RU2670105C1 - Method for obtaining mixed triaryl phosphates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a process for the preparation of mixed triarylphosphites and can be used in the chemical industry. In the proposed method, phenol is reacted with phosphoric acid, taken in a molar ratio of 2:1, when the temperature reaches 175–250 °C for 6.5–7 h in an inert gas atmosphere with continuous distillation of the azeotropic phenol-water mixture. P-tert-butylphenol is introduced into the reaction product in a 2:1 molar ratio to the phosphoric acid taken and the reaction mixture is kept at the same temperature for 6–7 hours. Water released in the process as an azeotropic phenol-water mixture is separated by continuous distillation. Desired product is obtained which is a mixture of mixed triaryl phosphate I–IV:triphenyl phosphate (I), p-tert-butylphenyl diphenyl phosphate (II), di(p-tert-butylphenyl)phenylphosphate (III), tri(p-tert-butylphenyl)phosphate (IV).

EFFECT: new efficient method for obtaining mixed total (neutral) triaryl phosphates is proposed.

1 cl, 1 tbl, 5 ex

Description

The invention relates to organic synthesis and relates to a method for producing mixed neutral triarylphosphates used as flame retardant oils and hydraulic fluids.

Triaryl phosphates are used as lubricants, hydraulic fluids that are highly resistant to oxidation and thermal decomposition. Triaryl phosphates are used as the base components of flame retardant oils. The most popular modern basic principles of fire-resistant oils are represented by mixed triaryl phosphate compositions in which aryl groups contain alkyl substituents, in particular, tert-butyl ones. Compositions are represented by neutral full esters of phosphoric acid with phenol and para-tert-butylphenol, including mixed. The operational properties of such compositions depend on their composition.

A known method for producing aryl esters of phosphoric acid is the interaction of phosphorus oxychloride with phenols substituted by phenols or a mixture thereof. The esterification of phosphorus oxychloride is carried out in the presence of a catalyst, for example anhydrous magnesium chloride, when heated from 80 ° C to 170 ° C. The process is easy, but complicated by the formation of products of incomplete esterification of phosphorus oxychloride, the separation of which requires multiple fractionation (K.A. Andrianov, L.M. Khananashvili. Technology of organoelement monomers and polymers. M., Chemistry, p. 333, 1973).

Known methods for producing mixed triaryl phosphates by the interaction of phosphorus oxychloride with phenols of the general formula:

where X = H, tert-C ₄ H ₉ .

At the first stage, phosphorus oxychloride is alkylated with tert-butylphenol to form mono- and dichlorophosphates, then phenol is introduced and a mixture of medium phosphates is obtained with a yield of ~ 92-94 wt%. As the catalyst used MgCl ₂ , TiCl ₄ (US 6242631 B1, publ. 05.06.2001).

According to the method described in US 4087386, publ. 05/02/1978, mixed triaryl phosphates are prepared by adding phosphorus oxychloride to a mixture of phenol and tert-butyl phenol under catalysis with magnesium chloride in a yield of 94 wt%.

A common disadvantage of the above methods for producing mixed phosphates based on phosphorus oxychloride is the formation of hydrogen chloride as a conjugated reaction product, the removal of which requires additional technological operations. The presence of phosphorus oxychloride and hydrogen chloride necessitates solving the problems of equipment corrosion and environmental pollution. In addition, phosphorus oxychloride is a highly hydrolyzable highly toxic substance with toxicological hazard class I (MPC 0.4 mg / m ³ ), work with which is allowed only at specialized chemical enterprises. Therefore, it is of practical interest to use alternative sources of phosphorus, in particular, low toxic and available phosphoric acid, to obtain triaryl phosphates.

A known method of producing tricresyl and triphenyl phosphate by esterification, respectively, of cresols and phenol with 85% phosphoric acid. In the case of phenol, the process is carried out by heating the reaction mixture from 115 ° C to 300 ° C with continuous distillation of the water-phenol azeotrope on a distillation column, partial separation of water in the separator and return of the organic phase to column irrigation. Triphenylphosphate formed upon completion of the reaction is isolated by distillation in vacuo with a yield of 59 wt%. The pour point of the obtained product is 44 ° C, which is lower than the known (48-50 ° C). Triphenyl phosphate is washed with a 5% aqueous sodium hydroxide solution, after which the yield inevitably falls (US 2805240 A, publ. 03.09.1957).

