WO2013077989A1

WO2013077989A1 - Process for preparation of aluminum salt of phosphonic acid ester

Info

Publication number: WO2013077989A1
Application number: PCT/US2012/063310
Authority: WO
Inventors: Joseph Zilberman; Julia Lee; Sergei V. Levchik; Yankai YANG
Original assignee: Icl-Ip America Inc.
Priority date: 2011-11-22
Filing date: 2012-11-02
Publication date: 2013-05-30

Abstract

There is provided herein a process for the preparation of aluminum salts of phosphonic acid esters by reacting phosphonic acid diesters with aluminum hydroxide in the presence of a catalyst. The catalyst is selected from the group consisting of a phase transfer catalyst, a thermally stable tertiary amine having a boiling point higher than about 140°C, a thermally stable tertiary phosphine having a boiling point higher than 140°C and combinations thereof. The aluminum phosphonates prepared can be used for making flame retarded thermoplastic polymers.

Description

PROCESS FOR PREPARATION OF ALUMINUM SALT OF PHOSPHONIC ACID ESTER

This international application claims priority under 35 U.S.C.§ 119(e) to U.S. provisional application number 61/562,594 filed on November 22, 2011.

Field of the invention

This invention relates to a novel process for the preparation of aluminum salts of phosphonic acid esters by reacting phosphonic acid diesters with aluminum hydroxide in the presence of a catalyst.

Background of the invention

Most of the known methods for preparing aluminum salts of phosphonic acid esters are based on the use of phosphonic acid diesters as a starting material.

Further some of these methods describe the direct reaction of aluminum metal, in the form of aluminum foil with a phosphonic dialkyl ester. This reaction requires prolonged heating at reflux, and in the course of the reaction hazardous by-products such as carbon monoxide, lower alkanes, and lower dialkyl ethers are formed depending on the phosphonate employed.

In addition, some methods disclose processes according to which aluminum phosphonate salts can be obtained by reacting the corresponding phosphonic dialkyl esters with anhydrous aluminum chloride or an aluminum alkoxide, e.g. aluminum iso-propoxide. However, these processes result in undesired by-products such as methyl chloride, ethyl chloride or other alkyl chlorides, and dialkyl ethers. These by-products cannot be recycled to the process and are to be incinerated. In addition, aluminum alkoxides are relatively expensive and difficult to handle chemicals.

In another method, an alkali salt of phosphonic acid ester prepared for example by reacting anhydrous phosphonic diester with an alkali metal can further be reacted in water medium with a water soluble aluminum salt (e.g A1C1₃ or A1₂(S0₄)₃) to precipitate a water insoluble aluminum phosphonate salt. This process consists of two chemical stages, requires water washing of the aluminum phosphonate salt in order to remove sodium chloride or sodium sulfate and produces large amount of aqueous waste.

Furthermore, some methods require the use of commercially unavailable monoalkyl phosphonic acids as a sole starting material for making aluminum phosphonate salts by the reaction with aluminum hydroxide (hereinafter abbreviated as ATH) in a water-organic solvent mixture. A disadvantage of this process is a large amount of aqueous and organic waste and the need to recover the organic solvent.

One more method discloses the preparation of aluminum salt of methyl methylphosphonic acid by the reaction of dimethyl methylphosphonate with a finely divided form of ATH whose average particle size has to be below 2 microns in order to make its reaction with dimethyl methylphosphonate faster, even though the reaction time is still relatively long. Furthermore, the reaction does not go to completion even with this very fine ATH. Unreacted ATH remains in the final aluminum phosphonate and therefore limits its application, because of the lower thermal stability of ATH. Such ATH consisting of very fine particles, is much more expensive compared to a variety of other coarser, but much cheaper grades of this product.

Summary of the invention

There is therefore a need for a process for the preparation of aluminum salts of phosphonic acid esters, which avoids the aforementioned disadvantages, can be easily implemented in the industry, proceeds within a relatively short reaction time, is based on cheap and available commercial raw materials, and provides the final aluminum phosphonate salts in high yield and purity.

