Method for producing dialkyl phosphate

Abstract

To provide a method enabling production of a dialkyl phosphate with enhanced safety, shortened reaction time, improved phosphorylation rate, and superior selectivity.SOLUTION: A dialkyl phosphate is produced by reacting a phosphonate diester with hydrogen peroxide in the presence of a halide salt.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a phosphoric acid diester, and more particularly to a method for producing a phosphoric acid diester with high safety, a shortened reaction time, a high phosphoric acid esterification rate, and high selectivity. [Background technology]

[0002] Phosphate esters are useful compounds as surfactants, antistatic agents, flame retardants, and anti-wear agents for lubricating oils, and the development of an efficient method for their production is desirable. A commonly known industrial method for producing phosphate esters involves reacting alcohol with phosphorus oxychloride. However, the starting material, phosphorus oxychloride, is highly toxic and is designated as a toxic substance under the law. Therefore, a safer method for synthesizing phosphate esters is desirable. Patent Document 1 discloses a technique for producing a phosphate ester compound in a one-step reaction using orthophosphoric acid as a starting material and an organosilane or siloxane compound having an alkoxy group or an aryloxy group. On the other hand, in the above-mentioned applications, phosphate esters are usually used as mixtures with phosphate monoesters, phosphate diesters, phosphate triesters, etc. Among these phosphate esters, phosphate diesters are particularly useful as metal extractants, and phosphate diester salts are useful as electrolytes for electrolytic capacitors. Therefore, a production method for obtaining high-purity phosphate diesters is significant, and various methods have been proposed. For example, Patent Document 2 discloses a method for producing a phosphoric acid diester salt by using a phosphoric acid triester as a starting material and reacting the phosphoric acid triester with a secondary amine in a pressure-resistant container at 125°C. However, this production method requires a reaction time of 30 hours or more at 100°C or higher, and considering industrial-scale production, a shorter reaction time is preferable. Patent Document 3 also discloses a method for producing a phosphoric acid diester and a phosphoric acid diester salt, which uses a phosphorus oxyhalide such as phosphorus oxychloride as a starting material, reacts the phosphorus oxyhalide with a base to obtain a dihalophosphate, and then reacts the dihalophosphate with a hydroxy compound in a PFA container. However, because this production method uses a phosphorus oxyhalide such as phosphorus oxychloride, gases such as hydrogen chloride are generated during production, requiring equipment to safely remove the gases from outside the system. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-143139 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-1459 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-166343 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a production method which is highly safe, can shorten the reaction time, has a high phosphoric acid esterification rate, and can produce a phosphoric acid diester with high selectivity. [Means for solving the problem]

[0005] Means for Solving the Problems The present inventors have conducted extensive research in view of the above problems and have found that by reacting a phosphonic acid diester with hydrogen peroxide in the presence of a halide salt, it is possible to avoid the use of phosphorus oxychloride, shorten the reaction time, and produce a phosphoric acid diester selectively with a high phosphoric acid esterification rate, thereby completing the present invention. That is, the present invention is as follows. [1] A method for producing a phosphoric acid diester, comprising reacting a phosphonic acid diester with hydrogen peroxide in the presence of a halide salt. [2] The method for producing a phosphoric acid diester according to [1] above, wherein the halide salt is at least one selected from the group consisting of alkali metals, alkaline earth metals, metals of Groups 4 to 14 of the Periodic Table, and tetraalkylammonium halide salts. [Effects of the Invention]

[0006] According to the present invention, it is possible to produce a phosphoric acid diester selectively in a short reaction time with a high phosphoric acid esterification rate by using a phosphonic acid diester, which is a compound with low toxicity, as a starting material. DETAILED DESCRIPTION OF THE INVENTION

[0007] The method for producing a phosphoric acid diester of the present invention is characterized by reacting a phosphonic acid diester as a starting material with hydrogen peroxide as an oxidizing agent in the presence of a halide salt as a catalyst, and the reaction system may contain a solvent as long as the object of the present disclosure is not impaired. Each raw material used in the production method of the present invention and the production steps will be described in detail below. In this specification, the method for producing a phosphoric acid diester of the present invention may be simply referred to as the "production method." In this specification, numerical ranges defined using the symbol "to" are inclusive of the numerical values ​​at both ends (upper and lower limits) of the symbol "to." For example, "2 to 5" means 2 or more and 5 or less.