The implementation of the method is also not without drawbacks. In particular, the densities of phenol and cresols are slightly higher than the density of water, which, without the use of an additional solvent, makes it difficult to separate the distillate in the separator and causes technical difficulties associated with supplying the lower organic phase for irrigation. In this case, the organic phase of phenols contains a significant amount of water (solubility in phenol is about 30 mass%, in cresol 10-15 mass%), which returns to the reaction system with an irrigation flow and slows down the process, shifting the reaction equilibrium towards the starting materials and thereby worsening yield of the final product. In addition, individual triphenylphosphate and tricresylphosphates without the addition of heavier phenolic substituents are unsuitable for use as a flame-retardant oil, and in the case of less "acidic" xylenols and other alkyl phenols suitable for this purpose, the reaction is extremely slow.

A known method of producing triarylphosphates by esterification of xylenols with 85% phosphoric acid. As a catalyst, triarylphosphites are used in an amount of 4-5% by weight of the phenol introduced. The reaction is carried out with a gradual increase in temperature from 200 to 300 ° C. The crude trixylene phenate is isolated by vacuum distillation. A commercial product is obtained after washing the raw material with alkali with a yield of 79-80 wt% on the reacted xylenol (SU 176895, publ. 01.12.1965).

The disadvantage of the described method is the additional stage of washing the crude product with alkali, as well as the use as a catalyst of a significant amount of expensive, inaccessible and prone to oxidation of organophosphorus compounds - trisilenylphosphite. Another disadvantage of this method is the fact that the high toxicity of xylenol-based triarylphosphates substantially inhibits their use as a flame-retardant oil. In addition, their production is not provided with a reproducible raw material base.

The closest technical solution to the proposed method is a method for producing triarylphosphates by the interaction of phosphoric acid with various hydroxyaryl compounds, namely, cresol or isopropylphenol. The method is carried out in the presence of a hard cation taken as a catalyst. Such a cation can be a cation selected from the list: B ³⁺ , Cd ²⁺ , Sb ⁵⁺ , Mg ²⁺ , Mn ²⁺ , Cu ²⁺ , Zn ²⁺ , Co ²⁺ , Li ⁺ , Fe ³⁺ , Al ³⁺ and taken in an amount of 1-5 mass%. The process of esterification of phosphoric acid with phenols is carried out with stirring and continuous removal of the reaction water by azeotropic distillation with phenol. An inert hydrocarbon solvent is used to facilitate the removal of water from the vapor and condensed phases. The resulting triaryl phosphate is isolated by distillation under reduced pressure, and the intermediate and catalyst are recycled to the reaction zone. In the process, 100% phosphoric acid is used, the reaction is carried out at a temperature of 240-255 ° C for 5.75 hours. By reaction with cresols, the composition of the reaction mixture is obtained, mass%: monocresyl phosphate - 3, dicresyl phosphate - 30, tricresyl phosphate - 27, unreacted cresol - 34. A similar reaction with ortho-isopropylphenol gives 43.2% by weight of tri-isopropylphenylphosphate and 56.8% by weight of di-isopropylphenylphosphate (US 5097056 A, publ. 17.03. 1992).

The disadvantages of the method are: a low yield of triaryl phosphate (43-56 mass% for cresol); low selectivity of the formation of the target product (56-61 wt% when reacting with cresol); the presence of incomplete (acidic) phosphates in the composition of the reaction products in amounts commensurate with the amount of the target product; the use of 100% phosphoric acid, which requires a special stage of concentration of acid of common use (87%).

The technical problem solved by the invention is to develop a method for producing mixed triarylphosphates, eliminating the disadvantages of the closest analogue, and simplifying the method for their preparation.

The technical result from the implementation of the invention is to simplify the method by eliminating the catalyst and using phosphoric acid of common use (87%), increasing the selectivity of the formation of mixed complete (neutral) triaryl phosphates and the yield of the target product.