The present inventors herein have unexpectedly discovered a process for the preparation of aluminum salts of phosphonic acid esters in a quantitative yield and with excellent purity, by the reaction between phosphonic acid diester and chemically non-active aluminum hydroxide in the presence of a catalyst, owing to which the time of the reaction is shortened significantly. The present invention provides a process for the preparation of aluminum phosphonate salts of the formula (I)

wherein:

R¹ and R² are each a linear or branched alkyl group having 1 to 10 carbon atoms, a linear or branched alkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 5 or 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 11 carbon atoms, a heterocyclic group having one or more of O, N and S as hetero atoms, R and R being unsubstituted or substituted by one or more halogen, hydroxyl, amino, alkoxy, carboxy or combinations of these groups; and, R¹ and R² are each specifically an ethyl, butyl,

hydroxymethyl, phenyl, benzyl, allyl, vinyl or cyclohexyl group.

There is provided herein, in another embodiment, a process comprising reacting aluminum hydroxide with phosphonic acid diester in the presence of a catalyst.

The aluminum phosphonates herein possess good hydrolytic and thermal stability and are useful as flame retardants in thermoplastic and thermosetting resins. The present invention further provides fire retarded polymeric and polymer-containing compositions comprising said aluminum salts of phosphonic acid esters.

Detailed description of preferred embodiments

There is provided herein a new process for the preparation of aluminum salts of phosphonic acid esters by reacting a phosphonic acid diester with alumina trihydroxide (ATH) in the presence of an effective amount of a catalyst. The aluminum phosphonate salts are produced by the process herein within a time period that is shorter than an equivalent process that is conducted in the absence of a catalyst.

Typical reaction temperatures for the reaction between a phosphonic acid diester and ATH are between about 150 to about 250°C, preferably from about 180 to about 210°C.

According to a specific embodiment of the invention, the reaction can be carried out using an excess of phosphonic acid diester as the reaction solvent and dispersing medium for the ATH and the aluminum salt obtained. Alternatively, a suitable high boiling solvent inert under the process conditions can be employed, such as the non-limiting examples of trichlorobenzenes and high boiling petroleum ether. The phosphonic acid diester /ATH molar ratio for the reaction is in the range of 3 to 15, more specifically in the range of 5 to 10. Using a molar ratio greater than 15 is inexpedient due to the need to recycle the larger quantities of the phosphonic acid diester. When the phosphonic acid diester /aluminum hydroxide molar ratio is below 5 it becomes difficult to achieve complete conversion of the ATH due to the fact that the aluminum phosphonate salt produced forms a coat on the surface of the unreacted aluminum hydroxide and stops the reaction well before completion thereby producing an unsatisfactory yield.

Furthermore, stirring of reaction media containing a less than 5 times molar excess of a phosphonic acid diester becomes problematic towards the end of the reaction because a thick dispersion of the aluminum phosphonate salt is formed.

Surprisingly, the process of the invention does not produce any hazardous by-products. Unreacted phosphonic acid diester may be recycled to the process and the alcohol or phenol formed may be easily removed and even recycled for the preparation of the starting phosphonic diesters.

In one non-limiting embodiment the catalyst is selected from the group consisting of phase transfer catalysts (PTC), thermally stable tertiary amines having a boiling point higher than about 140°C and thermally stable phosphines having a boiling point higher than about 140°C and combinations thereof. In one another embodiment of the invention the PTC is a quarternary phosphonium salt described by the formula:

wherein each R¹, R², R³ and R⁴ independently is a hydrocarbyl or inertly substituted hydrocarbyl radical containing from 1 to about 16 carbon atoms, specifically from 1 to about 6 carbon atoms, Y is an anion and m is the valence of the anion. In one embodiment, Y is an anion selected from the group consisting of bromide, fluoride, chloride, iodide, acetate, acetate complex, acetate/acetic acid complex, phosphate, phosphate complex, hydrogen sulfate and hydroxide. In one embodiment, m can be 1, 2 or 3.

Specific quaternary phosphonium salts are selected from the group consisting of, but not limited to, for example, tetrabutylphosphonium chloride, tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, tetrabutylphosphonium acetate complex, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, tetraphenylphosphonium iodide,

ethyltriphenylphosphonium chloride, ethyltriphenylphosphonium bromide,

ethyltriphenylphosphonium iodide, ethyltriphenylphosphonium acetate complex,

ethyltriphenylphosphonium phosphate complex, n-propyltriphenylphosphonium chloride, n- propyltriphenylphosphonium bromide, propyltriphenylphosphonium iodide,

butyltriphenylphosphonium chloride, butyltriphenylphosphonium bromide,

butyltriphenylphosphonium iodide, ethyltri-p-tolylphosphonium acetate/acetic acid complex, ethyltriphenylphosphonium acetate/acetic acid complex, hexadecyltributylphosphonium bromide, or combinations thereof, and the like, as are described in U.S. Patent Nos. 5,208,317, 5, 109,099 and 4,981 ,926, the contents of each of which are incorporated herein by reference in their entirety. In yet another embodiment of the invention, the PTC is a quaternary ammonium salt. Specific catalysts among quaternary ammonium salts are selected from the group consisting of, but not limited to, for example, tetraethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium hydrogen sulfate, methyltrioctylammonium chloride, benzyl triethylammonium chloride and combinations thereof.

