WO1999019252A1

WO1999019252A1 - Method for separating phosphorus oxyacids, organophosphates and organophosphites

Info

Publication number: WO1999019252A1
Application number: PCT/US1998/021182
Authority: WO
Inventors: Company Monsanto; Yinong Ma
Original assignee: Monsanto Co
Priority date: 1997-10-09
Filing date: 1998-10-08
Publication date: 1999-04-22
Also published as: AU9689598A

Abstract

Methods for the preparation and separation of phosphorus oxyacids, organophosphates, and organophosphites are disclosed. Phosphorus species are obtained from the contact of elemental phosphorus, oxygen, and an alcohol. Purification is effected by differential ester hydrolysis and biphasic partitioning. The disclosed methods are performed under mild conditions, and avoid the use of halogenated materials.

Description

METHOD FOR SEPARATING PHOSPHORUS OXYACIDS. ORGANOPHOSPHATES AND ORGANOPHOSPHITES

BACKGROUND OF THE INVENTION

Phosphorus-containing compounds such as oxyacids of phosphorus, organophosphates and organophosphites are important precursors for the synthesis of other phosphorus species, which have numerous applications, for example, in herbicides, insecticides, fertilizers, flame retardants and plasticizers. The syntheses of such oxyacids of phosphorus, organophosphates and organophosphites have commonly used a halogen derivative of phosphorus, such as PC1₃ or POCl₃, as a starting material. Nevertheless, because these derivatives are themselves prepared from elemental phosphorus, there would be an economic advantage to prepare oxyacids of phosphorus, organophosphates and organophosphites directly from elemental phosphorus. Such direct preparations could also provide environmental benefits by avoiding the use of halogen-containing phosphorus starting materials and production of their halogen-containing byproducts. White phosphorus, the elemental phosphorus allotrope also referred to as yellow phosphorus or tetraphosphorus (P₄), is a potential starting point for the synthesis of a variety of phosphorus species. The tetrahedral structure of white phosphorus contains six phosphorus-phosphorus bonds and can provide a large number of reactive species having an intermediate existence in phosphorus reactions. The competition of these reactive species for the organic reactants at hand, however, may give complex reaction mixtures with individual products appearing in low yields.

Variations of a reaction for the aerobic oxidation of white phosphorus in the presence of alcohols have been disclosed, although the reported processes have not provided an economical procedure for obtaining desirable phosphorus-containing compounds with high yield and purity. For example, Ernsberger et al. (U.S. Patent No. 2,661,364) refers to a process for preparing dialkylphosphite wherein oxygen is introduced into a mixture of small cut-up pieces of white phosphorus and a monomeric, saturated alcohol exemplified by ethanol, n-butanol, n-propanol, isopropanol and n-hexanol. Ernsberger et al. indicates that the various reaction products are isolated from the reaction mixture by conventional techniques, e.g., removal of phosphorous acid by aqueous extraction and recovery of alcohol by distillation. Ernsberger et al. further states that some dialkylphosphites are too unstable to be separated by distillation and may be used without isolation from the reaction mixture.

Kellerman et al. (British Patent No. 1,112,976) refers to a process for producing organophosphorus compounds involving the reaction of white phosphorus, oxygen and a hydrocarbon compound containing at least one phenolic hydroxy group, a hydrocarbon compound containing more than one alcoholic hydroxy group, or a hydrocarbon containing a thiol group, to produce a mixture of esters of oxyacids of phosphorus in which the overall oxidation state of phosphorus is substantially 4. The Kellerman et al. process may take place in an inert organic solvent. The product of the Kellerman et al. process is a viscous mixture of non-isolated esters of oxyacids of phosphorus.

