethyl acetate (20 mL each time). The organic phases were then combined.

[0051] The above organic phase was dried with anhydrous sodium sulfate, filtered, and concentrated to obtain a crude product. The crude product was then subjected to vacuum distillation at 60°C, a vacuum degree of 0.01 MPa (absolute pressure ≤ 0.01 MPa, i.e., about 1 kPa), and a condensation temperature of 2°C to remove residual dimethyl sulfate, finally yielding 11.36 g of the target product—di(1-methylheptyl) methylphosphonic acid, with a yield of 89%.

[0052] Example 2

[0053] This embodiment describes a method for synthesizing di(1-methylheptyl) methylphosphonic acid ester, and the specific steps are as follows:

[0054] Synthesis of S1. Di(1-methylheptyl) phosphonite:

[0055] In a 2.5L two-necked reaction flask, one neck was connected to a dropping funnel, and the other to a tail gas absorption device. 1L of dichloromethane and 1mol of phosphorus trichloride (PCl3) were added to the flask, and the reaction system was cooled in an ice-water bath. 3mol of 2-octanol was dissolved in 0.5L of dichloromethane and then slowly added dropwise to the phosphorus trichloride solution through the dropping funnel, controlling the dropping rate to keep the reaction temperature below 20°C. After the addition was complete, the reaction was stirred for 1 hour under ice-water bath conditions. After the reaction was completed... The solvent and unreacted 2-octanol were removed using a rotary evaporator at 40°C and a vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Subsequently, vacuum distillation was carried out at 60°C, a vacuum of 0.01 MPa (absolute pressure ≤ 0.01 MPa, i.e., approximately 1 kPa), and a condensation temperature of 5°C to further remove the byproduct 2-chlorooctane. The residue in the reaction flask was the target intermediate—di(1-methylheptyl) phosphonite—with a yield exceeding 99%.

[0056] S2. Methylation reaction generates the target product:

[0057] Add 100 mL of anhydrous tetrahydrofuran (THF) to a 250 mL two-necked reaction flask and cool the reaction system in an ice-water bath. Then add 44 mmol of NaH and stir until it is completely dissolved. Next, slowly add 40 mmol of di(1-methylheptyl) phosphonite through a dropping funnel. After the solution has been added, slowly add 44 mmol of dimethyl carbonate under ice-water bath conditions. After the addition is complete, remove the ice-water bath and let the reaction system continue to be stirred at room temperature for 1 h.

[0058] After the reaction was completed, the solvent and the generated tert-butanol were removed from the reaction system using a rotary evaporator at 40°C and a vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Subsequently, 50 mL of water and 20 mL of ethyl acetate were added to the residue, and the aqueous phase was extracted three times with ethyl acetate (20 mL each time). The organic phases were then combined.

[0059] The above organic phase was dried with anhydrous sodium sulfate, filtered, and concentrated to obtain a crude product. The crude product was then subjected to vacuum distillation at 80°C, a vacuum degree of 0.01 MPa (absolute pressure ≤ 0.01 MPa, i.e., about 1 kPa), and a condensation temperature of 5°C to remove residual dimethyl sulfate, finally yielding 11.36 g of the target product—di(1-methylheptyl) methylphosphonic acid, with a yield of 89%.

[0060] The NMR spectrum data of the intermediate di(1-methylheptyl)phosphonate obtained in this embodiment are as follows: Figure 1 As shown, the specific analysis is as follows.

[0061] Figure 1 A is 31 The P NMR spectrum analysis shows a single sharp peak, corresponding to the phosphorus atom (P) in the phosphonite, without obvious coupling effects or multiple peak splitting; it is located at approximately 5.36 ppm, which is consistent with the typical characteristics of phosphonite compounds.

[0062] Figure 1 B is 1 The H-NMR spectrum analysis shows that there are multiple overlapping multiplets in the range of 0.86 to 1.66 ppm, corresponding to hydrogen atoms on the alkyl chain (1-methylheptyl). The hydrogen atoms on the alkyl chain undergo coupling splitting due to the influence of neighboring carbon atoms, forming multiplets. The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the alkyl chain.