The technical result from the implementation of the invention is achieved by the fact that they carry out the interaction of phenol with phosphoric acid, taken in a molar ratio of 2: 1, when the temperature reaches 175-250 ° C for 6.5-7 hours in an inert gas atmosphere with continuous distillation of the azeotropic phenol mixture water, para-tert-butylphenol is introduced in the molar ratio 2: 1 to the taken phosphoric acid and the reaction mixture is kept at the same temperature for 6-7 hours, the water released in the process in the form of an azeotropic phenol-water mixture is separated no explicit distillation and obtain the target product, which is a mixture of mixed triaryl phosphates I-IV: triphenyl phosphate (I), p-tert-butylphenyl diphenyl phosphate (II), di (p-tert-butylphenyl) phenylphosphate (III), tri (p-tert-butylphenyl ) phosphate (IV):

These signs are very significant.

The organization of the process with the indicated sequence of introducing the components avoids the destruction of para-tert-butylphenol by the dealkylation reaction proceeding at elevated temperatures. The participation of unsubstituted phenol in the reaction with phosphoric acid at the initial stage of the process reduces the acidity of the reaction medium, which prevents the undesirable side process of dealkylation of alkyl phenol to phenol. Other sequences for introducing phenolic components lead, as shown in the examples, to an undesirable enrichment of the mixture of mixed triaryl phosphates with triphenyl phosphate.

The process is controlled by the amount of released water, taking into account the water introduced with H ₃ PO ₄ , the conversion of "anhydrous" phosphoric acid is calculated by the amount of released reaction water. The amount and composition of the resulting mixed triaryl phosphates is determined by gas-liquid chromatography. Selectivity for mixed triaryl phosphates (I-IV) is calculated based on the material balance of the process with respect to water, the amount and composition of the target esters. The reaction water and water contained in phosphoric acid are removed as an azeotrope, the phenol itself being the azeotroping agent, which, after separation of the water, is returned to the reaction mixture. The reaction proceeds through the sequential formation of mono-, di- and triesters of phosphoric acid. The formation of primary and secondary esters (acidic esters) occurs quite quickly, after which the equilibrium concentration of water becomes very low (0.01-0.1 mass%), and for the further course of the reaction it is necessary to ensure such an effective water removal that its concentration is lower equilibrium. The solubility of phenol in water is about 30 mass%, therefore, after separation of the azeotrope, the direct return of phenol to the reaction mixture is not able to provide a low concentration of water.

The problem of water removal in the present invention is solved as follows. The vapor phase of the reaction mixture, which is a mixture of phenol and water, enters the distillation column. In the upper part of the column, the phenol-water azeotrope is separated, which is in contact with a vapor of a hydrophobic solvent that dissolves phenol well but does not dissolve in water. A mixture of solvent vapor and the phenol-water azeotrope enters the device for condensation, cooling, and separation — the Dean-Stark nozzle with a reflux condenser. After cooling, water exfoliates in a separator from a mixture of phenol with a solvent and is discharged in the form of a lower layer, and the organic layer freed from water (phenol and solvent) is fed to the top of the column to be irrigated, where the solvent evaporates and again enters the separator together with azeotrope vapors. Due to the use of a hydrophobic solvent, the organic phase entering the column irrigation practically does not contain water.

As a solvent for delaminating the phenol-water azeotrope, organic compounds that are not soluble in water, poorly soluble in water and well soluble phenol can be used. The boiling point of the solvent should be lower than the boiling point of phenol (180 ° C) and more preferably comparable to the boiling point of the phenol-water azeotrope (99.6 ° C, water content 91 mass%) or slightly lower. In this case, the density of the solvent should be lower than the density of water to ensure its technologically convenient separation in the form of a lower layer. Aromatic hydrocarbons of a series of benzene with the number of carbon atoms up to 9, simple, esters and ketones with the number of carbon atoms from 5 to 8, as well as a number of other compounds satisfy all these requirements.

The implementation of the present invention is illustrated by the following examples, which do not limit the scope of the claims presented in the claims.

