Feb. 20, 1962
549
SYNTHESIS OF BIS-(PERFLUOROALKYL) -PHOSPHONITRILES
u. s. NAVALORDNANCE LABORATORY, CORONA, CALIFORNIA] Synthesis of Bis-(perfluoroalky1)-phosphonitriles
[CONTRIBUTION FROM
THE
BY G. TESI* AND C. M. DOUGLAS RECEIVEDJUNE 20, 1961 The synthesis of trimeric, tetrameric and polymeric bis-(trifluoromethy1)-phosphonitriles, [ (CFa)zPN]~ . 4 . ~ and , of trimeric bis-(heptafluoropropy1)-phosphonitrile, [ (C3F,)2PN]3, is accomplished by chlorination of bis-(trifluoromethy1)-phosphinous amide, ( C F S ) ~ P N Hand ~ , bis-(heptafluoropropy1)-phosphinousamide, (CaF,)2PNH2, followed by dehydrohalogenation with a tertiary amine. Evidence of the formation of the intermediate bis-(trifluoromethy1)-dichlorophosphinicamide (CF3)2P(C12)NH2is obtained by cleavage of the P-NHz bond with HCl to form trichlorobis-(trifluorornethy1)-phosphorane (CFs)zPCh.
The reaction of dialkyl and diary1 phosphorus by the equations trichloride with either ammonia or ammonium (RF)zPNHz Clz +( R F ~ P ( C ~ Z ) N H Z(1) chloride has been the object of extensive investi(RF)ZP(C~Z)XHZ f 2SRs + gations, and the prepamtion of alkyl and aryl (RF)PPNf 2NRa.HCl (2) phosphonitriles by this procedure has been reThe mechanism of this reaction also where Rp = CF3 and C3F7. has been investigated, and evidence has been A reported attempt8 to chlorinate bis-(trifluoroobtained for the formation of intermediate com- methyl) -phosphinous amide, (CF&PNH2 (I), by pounds containing P-C1 and N-H g r o ~ p s . ~use , ~ of C12 in the absence of solvent failed to provide Dehydrohalogenation of these intermediate com- evidence for the formation of bis-(trifluoromethy1)pounds leads to the formation of the desired dichlorophosphinic amide, (CF3)2P(Cl~)NH2 (11). phosphonitrilic derivatives. I t was found, however, that a chloroform solution The same synthetic approach has been attempted of I a t -30' reacts smoothly with an equimolar for the preparation of bis-(trifluoromethy1)-phos- amount of chlorine, turning the solution pale yellow phonitrile9; however, the desired final products with no formation of precipitate. When the solution were not formed. Extensive decomposition of the was warmed a t room temperature, extensive detrichlorobis-(trifluoromethy1)-phosphorane, (CF& composition occurred, which made i t difficult to isoPCl,, was observed, along with the formation, late and characterize the reaction products. Howamong other products, of a large amount of tri- ever, when the chloroform solution, a t -30', was fluoromethane, which indicates that ammonolysis treated with an excess of anhydrous HC1 after the of the carbon-phosphorus bond occurs, probably chlorination was completed, an 88% yield of trias a consequence of the highly electronegative - (trifluoromethyl) - phosphorane, (CF& character of the trifluoromethyl group. A poly- chlorobis Pc13, and 93% of ammonium chloride, calculated on meric material having the composition [ (CF3)z- the basis of the starting compound I, were obtained P N 1, has been obtained7by thermal decomposition according to of bis-(trifluoromethy1)-phosphinousazide, (CF& PN3. The formation was observed of a very small (CFz)zP(Clz)NH2 4- 2HC1 --f (CH3)zPCla NHaCl (3) amount of a crystalline material which was sepa- thus providing unequivocable evidence for the rated by vapor-phase chromatography into two formation and composition of compound 11. fractions melting a t 64' and log', respectively. Treatment of a chloroform solution of I1 with The yield, however, was insignificant, and no trimethylamine resulted in a rapid reaction and further characterization was attempted. formation