Tertiary amine catalysts, which are thermally stable under the conditions of the present process and which have a boiling point higher than about 140°C are those such as, for example, 2- or 4-(dimethylamino)pyridine and combinations thereof.

In another embodiment of this invention the tertiary amine catalysts are imidazole type compounds represented by the following general formula:

wherein each R¹, R², R³ and R⁴ independently is a hydrogen, or hydrocarbyl or inertly substituted hydrocarbyl radical, containing from 1 to about 16 carbon atoms, specifically from 1 to about 6 carbon atoms.

Specific imidazole type catalysts are selected from but not limited to the group 1 - methylimidazole; 2-methyl imidazole; 2-ethylimidazole, 2-propylimidazole, 2-butylirnidazole, 2- pentylimidazole, 2-hexylimidazole, 2-cyclohexylimidazole, 2-phenylimidazole, 2-nonyl-imidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenyl-4-methylimidazole, 1 -benzylimldazole, 1- ethyl-2-methylbenzimidazole, 2-methyl-5,6-benzimidazole, 1 -vinylimidazole, l-allyl-2- methylimidazole, 2-cyanoimidazole, 2-chloroimidazole, 2-bromoimidazole, l-(2-hydroxypropyl)- 2-methylimidazole, 2-phenyl-4,5-dimethylolimidazole, 2-phenyl-4-methyl-5- hydroxymethylimidazole, 2-cWoromemylbenzimidazole,2-hydroxyberizimidazole, 2-ethyl-4- memylimidazole; 2-cyclohexyl-4-memylimidazoles; 4-butyl-5-ethylimidazole; 2-butoxy-4-aUylimidazole; 2- carboe oxy-butylimidazole, 4-melhytimidazole; 2-octyI^hexylimidazole; 2-methyl-5-ethylirnidazole; 2- ethyl-4-(2-ethylamino)imidazole; 2-methyl-4-mercaptoethylimidazole; 2,5-cWoro-4-emylimidazole; and mixtures thereof. More specific are the 2-alkyl-substituted imidazoles; 2,5-chloro-4- ethylimidazole and mixtures thereof.

Phosphine catalysts, which are thermally stable under the conditions of the present process and which have a boiling point higher than about 140°C, can be those selected from the group consisting of triaryl phosphines, alkyl diaryl phosphines, dialkyl aryl phosphines, trialkyl phosphines, where the aryl is a substituted or ^substituted phenyl and the alkyl is a linear, branched or cyclic C4-C16 hydrocarbyl radical, and combinations thereof. One specific embodiment of a phosphine catalyst is triphenyl phosphine.

Other suitable catalysts will be easily recognized by the skilled person. Especially suitable catalysts are phase transfer catalysts such as ethyltriphenylphosphonium acetate, tetrabutylphosphonium bromide, tetrabutylammonium bromide, and catalysts such as 4- (dimethylamino)pyridine, triphenyl phosphine and 2-methylimidazole.

The concentration of the catalyst can be selected by those skilled in the art for specific reaction conditions. Illustrative - but non-limiting concentrations of the catalyst are in the range of about 0.1 to about 5 wt. % (weight percent) relative to the initial amount of aluminum hydroxide. The more specific concentrations of the catalyst are in the range of 1 to 3 wt. % relative to the initial amount of aluminum hydroxide.

The typical reaction time of the reaction described herein between ATH and a phosphonic acid diester is between about 3 to about 30 hours, more specifically between about 5 to about 20 hours.

The aluminum hydroxide used in the process herein can be any commercially available aluminum hydroxide with a mean particle size of below about 100 microns, preferably below 20 microns. Owing to the strong catalytic effect of the catalyst used there is no necessity to employ an expensive, finely divided aluminum hydroxide with an average particle size of less than 2 microns in order to finish the reaction within a reasonable time.