[0008] <Phosphonic acid diester> In the production method of the present invention, a phosphonic acid diester represented by the following formula (1) is used as a starting material.

[0009] [ka]

[0010] In formula (1), R 1 and R 2 Each of R independently represents a hydrocarbon group which may have a substituent. 1 and R 2 may be the same or different. The hydrocarbon group may be saturated or unsaturated, aliphatic or aromatic, and if aliphatic, may be linear, branched or cyclic. Examples of the hydrocarbon group include alkyl groups, alkenyl groups, aryl groups and aralkyl groups. Examples of the alkyl group include linear alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, decyl, lauryl, myristyl, palmityl, stearyl, and behenyl groups; branched alkyl groups such as isopropyl, isobutyl, t-butyl, isopentyl, isooctyl, 2-ethylhexyl, isononyl, 3,5,5-trimethylhexyl, isodecyl, isostearyl, 2-octyldecyl, 2-octyldodecyl, and 2-hexyldecyl groups; and cyclic alkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cycloheptyl groups. Examples of alkenyl groups include palmitoleyl (also known as cis-9-hexadecenyl), oleyl (also known as cis-9-octadecenyl), and linoleyl (also known as cis, cis-9,12-octadecadienyl). Aliphatic hydrocarbon groups such as alkyl and alkenyl groups with 23 or more carbon atoms may be difficult to obtain. Examples of the aryl group include a phenyl group, a naphthyl group, a tolyl group, a xylyl group, a cumenyl group, a mesityl group, an ethylphenyl group, a propylphenyl group, a butylphenyl group, a pentylphenyl group, a hexylphenyl group, a heptylphenyl group, an octylphenyl group, and a nonylphenyl group. Examples of the aralkyl group include a benzyl group, a phenethyl group, a naphthylmethyl group, a benzhydryl group, a trityl group, a methylbenzyl group, and a methylphenethyl group.

[0011] The substituent of the hydrocarbon group may be a substituent consisting of atoms other than carbon and hydrogen, or a substituent containing atoms other than carbon and hydrogen, and may further contain an unsaturated bond and / or a cyclic structure. Examples of substituents consisting of atoms other than carbon and hydrogen include halogen atoms such as fluorine, chlorine, bromine, and iodine. Examples of substituents containing atoms other than carbon and hydrogen include a hydroxyl group, a mercapto group, a carboxyl group, a cyano group, a silyl group such as methylsilyl, an alkoxy group such as ethoxy, a siloxy group such as trimethylsilyloxy, a carbonyl group such as formyl, an acyl group such as acetyl, propionyl, benzoyl, or (meth)acryl, and an acyloxy group such as (meth)acryloyloxy. The term "(meth)acryl group" refers collectively to both acrylic and methacrylic groups, and the term "(meth)acryloyloxy group" refers collectively to both acryloyloxy and methacryloyloxy groups. R 1 and R 2 An example of the phosphonic acid diester of formula (1) in which is a hydrocarbon group having a substituent includes di(2-methacryloyloxyethyl) phosphonate represented by the following formula (2).