of a white precipitate. From the resultBis-(perfluoroalky1)-phosphonitriles have now ing mixture were isolated two volatile crystalline been obtained by chlorination of bis-(perfluoro- compounds melting a t 64' and 109'. Elemental alkyl)-phosphinous amides, ( R F ) ~ P N H ~to, form analysis and molecular weight determinations bis-(peduoroalky1)-dichlorophosphinic amides, these two compounds to be [(CF&PN], (RF)~P(CL)NH~, and the subsequent dehydro- proved (m.p. 64') and [(CF&PN]4 (m.p. 109'). halogenation of these compounds. Chloroform A white solid nonvolatile material, insoluble in and carbon tetrachloride were found to be suitable common organic solvents, was recovered from the solvents for the chlorination reaction. The de- residue after removal of the trimethylamine hydrohydrohalogenation was achieved by use of a chloride. The elemental analysis of this compound nonprotonic base ( L e . , a tertiary amine) to avoid proved the composition (CF3)2PN. The X-ray cleavage of the carbon-phosphorus bond. diffraction patterns show that this material posThe mechanism of this synthesis can be expressed sesses a much lower degree of crystallinity than the * U. S. Naval Propellant Plant, Indian Head, Md. trimeric and tetrameric forms. A polymeric struc(1) C. P. Haber. D L. Herring and E. A. Lawton, J.A m . Chem. Soc., ture is therefore postulated. 80, 3116 (1958). Trimeric bis-(heptafluoropropy1)-phosphonitrile, (2) H . T. Searle, Proc. Chem. SOL.(London), I ( 1 9 5 9 ) . (3) A. J. Bilbo, 2. Naturfororsch., 16b, 330 (1960). [(CsF7)2PNl3,was obtained in 70y0yield by using (4) I. I. Bezman and J. H. Smalley, Chem. and Ind. (London), 839 bis-(heptafluoropropy1)-phosphinous amide as a (1960). starting compound and employing the same syn( 5 ) V. V. Korshak, I. A. Gribova, T. V. Artamonova and A. N. thetic method previously described. No tetraBushmarina, Vysokomolekulyavnye Soedineniya, 11, 377 (1960). (6) C . P. Haber and A. J . Bilbo, W A D C Technical Report 56-376. meric homolog was recovered-only a certain
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(7) G. Tesi, C. P. Haber and C. M. Douglas, Proc. Chem. Soc. (London) 219 (1960).
( 8 ) G. S Harris, J . Chem. Soc., 812 (1958).
550
G. TESIAND C. M. DOUGLAS
Vol. 84
amount of an oily material whose identity has not TABLE I yet been established. INFRARED ABSORPTIONSOF BIS-(PERFLUOROALKYL) Pr~osThe infrared absorption data for all these comPHONITRILES pounds are listed in Table I. The absorption [ (CFs),PP: laa [(CFdzPN IP [ (CFa)nPN 1b. [ (CsF1)zPNl a b bands for the P-N ring vibrations have been ten13OOc s 141T m 1430-1335" V.S. 132SCs tatively assigned. Strong shifting of these bands 1205 V.S. 1216 V.S. 1234 V.S. toward higher frequencies was noted, as compared 1190 s 1120 s 1166 m 1194 s with equivalent data for other phosphonitrilic 1138 s 1170 s 926 m corn pound^.^^^^ This result is, however, consistent 1152 s 868 m with the effect of the strongly electronegative per771 m 900 ni 750 m 771 m fluoroalkyl groups on the P-N cyclic system. It is 775 m 675 m interesting to note the similarity in position between 682 m the P-N ring vibration peaks of the [ ( C F J ~ P K ] I ~ a Spectra obtained in gas phase. * Spectra obtained in the (1300 cm.-l) and the (PNF2)3 (1297 cm.-l).ll solid phase. c-P=Nstretching vibration. The same similarity exists between [PN(CF3)2]4 PNH2 in 100 ml. of chloroform was cooled t o -40' and (1412 cm.-I) and (PNF2)4(1419 cm.-l).ll treated with 7.1 g. (0.1 mole) of chlorine with stirring. The Experimental addition was completed in 30 minutes. No precipitate was Materials .