In one embodiment, the herein described amounts of phosphonic acid diester and aluminum hydroxide are mixed and the suspension formed is heated at the desired reaction temperature. In one embodiment, the catalyst can be added to the suspension of aluminum hydroxide in phosphonic acid diester prior to, or after, the desired temperature has been reached. The catalyst can also be fed in during the heating of the suspension of ATH in phosphonic acid diester. After the reaction has finished, the slurry is either evaporated to dryness under vacuum to give the final pure aluminum phosphonate salt or is first diluted with an organic solvent such as acetone or ethanol, followed by filtration, solvent washing and vacuum drying.

The aluminum phosphonate salts of the invention may be used in various physical forms depending on the polymer used and the desired properties. For instance, the aluminum phosphonate salts may be ground to a finely divided form of less than 2 microns to enable better dispersion into the polymer. As another example, the aluminum phosphonate salts produced can be incorporated into a polymer in a granular form when there is a desire to avoid the handling of powdered material. According to a specific embodiment of the invention, granular aluminum salts of phosphonic acid esters can have a mean particle size of between about 200 to about 3000 microns, specifically 200 to about 2000 microns

The process herein provides the aluminum salts of phosphonic acid esters in a good yield and with a high purity. The process herein produces the duminum salts of phosphonic acid esters in a yield of greater than about 90%, specifically greater than about 97%, based on ATH. The aluminum salts of phosphonic acid esters are produced with a purity greater than 90%, specifically greater than 95%.

The aluminum salts of phosphonic acid esters produced are thermally very stable, as is evidenced by their thermogravimetric analysis (TGA). According to the TGA, the aluminum phosphonate salts herein lose 5% of their initial weight at a temperature in excess of about 290°C and, specifically, within the range of from about 300°C to about 320°C. The high TGA temperatures which are characteristic of the aluminum salts of phosphonic acid esters herein are believed to be due to the very high purity of the products. Such a complete or almost complete conversion of the aluminum hydroxide in the process of the invention results directly from the use of the catalyst described herein.

There is also provided herein a method of producing a flame retarded thermoplastic polymer comprising blending at least one thermoplastic polymer and at least one aluminum salt of phosphonic acid ester as produced in the manner described herein. There is also provided a flame-retarded thermoplastic polymer containing aluminum phosphonate produced by such a method.

In one non-limiting embodiment, the flame-retarded thermoplastic polymer made by the process herein described can be a translucent or transparent polymer. The amount of an aluminum salt of phosphonic acid ester herein used in such a method of blending with a thermoplastic polymer can be in an amount effective as a flame-retardant as determined by those skilled in the art, but can in one non- limiting embodiment, be from about 3 to about 30 weight percent, specifically from about 10 to about 30 weight percent, said weight percent being based on the weight of the polymer. The optimal amount used depends on the nature of the polymer and the actual aluminum salt used. In one non-limiting embodiment the thermoplastic polymer can be selected from the group consisting of thermoplastic polyesters, nylons, polycarbonate and its blends, polystyrene and its copolymers, polyethylene and its copolymers, polypropylene and its copolymers and combinations thereof. The aluminum phosphonate salts herein can be used in any thermoplastic for which processing temperature doesn't exceed its decomposition temperature. For example, the aluminum phosphonate salts of the invention can be used as a flame retardant additive in thermoset resins, in textiles and in coating applications, amongst others.

In one embodiment, the process of the present invention does not require (i.e., is in the absence of ) a water and/or organic solvent mixture. An advantage of the inventive process herein is the avoidance of a large amount of aqueous and organic waste and the avoidance of the need to recover the organic solvent. A number of illustrative and non-limitative embodiments of the invention will now be described, with reference to the examples below.

EXAMPLES

Analytical methods

Thermogravimetric analysis (TGA) was used to test the thermal behavior of the products herein. The TGA values were obtained by the use of a TA Instruments Thermogravimetric Analyzer. Each sample was heated on a Pt pan from 25°C to 400-500°C at 10°C/min with a nitrogen flow of 50 ml/min.

Differential scanning calorimetry (DSC) was used to measure the melting temperature of crystalline products. The DSC measurements were obtained by using a TA Instruments DCS. A sample of 5-10 mg was sealed in an aluminum pan and heated from 25°C to 450°C at 10°C/min with a nitrogen flow of 50 ml/min

Scanning electron microscope (SEM) images showing the crystalline shape of the product were taken by a Scanning Electron Microscope Geol 5400.