[0012] [ka]

[0013] R 1 and R 2From the viewpoint of availability, is preferably an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 1 to 22 carbon atoms, an aryl group having 6 to 16 carbon atoms, an aralkyl group having 6 to 14 carbon atoms, or an alkyl group having 1 to 22 carbon atoms, an alkenyl group having 1 to 22 carbon atoms, an aryl group having 6 to 16 carbon atoms, or an aralkyl group having 6 to 14 carbon atoms, which contains an acyl group having 2 to 8 carbon atoms or an acyloxy group having 2 to 8 carbon atoms as a substituent, and more preferably an alkyl group or alkenyl group having 2 to 18 carbon atoms.

[0014] The method for producing the phosphonic acid diester represented by the above formula (1) is not particularly limited, but one example is a method in which esterification reaction is carried out using phosphonic acid and alcohol at, for example, 80 to 180° C. This esterification reaction is preferably carried out using alcohol in an amount at a molar ratio of at least two times that of phosphonic acid. The purity of the starting phosphonic acid diester is not particularly limited, but is preferably 95 mol % or more from the viewpoint of the phosphate conversion rate and the selectivity of the phosphate diester. In the present invention, the purity of the phosphonic acid diester used as a starting material refers to the ratio of the phosphonic acid diester contained in the starting material to the total amount of the phosphonic acid diester and all impurities contained in the starting material. The impurities in the starting material refer to by-products generated in the production process of the phosphonic acid diester and raw materials remaining unreacted. For example, when an esterification reaction is carried out using phosphonic acid and alcohol, the impurities are the phosphonic acid monoester as a by-product and the phosphonic acid and alcohol as unreacted raw materials. The content of impurities such as by-products and unreacted raw materials is preferably less than 5 mol%.

[0015] <Phosphate diester> The phosphoric acid diester obtained by the production method of the present invention is represented by the following formula (3): 1 and R 2 The meaning of is R in the above formula (1). 1 and R 2 is the same as

[0016] [ka]

[0017] <Hydrogen peroxide> In the production method of the present invention, hydrogen peroxide is used as an oxidizing agent. By using hydrogen peroxide, a phosphate diester can be produced with a high esterification rate and high selectivity. Hydrogen peroxide is generally used in the form of aqueous hydrogen peroxide. The concentration of hydrogen peroxide in the aqueous hydrogen peroxide is not particularly limited, but from the viewpoints of reaction efficiency and ease of handling, it is preferably 20 to 70% by mass, more preferably 30 to 60% by mass.

[0018] <Halide salts> In the production method of the present invention, a halide salt is used as a catalyst. The halide salt is not particularly limited as long as it is a salt containing a halogen, and may be an inorganic salt or an organic salt, but from the viewpoint of reaction efficiency, an inorganic salt is preferred. The type of halogen that forms the halide salt is not particularly limited and may be any of fluorine, chlorine, bromine, and iodine. From the viewpoint of improving the phosphoric acid esterification rate and the selectivity for the phosphoric acid diester, however, chlorine, bromine, and iodine are preferred, bromine and iodine are more preferred, and iodine is particularly preferred. Examples of inorganic salts include halide salts of alkali metals, alkaline earth metals, metals of Groups 4 to 14 of the periodic table, and the like, such as lithium, sodium, and potassium as alkali metals, magnesium and calcium as alkaline earth metals, and iron, aluminum, and zinc as metals of Groups 4 to 14 of the periodic table. From the viewpoint of improving the phosphate conversion rate and the selectivity for the phosphate diester, halide salts of alkali metals and alkaline earth metals are preferred, alkali metal salts are more preferred, and potassium salts are particularly preferred. Specifically, potassium bromide and potassium iodide are preferred, and potassium iodide is particularly preferred. Examples of the organic salt include halide salts of tetraalkylammonium, such as halide salts of tetramethylammonium, tetraethylammonium, and tetrabutylammonium. From the viewpoint of improving the phosphoric acid esterification rate and the selectivity for the phosphoric acid diester, halide salts of tetraethylammonium and tetrabutylammonium are preferred, and halide salts of tetrabutylammonium are particularly preferred. Specifically, tetrabutylammonium bromide and tetrabutylammonium iodide are preferred, and tetrabutylammonium iodide is particularly preferred.

