PROCESS FOR PREPARING ISOMERIC TRISARYLOXYCYCLOTRIPHOSPHAZENE POLYMER PRECURSORS AND INTERMEDIATES

Abstract: Hexachlorocyclotriphosphazene or trischlorotrisphenoxycyclotriphosphazene is reacted with one or more of phenol, 4-nitrophenol, an alkaline metal phenolate salt, and an alkaline metal 4-nitrophenolate salt to prepare isomeric tris(4-nitrophenoxy)tris(phenoxy)cyclotriphosphazene, which can be reduced in an ethyl acetate solvent with molecular hydrogen in the presence of a platinum oxide catalyst to produce isomeric tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene.

Description: PROCESS FOR PREPARING ISOMERIC TRISARYLOXYCYCLOTRIPHOSPHAZENE POLYMER PRECURSORS AND INTERMEDIATES Field of the Invention The present invention relates generally to the synthesis of cyclotriphosphazene based monomers and polymer precursors. It relates particularly to the preparation of trisaryloxycyclotriphosphazenes, especially isomeric tris- (4-nitrophenoxy)tris (phenoxy)cyclotriphosphazenes and isomeric tris(4-aminophenoxy)tris(phenoxy)cyclotri¬ phosphazenes. Background Art Cyclotriphosphazene based monomers and polymer precursors are an integral part of some present day programs which are directed toward the synthesis of high performance thermoplastic polymers for adhesives and graphite-reinforced composites. A major goal of these programs is to develop composites having enhanced properties, including toughness, thermal stability, and melt processability. Indeed, cyclotriphosphazene based monomers and polymer precursors have led to the development of important high-temperature materials. In this regard, reference is made to U.S. 4,550,177; U.S. 4,634,759; D. Kumar et al, J. Polym. Sci., Polym. Chem. Ed., 22, 927(1984); and D. Kumar, J. Polym. Sci., Polym. Che . Ed., 23, 1661(1985), wherein the synthesis of cyclotriphosphazene-derived hexakisamine, trisamine (m.p. 115-145) , and bisa ine suitable for the preparation of thermoset matrix resins and their utilization for composites have been reported. Summary of the Invention ' It is the primary object of the present invention to present improved methods for the preparation of isomeric trisaryloxycyclotriphosphazenes, especially nitro- and aminoaryloxycyclotriphosphazenes. According to the present invention, the foregoing and other objects and benefits are attained by reacting either hexachlorocyclotriphosphazene or trischlorotrisphenoxycyclo- triphosphazene with one or more of phenol, 4-nitrophenol, an alkaline metal phenolate salt, and an alkaline metal 4-nitrophenolate salt to prepare tris(4-nitrophenoxy)tris- (phencxy)cyclotriphosphazene followed by reduction thereof in a solvent with molecular hydrogen and a platinum oxide catalyst. Brief Description of the Drawings FIG. 1 sets forth a reaction scheme for a first method for the preparation of tris(4-nitrophenoxy)tris(phenoxy)- cyclotriphosphazene (III) according to the present invention; FIG. 2 sets forth a reaction scheme for a second method for the preparation of tris(4-nitrophenoxy)tris(phenoxy)- cyclotriphosphazene (III*) according to the present invention; FIG. 3 sets forth a reaction scheme for a third method for the preparation tris (4-nitrophenoxy)tris (phenoxy)- cyclotriphosphazene (III*) according to the present invention; FIG. 4 sets forth a reaction scheme for a method for the preparation of tris (4-aminophenoxy)tris(phenoxy)cyclo¬ triphosphazene (IV) according to the present invention; FIG. 5 sets forth a reaction scheme for the same method of FIG. 4, except that tris (4-nitrophenoxy)tris (phenoxy)- cyclotriphosphazene (III*) is employed as starting material to produce tris (4-aminophenoxy)tris (phenoxy)cyclotri¬ phosphazene (IV*) ; FIG. 6 represents the results of differential scanning calorimetry of III, at a heating rate of 20 β C/min in static air; FIG. 7 is a mass spectrum of III; FIG. 8 is a mass spectrum of IV; FIG. 9 represents the results of differential scanning calorimetry of IV*, at a heating rate of 20°C/min in static air; and FIG. 