The X-ray diffraction (XRD) "finger prints" were obtained by the use of an X-ray diffractometer Rigaku Ultima+. XRD was used to check the crystalline structure and the purity of the product of the invention.

ATH produces its own XRD "finger prints" as shown in Figure. 1. Thus, the presence or absence of these ATH "finger prints" on the XRD of the product would indicate the degree of the ATH conversion.

TGA of aluminum hydroxide

Figure 2 shows the TGA of aluminum hydroxide (ATH). ATH starts to decompose at about 220°C with a 2% wt. loss at 228°C. ATH ceased its main decomposition at about 280°C, with a weight loss of about 30%. Since ATH decomposes at a relatively lower temperature than an aluminum salt of a phosphonic acid ester, thermogravimetric analysis was selected to monitor the completion of the reaction of phosphonic acid diesters with ATH.

Setup of Littleford reactor

A Littleford Day, horizontal plow mixer, model DVT-22 or model DVT- 130 with one 4" multi-blade chopper, was fitted with a vertical reflux condenser on its exhaust port. The condenser was supplied with atmospheric steam as its heating/cooling medium. In-line, but after the reflux condenser was a recovery condenser supplied with cold water to condense any vapors from the mixer vessel. The exhaust line from the mixer was set up so that it could easily be switched to a vacuum line that would allow for the quick removal of dimethyl

methylphosphonate.

Comparative Example 1

14.76 Kg (118.96 mol) of dimethyl methylphosphonate and 1.157 Kg (14.83 mol) of Al(OH)₃ were charged into the DVT-22 vessel and it was sealed. The horizontal plow mixer was set to a speed of 165 rpm. The chopper was set to a speed of 3600 rpm. A 1.5 standard liters per minute (slpm) N₂ purge was applied to the inside of the vessel and it was heated to reflux temperature. The first droplets of condensate appeared in the recovery condenser sight glass at a temperature of 177°C. The oil temperature in the reactor jacket was 210°C for a period of 27 hours. At this time, vacuum was applied and the excess dimethyl methylphosphonate was removed. After cooling, 3.56 kg (63.90% yield) of a fine, white powder was removed from the vessel. Figure 3 shows the TGA of the final product. The two-step decomposition pattern indicates that considerable amount of the ATH was not converted to aluminum methyl methylphosphonate (AMMP). This unreacted ATH is responsible for low thermal stability of the final product.

The presence of unreacted ATH can be seen on the product XRD shown in Figure 4. Example 1

The same physical configuration, mixing speeds and N₂ purge were used as in

Comparative Example 1. 94.6 kg (762.9 mol) of dimethyl methylphosphonate and 7.41 Kg (95 mol) of Al(OH)₃ were added to the DVT-130 vessel. In addition, 55.6 g of the catalyst, tetra-n- butyl phosphonium bromide, was added. The vessel was sealed and heated to reflux

temperature. The first drops of condensate appeared in the recovery condenser sight glass at a temperature of 174°C. The reaction was run for 9 hours maintaining it at the reflux temperature. The oil temperature in the reactor jacket was 210°C. At the end of the reaction, vacuum was applied and the dimethyl methylphosphonate was removed. A total of 32.1 kg (95.5% yield) of product was removed from the vessel. The thermogravimetric analysis of the final product is shown in Figure 5. It had a very good thermal stability with a 2 % weight loss at 290°C. This AMMP product had a one-step weight loss, which is indicative of a good conversion. A DSC measurement was performed on this final product. No melting endotherm was detected before thermal decomposition. The only endotherm, with a minimum at 373°C, was attributed to thermal decomposition or volatilization. A scanning electron microscopy image of the AMMP obtained in this example is shown in Figure 6. It is seen that AMMP prepared by this method has distinctive needle shaped crystals.

Example 2

A 3-necked, 1 OOmL round-bottom flask, equipped with an overhead stirrer, a

thermometer and a distillation setup, was charged with diethyl ethylphosphonate (57.6 g, 0.347 mol), Al(OH)₃ (3.0 g, 0.385 mol) and tetrabutyl phosphonium bromide catalyst (0.13 g). The reaction mixture was heated to 180°C, under nitrogen, for 20 hours. The white suspension changed gradually from a free-flowing slurry to a thick but stirrable paste. Aliquots were taken every 2 hours to monitor the reaction progress. The aliquots were washed with acetone and filtered to afford a white powder, which was dried in a 100°C oven and then sent to TGA analysis. The reaction was complete after about 18 hours. The final reaction mixture was cooled to ambient temperature and the excess diethyl ethylphosphonate was filtered off. The solid was washed with acetone (50 mL x 3) and the resulting white powder was dried in an oven at 100°C to afford 16.1 g aluminum ethyl ethylphosphonate (AEEP) with the acid number 0.21 mg KOH/g and in a 95% yield. 22.2 % phosphorus (21.2% calc.) and 6.7 % Al (6.16% calc.) were found in the AEEP product. This solid was insoluble in most commonly available solvents.