-Bis-( trifluoromethy1)-phosphinous amide, formed and the solution turned pale yellow. The stirring ( CF3)2PNH2, and bis-( heptafluoropropy1)-phosphinous was continued for about 30 minutes and the temperature was amide, ( CaF7)2PNH?, were prepared as previously de- allowed to rise t o -30". A slow stream of anhydrous HCl was then introduced in scribed.*J* The purity of these compounds was determined by gas chromatography and infrared spectroscopy. Chlo- the flask. An almost immediate reaction occurred with rine was purified by passage, in succession, through a water formation of a white precipitate. The addition of HCl was scrubber, concentrated H2SO4 and a heater maintained a t continued for 12 hr., during which time the temperature was 350'. Trimethylamine was purified by contact with P ~ O I O . maintained a t -30" and then for 6 hr. a t room temperaAll reactions were run under a blanket of dry nitrogen to ture. The flask was connected to a vacuum system and all the volatile material was transferred under pumping vacuum prevent contamination by air and moisture. to a trap kept a t -78'. The residue, ?fter recrystallization Bis-( trifluoromethy1)-phosphonitriles, [ (CF&PN ) ] 3 ,4,n.A solution containing 37.0 g. (0.2 mole) of (CF&PNHz in from a water-ethanol solution, was identified as SHdCI (5.0 g., 93%). 300 ml. of chloroform was cooled a t -40" and under vigorous stirring was treated with 14.2 g. (0.2 mole) of chlorine. The Anal. Calcd. for SH4CI: Cl, 66.26; Found: C1, 66.15. addition took about 1 hr. The chloroform solution turned By fractional distillation of the volatile materials, a liquid pale yellow and no precipitate was formed. The solution boiling a t 44-45' (86 mm.) was obtained (24.2 g., 8870)b). was stirred for 30 minutes and the temperature was allowed Analysis of the ( CF3)2PC13was performed by hydrolysis t o rise t o -30'. Trimethylamine (25.6 g., 0.44 mole), was with an excess of 10% NaOH solution. One-half of the trithen slowly added under vigorous stirring. A rapid reaction fluoromethyl groups were hydrolyzed as trifl~oromethane'~ took place with formation of a white precipitate. The mix- according to the equation ture was allowed t o warm slowly t o room temperature and (CF3)2PCla 5XaOH --+ then refluxed gently for 2 hr., using a n ice-water condenser. CFaH f 3PiaC1 f CFaP(0)(ONa)z (4) All the volatile materials were removed from the flask under pumping vacuum and collected in a trap maintained a t The chlorine was determined by titration of the resulting -78'. This transfer was continued for 4 hr. with the flask a t room temperature and then for 8 hr. with the flask heating solution with 0.1 N Hg( NO,), standard solution. Anal. Calcd. for (CFs)zPC13: CF3 (one-half) 25.45; C1, on a steam-bath. Fractionation of the volatile materials was 38.7. Found: CF3, 25.2; C1, 38.4. achieved by vacuum transfer through U-traps maintained The trifluoromethane recovered was identified by infrared a t -loo, -44' and -78'. At -44O, 4.4 g. (120%) of a white crystalline material was recovered (m.p. 64 , sealed spectroscopy and molecular weight determination (vapor density). capillary). Calcd. for CF3H: mol. wt., 70. Found: mol. wt., 70. Anal. Calcd. for (CF&P3X3: C, 13.1; N, 7.6; P , 16.9, was determined tenThe moIecular weight of (. CF3)2PC13 . F,62.3. Found: C, 13.4; N, 7.8; P , 16.6; F, 62.2. siometrically The molecular weight was determined tensiometrically Calcd. for (CFa)2PCh: Mol. wt., 275. Found: Mol. wt., Calcd. forPaNs(CF3)~: mol. wt.,549. Found: mol. wt., Z(Z. 536,538. Bis-(heptafluoropropy1)-phosphonitriles, [ ( C3F7)2PN]3.The second fraction collected a t -10" was purified by solution containing 44.5 g. (0.1 mole) of (CaF7)2PNH2 in crystallization from n-pentane, followed by vacuum subli- A 100 ml. of chloroform was cooled a t -30" and under vigorous mation (9.1 g., 2570, m.p. log', sealed capillary). stirring was treated with 7.1 g. (0.1 mole) of chlorine. The Anal. Calcd. for (CFa)aP4N4: C, 13.1; N, 7.6; P , 16.9; addition took place in about 30 minutes. No precipitate F,62.3. Found: C, 12.9; N, 7.6; P, 16.6; F,62.5. was formed. The solution was stirred for an additional 30 The molecular weight was determined tensiometrically. minutes a t the same temperature and then combined with 13.0 g. (0.22 mole) of trimethylamine. This resulted in the Calcd. for (CFa)sPdNd: mol. wt., 732. Found: mol. wt., formation of a white precipitate. After the addition was 716. The solid residue remaining in the flask after the vacuum completed, the solution was allowed to warm to room temperature and was then refluxed for 2 hr. The chloroform was transfer was extracted with water to remove the trimethylamine hydrochloride. The white solid material (19.4 g., removed under reduced pressure (20 mm.) and the white 53%, m.p. 95-100°) that remained was found to be insoluble solid material remaining was extracted with ligroin (6j-70') in a Soxhlet apparatus. Crystallization from hot li_groin in common organic solvents. Anal. Calcd. for [(CFa)zPN;ln: C, 13.1; S, 7.6; P , solution yielded a white crystalline material (31 g., 1070, m.p. 85'). 16.9; F,62.3. Found: C, 13.1; N,7.9; P , 16.9; F, 62.3. Anal. . Calcd. for (C3F7)~PsN3: C, 18.85; N, 3.65; P, Reaction Between Bis-( trifiuoromethy1)-dichlorophos8.1:. F,. 69.4. Found: C, 19.05; N,3.8; P,8.1; F,69.25. phinic Amide, (CF3)2P(C1)2NH2,and Anhydrous Hydrochloric Acid.-A solution containing 18.5 g. (0.1 mole) of (CF3)ZThe molecular weight was determined ebullioscopically in CClp. (9) L.W.Daasch, J . A m . Chem. Soc., 76,3403 (1Y.54). Calcd. for (C3F7)ePaN3:mol. wt., 1149. Found: niol. (10) R.A. Shaw, Chem. and I n d . (London), 54 (1959). wt., 1139.
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(11) H. J. Becher and F. Seel, 2. anorg. allgem. Chenz., 306, 148 (1960). (12) H. J. Ern6Eus and J. D. Smith, J . Chem. Soc., 375 (1959).
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n--
(13) H. J. Em&ldus, R. N. Haszeldine and R. C. Paul, ibid., 563 (1965).
Feb. 20, 1962
POLYFLUOROALKYL PHOSPHONITRILATES
The mother liquor was evaporated to dryness. Upon removal of the residual [( C3F7)zPN]aby vacuum sublimatio?, a brown oily material was obtairled which was dissolved in boiling benzene. The mixture was cooled t o room temperature and a colorless oil was recovered by decantation of the benzene solution. The remaining benzene was removed under vacuum. An extremely viscous colorless oil was obtained whose nature has not yet been established. Infrared sPectroscoPY of this m t e r i a l Strongly suggests the Presence of P-N and C-F bonds. Infrared Spectral Analysis .-The infrared spectra of [(CF&PN]3 and [( CF3)zPiV]rwere recorded in the gas and phase. The infrared spectra of polymeric [(CF3)zPN]a
55 1
[ ( C ~ F ~ ) Z Pwere N ] ~ obtained from thin films prepared by melting the compounds between two sodium chloride plates. The data are shown in Table 1.
Acknowledgments,-This investigation was supported by the Bureau Of Weapons, Department of the Navy, through the Foundational Research Program. It is a pleasure to acknowledge the helpful discussions of Dr. C. p. Haber and Dr. P. J. Slota, Jr. The elemental analyses were performed by the Schwarzkopf MicroanalYtical Laboratory, Woodside, N. y.
