JP7462294B2 - Method for producing phosphoric acid ester compound - Google Patents

Description

The present invention relates to a method for esterifying phosphoric acid compounds such as orthophosphoric acid.

Phosphate esters (PO(OR) ₃ ), which are one type of organic phosphorus compound, are chemical products with diverse physical properties depending on the structure of the organic group R in the ester moiety, and are used for various applications such as flame retardants, plasticizers, and stabilizers for various resins. With the recent technological innovations in the automobile and electronic parts industries, the performance required of resins has been increasing year by year, and there is a strong demand for the development of phosphate ester compounds as resin additives and improvements in their production methods.

A typical industrial method for producing phosphate esters involves first producing phosphorus trichloride (PCl ₃ ) by reacting yellow phosphorus (P ₄ ) with chlorine, then oxidizing this with oxygen to give phosphorus oxychloride (POCl ₃ ), which is then treated with an alcohol to obtain the desired phosphate ester (Patent Documents 1-4, Non-Patent Document 1).

However, yellow phosphorus, phosphorus trichloride, and phosphorus oxychloride are all designated as toxic substances by law, and are compounds that are difficult to handle due to their spontaneous combustion, irritation, and smoke generation, and therefore a safer method for synthesizing phosphate esters is desired. In particular, orthophosphoric acid (PO(OH) ₃ ), which is commonly used as a fertilizer, is an inexpensive and easily available phosphorus compound, and if it can be converted into a phosphate ester using this as a starting material, it will be a method that is superior to conventional methods. Although a few examples of catalysts effective for the dehydration esterification reaction of orthophosphoric acid and alcohol have been found (Non-Patent Documents 2-4), only monoesters can be produced, and there are almost no examples of methods for producing triesters (PO(OR) ₃ ), which are more useful as industrial products.

Regarding the esterification of phosphonic acid (XPO(OH) ₂ ) (X is an organic group R or hydrogen H) or phosphinic acid ( _X2PO (OH)) containing an organic group R or hydrogen H on the phosphorus atom, several prior examples have been reported, such as a method using orthosilicate esters (Non-Patent Documents 5 and 6), a method using silica chloride (Non-Patent Document 7), a method of alkylation in the presence of a base (Non-Patent Document 8), or an air oxidative esterification reaction using a copper catalyst (Non-Patent Document 9). However, no method has been reported so far for producing phosphate esters directly using orthophosphoric acid, which has a higher acidity, as a raw material.

Japanese Patent Application Laid-Open No. 10-310593 JP 2000-095786 A JP 2000-128890 A JP 2000-351789 A

"Encyclopedia of Phosphorus" edited by Hisao Ohtake et al., Asakura Publishing (2017) K. Ishihara et al. Org. Lett. (2005) Vol.7, p.1999-2002 K. Ishihara et al. Green. Chem. (2007) Vol.9, p.1166-1169 K. Ishihara et al. Angew. Chem. Int. Ed. (2007) Vol.46, p.1423-1426 J. L. Montchamp et al. Org. Lett. (2000) Vol.2, p.3341-3344 J. L. Montchamp et al. J. Organomet. Chem. (2002) Vol.643-644, p.154-163 M. P. Kaushik et al. Tetrahedron Lett. (2006), Vol.47, p.3107-3109 S. F. Yin et al. Tetrahedron (2014) Vol.70, p.9057-9063 S. F. Yin et al. ACS Catal. (2015) Vol.5, p.537-543

The objective of the present invention is to provide a method for directly producing a corresponding phosphate ester compound using a phosphoric acid compound selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid, and their anhydrides as a raw material.

As a result of intensive research to solve the above problems, the inventors discovered that by using an aqueous solution of a phosphoric acid compound selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid, and their anhydrides and reacting it with a siloxane compound or an organic silane compound, particularly an orthosilicate ester, by heating, the corresponding phosphoric acid ester can be efficiently produced without the need for a catalyst, and thus completed the present invention.

The present invention relates to the following methods for producing phosphoric ester compounds (1) to (9).
(1) A method for producing a phosphoric acid ester compound, comprising reacting a phosphoric acid compound selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid, and anhydrides thereof with an organosilane or siloxane compound having an alkoxy group or an aryloxy group.
(2) A method for producing the phosphoric acid ester compound according to (1) above, which is carried out under heating conditions in the absence of a catalyst.
(3) The method for producing a phosphoric acid ester compound according to (2) above, wherein the reaction temperature under the heating conditions is 100 to 250° C.
(4) The method for producing a phosphoric acid ester compound according to any one of (1) to (3) above, wherein the phosphoric acid compound is used as an aqueous solution of the phosphoric acid compound.
(5) A method for producing a phosphoric acid ester compound according to any one of (1) to (4) above, which is carried out in an organic solvent in which the phosphoric acid compound is soluble.
(6) The method for producing a phosphoric acid ester compound according to any one of (1) to (5) above, wherein the molar ratio of the phosphoric acid compound to the organosilane or siloxane compound having an alkoxy group or an aryloxy group is within the range of 1:1 to 10.
(7) The method for producing a phosphoric acid ester compound according to any one of (1) to (6) above, wherein the phosphoric acid compound is orthophosphoric acid.
(8) The method for producing a phosphoric acid ester compound according to any one of (1) to (7) above, wherein the organosilane having an alkoxy group or an aryloxy group is a tetraalkyl orthosilicate or a tetraaryl orthosilicate.