Okamoto et al., Yukagaku 19(10):968-72 (1970) (translated) refers to a process for preparing diethylphosphite by reacting white phosphorus, oxygen and ethanol, after which excess ethanol is removed by vacuum distillation to obtain a 43% yield of diethylphosphite. The reaction was also performed in water and carbon tetrachloride. There is a need in the art for a process of economically separating mixtures of phosphorus species including oxyacids of phosphorus, organophosphates and organophosphites. There is a further need in the art for a process that directly converts white phosphorus to oxyacids of phosphorus, organophosphates and/or organophosphites, wherein the various desired products are obtained in high yield and purity and with economical isolation techniques. There is also a need for such a process that is environmentally safe, preferably by using lower levels of solvents and avoiding the use of halogen-containing starting materials.

SUMMARY OF THE INVENTION This invention relates to a process for economically separating mixtures of phosphorus species including oxyacids of phosphorus, organophosphates and organophosphites. The inventive separation method isolates various desired products from such mixtures based on the rate difference in hydrolysis of organophosphorus species of different oxidation states as well as the efficient partitioning of phosphorus species of different polarities in a biphasic system. This invention further relates to a process for preparing the mixture of oxyacids of phosphorus, organophosphates and organophosphites from white phosphorus, and subsequently separating the various phosphorus species in the product mixture. More particularly, this invention is directed to a method for directly converting white phosphorus to a product mixture of oxyacids of phosphorus, organophosphates and/or organophosphites and subsequently separating those products to economically obtain desired products in high yield and purity. The process involves contacting white phosphorus, oxygen and an alcohol under mild conditions and isolating desired products from the reaction mixture based on the rate difference in hydrolysis of organophosphorus species of different oxidation states as well as the efficient partitioning of phosphorus species of different polarities in a biphasic system.

The process according to the invention preferably offers significant advantages over other syntheses for phosphorus-containing compounds based on white phosphorus in that it provides an economical route to phosphorus oxyacids, organophosphates and organophosphites with high selectivity and yield. The process according to the invention is also environmentally safe.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS The invention is broadly directed to a process for economically separating mixtures of phosphorus species including at least two or more oxyacids of phosphorus, organophosphates and organophosphites. The separation method isolates various desired products from such mixtures based on the rate difference in hydrolysis of organophosphorus species of different oxidation states as well as the efficient partitioning of phosphorus species of different polarities in a biphasic system.

The inventive process is particularly applicable for the separation of a product mixture obtained by contacting white phosphorus, alcohol, and oxygen, which produces various phosphorus species including oxyacids of phosphorus, organophosphates and/or organophosphites. In a preferred embodiment, the reaction system for such an oxidation reaction contains no catalyst, and in a further preferred embodiment, the reaction system contains no additional solvent (beyond the alcohol reactant, which also enhances solubility and provides a reaction medium). A variety of reaction mechanisms can occur in such a reaction system to produce a mixture of products including phosphorous acid (H₃PO₃), phosphoric acid (H₃PO₄), hypophosphorous acid (H₃PO₂), mono-, di- and tri- alkylphosphites and phosphates.

The oxidation reaction generally proceeds by charging a reaction vessel with an alcohol and white phosphorus. If the reaction is to take place at a temperature above the melting point of white phosphorus, the reaction mixture is generally heated to the melting point of white phosphorus (approximately 44°C) prior to the addition of oxygen, after which external heating is removed due to the exothermic nature of the oxidation reaction. If the reaction is to take place at a temperature below the melting point of white phosphorus, a highly dispersive form of white phosphorus solid, also referred to as white phosphorus "sand," is prepared before the introduction of oxygen. The oxidation reaction is then started by supplying the reaction mixture with oxygen, after which the rate of oxygen addition can be used to control the reaction rate and temperature. The oxidation reaction is generally complete when essentially all of the white phosphorus is consumed, which is indicated by a temperature decrease and the disappearance of white phosphorus.