10 represents the results of differential scanning calorimetry of IV, at a heating rate of 20 β C/min in static air. Description of the Preferred Embodiments Useful efficient procedures for the synthesis of tris (4-nitrophenoxy)tris (phenoxy)cyclotriphosphazene starting from hexachlorocyclotriphosphazene and trichlorotriphenoxycyclotriphosphazene have been carried out according to the present invention. Tris (4-nitrophenoxy)- tris (phenoxy)cyclotriphosphazene III and III* have shown melting points of 111-112°C and 133-135°C, respectively. A process has been given to separate III and III* by chemical crystallization from a reaction product. The low-pressure hydrogenation of III and III* in solution (in an organic solvent) in the presence of the catalyst platinum oxide has resulted in the reduction of nitro groups to the corresponding tris (4-aminophenoxy)tris(phenoxy)cyclotri¬ phosphazene IV and IV*, melting at 138-141 β C and 106-107°C, respectively. FT-IR, H-NMR, mass spectrometry and elemental analysis have been used to characterize their structures. Differential scanning calorimetry has been used to determine their melting behavior. Hexachlorocyclotriphosphazene (I) (Shin Nasso Kako, Japan) was purified by recrystallization from hot n-heptane followed by sublimation at 80-82°C (0.1 mm); differential scanning calorimetry showed a sharp endotherm at 113°C. 4-Nitrophenol (Aldrich) was purified by recrystallization from ethyl alcohol. Phenol (Mallinckrodt Chemical Works) was purified by distillation. Platinum oxide (Alpha 0 Products, 40 mesh) was used as received. o-Dichlorobenzene (Alpha) was purified by distillation. Aniline was boiled at reflux and distilled from zinc dust. Ethyl acetate (Mallinckrodt Chemicals) was dried over molecular sieves and distilled. Acetonitrile (Fisher) was distilled before use. 5 Tetrahydrofuran (Aldrich) was refluxed and distilled from sodium benzophenone. Sodium hydride (55-60% Aldrich) was washed with n-hexane before use. Xylene was dried over 4A molecular sieves and distilled. Tetrabutylammonium bromide (TBAB) (Aldrich) was used as received. 0 Proton NMR spectra were recorded on a Varian EM 360A spectrometer. The chemical shift (δ) is given in parts per million (ppm) with tetramethysilane as the internal standard. Infrared (IR) spectra were recorded on a Nicolet FT-IR 60SX spectrophotometer with KBr in the diffused 5 internal reflectance Mode. Differential scanning calorimetry (DSC) was performed on a DuPont 1090 instrument at a heating rate of 20°C/min in a static air atmosphere. All melting points were taken on a Thomas-Hoover capillary apparatus and are uncorrected. 31P-NMR and mass spectra C were obtained from commercial laboratories. 31P-NMR spectra chemical shift (δ) is given in parts per million with 85% aqueous H-PO. as an external standard. Mass spectra were recorded using electron impact ionization at 70 eV. The compounds which have been prepared (viz.. Ill, 5 III*, IV, and IV*) show single endotherms in DSC, evidencing substantial improvements over the prior art. 0 Tris (4-nitrophenoxy) ris (phenoxy)cyclotriphosphazene Method 1; Step 1: In a 500-mL, three-necked flask equipped with a nitrogen inlet, calcium chloride guard tube and a stopper, a solution of hexachlorocyclotriphosphazene (I) (17.383 g, 0.05 mol) in 100 mL of tetrahydrofuran was magnetically stirred at -78°C. To this solution sodium phenoxide, prepared from phenol (14.2165, 0.15 mol) and sodium hydride (6.5 g) in THF (175 mL) , was added dropwise in about one-half hour in sequence. The stirring was continued for one and one-half hours at -78°C. Step 2; A slurry of sodium 4-nitrophenoxide, prepared from 4-nitrophenol (20.865 g, 0.10 mol) and sodium hydride (6.6 g) in THF (100 mL) , was added to the stirring reaction at ambient temperature. After refluxing for 65 hours with continuous stirring in a nitrogen atmosphere, the reaction mixture was filtered hot and the solvent distilled off on a rotary vacuum evaporator. The residue obtained was poured