According to the present invention, it is possible to produce the corresponding phosphate ester compound in a one-step reaction without using a catalyst, using a phosphorus compound selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid, and their anhydrides, which are stable compounds with excellent handling properties, as a raw material, without using yellow phosphorus, which is pyrophoric and toxic, as a phosphorus source.

In particular, if orthophosphoric acid is used as a raw material, it is an industrially excellent method that can stably and inexpensively produce high-added-value phosphate esters that are used for a variety of applications, such as flame retardants, plasticizers, and stabilizers for various resins, from a stable and inexpensive aqueous solution of orthophosphoric acid.

The present invention is characterized by producing a phosphate ester compound in a one-step reaction from an inorganic or organic phosphoric acid compound and an organic silane or siloxane compound having an alkoxy group or an aryloxy group.

The inorganic or organic phosphoric acid compound used as a starting material in the production method of the present invention may be one selected from orthophosphoric acid, phosphonic acid, phosphinic acid, or anhydrides thereof. These anhydrides include pyrophosphoric acid, which is an anhydride of orthophosphoric acid, an anhydride of phosphonic acid, and an anhydride of phosphinic acid.
Corresponding phosphoric acid ester compounds can be produced from any phosphoric acid compound, and when orthophosphoric acid is used as a raw material, a mixture of at least two or more of the three types of orthophosphoric acid mono-, di-, and triesters is obtained as a product. Similarly, when phosphonic acid is used as a raw material, a mixture of phosphonic acid mono- and diesters is obtained as a product, and when phosphinic acid is used as a raw material, a phosphinic acid monoester is obtained as a product.
Orthophosphoric acid is preferably used because it is easily available and inexpensive as a raw material, but it is possible to produce the corresponding phosphate ester using any phosphoric acid compound as a raw material.

（式中、Ｘは、有機基Ｒまたは水素Ｈであり、Ｒは、炭素数１～２０の直鎖状または分岐したアルキル基またはアリール基である。）

(In the formula, X is an organic group R or hydrogen H, and R is a linear or branched alkyl group or aryl group having 1 to 20 carbon atoms.)

The reactivity of the phosphoric acid compound as a raw material increases when it is dissolved in an organic solvent. It is also possible to use an aqueous solution close to the saturation concentration of the phosphoric acid compound; for example, when using orthophosphoric acid, it is recommended to use an 85% aqueous solution. The above reaction proceeds simply by mixing the phosphoric acid compound with an organosilane having an alkoxy or aryloxy group, but various additives such as a catalyst (metallic Lewis acid or organic base) or a dehydrating agent (molecular sieve or silica gel) may also be present as necessary.

In order to produce a phosphoric acid ester from a phosphoric acid compound as a raw material in a one-step reaction, an organic silane or siloxane compound having an alkoxy group or an aryloxy group is used. Examples of organic silanes having an alkoxy group include tetraalkyl orthosilicates, monoalkyltrialkoxysilanes, and dialkyldialkoxysilanes, in which the alkyl group is a linear or branched alkyl group having 1 to 20 carbon atoms. The alkyl group may contain a heteroatom. In particular, among tetraalkyl orthosilicates, tetramethyl orthosilicate, tetraethyl orthosilicate, tetrapropyl orthosilicate, tetrabutyl orthosilicate, and tetrapentyl orthosilicate, in which the alkyl group has 1 to 5 carbon atoms, are preferably used.
As the organic silane having an aryloxy group, tetraaryl orthosilicate is preferred, and as the siloxane compound, an organic siloxane compound in which R is an alkyl group or an aryl group, particularly hexaalkoxydisiloxane, is preferred.

When using tetraalkyl orthosilicate, the molar ratio of its use is preferably in the range of about 1 to 10 parts per phosphate compound. When using a phosphoric acid compound in an aqueous solution, the tetraalkyl orthosilicate reacts with water to partially turn into silicon dioxide (silica), so it is best to use an excess of 3 or more parts tetraalkyl orthosilicate per phosphate compound.

In order to increase the reactivity of the reaction of the present invention, it is preferable to use an organic solvent. Any organic solvent that dissolves the phosphoric acid compound is acceptable, but dimethylformamide (N,N-dimethylformamide: DMF) or dimethylacetamide (N,N-dimethylacetamide: DMAc) is particularly preferable.