[0019] <Reaction process> In the present invention, a phosphonic acid diester as a starting material, hydrogen peroxide as an oxidizing agent, a halide salt as a catalyst, and, if necessary, an organic solvent are mixed together to oxidize the phosphonic acid diester and produce a phosphoric acid diester. The order in which the materials are mixed is not particularly limited. For example, a phosphonic acid diester, a catalyst, and an organic solvent are mixed, the mixture is adjusted to a predetermined reaction temperature, and then hydrogen peroxide is added little by little to the mixture, whereby a phosphoric acid diester can be produced from the phosphonic acid diester. According to the production method of the present invention, a phosphoric acid diester can be produced selectively in a short reaction time with a high phosphoric acid esterification rate. The amount of by-products, such as a phosphoric acid monoester and a phosphoric acid triester, produced is small. Furthermore, since the production method of the present invention uses a phosphonic acid diester as a starting material, it is possible to avoid the use of phosphorus oxychloride, which is difficult to handle due to its irritating properties and fuming properties. In the production method of the present invention, it is preferable to optimize the reaction conditions from the viewpoint of increasing the phosphate conversion rate and the selectivity for the phosphate diester. Specifically, it is preferable to select the reaction conditions as follows. The amount of hydrogen peroxide used is usually 0.5 to 4.0 in molar ratio relative to the phosphonic acid diester, preferably 1.0 to 3.0. By using an amount of hydrogen peroxide of 0.5 or more, the yield of the phosphoric acid diester is improved. Furthermore, by using an amount of hydrogen peroxide of 4.0 or less, the selectivity of the phosphoric acid diester is improved. From this viewpoint, the amount of hydrogen peroxide used is more preferably 1.1 to 2.0 in molar ratio, and even more preferably 1.1 to 1.8. The amount of the halide salt used is preferably 0.001 to 1.0 in terms of molar ratio relative to the phosphonic acid diester. By using an amount of the halide salt of 0.001 or more, the phosphoric acid esterification rate and the selectivity for the phosphoric acid diester are improved. Furthermore, by using an amount of the halide salt of 1.0 or less, the color of the resulting phosphoric acid diester is improved. From this viewpoint, the amount of the halide salt used is more preferably 0.005 to 0.5 in terms of molar ratio, and even more preferably 0.008 to 0.05. The reaction temperature is not particularly limited, and the reaction can usually be carried out within a range of 0°C or higher and 100°C or lower. By setting the reaction temperature to 0°C or higher, a sufficient reaction rate can be ensured, and the reaction efficiency can be improved. Furthermore, by setting the reaction temperature to 100°C or lower, decomposition of the raw material phosphonic acid diester can be suppressed, and the phosphoric acid esterification rate and the phosphoric acid diester selectivity can be improved. From this viewpoint, the reaction temperature is more preferably 20 to 90°C, and even more preferably 30 to 80°C.

[0020] In addition, in the production method of the present invention, it is preferable to use an organic solvent in addition to the above-mentioned phosphonic acid diester, hydrogen peroxide, and halide salt in order to further improve reaction efficiency and safety. The type of organic solvent is not particularly limited, and one type may be used alone, or two or more types may be used in combination. Examples of the organic solvent include hydrocarbon solvents, alcohol solvents, ether solvents, ester solvents, ketone solvents, aromatic solvents, nitrile solvents, amide solvents, and chlorine solvents, among which hydrocarbon solvents, ether solvents, aromatic solvents, nitrile solvents, and amide solvents are preferred from the viewpoint of improving the reaction efficiency. Specific examples of the organic solvent include methylcyclohexane, tetrahydrofuran, toluene, acetonitrile, N,N-dimethylformamide, and N,N-dimethylacetamide, among which toluene, methylcyclohexane, and N,N-dimethylacetamide are preferred, and N,N-dimethylacetamide is more preferred. The amount of the organic solvent to be added to the reaction system is not particularly limited, but is usually 10 to 250 parts by mass relative to the phosphonic acid diester. From the viewpoint of improving the reaction efficiency and safety, the amount is preferably 30 to 150 parts by mass, more preferably 50 to 100 parts by mass relative to the phosphonic acid diester.