Example 1

Into a three-necked flask equipped with a thermocouple for measuring the temperature of the cube, a dropping funnel for introducing the phenol melt and a packed distillation column (∅20 × 200 mm, spiral nozzle ∅3.5 × 3 mm from wire ∅0.5 mm steel 12X18H10T), on top of which a Dean-Stark nozzle was installed with a cooling jacket and a reflux condenser; 20.05 g (0.21 mol) of phenol and 12.00 g (7.1 ml, 0.107 mol of H ₃ PO ₄ ) of a solution of 87% phosphoric acid were placed. The Dean-Stark nozzle is filled with 25 ml of a mixture of methyl isobutyl ketone-toluene in a volume ratio of 7: 3. The reaction mixture was heated under argon for 6.5 hours, continuously dropping a phenol-water azeotropic mixture through a column and separating water in a Dean-Stark nozzle. The temperature of the cube spontaneously rises from 175 to 250 ° C. Then, 32.00 g (0.213 mol) of para-tert-butylphenol was introduced into the reaction mixture and kept at the same temperature for 6 hours. A total of 4.7 ml of water is separated. The reaction results in the formation of mixed triaryl phosphates with the indicated phenols, the composition of which is given in the table. The selectivity of the formation of complete mixed triaryl phosphates (I-IV) is 79 mol%, the conversion based on anhydrous H ₃ PO ₄ 82 mol%. The yield of the target product is 64.8 mol%, the content of triphenylphosphate does not exceed 30.7 mol%.

Example 2

The process is carried out as described in example 1, but para-tert-butylphenol is introduced in an amount of 17.60 g (0.117 mol). During the reaction, 5 ml of water is separated, which amounts to a conversion of H ₃ PO _{4 of} 60 mol% and a selectivity of formation of complete mixed triarylphosphs of 81 mol%. The yield of the target product is 48.6 mol%. The example shows that a decrease in the amount of introduced para-tert-butylphenol leads to a decrease in conversion and yield, as well as an increase in the content of triphenyl phosphate in the composition of the resulting composition of mixed triaryl phosphates.

Example 3

The process is carried out as described in example 1, but with the following sequence of administration of phenolic components: 1) para-tert-butylphenol, 2) phenol. The amount of water released as a result of the reaction is 3.7 ml, which corresponds to the conversion of H ₃ PO ₄ 65 mol% and the selectivity of the formation of complete mixed triaryl phosphates 100 mol%. The yield of the target product is 65 mol%. The full ester composition is predominantly represented by triphenylphosphate, which is associated with the undesired process of dealkylation (degradation) of para-tert-butylphenol.

Example 4 (comparison example).

The process is carried out as described in example 3, but with simultaneous loading into the reaction zone of phenolic components as in the closest analogue. When compared with example 1, there is an increase in the content of triphenylphosphate associated with the occurrence of an undesirable process of dealkylation (degradation) of para-tert-butylphenol. The yield of the target product is 86 mol%.

Example 5 (comparison example).

The process is carried out as described in example 4, but with a reduced reaction time. Shortening the contact time leads to a decrease in the content of triphenylphosphate in the product, which indicates a lower degree of degradation of alkyl substituted phenol. The yield of the target product is 41.5 mol%.

Claims (2)

A method for producing mixed triaryl phosphates, involving the interaction of phenol with phosphoric acid, taken in a molar ratio of 2: 1, when a temperature of 175-250 ° C is reached for 6.5-7 hours in an inert gas atmosphere with continuous distillation of the phenol-water azeotropic mixture, the resulting reaction product is introduced para-tert-butylphenol in a molar ratio of 2: 1 to the taken phosphoric acid and the reaction mixture is kept at the same temperature for 6-7 hours, the water released in the process as an azeotropic phenol-water mixture is separated by continuous distillation and get the target product, which is a mixture of mixed triaryl phosphates I-IV: triphenyl phosphate (I), p-tert-butyl phenyl diphenyl phosphate (II), di (p-tert-butyl phenyl) phenyl phosphate (III), tri (p-tert-butyl phenyl) phosphate (Iv):