A method for synthesizing a dialkylphosphinic ester

Abstract

This invention discloses a method for synthesizing dialkylphosphinates, belonging to the field of organic synthesis technology. The method uses hypophosphite and haloalkanes as starting materials. First, a hypophosphite is generated through a heated and pressurized reaction under the action of a phase transfer catalyst. The obtained hypophosphite does not require complex purification; it is directly reacted with an olefin under heated and pressurized conditions in the presence of a free radical initiator to obtain the target product, dialkylphosphinate. The method of this invention uses inexpensive and readily available raw materials, has a simple process route, includes only two core reactions, operates under mild conditions, is safe and convenient, produces few and easily treatable byproducts, has a high product yield, and is simple to purify. It is very suitable for large-scale industrial production, providing an economical and efficient synthetic route for the preparation of high-performance halogen-free flame retardants.

Description

Technical Field

[0001] This invention belongs to the field of organic chemical synthesis technology, and relates to a method for preparing halogen-free flame retardant compounds, and more specifically to a method for synthesizing dialkylphosphinates. Background Technology

[0002] Polyurethane resins are widely used in various fields of everyday products, such as automotive interiors, furniture, and electrical equipment materials, due to their low cost, light weight, and ease of molding. In terms of implementation, most polyurethane resins are typically used as polyurethane foams. In the polyurethane foam manufacturing industry, flame-retardant technology is incorporated into the foam to prevent fires. Halogenated flame retardants are widely used as flame retardants for polyurethane foams. Although halogenated flame retardants have excellent performance, they contain halogen elements such as chlorine and bromine, which produce environmentally harmful substances such as hydrogen halides and halodioxins when disposed of and incinerated.

[0003] Dialkylphosphinates are excellent halogen-free flame retardants with advantages such as low viscosity and high flame retardancy. A reported synthetic route is as follows: CN 108017669 A reports the reaction of trichlorophosphine with ethyl magnesium bromide in tetrahydrofuran, followed by quenching with dilute sulfuric acid, extraction with diethyl ether, drying, vacuum distillation, and recrystallization from toluene and ethanol to obtain intermediate 1; intermediate 1 is then reacted with antimony trifluoride under reduced pressure and heated, followed by vacuum distillation to obtain intermediate 2; intermediate 2 is then reacted with water and n-butanol, followed by vacuum distillation to obtain diethylphosphite n-butyl ester. This reaction route is relatively complex and uses chemicals such as ethyl magnesium bromide and SbF3, which are extremely sensitive to water and air, making it unsuitable for industrial production. CN101830926A reports the reaction of alkyl dichlorophosphine with alcohols to obtain monoalkyl phosphinates; the monoalkyl phosphinates then undergo free radical reactions with olefins under the action of an initiator to obtain dialkylphosphinates. This reaction route is simple, but the raw material alkyl dichlorophosphine is expensive, making it unsuitable for large-scale production.

[0004] Therefore, developing a method for synthesizing dialkylphosphinates that uses readily available raw materials, has a simple process route, mild reaction conditions, is safe and environmentally friendly, and is suitable for large-scale industrial production is of great practical significance and economic value. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to overcome the shortcomings of existing technologies and provide a novel method for synthesizing dialkylphosphinates, a new preparation method suitable for large-scale industrial production with a more rational process route. This method uses inexpensive and readily available hypophosphites and haloalkanes as starting materials, and efficiently prepares the target product through a two-step reaction. It has advantages such as a rational process route, simple operation, mild conditions, environmental friendliness, low production cost, and ease of industrialization.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention discloses a method for preparing dialkylphosphinates. The method involves reacting hypophosphite with a haloalkane in a high-pressure reactor under the catalysis of a phase transfer catalyst, heating to produce a dialkylphosphinate. The salt is removed by filtration, and excess haloalkane is recovered by vacuum distillation. The remaining material is then returned to the high-pressure reactor, purged with nitrogen, and an olefin is introduced. The reactor is then heated under high pressure, and a peroxide is slowly added as an initiator. Under the initiation of the peroxide, a dialkylphosphinate is generated. High-purity dialkylphosphinates are obtained by vacuum distillation. (See reaction formula).