The white phosphorus reactant is generally available in the form of solid pieces or particles. For example, white phosphorus is commercially available from Aldrich

Chemical Co. in the form of yellow sticks having 99% purity stored in water. The white phosphorus may be prepared for addition to the reaction mixture by cutting the white phosphorus into smaller pieces and/or by washing, for example, in acetone and/or the alcohol reagent. The white phosphorus may be added to the reaction mixture all at once or over a period of time. The white phosphorus may also be prepared in molten form by heating to a temperature above its melting point of approximately 44.1°C, for example, to a temperature of about 45°C to about 47°C, and the molten phosphorus may be pumped directly into the reaction mixture. Alternatively, the white phosphorus may be in a highly dispersive solid form referred to as white phosphorus "sand," which may be prepared by heating the white phosphorus in the alcohol and/or a cosolvent to a temperature above the melting point of white phosphorus, after which the molten white phosphorus-containing mixture is vigorously stirred as it is cooled below the melting point of white phosphorus. In one embodiment according to the invention, no cosolvent is added to the reaction mixture. Alternatively, a cosolvent is added to the reaction mixture that is suitable for enhancing the solubility of the reactants or providing a medium for the reaction. For example, the cosolvent may be selected from arenes, including benzene, toluene and xylene; alkanes, including pentane, hexane, isooctane and dodecane; carbon tetrachloride; carbon disulfide or mixtures thereof. More preferably, the cosolvent is toluene. The reaction system may optionally contain a water component, e.g., in the alcohol reagent, which may affect the composition of the product mixture. The alcohol reagent is generally any alcohol or mixture of alcohols suitable for participating in the inventive process for producing phosphite or phosphate esters. In a preferred embodiment, the alcohol is represented by the formula R-OH, wherein R is an alkyl group having from 1 to 30 carbon atoms, more preferably 1 to 18 carbon atoms and most preferably 1 to 10 carbon atoms. For example, the alcohol may be methanol, ethanol, propanol, butanol, isobutanol, hexanol, octanol, 2-ethylhexanol, nonyl alcohol or mixtures thereof. More preferably, the alcohol is hexanol. The alcohol may be further selected from benzyl alcohol and glycols. The alcohol may be a primary, secondary or tertiary alcohol, although primary alcohols are preferred. In the event that a higher alcohol is used, a sufficient amount of cosolvent is preferably added, if necessary, to dissolve the alcohol and the copper compound. In a further preferred embodiment, the alcohol is immiscible with water, particularly in processes that proceed to phosphorous acid. The alcohol is preferably added to the reaction mixture in at least stoichiometric amount to white phosphorous, and more preferably is added in excess of the stoichiometric amount such that alcohol is also available as a solvent and medium for the reaction.

Oxygen may be added to the reaction mixture in the form of O₂ or air and is preferably delivered by flow or static pressure. The rate of oxygen consumption is generally related to the molar ratio of copper compound to white phosphorus. Oxygen is delivered at a sufficient rate to initiate and maintain an ongoing reaction as can be determined by one of ordinary skill in the art. The pressure of the reaction system is preferably within the range from atmospheric pressure up to the pressure at which the reaction system can proceed safely, e.g., without entering explosion conditions for oxygen, and more preferably ranges from 1-100 psig.

The reaction time will vary widely, depending upon the type and amount of reactants and any cosolvent, the reaction conditions such as temperature and pressure and the desired product. The reaction is generally considered complete when the white phosphorus is substantially all consumed. The overall reaction time is preferably under 8 hours, and more preferably in the range of 1.0 to 5.0 hours, and most preferably in the range of 1.0 to 3.5 hours. The oxidation reaction can take place within a wide range of temperatures as the reaction can take place above or below the melting point of white phosphorus. The reaction temperature is preferably within a range where the reaction can proceed safely and without causing undesirable reactions, preferably in the range of 25-100°C, more preferably in the range of 30-80°C, and most preferably in the range of 30-40°C. For oxidation reactions taking place at a temperature below the melting point of white phosphorus, the white phosphorus is preferably prepared as white phosphorus sand. The pressure of the reaction system is preferably within the range from atmospheric pressure up to the pressure at which the reaction system can proceed safely, e.g., without entering explosion conditions for oxygen, and more preferably ranges from 1 -3 atm.

