V O L U M E 23, NO. 6, J U N E 1 9 5 1
.bthe alpha-particle will not paletrate any appreciable thickness of filter paper, the distributions reported are for the surface of each sample of filter paper. I n Figure 5 there appears to be a decrease in the count frequency in going from 0.4 to 0.2 micron. This is probably due to penetration of the paper (HollingsworthVose H-70) to a greater depth by the smaller particles. The presence of agglomerzttos may also be detected by this method. Figure 6 shows a track cluster of an agglomerate consisting of radioactive and nonradioactive material. The latter stops the alpha-particles from reaching the emulsion, which results in a very irregular cluster pattern. The particle shown was greater than 5 microns, and is probably duct scale. Only two such particles wwc prescnt in a total of about 1000 particltv observed. For the material used in the% particular tests, the value of K in Equation 1 was 5.04. A calibration curve for the formula:
was constructed to give the particle size as a function o f the number of tracks for a given exposure time (Figure i ) . Cascade impactor samples of the feed to the system taken a t a later date verified the results obtained by radioautograph. Analysis by the method of Hatch and Choate ( 1 ) indicated that 50% of the mass of sample was composed of particles less than 0.9 micron, while 98.6% of the mass was made up of particles lea8 than 5 microns.
853 If there is a very great abundance of large particles, the finer particles will be obscured in the radioautograph unles? the large particles can be removed and studied separately. The isotope being studied (as well as interfering decay products) must be identified. In addition to standard electronic detection devices, the range and track appearance in the emulsion d l help determine the radiation characteristics of the particle. The method is feasible as a research tool on only a few samples, as counting tracks in hundreds of clusters is a tedious and expensive procedure. Projection of the field on a screen is helpful in counting individual tracks. A simpler modification of this method would be to observe the entire cluster for each particle rather than individual tracks. By establishing a standard minimum cluster of about 300 tracks and making several exposures, the particles can be grouped by size range. A photodensitometer could be used to count such large clusters. However, this method is not ap pwcise as counting individual tracks. .b the actual particles are never obuerved, this method does not reveal the true particle shape. An effective diameter for the particle is measured, which is bawd on the mass of each particle. Gamma-emitters must be considered as a separate problem, because they do not produce tracks. By a previous exposuredensity calibration, the size of the particle might, be determined, but this possibility has not been .investigated. LITERATURE CITEII
(1) Ualla Valle, J. hl.. “Mioromeritics.” N e w York. P i t m a n PublishLIMITATIONS OF RADIOAUTOGRAPH METHOD
ing Co., 1943.
RECEIVEDJanuary 3, 1951. Presented before the Division of Industrial
Obviously, the aerosol being studied must consist of radioactive particulates, as inert material is not detected. However, if inert material is also present, the method gives an analysis for this hazardous material only
and Engineering Chemistry, Symposium on Dispersions in Gases, a t the 17th .4nnual Chemical Engineering Symposium, Baltimore, Md., December 28 and 29, 1950. Based on work performed at Los Alamos Scientific Laboratory of the University of California, under A E C Contract W-7405Eng-36.
Infrared Spectra of Phosphorus Compounds L. W. DAASCH AND D. C. SMITH Naval Research Laboratory, Washington, D. C.
,ipplication of infrared spectroscopy to analytical and structural problems in phosphorus chemistry has been limited by the lack of spectral data on reference compounds, and by the inadequacy of information concerning characteristic frequencies of molecular groups containing phosphorus. This information was sought through study of a large number of phosphorus compounds containing a variety uf moleeular groups of interest. Empirical correlation of sixty reference spectra yielded characteristic
C
ONSIDEXABLE work has been published on the Raman spectra of phosphorus compounds, but infrared data on only a few of the simpler compounds are found in the literature (11, 1 7 ) . A study more extensive than heretofore reported hag therefore been =de of the infrared spectral properties of phosphorus compounds. It has dealt mainly, but not entirely, with organophosphorus compounds. For this type of compound, in particular, very few data have been published.
frequency ranges for a number of groups: P-H, 2350 to 24-40 cm.-’; P-F, 850 to 980 cm.-’; P - C I , 430 to 585 cm.-’; P++ 0-, 1170 to 1310 em.-’; P+-t S-, TOO to 770 cm.-l; P-C (aliphatic), 650 to 750 cm.-’; phenyl-phosphorus group, near 1000 cm.-’ 2550 to 2700 cm.-’; and 1440 cm.-’; P - 0 - H , P-0-C, 1030 to 1090 cm.-’; phosphinic acids, near 1665 cm.-’ The usefulness of these group frequencies for qualitative interpretation of spectra in terms of molecular structure is discussed and illnstrated.
EXPERIMENTAL
and Materials* The Of phosphorus compounds is somewhat complex and at present in a state of flux. Accordingly, a few definitions will simplify discussion of materials and data. Chemical Abstracts has been followed wherever possible in the scheme of nomenclature prwented in Table I.