[0007] The reaction formula is as follows:

[0008] In the formula: R1 refers to a C2-C6 alkyl group, and R2, R3, R4, and R5 refer to H or a C1-C4 alkyl group.

[0009] Specifically, the present invention provides a method for synthesizing a dialkylphosphinate, comprising the following steps: S1: Hypophosphite, haloalkanes and phase transfer catalyst are placed in a high-pressure reactor and reacted under the catalysis of the phase transfer catalyst. After the reaction is completed, inorganic salts are removed by filtration, and excess haloalkanes are recovered by vacuum distillation of the filtrate to obtain hypophosphite. S2: The phosphonates obtained in step S1 are put into a high-pressure reactor, purged with nitrogen, and then olefins are introduced. Under heating and pressure conditions, an initiator is slowly added and the reaction proceeds. The reaction solution is then distilled under reduced pressure to obtain dialkylphosphonates.

[0010] Furthermore, the hypophosphite is selected from one of sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, zinc hypophosphite, and aluminum hypophosphite.

[0011] Furthermore, the halogenated hydrocarbon is a C2-C6 chloroalkane, preferably at least one of various isomers of chloroethane, chloropropane, chlorobutane, chloropentane, or chlorohexane. For example, the halogenated hydrocarbon can be chloroethane, 1-chloropropane, 2-chloropropane, 1-chlorobutane, 2-chlorobutane, 1-chloro-2-methylpropane, 2-chloro-2-methylpropane, 1-chloropentane, 2-chloropentane, 3-chloropentane, 1-chloro-2-methylbutane, 2-chloro-2-methylbutane, 2-chloro-3-methylbutane, 1-chloro-3-methylbutane, 1-chloro-2,2-dimethylpropane, 1-chlorohexane, 2-chlorohexane, or 3-chlorohexane. 1-Chloro-2-methylpentane, 2-Chloro-2-methylpentane, 3-Chloro-2-methylpentane, 2-Chloro-4-methylpentane, 1-Chloro-4-methylpentane, 1-Chloro-3-methylpentane, 2-Chloro-3-methylpentane, 3-Chloro-3-methylpentane, 3-(Chloromethyl)pentane, 1-Chloro-2,3-dimethylbutane, 1-Chloro-2,2-dimethylbutane, 2-Chloro-3,3-dimethylbutane, 1-Chloro-3,3-dimethylbutane, etc.

[0012] Furthermore, based on the number of phosphorus atoms in the hypophosphite, its molar ratio to the haloalkanes is 1:(5.0-10.0), preferably 1:(7.0-7.5).

[0013] Furthermore, the phase transfer catalyst is one of tetraethylammonium bromide, tetrapropylammonium bromide, tetraisopropylammonium bromide, tetrabutylammonium bromide, tetraisobutylammonium bromide, and hexadecyltrimethylammonium bromide; the amount of phase transfer catalyst is 1-5% of the mass of hypophosphite, preferably 2.5-3%.

[0014] Furthermore, the reaction temperature in step S1 is 60-110℃, preferably 80-90℃; the reaction pressure is 0.2-0.8MPa, preferably 0.4-0.5MPa; and the reaction time is 6.0-16.0 h, preferably 8.0-10.0 h.

[0015] Furthermore, the olefin is a C2-C6 straight-chain or branched olefin; preferably at least one of various isomers of ethylene, propylene, butene, pentene, or hexene. For example, the olefin can be ethylene, propylene, 1-butene, 2-butene, 1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 1-hexene, 2-hexene, 3-hexene, 2-methyl-1-pentene, 2-methyl-2-pentene, 4-methyl-2-pentene, 4-methyl-1-pentene, 3-methyl-1-pentene, 3-methyl-2-pentene, 2,3-dimethyl-1-butene, 2,3-dimethyl-2-butene, 3,3-dimethyl-1-butene, etc.

[0016] Furthermore, the molar ratio of the hypophosphite to the olefin is 1:(2.01-2.20), preferably 1:(2.05-2.10).

[0017] Furthermore, the initiator is one of benzoyl peroxide, dibenzoyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, dicumyl peroxide, and m-chloroperoxybenzoic acid; the amount of the initiator is 2%-8% of the mass of hypophosphite, preferably 4%-5%.