In a preferred embodiment, the oxidation reaction is run under conditions that suppress the creation of white smoke, which can adversely affect the product distribution, particularly the selectivity of lower oxidation species by causing over oxidation due to a significant level of vapor phase reaction. The white smoke can potentially occur in both reactions run above the melting point of white phosphorus (i.e., the molten state) and below the melting point of white phosphorus (e.g., the highly dispersive solid state referred to as sand). Smoking conditions are generally avoided by using lower alcohols (methanol, ethanol and isopropanol) or by using higher alcohols (butanol, pentanol and hexanol) in a wet condition. In the event that smoking occurs, the mixture can be settled into a non-smoking condition by cooling for a few hours.

The product of the step of contacting white phosphorus, alcohol, and oxygen is preferably a mixture of oxyacids of phosphorus, organophosphates and organophosphites, thereby representing a range of oxidation states. For example, a typical completed reaction mixture may contain about 75% of P(III) species, about 15% of P(V) species, about 4% of P(I) species and 6% of higher aggregates of P(V) and P(III) species. The state of oxidation of phosphorus indicates the number of bonds of a phosphorus atom in the molecule linked with more electronegative elements such as oxygen or halogen diminished by the number of bonds thereof linked with more electropositive elements, e.g., hydrogen, sodium or carbon. Thus the state of oxidation of phosphorous acid (H₃PO₃) is three, and phosphorous acid and its esters are referred to as P(III) species. The products of the step of aerobic oxidation of white phosphorus may then be processed by the inventive separation procedure to economically obtain desired products in high yield and purity. In the separation process according to the invention, a mixture of phosphorus- containing compounds, which may include oxyacids of phosphorus, organophosphates and organophosphites, is separated by a procedure that utilizes the rate difference in hydrolysis of organophosphorus species of different oxidation states as well as the efficient partitioning of phosphorus species of different polarities in a biphasic system.

In a preferred embodiment, the inventive separation process is applied to the product mixture from the oxidation reaction of white phosphorus, alcohol and oxygen as described above. The components of that product mixture may be isolated in the form that they exist in the product mixture or they may be converted into another compound in the course of the isolation procedure. For example, a P(I) oxidation product can be either converted to P(III) in situ to increase the overall yield of P(III) or it can be isolated in high purity as a by-product of the process. In another embodiment, the P(III) species may be completely esterified followed by reduced pressure distillation to afford a high yield of isolated dialkylphosphite.

In a first embodiment, the inventive separation process involves (i) azeotropic distillation to place all P(III) species in ester form, (ii) aqueous extraction to remove water- soluble phosphorus species, such as H₃PO₄ and the P(I) species, and (iii) hydrolysis to convert phosphites to phosphorous acid. This embodiment takes advantage of efficient partitioning of phosphorus species of different polarities in a biphasic system as well as the rate difference in hydrolysis of organophosphorus species of different oxidation states.

The mixture of phosphorus species is first subjected to azeotropic distillation, preferably with addition of a solvent such as benzene or toluene depending on the desired boiling point. The azeotropic distillation will break up the aggregates of various phosphorus species and convert residual phosphorous acid into its ester forms so that all of the P(III) species will become less soluble in water. The azeotropic distillation is generally stopped after phosphorous acid (H₃PO₃) is converted to its ester forms, i.e., HP(=O)(OR₂) and HP(=O)(OR)(OH). Subsequent extraction of the resulting mixture with water will then remove water- soluble phosphorus species, such as phosphoric acid (H₃PO₄) and the P(I) species. This takes advantage of both slow esterification of phosphoric acid under the azeotropic conditions and fast hydrolysis of H₂P(=O)(0R) under the extraction conditions. The organic layer containing P(III) and P(V) esters is then hydrolyzed with water under reflux conditions. Because of the significant differences in hydrolysis rates between the phosphite and phosphate esters, conditions have been identified where phosphite esters are nearly quantitatively hydrolyzed to phosphorous acid (H₃PO₃) while phosphate esters remain intact in the organic phase. The aqueous layer is then separated from the hydrolysis mixture. The combined aqueous portions can contain up to 99% of phosphorus content in the form of H₃PO₃ by P NMR spectroscopy. The organic layer contains mostly phosphate esters with a small residual amount of unhydrolyzed HP(=O)(OR)(OH). In a second embodiment, the inventive separation process involves (i) contacting the phosphorus species mixture with oxygen to convert P(I) to P(III), (ii) azeotropic distillation to convert acid species to an ester form, (iii) steam distillation to hydrolyze P(III) esters to H₃PO₃, and (iv) aqueous extraction to remove H₃PO₃. To avoid the step of separating P(I) from the mixture, air or oxygen is first bubbled through the mixture to convert P(I) to P(III). The resulting mixture then undergoes azeotropic esterification until the free phosphoric acid is no longer detected.