over crushed ice and the resulting solid was filtered and powdered. The powder was washed with ten percent aqueous potassium hydroxide solution and then with water. Drying in air and a vacuum desiccator provided a white solid (32 g, 78% yield) , m.p. 108-112°C. Tris (4-nitrophenoxy) tris (phenoxy)cyclotriphosphazene Method 2; Trichlorotriphenoxycyclotriphosphazene (II) was prepared by the method of Dell, Fitzsimmons and Shaw, which is known to those of skill in the art. Sodium phenoxide was ^ prepared from proper amounts of phenol and sodium hydride and reacted with hexachlorocyclotriphosphazene (I) in tetrahydrofuran at -78°C. In a 250-mL, three-necked flask equipped with a stirrer, nitrogen inlet and a drying tube, a mixture consisting of (9.04 g, 0.065 mol) 4-nitrophenol, 4.04 g of potassium hydroxide, and 60 mL of xylene was heated to 80 β C with vigorous stirring under nitrogen atmosphere. At this stage a solution of II (10.41 g, 0.02 mol) in 40 L of xylene was added incrementally. The mixture was then refluxed with stirring until the water was collected in a Dean-Stark trap (eight-nine hours) . The product obtained after distilling off xylene was poured over crushed ice. The solid obtained was filtered, suspended in a ten percent aqueous solution of potassium hydroxide and washed successively with water. Drying in air and a vacuum desiccator provided a white solid (27 g, 65% yield) , m.p. 130-132°C. It was recrystallized using acetronitrile to give a white solid III* melting at 133-135 β C. Tris (4-nitrophenoxy)tris (phenoxy)cyclotriphosphazene Method 3: In a separate method, the potassium salt of 4-nitrophenol was made by adding an ethanolic solution of potassium hydroxide to a stirred solution of 4-nitrophenol in ethanol. The orange solid obtained was filtered and dried for several hours in a vacuum oven at 125°C. Tris (4-nitrophenoxy) tris (phenoxy)cyclotriphosphazene (III*) was prepared by adding the proper amount of potassium 4-nitrophenoxide into a stirring solution of II in xylene (100 ml) . Tetra-n-butyl-ammonium bromide (TBAB) was added in a small amount. The stirring reaction mixture was refluxed under nitrogen for seven to eight hours. Work-up as described in Method 2 supra provided III* as white solid (30.7 g, 65% yield), m.p. 130-321°C. When the reaction was performed without the addition of TBAB, a longer time was required for completion of the reaction. Tris(4-aminophenoxy)tris (phenoxy)cyclotriphosphazene (IV) Ethyl acetate as solvent; In a general method, a 250 mL, heater equipped, autoclave pressure bottle was charged with a solution of tris(4-nitrophenoxy)tris- (phenoxy)cyclotriphosphazene III (m.p. lll-112 β C) , (12.0 g) in ethyl acetate (80 mL) . To this solution platinum oxide (0.045 g) was added. The mixture was agitated at 40-50°C and 40 psi of hydrogen for one to one and one-half hours until no pressure drop was observed. Filtering off the catalyst provided a clear solution, which was concentrated on a rotary evaporator under reduced pressure. The residue obtained was treated with hexane and the latter was distilled off. The cooled product was filtered and dried in air to provide IV as a creamy-white solid (8 g, 75% yield) . Aniline as solvent; Using a process otherwise identical to that described immediately above, aniline was used as the solvent for the reduction of nitrophenoxycyclo- , triphosphaze III, m.p. 111-112°C, which was completed in two and one-half to three hours. The reaction was carried out as described above to provide IV as an off-white solid (7g, 66% yield) . Tris (4-aminophenoxy)tris (phenoxy)cyclotriphosphazene (IV*) Ethyl acetate as solvent; A solution of tris(4-nitrophenoxy)tris (phenoxy)cyclotriphosphazene III*, m.p. 133-135 β C, was reduced in ethyl acetate in about two hours following the procedure described immediately above. IV* being obtained as an off-white solid (9.5 g, 90% yield). Aniline as solvent; The reduction of tris (4-nitrophenoxy)tris (phenoxy)cyclotriphosphazene III*, m.p. 