The reaction of the present invention is preferably carried out, for example, by adding appropriate amounts of an organic solvent and a tetraalkyl orthosilicate to an aqueous solution of a phosphoric acid compound in a reaction vessel under an air atmosphere, and then heating and stirring the sealed reaction mixture.
The reaction temperature under the heating conditions of the present invention may be about 100°C to 250°C, and more preferably in the range of 150°C to 200°C.
The reaction time can be any time depending on the production scale, the amount of the phosphate ester produced, etc., but can be about 5 to 24 hours.

The resulting reaction product is cooled at room temperature, washed and neutralized with water, an alkaline aqueous solution or an acidic aqueous solution as necessary, and then purified to produce the final product. The purification process can be carried out using vacuum distillation, silica gel column chromatography, etc.

An example of the production method of the present invention will be described below using examples, but the present invention is not limited to these examples. The percentage of yield indicates mole percent.

Example 1
In an air atmosphere, 57.6 mg (0.5 mmol) of an 85 wt % aqueous orthophosphoric acid solution was added to 0.50 mL of each of the solvents shown in Table 1 and 0.30 mL (2.0 mmol) of tetraethyl orthosilicate in a screw-cap test tube, and the mixture was then sealed and heated with stirring at 150° C. or 200° C. After 15 hours, the reaction mixture was returned to room temperature, and 53.3 μL of dimethyl methylphosphonate as an internal standard was added. The ³¹ P NMR was measured to determine the yield of the desired hydrosilylated product.

The above reaction is represented by the following formula (4). Of the products, 1 is orthophosphoric acid monoethyl ester, 2 is orthophosphoric acid diethyl ester, and 3 is orthophosphoric acid monoethyl ester, and a mixture of two or more of these was produced by the reaction. The yields of each of the phosphate esters 1 to 3 are shown in Table 1 below.

Example 2
As shown in the following formula (5), the organic solvent was dimethylformamide (N,N-dimethylformamide: DMF), the tetraalkyl orthosilicate was tetramethyl orthosilicate, tetraethyl orthosilicate, tetrabutyl orthosilicate, tetraisopropyl orthosilicate, or tetrapropyl orthosilicate, respectively, and the reaction temperature was 180° C., and the rest of the reaction was carried out under the same conditions and method as in Example 1. The yields of each of the phosphoric acid esters 4 to 6 produced as a mixture were determined, and the results are shown in Table 2 below.

Example 3
As shown in the following formula (6), the reaction was carried out under the same conditions and by the same method as in Example 2, except that the starting phosphoric acid compound was phenylphosphonic acid and the tetraalkyl orthosilicate was tetraethyl orthosilicate. The yields of phenylphosphonic acid monoethyl ester (7) and phenylphosphonic acid diethyl ester (8) produced as a mixture were determined. The results are shown in Table 3 below.

Example 4
As shown in the following formula (7), except that the starting phosphoric acid compound was diphenylphosphinic acid, the reaction was carried out under the same conditions and by the same method as in Example 3, and the yield of the produced diphenylphosphinic acid monoethyl ester 9 was determined. The results are shown in Table 4 below.

The process for producing a phosphate ester compound of the present invention is an excellent process which can use various phosphoric acid compounds as starting materials and can produce a phosphate ester compound in a one-step reaction without the use of a catalyst.
In addition, there are concerns about the future depletion of phosphorus resources worldwide, and it has become an important issue to recycle phosphorus resources discharged from industry, such as sludge and incineration ash. Since most of these recycled phosphorus resources are ultimately recovered in the form of orthophosphoric acid aqueous solution or metal phosphates, a method for directly converting these phosphate compounds into high-added-value phosphate esters may become an important technology in the future for sustainable development.

Claims (7)

A method for producing a phosphoric acid ester compound , comprising reacting a phosphoric acid compound selected from the group consisting of orthophosphoric acid, orthophosphoric acid anhydride, phosphonic acid, phosphonic acid anhydride, and a di-substituted phosphinic acid represented by formula (A) with an organosilane or siloxane compound having an alkoxy group or an aryloxy group at 150 to 250°C .
(In the formula, each X is independently a linear or branched alkyl group or an aryl group having 1 to 20 carbon atoms.) The method for producing the phosphoric ester compound according to claim 1, which is carried out in the absence of a catalyst . The method for producing a phosphoric acid ester compound according to claim 1 or 2 , wherein the phosphoric acid compound is used as an aqueous solution of the phosphoric acid compound. 4. The process for producing a phosphoric acid ester compound according to claim 1, which is carried out in an organic solvent in which the phosphoric acid compound is soluble. 5. The method for producing a phosphoric acid ester compound according to claim 1, wherein the molar ratio of the phosphoric acid compound to the organosilane or siloxane compound having an alkoxy group or an aryloxy group is in the range of 1:1 to 10. The method for producing a phosphoric acid ester compound according to any one of claims 1 to 5 , wherein the phosphoric acid compound is orthophosphoric acid. 7. The method for producing a phosphoric acid ester compound according to claim 1, wherein the organosilane having an alkoxy group or an aryloxy group is a tetraalkyl orthosilicate or a tetraaryl orthosilicate.