[0021] <Other processes> If it is desired to further improve the purity of the phosphoric acid diester obtained by the production method of the present invention, the purity can be increased by known purification methods such as recrystallization, distillation, drying, washing, etc., or the use of an adsorbent, etc. The phosphoric acid diester obtained by the production method of the present invention can be used in a wide range of applications, such as detergents, emulsifiers, antistatic agents, textile oils, metal extractants, lubricating oil additives, rust inhibitors, flame retardants, and electrolyte materials for electrochemical devices. [Example]

[0022] The present invention will be described in more detail below with reference to examples and comparative examples. [Example 1] A 1 L four-neck flask equipped with a thermometer, nitrogen inlet tube, stirrer, and condenser was charged with 330.0 g (1.07 mol) of di-2-ethylhexyl phosphonate with a purity of 99 mol% as the starting material, 205.2 g of N,N-dimethylacetamide as the solvent, and 1.8 g (0.011 mol) of potassium iodide as the catalyst, and then heated to 75°C with stirring. After reaching 75°C, 187.2 g (1.93 mol) of 35% hydrogen peroxide solution as an oxidant was added dropwise over 1 hour, and the mixture was stirred at 75°C for 2 hours. After stopping the stirring, the mixture was left to stand and the aqueous layer that separated into the lower layer was removed, followed by removing the methylcyclohexane at 150°C under reduced pressure. The reaction mixture was returned to room temperature, and 4.1 g (0.011 mol) of trioctylphosphine oxide, an internal standard, was added. 31 The phosphorylation rate, yield and selectivity of phosphoric acid diester were determined by P-NMR measurement using a nuclear magnetic resonance spectrometer. Below 31 The P-NMR measurement conditions are as follows: <Measurement conditions> Frequency: 400MHz Solvent: deuterated chloroform The above reaction is shown in the following formula (4): As shown in formula (4), the product is a mixture of a phosphoric acid monoester (M), a phosphoric acid diester (D), and a phosphoric acid triester (T).

[0023] [ka]

[0024] 31 The peak positions and integral values ​​of each of the phosphate esters M, D, and T and the internal standard trioctylphosphine oxide in P-NMR are shown below. Phosphate monoester (M): 2.60 ppm (integral value: 5) Phosphate diester (D): 2.10 ppm (integral value: 88) Phosphate triester (T): 0.16 ppm (integral value: 2) Trioctylphosphine oxide: 53.82 ppm (integral value: 1) [Phosphate esterification rate] The phosphate esterification rate represents the total value of the phosphate monoester (M), the phosphate diester (D) and the phosphate triester (T). 31 The integral value of P-NMR was set to 1, and the integral values ​​of the phosphate monoester (M), phosphate diester (D), and phosphate triester (T) were summed to calculate the phosphate esterification rate. [Phosphate diester yield] The yield (%) of the phosphoric acid diester was determined as the integral value of the phosphoric acid diester in the same manner as described above. [Phosphate diester selectivity] The selectivity (%) of the phosphoric acid diester is the ratio of the yield of the phosphoric acid diester to the phosphoric acid esterification rate, and was calculated by the following formula. Phosphate diester selectivity (%) = (phosphate diester yield / phosphate esterification rate) × 100