133-135°C, was carried out in aniline during three-four hours utilizing the above described method. After work-up, IV* was obtained as an off-white solid (7.4 g, 70% yield). The specific reaction sequences used for the preparation of cyclotriphosphazene derived nitro- and aminophenoxy monomers are outlined in FIGS. 1-5. In step 1, the cyclic trimmer hexachlorocyclotri¬ phosphazene (I) was reacted in tetrahydrofuran solution at -78°C with three moles of sodium phenoxide to give trichlorotriphenoxycyclotriphosphazene (II) . The sodium phenoxide was prepared from phenol and sodium hydride in tetrahydrofuran. The direct addition of sodium phenoxide was preferred over the addition of phenol and sodium, for better control of the substitution reaction. It appears that the phenoxide ion under the experimental conditions is a fairly reactive nucleophile toward 4-coordinated phosphorus atoms, possibly being less solvated by tetrahydrofuran than the sodium ion. The reaction was also performed in an acetone and chloroform medium, but was slow. In the partial replacement reaction of hexachlorocyclotriphosphazene (I) with sodium and phenol in polar solvents, previous workers had reported that the substitution follows completely or almost completely by non-geminal pathway. The reaction proceeds similar to an S„2 type mechanism with kinetic and steric effects predominating. Also scattering in substitution has been reported. Under the instant conditions the reaction proceeds relatively clean. The trichlorotriphenoxycyclo- 0 triphosphazene (II) has been assigned a non-geminal structure in view of the reports of earlier workers and by recording phosphorus -31 NMR spectra. The proton decoupled phosphorus -31 NMR spectrum showed A- spin singlets at 19.0 ppm due to the presence of 5 ,C1 ~ P ^O-CgH- groups. The proton NMR spectrum showed the presence of phenoxy groups at 7.45 - 7.15 ppm. 0 In Method 1, step 2, (FIG. 1), trichlorotriphenoxy- cyclotriphosphazene (II) , obtained jLn situ was further reacted with sodium (4-nitrophenoxy)tris (phenoxy)cyclotri¬ phosphazene (III) . The product obtained melted in an open-end capillary at 108-109°C. In Method 2 (FIG. 2) , 5 trichlorotriphenoxycyclotriphosphazene (II) prepared at -78°C was reacted with a 4-nitrophenol and potassium hydroxide mixture in refluxing xylene. The potassium hydroxide was used for the total replacement of chlorine atoms with nitrophenoxy groups. The vigorous stirring and Qm . bubbling of nitrogen is considered important here for azeotropical removal of water from the reaction. The product obtained melted at 130-132°C in an open end capillary. In Method 3 (FIG. 3) the trichlorotriphenoxy- cyclotriphosphazene (II) prepared was reacted in refluxing 5 xylene with the potassium salt of 4-nitrophenol yielding III*. Although the extra step of preparation of potassium salt of phenol is required, reaction time required is almost the same as in Method 2. However, this extra step is justified since the reaction conditions appear slightly 0 better. The addition of a phase transfer .catalyst showed increased lipholicity and possible improved nucleophilicity of the oxyanion; however, no frothing was observed in either method. Characterization of Tris (_4-nitrophenoxy) tris (phenoxy)- cyclotriphosphazene Chemical Separation Tris (4-nitrophenoxy) tris (phenoxy)cyclotriphosphazene obtained in Method 1 melted at 108-110°C, and was purified by dissolving 30 gm of solid in 50 mL of warm acetonitrile. After filtering, the clear solution was allowed to stand. A small amount of white solid (III*) was obtained on filtration and drying. This solid III* showed a melting at 133-135 β C. Addition of methanol to the remaining clear solution produced a white precipitate which was collected by filtration. The dired white powder (III) melted at 111-112°C. Tris (4-nitrophenoxy) tris (phenoxy) cyclotriphosphazene (III*) obtained in Methods 2 and 3 was recrystallized with warm acetronitrile, resulting in a white solid melting at 133-135°C. In