[0063] Figure 1 C is 13 The C-NMR spectrum analysis shows that: in the lower chemical shift region (about 20-40 ppm), there are multiple peaks, corresponding to carbon atoms on the alkyl chain (1-methylheptyl); in the higher chemical shift region (about 70-80 ppm), there are multiple peaks, corresponding to carbon atoms in the phosphonite group.

[0064] In summary, 1 Multiple peaks in the 0.86–1.66 ppm range in the H-NMR spectrum, and 13Multiple peaks in the 20–40 ppm range of the C-NMR spectrum jointly confirmed the presence of the alkyl chain (1-methylheptyl). The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the alkyl chain. 31 A single sharp peak at approximately 5.36 ppm in the P-NMR spectrum, and 13 Multiple peaks in the 70–80 ppm range of the C-NMR spectrum collectively confirm the presence of phosphonite groups. The distribution and integral values ​​of these peaks are consistent with the structural characteristics of phosphonite groups. Based on the data from these three NMR spectra, the target compound can be confirmed as di(1-methylheptyl) phosphonite, and the chemical shift values ​​and peak distribution are consistent with the typical characteristics of this compound.

[0065] The NMR spectrum data of the target product, di(1-methylheptyl) methylphosphonate (P350), prepared in this embodiment is as follows: Figure 2 As shown, the specific analysis is as follows.

[0066] Figure 2 A is 31 The P NMR spectrum analysis shows a single, sharp peak at approximately 28.83 ppm. This single, sharp peak indicates that the phosphorus atom is in a chemically equivalent environment, without significant coupling effects or multiplet splitting. The chemical shift value (approximately 28.83 ppm) is consistent with the typical characteristics of methylphosphonate compounds. The well-symmetric single peak further supports the structure of the disubstituted methylphosphonate.

[0067] Figure 2 B is 1 The H-NMR spectrum analysis shows that: in the range of 0.86–1.63 ppm, there are multiple overlapping multiplets, corresponding to hydrogen atoms on the alkyl chain (1-methylheptyl). This indicates that the hydrogen atoms on the alkyl chain undergo coupling splitting due to the influence of neighboring carbon atoms. The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the alkyl chain. The peaks in the range of approximately 4.5 ppm generally correspond to the methylene (-CH2-) hydrogen atoms in the ester group (-COO-). The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the ester group. The peak at approximately 7.3 ppm may correspond to hydrogen atoms in the phosphonic acid group (-PO(OH)2). The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the phosphonic acid group.

[0068] Figure 2 C is 13C-NMR spectrum analysis shows multiple peaks in the lower chemical shift region (approximately 10–40 ppm), corresponding to carbon atoms on the alkyl chain (1-methylheptyl). The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the alkyl chain. Peaks in the approximately 30–40 ppm range may correspond to carbon atoms in the phosphonic acid group. The distribution and integral values ​​of these peaks are consistent with the structural characteristics of the phosphonic acid group.

[0069] In summary, the data from the three types of NMR spectra confirm that the target compound is di(1-methylheptyl) methylphosphonic acid, and the chemical shift values ​​and peak distribution are consistent with the typical characteristics of this compound.

[0070] Example 3

[0071] This embodiment describes a method for synthesizing di(1-methylheptyl) methylphosphonic acid ester, and the specific steps are as follows:

[0072] Synthesis of S1. Di(1-methylheptyl) phosphonite:

[0073] In a 2.5L two-necked reaction flask, one neck was connected to a dropping funnel and the other to a tail gas absorption device. 0.5L of 1,2-dichloroethane and 1 mol of phosphorus trichloride (PCl3) were added to the flask, and the reaction system was cooled in an ice-water bath. 3 mol of 2-octanol was dissolved in 0.5L of dichloromethane and then slowly added dropwise to the phosphorus trichloride solution through the dropping funnel, controlling the dropping rate to keep the reaction temperature below 20°C. After the addition was complete, the reaction was stirred for 1 hour in an ice-water bath. After the reaction was complete, the solvent and unreacted 2-octanol were removed using a rotary evaporator at 30°C and a vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Subsequently, vacuum distillation was performed at 70°C, a vacuum of 0.03 MPa, and a condensation temperature of 8°C to further remove the byproduct 2-chlorooctane. The residue in the reaction flask was the target intermediate—di(1-methylheptyl) phosphonite—with a yield exceeding 99%.