[0025] [Evaluation criteria] (1) Phosphate esterification rate ◎: Phosphate esterification rate is 90 mol% or more Good: Phosphate esterification rate is 70 mol% or more and less than 90 mol% ×: Phosphate esterification rate is less than 70 mol% (2) Phosphate diester yield ◎: The yield of phosphoric acid diester is 75 mol% or more Good: The yield of phosphoric acid diester is 60 mol% or more and less than 75 mol% ×: The yield of the phosphoric acid diester is less than 60 mol% (3) Phosphate diester selectivity ◎: Selectivity for phosphate diester is 90% or more 〇: Selectivity of phosphate diester is 75% or more but less than 90% ×: Selectivity of phosphate diester is less than 75%

[0026] [Examples 2 to 10 and Comparative Examples 1 to 4] The phosphoric acid esterification rate, and the yield and selectivity of phosphoric acid diester were determined in the same manner as in Example 1, except that the type and amount of oxidizing agent, type of catalyst, type of solvent, reaction temperature, and reaction time in Example 1 were changed according to Tables 1 and 2. The results are shown in Tables 1 and 2.

[0027] Comparative Example 5 A 1 L four-neck flask equipped with a thermometer, a nitrogen inlet tube, a stirrer, and a condenser was charged with 180.8 g (1.18 mol) of phosphorus oxychloride and heated to 35°C. After the temperature reached 35°C, 307.0 g (2.36 mol) of 2-ethylhexanol was added dropwise over 1 hour, and the mixture was stirred at 35°C for 8 hours. Then, 180.0 g (11.79 mol) of ion-exchanged water was added, and the mixture was stirred at 75°C for 4 hours. After stopping the stirring, the mixture was left to stand and the aqueous layer that separated into the lower layer was removed, followed by dehydration at 80°C under reduced pressure. Thereafter, the phosphate conversion rate, and the yield and selectivity of the phosphate diester were determined in the same manner as in Example 1. The results are shown in Table 2.

[0028] [Table 1]

[0029] [Table 2]

[0030] (Explanation of abbreviations) H2O2: Hydrogen peroxide (reagent, Kishida Chemical Co., Ltd.) KI: Potassium iodide (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) TBAB: Tetrabutylammonium bromide (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) KBr: Potassium bromide (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) MCH: Methylcyclohexane (reagent, Fujifilm Wako Pure Chemical Industries, Ltd.) DMAc: N,N-dimethylacetamide (reagent, Tokyo Chemical Industry Co., Ltd.) tBuOOtBu: t-butyl peroxide CHP: Cumene hydroperoxide TBAOac: tetrabutylammonium acetate

[0031] [result] As is clear from the results shown in Table 1, Examples 1 to 10 show that the phosphoric acid diester can be produced with high selectivity and high phosphoric acid esterification rate. As shown in Table 2, in Comparative Example 1, di-t-butyl peroxide was used as the oxidizing agent instead of hydrogen peroxide, and therefore the phosphoric acid esterification rate was extremely low (both the yield and selectivity were zero). In Comparative Example 2, cumene hydroperoxide was used as the oxidizing agent instead of hydrogen peroxide, and therefore the selectivity of the phosphoric acid diester was high, but the phosphoric acid esterification rate was moderate. In Comparative Example 3, tetrabutylammonium acetate was used as the catalyst instead of a halide salt, and therefore the phosphate conversion rate and the selectivity for phosphoric diester were low. In Comparative Example 4, the phosphate conversion rate and the selectivity for phosphoric diester were low because no catalyst was used. In Comparative Example 5, unlike the production method of the present invention, a production method using phosphorus oxychloride as a raw material was used, and therefore the time required for the reaction was long and the phosphate conversion rate was high, but the phosphate diester selectivity was moderate.

Claims

1. A method for producing a phosphoric acid diester, comprising reacting a phosphonic acid diester with hydrogen peroxide in the presence of a halide salt.

2. 2. The method for producing a phosphoric acid diester according to claim 1, wherein the halide salt is at least one selected from the group consisting of alkali metals, alkaline earth metals, metals of Groups 4 to 14 of the Periodic Table, and tetraalkylammonium halide salts.

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