Methods 2 and 3, a small amount of III was also obtained in crude form. Elemental analyses were performed for III and III* and were consistent with the proposed structures (Table 1) . - 9/12639 • -10- Table I Elemental Anal ysis of Cyclotriphosphazenes III and III* Microanalysis (%) Melting Molecular Saπple Point Formula H N III 111-112-C C 36 H 27 N 6 0 12 3 Calc: 52.17 3.26 10.14 11.23 Found: 52.04 3.31 10.16 11.14 III* 133-135 β C C^H^NgO j ^ Calc: 52.17 3.26 10.14 11.23 Found: 51.98 3.35 10.12 10.98 Infrared spectra of tris(4-nitrophenoxy)tris (phenoxy)cyclo¬ triphosphazene III and III* showed sharp bands for the presence of nitrophenoxy (asymmetrical and symmetrical stretchings) , cyclotriphosphazene ring (P-N-P and P-N-C stretchings) , aromatic and ether groups as shown in Table 2. - 2639 -11- Table 2 IR Spectra of Tris (4-nitrophenoxy) tris (phenoxy) cyclotriphosphazene III and III* Melting Saπple Point Wavenumber, CMrl III 111-112°C Nitro group 1523 asyi etrical stretching 1348 syπmetrical stretching Aromatic 1591, 1489 Cyclotriphosphazene 1201 P-N-P asyπmetrical stretching 1177 1118 951 P-N-C syπmetrical stretching 770 P-N-P syπmetrical stretching Ether 1270 III* 133-135°C Nitro group 1522 asyimetrical stretching 1348 syπmetrical stretching Aromatic 1591, 1489 Cyclotriphosphazene ! 1200 P-N-P asyπmetrical stretching 1178 1117 947 P-N-C syπmetrical stretching 770 P-N-P syπmetrical stretching Ether 1270 The patterns of the infrared were essentially identical, indicating that IR is unable to distinguish III and III*. Proton NMR of III and III* were recorded in DMSO-d 6 * A 3:3 substitution of phenol and 4-nitrophenol has been seen from the ratio of the integration of a downfield double doublet observed in H-HMR at 8.20-8.10 ppm (six protons ortho to nitro groups) with combined integration of phenoxy and meta protons of nitro phenoxy groups. A mass spectrum confirmed the 3:3 substitution as the molecular ion M is observed at m/z 828 for C_ fi H 2 _N.O : , -P-, consistent with the structure. FIG. 7 showed mass spectrum of tris(4-nitrophenoxy)tris- (phenoxy)cyclotriphosphazene III with major fragmentations at m/e 735, 690 (base peak) 614, 414, 77 and 65. The observations of fragmentations with a loss of phenoxy (93) 0 and nitrophenoxy (138) from the parent peak clearly support the tris/tris structure. In step 3, the nitro groups of tris (4-nitrophenoxy)- tris (phenoxy)cyclotriphosphazene III and III* were reduced with molecular hydrogen (40 psi) at 40-50°C in the presence 5 of platinum oxide catalyst. The reduction of nitro groups in ethyl acetate was a little faster than in aniline or DMF. The reaction was exothermic as the adsorption of molecular hydrogen began. Tris (4-nitrophenoxy)tris (phenoxy)cyclotri¬ phosphazene (III, m.p. lll-112 β C) on reduction gave 0 tris (4-aminophenoxy)tris(phenoxy)cyclotriphosphazene (IV, m.p. 138-141 C C) . Similarly, tris (4-nitrophenoxy)tris- (phenoxy)cyclotriphosphazene III* (m.p. 133-135 β C) gave tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene IV*. Recrystallization of IV* was performed with an ether- 5 petroleum ether mixture to give a solid melting a 107-108°C. IV was recrystallized from warm o-dichlorobenzene to give a solid melting at 149-153 C C. Infrared spectra of the trisamine (IV*, m.p. 107-108°C) and the trisamine (IV, p.m. 149-153°C) were recorded <T (Table 3) and are found consistent with the structure. 