[0074] S2. Methylation reaction generates the target product:

[0075] Add 100 mL of anhydrous tetrahydrofuran (THF) to a 250 mL two-necked reaction flask and cool the reaction system in an ice-water bath. Then add 46 mmol of sodium tert-butoxide and stir until it is completely dissolved. Next, slowly add 40 mmol of di(1-methylheptyl) phosphonite through a dropping funnel. After the solution has been added, slowly add 46 mmol of dimethyl carbonate under ice-water bath conditions. After the addition is complete, remove the ice-water bath and let the reaction system continue to be stirred at room temperature for 1 h.

[0076] After the reaction was completed, the solvent and the generated tert-butanol in the reaction system were removed by rotary evaporator at 30°C and vacuum of -0.09 MPa (approximately 0.1 MPa absolute pressure). Then, 50 mL of water and 20 mL of ethyl acetate were added to the residue, and the aqueous phase was extracted three times with ethyl acetate (20 mL each time). The organic phases were then combined.

[0077] The above organic phase was dried with anhydrous sodium sulfate, filtered, and concentrated to obtain a crude product. The crude product was then subjected to vacuum distillation at 90°C, 0.03 MPa, and 8°C to remove residual dimethyl sulfate, finally yielding 11.36 g of the target product—di(1-methylheptyl) methylphosphonate, with a yield of 89%.

[0078] The above provides a detailed description of the synthesis method of di(1-methylheptyl) methylphosphonic acid disclosed in this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A method for synthesizing di(1-methylheptyl) methylphosphonic acid, characterized in that, Includes the following steps: S1. Synthesis of di(1-methylheptyl) phosphonite: Phosphorus trichloride and an appropriate amount of selected solvent were added to a reaction vessel, and the reaction system was placed in an ice-water bath. Under stirring, 2-octanol was slowly added dropwise to the phosphorus trichloride solution, and the reaction was carried out at 0-50℃ for 1 h. After the reaction was completed, the solvent and unreacted 2-octanol were removed by vacuum distillation to obtain the intermediate di(1-methylheptyl) phosphonite. S2. Methylation reaction to generate the target product: Under stirring conditions, the di(1-methylheptyl) phosphonate obtained in step S1 was added to an alkaline solution, and the reaction system was also placed in an ice-water bath to remove the active hydrogen on the phosphorus atom. The temperature was controlled not to exceed 50°C during the reaction. After the deprotonation reaction was completed, a methylating agent was added to the system, and the reaction was continued to be stirred at room temperature for 1 to 5 hours. After the reaction was completed, the reaction solution was washed with water until neutral, and the volatile components were removed by vacuum distillation to obtain the target product di(1-methylheptyl) phosphonate.

2. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 1, characterized in that, In step S1, the selected solvent is one of dichloromethane, 1,2-dichloroethane, chloroform, tetrahydrofuran, n-hexane, and petroleum ether.

3. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 2, characterized in that, In step S1, the molar ratio of 2-octanol to phosphorus trichloride is (2.5-5):

1.

4. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 3, characterized in that, In step S1, the vacuum distillation is carried out at a distillation temperature of 40–80°C, a vacuum degree of 0.01–0.05 MPa, a condensation temperature of 0–10°C, and a distillation time of 30–90 min.

5. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 1, characterized in that, In step S2, the alkali in the alkali solution is one of NaOH, KOH, NaH, EtONa, EtOK, MeONa, MeOK, t-BuONa, and t-BuOK; the solvent in the alkali solution is one of diethyl ether, tetrahydrofuran, and 1,4-dioxane; and (0.04-0.05) mol of [a specific ingredient] is added to 100 mL of the solvent in the alkali solution.

6. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 5, characterized in that, In step S2, the molar ratio of the base to di(1-methylheptyl)phosphonate is (1-1.5):1; the molar ratio of the base to the methylating agent is 1:

1.

7. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 6, characterized in that, In step S2, the methylating agent includes, but is not limited to, dimethyl sulfate and dimethyl carbonate.

8. The method for synthesizing di(1-methylheptyl) methylphosphonic acid according to claim 7, characterized in that, In step S2, the vacuum distillation is carried out at a distillation temperature of 60–100°C, a vacuum degree of 0.01–0.05 MPa, a condensation temperature of 0–10°C, and a distillation time of 60–120 min.

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