The resulting esterification mixture is then subjected to steam distillation, wherein only the hydrolysis of P(III) esters is effected and the composition of the phosphate esters remains unchanged. Upon completion of hydrolysis of the P(III) esters to H₃PO₃, the aqueous layer is combined with one aqueous wash of the organic layer to give an aqueous solution of H₃PO₃. The organic layer contains mainly phosphate esters. By converting P(I) to P(III), the procedure not only eliminates the need for separating P(I) species from the reaction mixture but can also increase the yield of P(III). Using steam distillation in the hydrolysis stage combined two tasks into a single step, i.e., alcohol recovery and hydrolysis. Removing alcohol from the ester mixture also improves the efficiency of the hydrolysis.

The following examples are included to demonstrate preferred embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventors to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention. EXAMPLES Example 1.

This example illustrates a process of isolating high purity phosphorous acid (H3PO3) (aq.) and phosphate esters from a reaction mixture of aerobic oxidation of white phosphorus (P₄) in hexanol.

A 250 ml Fisher-Porter vessel containing 20.0 g of P4 (0.646 mol) and 160 g anhydrous hexanol was mounted onto a reactor assembly. The system was purged with N2 and then heated to 45°C with a heat gun while stirring. Upon melting of P4, heating was stopped and a highly dispersive P4 sand was formed as the mixture was cooled to room temperature with stirring. Smoke was observed when oxygen was briefly admitted as the white phosphorus and alcohol suspension cooled to room temperature. Oxygen was reintroduced without white smoking after the mixture was allowed to stir for two hours at room temperature. The oxygen delivery pressure was set at 2.5 psi and the temperature control was set for 35°C. For efficient heat transfer, the Fisher-Porter reaction vessel was cooled via a water bath.

After 12 h, a clear solution resulted and oxidation was complete based on the 31p NMR spectrum. The resulting solution was mixed with 93.0 g hexanol and divided into two parts which were 46.6 and 53.4 wt% respectively. One portion (46.6 wt%) was subjected to reflux at 160°C with a Dean-Stark distillation set-up. During the first hour of reflux, air was bubbled through the mixture and it was followed by nitrogen bubbling for an additional 5 h of reflux. The resulting mixture was mixed with 300 ml water and subjected to steam distillation-hydrolysis at 105°C. After 7 hours, 1 10 ml hexanol was recovered and the residual two-phase mixture in the distillation flask was separated. The organic layer was washed with 50 ml water. The combined aqueous layer yielded 80.3% phosphorous acid with 98.3% phosphorus purity by 31p NMR spectrum based calibration with a known amount of authentic phenylphosphonic acid. The organic layer contained 19.2% of total phosphorus added based on calibration with a known amount of authentic diethylphosphite, mostly in the form of dihexylphosphate (70%) and monohexylphosphate (20%). The second part of the oxidation mixture (53.4 wt%) was worked up similarly and gave a phosphorous acid yield of 80.0 % with a purity 99.2% based on phosphorus. Example 2.

This example illustrates the process described in Example 1 with an alcohol reactant of pentanol.

An oxidation run was carried out as in Example 1 with 20.34 g of P4 and 140 g of pentanol instead of hexanol. The workup was similar to that of Example 1 except that the azeotropic reflux was at 150°C instead of 160°C as in Example 1. The yield of phosphorous acid was 78.2% and purity based on phosphorus was 96.6%. Distillation residue weighed 42.3 g. Example 3. This example illustrates the process described in Example 1 with an alcohol reactant of butanol.