5 0 Table 3 IR Spectra of Tris (4-aminophenoxy)tris (phenoxy) cyclotriphosphazene IV and IV* Melting Saπple Point Wavenumber, CM IV* 107-108°C Amino group 3467 stretching 3365 1624 bending 1591 Aromatic group 1508 1488 Cyclotriphosphazene 1200 1178 953 769 Ether 1265 IV 149-153 β C Amino group 3460 stretching 3419 3371 3329 1624 bending 1591 Aromatic 1508 1487 Cyclotriphosphazene 1200 1178 951 765 Ether 1263 The spectra showed the presence of amino groups, cyclotri¬ phosphazene ring and the absence of nitro group stretchings. The proton NMR spectra clearly showed the presence of amino groups observed as a broad singlet exchangeable to D 2 0. The ratio of integration (6:27) of amino proton singlet to that of aromatic protons indicated the presence of three amino groups. The spectra were consistent with the structure. A mass spectrum (FIG. 8) of IV (m.p. 149-153 β C) showed M at m/z 738 (base peak) with major fragmentations at m/e, 654, 630, 429, 108, 75 and 74, confirming its tris/tris structure. Its proton decoupled phosphorus -31 NMR spectrum showed the presence of phosphorus as A- spin singlet at 10.41 ppm, depicting its symmetrical structure. Differential scanning calorimetry of IV* (m.p. 0 107-108 β C) gives a single endothermic peak at 108°C as shown in FIG. 4, while differential scanning calorimetry of IV did not show sharp melting. This may be explained by considering IV to be a mixture of isomers. Thin layer chromatography of IV on silica gel plates was performed in 5 the solvent system chloroform (201:5): Methanol (42:5): acetic acid (6.5) . Tris(4-aminσphenoxy)tris(phenoxy)- cyclotriphosphazene IV (m.p. 149-153 β C) showed a major spot with R f 0.24 along with two minor spots with R- 0.37 and 0.64. It was possible to recrystallize IV with tetra- 0 hydrofuran-hexane and obtain off-white crystals melting at 161-172°C. On TLC examination this was seen to be homoge¬ neous with Rm 0.24. Its differential scanning calorimetry scan also showed a sharp single endotherm at 162°C (FIG. 10). Its mass spectrum showed M at m/z 738. Based on 5 this study, it was concluded that tris(4-aminophenoxy)tris- (phenoxy)cyclotriphosphazene IV, m.p. 161-162 β C is a pure isomer. It can have either a cis-2,4,6-tris(4-aminophenoxy)- 2,4,6-tris(phenoxy)cyclotriphosphazene structure or a trans-2,4,6-tris(4-aminophenox ) 2,4,6-tris(phenoxy)cyclotri¬ (1 phosphazene structure. However, the cis structure is preferred here based upon the observed relatively stronger chromatographic adsorption and higher melting point. Because the trisamines IV and IV* have different melting points, polymers synthesized from these monomers 5 under the same conditions are expected to have different properties. What is new and desired to be secured by Letters Patent is: 0

Claims: Claims : 1. A process for preparing tris (4-nitrophenoxy)tris- (phenoxy)cyclotriphosphazene having a sharp melting point, comprising reacting a member of the group consisting of hexachlorocyclotriphosphazene and trischlorotrisphenoxy- cyclotriphosphazene with a member of the group consisting of phenol, 4-nitrophenol, alkaline metal phenolate salts and f) alkaline metal 4-nitrophenolate salts in the presence of an organic solvent. 2. The process of claim 1, wherein the reaction mixture additionally comprises a phase transfer agent. 3. The process of claim 2, wherein the phase transfer agent is tetra-n-butyl-ammonium bromide. 4. A process for preparing tris (4-nitrophenoxy) tris- (phenoxy)cyclotriphosphazene, comprising reacting hexachlorocyclotriphosphazene with an alkaline metal phenolate salt in an organic solvent, followed by reacting in situ with an alkaline metal 4-nitrophenolate salt in an organic solvent. 5. A process for preparing tris (4-nitrophenoxy)tris- - (phenoxy)cyclotriphosphazene, comprising reacting trischlorotrisphenoxycyclotriphosphazene with an alkaline metal 4-nitrophenolate salt in an organic solvent. 6. A process for preparing tris (4-nitrophenoxy)tris- (phenoxy)cyclotriphosphazene, comprising reacting trischlorotrisphenoxycyclotriphosphazene with 4-nitrophenol and an alkali in an organic solvent. 7. A process for the production of isomeric tris(4-aminophenoxy)tris (phenoxy)cyclotriphosphazene, comprising reducing tris(4-nitrophenoxy)tris(phenoxy)- cyclotriphosphazene in an ethyl acetate solvent with molecular hydrogen in the presence of a platinum oxide catalyst.

Inventors: KUMAR DEVENDRA, ST CLAIR TERRY L, KUMAR, DEVENDRA, ST. CLAIR, TERRY, L.
Applicants: US HEALTH, THE GOVERNMENT OF THE UNITED STATES AS REPRESENTED
Application year: 1989
Main classification: C07F9
IPC codes: C07F9