[CONTRIBUTION FROM THE OHIOSTATEUNIVERSITY RESEARCH FOUNDATION, COLUMBUS 10, Omo]
A New Class of Stable PhosphonitrilicAcid Esters. Polyfluoroalkyl Phosphonitrilates'V2 B Y RUDIR:;Tz,3s4 HANSJUERGEN SCHROEDER,3 HENRIULRICH, EHRENFRIED I(OBER3
AND
CHRISTOPH GRUNDMANN RECEIVED APRIL 14, 1961 A series of tri- and tetrameric polyfluoroalkyl phosphonitrilates (I and 11) has been synthesized. These novel compounds possess remarkable chemical and thermal stability; however, prolonged heating of trimeric bis-( 1,l-di-H-heptafluorobuty1)phosphonitrilate gave ring enlargement to the corresponding tetramer. Most of the compounds of type I and I1 can be fully chlorinated t o hydrogen-free polychloro-polyfluoroalkyl phosphonitrilates.
Esters oi the so-called phosphonitrilic acids, [-N=P(OR)z]n (n = 3, 4) can be obtained by complete exchange of the chlorine functions in the cyclic tri- and tetrameric phosphonitrilic chloride by alkoxy- or aryloxy groups. In contrast to the esters of the isomeric trimeta-phosphinic acid5
the phosphonitrilic acid esters have never been positively identified and characterized despite the fact that considerable work has been done on this subject? This can be explained by the thermal instability of the phosphonitrilic acid esters. The alkyl phosphonitrilates seem to be especially sensitive compounds which decompose on heating in the range of 100°.5.7 In connection with a research program on cyclic phosphorus-nitrogen compounds, a series of new tri- and tetrameric polyfluoroalkylphosphonitrilates (I, 11) has been prepared. Their phosphonitrilate structure was elucidated by infrared spectroscopy. The infrared spectra are in agreement with the phosphonitrilate formulas I and 11, (1) This article is based on work performed in I957 under Project 116-B of T h e Ohio S t a t e University Kesearch Foundation sponsored by the Oiin Mathieson Chemical Corporation, New York, N. Y. ( 2 ) This article represents part of a paper delivered by R. R a t z a t the Gordon Research Conference on Inorganic Chemistry, New Harnpton, N. H . , August 1960; parts of the content of this paper are t h e subject of U. S. Patents 2,876,247 and 2,876,248 (K.F. W. R l t z and C . J. Grundmann to Olin Mathieson Chemical Corporation). ( 3 ) Oliu Mathieson Chemical Corporation, New Haven, Connecticut. (4) T o whom inquiries should be directed, ( 5 ) K . KBtz and M. Hess, Bcr., 84, 889 (1951). (6) L. F. Audrieth, R . Steinmann and A . D. F . Toy, Chcrn. Rcws., 32, 129 (1943). (7) Only recently, boiling points of some alkylphosphonitrilates have been reported; B. W. Fitzsimmons and R A. Shaw, Chcm a n d I n d . (London). 109 (1961).
since strong absorptions are present a t 1231 cm.-', indicative for the retention of the aromatic -P=Nring system. Normally, the -P=N-ring vibration in phosphonitrilic derivatives has been ioucd a t 1218 cm.-', but it can be expected that the cumulation of negative fluorine atoms causes a shift to higher frequencies. These esters are accessible in excellent yields by reaction of the cyclic phosphonitrilic chlorides (111) with excess of sodium polyfluoroalkoxides. I n contrast to all known phosphonitrilic acid esters, the polyfluoroalkyl phosphonitrilates of the general formulas I and I1 are thermally very stable, that is, they can be distilled, even a t atmospheric pressure, w'thout any decomposition. These compounds are so inert that some of them were purified by distillation in the presence of metallic sodium. [OCH~(CFS),,CF~X]Z
I1
P
/ \
N
X
II
I
n = 1, 3, 5, 7, 9 X = ForH n = 0, 2 only in cases where S = F
While all reported cyclic phosphonitrilic compounds undergo thermal cleavage a t approximately 300' to give highly crosslinked polymeric materials, the polyfluoroalkyl phosphonitrilates of type I and I1 are stable even above this temperature, probably