An oxidation run was carried out as in Example 1 with a one time P4 charge of

10.44 g and 107 g of butanol instead of hexanol. The workup was similar to that of Example 1 except that the azeotropic reflux was conducted at 130°C instead of 160°C. The purity of the isolated phosphorous acid was 96.8% and yield was 80.1%. Example 4.

This example illustrates a process of isolating high purity phosphorous acid (H3PO3) (aq.), hypophosphorous acid H3PO2 (aq.) and phosphate esters from a reaction mixture of aerobic oxidation of white phosphorus in an alcoholic solvent. A 120 ml Fisher-Porter vessel containing 10.51 g of P4 and 80.0 g of water saturated hexanol (6.3% wt) was mounted onto the reactor assembly. The system was purged with N2 and then heated to 45°C with a heat gun while stirring. Upon melting of

P4, heating was discontinued and the mixture was stirred vigorously to produce a highly dispersed suspension. When the temperature of the mixture dropped below 40°C, P4 solidified forming a highly dispersive P4 sand. On cooling to room temperature, oxygen was introduced at 4.5 psi and the temperature control was set at 35°C. As the reaction temperature reached 35°C, cooling via water bath was introduced to maintain the reaction temperature slightly below 35°C. A clear solution resulted after 4 hours and the mixture was allowed to cool to room temperature. The resulting solution was mixed with an additional 80 g hexanol. The mixture was subjected to azeotropic reflux at 160°C for 12 hours with the aid of a nitrogen stripper. After the azeotropic distillation mixture was cooled to room temperature, it was washed with 2 x 25 ml water. The isolated aqueous layer contained H3PO2 and 3.5% of total phosphorus. The organic layer was charged with 350 ml water and subjected to steam distillation-hydrolysis at 105°C. After 7 hours, 150 g hexanol was recovered. The distillation residue was separated and the organic layer was washed with 2 x 25 ml water. The combined aqueous layer contained 73.4% total phosphorus and H3PO3 was higher than 99% of the phosphorus in solution. The organic layer was a mixture of dihexylphosphate (50%) and monohexylphosphate (50%), which weighed 21.76 g.

Example 5.

This example illustrates a process of isolating dialkylphosphite and phosphate esters from a reaction mixture of aerobic oxidation of white phosphorus in an alcoholic solvent. A resulting oxidation mixture obtained similarly to that of Example 1 from 5.08 g of P4 and 81 g of wet hexanol (1.3% water) was subjected to azeotropic reflux at 160°C for 7.5 hours with an additional 80 g hexanol. During the first three hours of azeotropic distillation, air was used as the purge gas. The resulting mixture was then distilled initially under 0.5 mm Hg at 52°C to remove hexanol (110 g). Dihexylphosphite was subsequently distilled at 60-80°C under 50 μm Hg and yielded 30.1 g (73.5%). The distillation residue weighed 9.76 g which contained mostly the P(V) esters. Example 6.

This example illustrates a process of isolating an aqueous mixture of H3PO3,

H3PO2 and H3PO4 from a reaction mixture of aerobic oxidation of white phosphorus in an alcoholic solvent.

A 120 ml Fisher-Porter vessel containing 5.44 g P4 (0.176 mol) and 49.44 g anhydrous ethanol was mounted onto the above mentioned reactor assembly. The system was purged with N2 and then heated to 45 °C with an oil bath while stirring. Upon melting of P4, heating was removed and the mixture was stirred vigorously to produce a highly dispersed suspension. As soon as the P4 sand was formed (38°C), oxygen was introduced at 1.5 psi and the temperature control was set at 52°C maximum. The reaction was complete in 5 h. The resulting mixture was treated with 50 ml of water and subjected to fractional distillation using a 10 cm helices packed column. After 9 h, the distillation temperature reached 100°C, the aqueous distillation residue contained 75.4 % H3PO3, 6.8

% H₂P(=O)(OH) and 17.8 % P(V) species.