The thermogravimetric analysis of the final product is shown in Figure 7. It shows very good thermal stability with a 2% weight loss at 301 °C. This product had a one-step weight loss, which is indicative of a good conversion. No melting endotherm was detected by a DSC measurement. The only endotherm, with a minimum at 348°C, was attributed to thermal decomposition or volatilization. The XRD spectrum of the AEEP product (Figure 8) shows no unreacted ATH. A scanning electron microscopy image of the AEEP obtained in this example is shown in Figure 9. It is seen that AEEP prepared by this method has needle shaped crystals similar to AMMP (Figure 6).

Comparative Example 2

Example 2 was repeated with the only difference that tetrabutyl phosphonium bromide catalyst was not used. The reaction was stopped after 26 hours. Figure 10 shows TGA analysis of the final product. Significant weight loss step attributed to ATH indicates that the reaction was not completed. 16.2 % phosphorus (21.2% calc.) and 14.7 % Al (6.16% calc.) were found in this product. Significant shortage of phosphorus and excess of aluminum indicates that large part of ATH was not converted into AEEP.

Example 3

A 3 -necked, 5 L round-bottom flask, equipped with an overhead stirrer, a thermometer and a distillation setup, was charged with dibutyl butylphosphonate (2253 g, 9 mol), Al(OH)3 (78 g, 1 mol) and tetrabutyl phosphonium bromide (3.4 g). The reaction mixture was heated to 180°C, under nitrogen, for 22 hours. The white suspension maintained the same appearance throughout the reaction. Aliquots were taken every 2 hours to monitor the reaction progress. The aliquots were washed with acetone and filtered to afford a white powder, which was dried in a 100°C oven and then sent to TGA analysis. The reaction was completed in about 20 hours. The final reaction mixture was cooled to ambient temperature and the excess dibutyl

butylphosphonate was filtered off. The solid was washed with acetone (1 L x 3) and the resulting white powder was dried in an oven at 100°C to afford 600 g aluminum butyl butylphosphonate (ABBP) in a 99% yield. 15.4 % phosphorus (15.3% calc.) and 4.52 % Al 12 063310

(4.46% calc.) were found in the ABBP product. This solid was insoluble in most commonly available solvents.

The thermogravimetric analysis of the final product is shown in Figure 11. It shows very good thermal stability with a 2% weight loss at 292°C. This product had a one-step weight loss, which is indicative of a good conversion. No melting endotherm was detected by a DSC measurement. The only endotherm, with a minimum at 354°C, was attributed to thermal decomposition or volatilization. The XRD spectrum of the ABBP product (Figure 12) shows no unreacted ATH.

Example 4

A 3-necked, 110 mL round-bottom flask, equipped with an overhead stirrer, a thermometer and a distillation setup, was charged with diphenyl methylphosphonate (57.3 g, 0.231 mol), Al(OH)₃ (2 g, 0.0256 mol) and tetrabutyl phosphonium bromide (0.09 g). The reaction mixture was heated to 180°C, under nitrogen, for 6 hours. The white suspension maintained the same appearance throughout the reaction. Aliquots were taken every 2 hours to monitor the reaction progress. The aliquots were washed with acetone and filtered to afford a white powder, which was dried in a 100°C oven and then sent to TGA analysis. The reaction was complete after about 4 hours. The final reaction mixture was cooled to ambient temperature and the excess diphenyl methylphosphonate was filtered off. The solid was washed with acetone (50 mL x 3) and the resulting white powder was dried in an oven at 100°C to afford 13 g aluminum phenyl methylphosphonate (APMP) in a 94% yield. 17.0 % phosphorus (17.2% calc.) and 4.97 % Al (5% calc.) were found in the APMP product. This solid was insoluble in most commonly available solvents.