[0018] Furthermore, the reaction temperature in step S2 is 70-110℃, preferably 80-90℃; the reaction pressure is 0.5-2.0MPa, preferably 0.7-1.0 MPa; and the reaction time is 4.0-10.0 h, preferably 5.0-6.0 h.

[0019] Compared with the prior art, the present invention has the following outstanding substantive features and significant progress: (1) The raw materials are cheap and readily available, with a significant cost advantage: The industrially produced hypophosphite and common halogenated hydrocarbons are used as starting materials, replacing expensive or dangerous alkyl dichlorophosphine, Grignard reagents, etc., which significantly reduces the cost of raw materials and ensures a stable source.

[0020] (2) The process route is simple and efficient: the entire synthesis process requires only two steps of reaction, without the need for complex intermediate separation and purification. The operation process is clear and easy to control, making it very suitable for continuous and automated large-scale industrial production.

[0021] (3) Green and environmentally friendly, with less waste: The main byproducts of the reaction are inorganic salts (such as NaCl), which can be sold as byproducts after simple purification. Basically, no difficult-to-treat organic wastewater and waste gas are generated, which is in line with the concept of modern green chemistry and sustainable development.

[0022] (4) Mild and controllable reaction conditions: Both steps of the reaction are carried out at medium temperature and medium pressure, without the need for extreme conditions, with high safety, relatively low equipment requirements, and low investment cost.

[0023] (5) High product yield and high purity: Through optimized process parameters, the yield of the target product dialkylphosphinate can reach more than 80%, and high-purity products can be obtained by simple vacuum distillation, which meets the strict requirements of downstream applications. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] Example 1: Synthesis of diethylphosphine n-butyl ester In a high-pressure reactor, 87.98 g (1.0 mol) of sodium hypophosphite, 740.54 g (8.0 mol) of 1-chlorobutane, and 6.45 g (0.02 mol) of tetrabutylammonium bromide phase transfer catalyst were added sequentially. After purging the air in the reactor with nitrogen, the reactor was sealed and heated to 90°C. The reaction pressure was maintained at approximately 0.45 MPa, and the reaction was stirred for 8.5 hours.

[0026] After the reaction was complete, the mixture was cooled to room temperature and the pressure was released. The reaction solution was filtered to obtain 87.66 g of wet filter residue (mainly sodium chloride). The filtrate was distilled under reduced pressure to recover 601.69 g of excess 1-chlorobutane. The remaining liquid (mainly crude n-butyl hypophosphite) was directly transferred to a clean autoclave.

[0027] The pressure vessel containing the crude product was purged three times with nitrogen to remove air. Ethylene gas was then introduced, and the temperature was raised to 80°C, maintaining a reaction pressure of approximately 0.8 MPa. During the reaction, a solution of benzoyl peroxide (9.69 g, approximately 0.04 mol, dissolved in a suitable amount of toluene) was slowly added dropwise using a feed pump. After the addition was complete, the reaction continued at 80°C for a total of 5.5 hours.

[0028] After the reaction was completed, the mixture was cooled and depressurized. The reaction solution was then distilled under reduced pressure, and a specific fraction was collected to obtain 147.91 g of colorless and transparent n-butyl diethylphosphonate, with a yield of 83%.

[0029] Example 2: Synthesis of dipropylphosphonic acid-2-pentyl ester The operating steps are the same as in Example 1, except that the raw materials are changed to: 104.09 g (1.0 mol) potassium hypophosphite, 906.01 g (8.5 mol) 2-chloropentane, and 4.84 g (0.015 mol) tetraisobutylammonium bromide phase transfer catalyst. The reaction conditions for the first step are: temperature 100℃, time 7.5 hours.

[0030] The second step reaction used crude 2-pentyl hypophosphite obtained in the first step as the starting material, and propylene as the olefin introduced. The reaction temperature was 90℃, and the reaction time was 4.5 hours. The initiator was 6.31 g (0.03 mol) of methyl ethyl ketone peroxide.

[0031] The final yield was 178.43 g of dipropylphosphonic acid-2-pentyl ester, with a yield of 81%.