Table 1 summarizes the results of reaction run with this procedure.

Table 1. Compositions of the hydrolysis mixtures from the oxidation reactions using ethanol and isopropanol as solvents.

Pr' = isopropanol Et = ethanol

Example 7.

The following table illustrates the effect of water and reaction temperature on the percentage of hypophosphorous species in a reaction mixture of aerobic oxidation of white phosphorus in an alcoholic solvent.

Oxidation reaction was carried out similarly to that of Example 4 for the 35°C experiments using hexanol of varying percentages of water (0 to 6.3%). The reaction time of the oxidation with a charge of 5 g P4 and 80 g hexanol was about 2.5 h. For the 65°C experiments, the oxidation was carried out similarly but with air cooling and the reaction time was about 2 h. The P(I) percentage was obtained by integrating both the

H₂P(=O)(OH) and H₂P(=O)(Ohexyl) chemical shifts in the ³¹P NMR spectra. Table 2. P(I)% vs water in hexanol and oxidation temperature.

While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the process described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention.

Claims

1. A process for separating a mixture of phosphorus species containing two or more P(I), P(III) and P(V) species comprising:

(a) esterifying the mixture by azeotropic distillation;

(b) removing water soluble phosphorus species from the esterified mixture by aqueous extraction; and

(c) hydrolyzing the mixture to selectively convert phosphites to phosphorous acid.

2. A process for separating a mixture of phosphorus species containing two or more P(I), P(III) and P(V) species comprising:

(a) contacting the mixture with oxygen to convert P(I) species to P(III) species;

(b) esterifying the mixture by azeotropic distillation; (c) hydrolyzing the mixture to selectively convert phosphites to phosphorous acid; and (d) removing phosphorous acid from the mixture by aqueous extraction.

3. A process for producing phosphorus oxyacids, organophosphates and organophosphites comprising:

(a) contacting white phosphorus, oxygen, and an alcohol to produce a product mixture comprising a mixture of phosphorus species containing at least two or more P(I), P(III) and P(V) species;

(b) esterifying the product mixture by azeotropic distillation; (c) removing water soluble phosphorus species from the esterified mixture by aqueous extraction; and (d) hydrolyzing the resulting mixture to selectively convert phosphites to phosphorous acid.

4. A process for producing phosphorus oxyacids, organophosphates and organophosphites comprising:

(a) contacting white phosphorus, oxygen, and an alcohol to produce a product mixture comprising a mixture of phosphorus species containing at least one or more P(I), P(III) and P(V) species;

(b) contacting the product mixture with oxygen to convert P(I) species to P(III) species;

(c) esterifying the resulting mixture by azeotropic distillation;

(d) hydrolyzing the esterified mixture to selectively convert phosphites to phosphorous acid; and

(e) removing phosphorous acid from the mixture by aqueous extraction.

5. The process as in claims 3 or 4, wherein the alcohol is represented by the formula R-OH, wherein R is an alkyl group having from 1 to 10 carbon atoms.

6. The process as in claims 3 or 4, wherein the alcohol is hexanol.

7. A process as in claims 3 or 4, wherein the contacting step takes place in a reaction mixture further comprising a cosolvent.

8. A process as in claim 7, wherein the cosolvent is benzene, toluene, carbon tetrachloride, xylene, hexane, isooctane, chloroform or mixtures thereof.

9. A process as in claims 3 or 4, wherein the reaction temperature is in the range of 25-100┬░C.

10. A process as in claim 9, wherein the reaction temperature is in the range of 30- 40┬░C.

11. A process as in claims 3 or 4, wherein the pressure of the reaction system is in the range of 1 to 3 atmospheres.

12. A process as in claims 3 or 4, wherein the white phosphorus is in the form of molten white phosphorus.

13. A process as in claims 3 or 4, wherein the white phosphorus is in the form of white phosphorus sand.

14. A process as in claims 3 or 4, wherein the conversion of white phosphorus in step (a) is at least 98%.