The thermogravimetric analysis of the final product is shown in Figure 13. It shows very good thermal stability with a 2% weight loss at 285°C. This product had a one-step weight loss, which is indicative of a good conversion. No melting endotherm was detected by a DSC measurement. The only endotherm, with a minimum at 3 1 °C, was attributed to thermal decomposition or volatilization. The XRD spectrum of the APMP product (Figure 14) shows no unreacted ATH. Example 6

800 g of the powdered product of Example 12 was compacted using a double-roll press (Hutt, Germany). The diameter of the roll was 22 cm, and its length was 6 cm. The roll compactor produced "curtain" shaped bodies. The force applied was 6 ton/ cm² and the rotation speed was 6 rpm. The material was recycled six times in the compactor in order to increase the strength of the compacts. The compacted material was then ground and sieved through 1 mm and 0.5 mm sieves. The fraction of granules with a size in the range of 0.5 to 1 mm was separated (400 g). The fines (below 0.5 mm, 400 g) were mixed with 400 g fresh powder, and the aforementioned compaction / grinding / sieving procedure was repeated several times to obtain a granular AMMP. The granular product had a bulk density of 0.55-0.6 g/cm³. The granules were composed of particulates having an average size of 2.3 micron, as determined by laser diffraction, and the particle size distribution was as follows: dso 0.3 micron, d₉o 5.6 micron.

The AMMP showed good compaction ability without using a binder. The final compacted AMMP exhibits the features of a free flowing material and therefore will be beneficial for consistent feeding to the extruders.

Example 7

In order to illustrate the invention, flame retardant thermoplastic formulations were prepared using polypropylene random copolymer (R12C-00, INEOS). PP and FRs were compounded using a Brabender Intelli-Torque mixer at 170°C for 5-6 minutes at 60 rpm. The plaques of 1.6 mm thickness were pressed at 200°C using Wabah press at 2 tons pressure.

Specimens of 0.5 inch width were cut from the plaques and tested according to the UL-94 vertical bum protocol. Compositions of the formulations and results of the bum tests are reported in the table below. AMMP, AEEP, ABBP and APMP were compounded in PP to evaluate their efficacy as FR for PP. Table 2 lists all the formulations:

T - translucent

O - opaque

NR - Not rated

The formulations 1 and 2 passed the V-2 rating but formulations 3 and 5 failed to obtain the V-2 rating. Also, plaques made from formulations 1 and 2 were translucent but plaques from formulations 3, 4 and 5 were opaque. A 15% ABBP loading (formulation 4) can also pass the V- 2 rating.

The contents of U.S. Patent Nos. 5,208,317; 5,109,099; and, 4,981,926 are incorporated by reference herein in their entirety.

While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode

contemplated for carrying out the process of the invention but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

Claims:

1. A process for the preparation of an aluminum salt of a phosphonic acid ester, which comprises reacting the phosphonic acid diester with aluminum hydroxide in the presence of an efficient catalyst.

2. The process of Claim 1 , wherein the catalyst is selected from the group consisting of a phase transfer catalyst, a thermally stable tertiary amine having a boiling point higher than about 140°C, a thermally stable tertiary phosphine having a boiling point higher than 140°C and combinations thereof.

3. The process of Claim 2, wherein the phase transfer catalyst is a quaternary phosphonium salt selected from the group consisting of tetrabutylphosphonium chloride,

tetrabutylphosphonium bromide, tetrabutylphosphonium iodide, tetrabutylphosphonium acetate complex, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide,

tetraphenylphosphonium iodide, ethyltriphenylphosphonium chloride,

ethyltriphenylphosphonium bromide, ethyltriphenylphosphonium iodide,

ethyltriphenylphosphonium acetate complex, ethyltriphenylphosphonium phosphate complex, n- propyltriphenylphosphonium chloride, n-propyltriphenylphosphonium bromide,

propyltriphenylphosphonium iodide, butyltriphenylphosphonium chloride,

butyltriphenylphosphonium bromide, butyltriphenylphosphonium iodide, ethyltri-p- tolylphosphonium acetate/acetic acid complex, ethyltriphenylphosphonium acetate/acetic acid complex, hexadecyltributylphosphonium bromide and combinations thereof.

4. The process of Claim 2, wherein the phase transfer catalyst is a quaternary ammonium salt selected from the group consisting of tetraethylammonium bromide, tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium hydrogen sulfate, methyl trioctylammonium chloride, benzyl triethylammonium chloride and combinations thereof.