[0032] Example 3: Synthesis of 2-propyl diisobutylphosphinoate The operating steps are the same as in Example 1, except that the raw materials are changed to: 77.14 g (0.5 mol) magnesium hypophosphite, 589.06 g (7.5 mol) 2-chloropropane, and 5.25 g (0.025 mol) tetraethylammonium bromide phase transfer catalyst. The reaction conditions for the first step are: temperature 80℃, time 10.5 hours.

[0033] The second step reaction used crude isopropyl hypophosphite obtained in the first step as the starting material, and introduced 2-butene as the olefin. The reaction temperature was 85℃, and the reaction time was 4.5 hours. The initiator was 8.62 g (0.035 mol) of cyclohexanone peroxide.

[0034] The final yield was 176.23 g of diisobutylphosphonic acid-2-propyl ester, with a yield of 80%.

[0035] The above embodiments fully illustrate the feasibility and effectiveness of the present invention. The advantages of the present invention are its simple operation, straightforward reaction, and environmental friendliness. The reaction process generates virtually no wastewater or waste gas; solid waste such as sodium chloride can be used as a byproduct after appropriate purification. It offers high economic benefits, low cost, and minimal equipment investment, making it suitable for large-scale industrial production. The method of the present invention synthesizes various structures of dialkylphosphinates with high yield using inexpensive raw materials through a simple two-step reaction, and the process route has significant prospects for industrial application.

[0036] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for synthesizing dialkylphosphinates, characterized in that, Includes the following steps: S1: Hypophosphite, haloalkanes and phase transfer catalyst are placed in a high-pressure reactor. Under the catalysis of the phase transfer catalyst, the reaction is carried out by heating and pressurization. After the reaction is completed, the inorganic salt is removed by filtration, and the excess haloalkanes are recovered by vacuum distillation of the filtrate to obtain hypophosphite. S2: The phosphonates obtained in step S1 are put into a high-pressure reactor, purged with nitrogen, and then olefins are introduced. Under heating and pressure conditions, an initiator is slowly added and the reaction proceeds. The reaction solution is then distilled under reduced pressure to obtain dialkylphosphonates.

2. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The hypophosphite is selected from one of sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, zinc hypophosphite, and aluminum hypophosphite.

3. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The halogenated hydrocarbon is a C2-C6 chloroalkane, preferably at least one of various isomers of chloroethane, chloropropane, chlorobutane, chloropentane, or chlorohexane.

4. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The molar ratio of phosphorus atoms in hypophosphite to haloalkanes is 1:(5.0-10.0), preferably 1:(7.0-7.5).

5. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The phase transfer catalyst is one of tetraethylammonium bromide, tetrapropylammonium bromide, tetraisopropylammonium bromide, tetrabutylammonium bromide, tetraisobutylammonium bromide, and hexadecyltrimethylammonium bromide; the amount of phase transfer catalyst used is 1-5% of the mass of hypophosphite.

6. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The reaction temperature in step S1 is 60-110℃, preferably 80-90℃; the reaction pressure is 0.2-0.8 MPa, preferably 0.4-0.5 MPa; and the reaction time is 6.0-16.0 h, preferably 8.0-10.0 h.

7. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The olefin is a C2-C6 straight-chain or branched olefin; preferably at least one of various isomers of ethylene, propylene, butene, pentene or hexene.

8. The method for synthesizing a dialkylphosphinate according to claim 7, characterized in that, The molar ratio of the hypophosphite to the olefin is 1:(2.01-2.20), preferably 1:(2.05-2.10).

9. The method for synthesizing a dialkylphosphonate according to claim 1, characterized in that, The initiator is one of benzoyl peroxide, dibenzoyl peroxide, methyl ethyl ketone peroxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, tert-butyl hydroperoxide, dicumyl peroxide, and m-chloroperoxybenzoic acid; the amount of the initiator is 2%-8% of the mass of hypophosphite, preferably 4%-5%.

10. The method for synthesizing a dialkylphosphinate according to claim 1, characterized in that, The reaction temperature in step S2 is 70-110℃, preferably 80-90℃; the reaction pressure is 0.5-2.0 MPa, preferably 0.7-1.0 MPa; and the reaction time is 4.0-10.0 h, preferably 5.0-6.0 h.

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