5. The process of Claim 2, wherein the thermally stable tertiary amine having a boiling point higher than 140°C is selected from the group consisting of 2-(dimethylamino)pyridine, 4- (dimethylamino)pyridine and combinations thereof.

6. The process of Claim 2 wherein the thermally stable tertiary amine having a boiling point higher than about 140°C is selected from the group consisting of 1 -methylimidazole; 2-methyl imidazole; 2-ethylimidazole, 2-propylimidazole, 2-butylimidazole, 2-pentylimidazole, 2- hexylimidazole, 2-cyclohexylimidazole, 2-phenylimidazole, 2-nonyl-imidazole, 2- undecylimidazole, 2-heptadecylimidazole, 2-phenyl-4-methylimidazole, 1 -benzylimldazole, 1- ethyl-2-methylbenzimidazole, 2-methyl-5,6-benzimidazole, 1 -vinylimidazole, l-allyl-2- methylimidazole, 2-cyanoimidazole, 2-chloroimidazole, 2-bromoimidazole, l-(2-hydroxypropyl)- 2-methylimidazole, 2-phenyl-4,5-dimethylolimidazole, 2-phenyl-4-methyl-5- hydroxymethylimidazole, 2-chloromemylbenzimidazole,2-hydroxybenzirnidazole, 2-ethyl-4- methylimidazole; 2-<^clohexyl-4-methylirnidazoles; 4-butyl-5-elhylimidazole; 2-butoxy^allylimidazole; 2- caroMthyoxy-burylirnidazole, 4-melhytirnidazole; 2-octyl- -hexylimidazole; 2-me1hyl-5-e1hylimidazole; 2- ethyl -(2-ethylarnmo)irnidazole; 2-methyl-4-mercaptoethylimidazole; 2,5-chloro-4-ethylimidazole; and mixtures thereof.

7. The process of Claim 6 wherein the thermally stable tertiary amine having a boiling point higher than about 140°C is 2-methyl imidazole.

7. The process of Claim 2 wherein the thermally stable tertiary phosphine having a boiling point higher than 140°C is selected from the group consisting of triaryl phosphines, alkyl diaryl phosphines, dialkyl aryl phosphines, trialkyl phosphines, where the aryl is a substituted or unsubstituted phenyl and the alkyl is a linear or branched or cyclic C4-C16 hydrocarbyl radical, and combinations thereof.

8. The process of Claim 7 wherein the thermally stable tertiary phosphine having a boiling point higher than 140°C is triphenyl phosphine.

9. The process of Claim 1 wherein the molar ratio of phosphonic acid diester to aluminum hydroxide is in the range of about 3 to about 15.

10. The process of Claim 1 wherein the molar ratio of phosphonic acid diester to aluminum hydroxide is in the range of about 5 to about 10.

11. The process of Claim 1 wherein the concentration of said catalyst is in the range from about 0.1 to about 5 wt. % relative to said aluminum hydroxide.

12. The process of Claim 1 wherein the reaction temperature is between about 150 to about 250°C.

13. The process of Claim 1 wherein an aluminum salt of phosphonic acid ester has the TGA temperature for 5% weight loss within the range of from about 290°C to about 325°C.

14. A process comprising roller-compacting an aluminum salt of phosphomc acid ester produced by the process of Claim 1 into granular aluminum salt of phosphonic acid ester.

15. The process of Claim 14 wherein the granular aluminum salt of phosphonic acid ester is a free flowing material.

16. A method of producing flame retarded thermoplastic polymer comprising blending thermoplastic polymer and an aluminum salt of phosphonic acid ester produced by the process of Claim 1.

17. A flame retarded thermoplastic polymer obtained according to the process of Claim 16.

18. Translucent flame retardant material obtained according to the process of Claim 16.

1 . The process of Claim 1 wherein the aluminum salt of a phosphonic acid ester is an aluminum phosphonate salt of the formula (I)

wherein:

R¹ and R² are each a linear or branched alkyl group having 2 to 10 carbon atoms, a linear or branched alkenyl group having 2 to 10 carbon atoms, a cycloalkyl group having 5 or 6 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 11 carbon atoms, a heterocyclic group having one or more of O, N and S as hetero atoms, R¹ and R² being unsubstituted or substituted by one or more halogen, hydroxyl, amino, alkoxy, carboxy or combinations of these groups.

20. The process of Claim 1 wherein R¹ and R² are each selected from the group consisting of ethyl, butyl, hydroxymethyl, phenyl, benzyl, allyl, vinyl or cyclohexyl group.