854
A N A L Y T I C A L CHEMISTRIY
The sources or materials are given in the legends of the eixty spectra (Figures 1 to 60). The samples were the best available, Iiut in many cases some evidence of impurity was found in the .spect'ra. Samplw prepared a t the S a v a l Research Laboratory were constant-boiling liquids or recrystallized solids of constant melting point, Equipment and Measurements. A research-t ype, recording prism spectrometer ( I S ) was used for all spectral measurements. Liquid samples were placed in amalgam-sealed cells; the thickness of the cell used is given on the spectral curve in millimet~era. I n those cmes where solutions were used, the solvent is also noted. Solid samples were mortar-ground to a fine powder and mulled with a small amount of petrolatum t o form a smooth paste, which was then placed between potassium bromide plates separated by a spacer and mounted in a suitable holder. The effect of petrolatum absorption was canceled out roughly by measuring the mulls relative t o a petrolatum blank.
Table I.
Vomenclature of Phosphorus Compounds
/OH P-OH
/OR
P-OR
H-P
\OR
Phosphorous Acid -0 O K
Phosphite -0 OR
*
\OR Phosphonite H -0 \-
/
O 'R
\OH
/
0H'
H--P
Phosphonic 4cid
OR
H--P
F h o ~ p h o n o u sAcid H -0 ' I 'P OH
-I /
/'
OH
\
'0 H
H-P
/
ti
Phosphonate
H
I'ho\phinic .kcid -0 R
/P-oR
Phosphinate
+I/ R--P \
R Phosphine Oxide IR = alkyl or aryl) Phosphoril Halide ( R = halogen)
GROUP FREQUENCIES I N PHOSPHORUS COMPOUNDS
P-H and P-D bonds. I n phosphine, the fundamental stretching vibrations of the P-H bonds appear a t 2327 and 2421 c m - l , while those a t 991 and 1121 cm.-l may be described approximately as bending motions of P-H bonds ( I O ) . Seven compounds believed to contain a P-H hond have been studied, and, as summarized in Table 11, all have an abeorpt,ion hand in the region 2350 to 2440 cm.? Because other phosphorus compounds exhibit little or no absorption in this region, t,hese h i i d s may confidently be assigned to stretching vibrations of the P-H bond. Little can be said concerning the dependence of the P-H stretching vibrations within this 100 cni.-l range. -411 of the compounds st,udied have one P-H hond only, and none contained trivalent phosphorus. Replacement of hydrogen by deuterium should produce a n isotopic frequency shift of ahout 650 em.-' for the Etretching vibrations. Upon deuteration of benzenephosphinic acid (with heavy water) i t v.-ae observed that the P-H absorption a t 2381 c m - ' decreased in intensity while a new band, undoubtedl>- due to the P-D vibration, appealed a t 1750 cm.-l .Ibsorpt,ion due to the P-H bending vibrat,ion has not been identified in these compounds. It is evidently weak and spread
Table 11.
P-H
Absorption Frequencies Position
Compound Diethyl phosphonate Di-n-butyl phosphonate Ethyl benzenephosphinate Benaenephosphinic acid p-Toluenephosphinic acid Saphthalenephosphinic acid p-Ethylbenzenephosphinic acid
___
I'igrire i
17 .5 4 R
10 11
Cm. - 1 2433 2410 2350 2381 2440 2391 2391
~~~~
o w r a greater spectral interval than the stretching vibration, facts which make i t difficult to identify. It probably occurs in the region from 950 to 1150 cm.-', where it is masked by other intense hands not related to P-H bonds. P-F Bond. The P-F stretching frequencies may be expected in the region from about 840 to 980 crn.-I by analogy with the positions of these frequencies in phosphorus trifluoride (9) and phosphoryl trifluoride ( 6 ) ,as listed in Table 111. Three additional compounds of higher-valent phosphorus, all containing a single P-F bond, have strong bands between 850 and 900 cm -1 which are undoubtedly due to this vibration. Compounds of this
I I
WAVE Figure 3.
LENGTH-
P
4.11 4.15 4 25 4.20 4.10 4.18 4 18
r*w
Figure 1. Trimethyl Phosphate (Naval Research Laborator)-) Figure 2. Tetramethyl Pyrophosphate (Victor Chemical Works) Trimethyl Thionophosphate (University of Chicago Toxicological Laboratory)
V O L U M E 23, N O . 6, J U N E 1 9 5 1 Table 111.
P-F
C onipoiind
Phosphorus rnfluoride Phosphoryl trifluoride Thiophosphoryl dichloride fliioride Dimethyl fluorophosiihate Diethyl fluorophosphate .\-.S-diethvlaininopliosphorus diflrioride
855 500 cni.-l which correspond ioughly to stretching motionF (In phase and o u t of phase) of P-CI bonds. These frequencies are listed in Table IV, together with the observed positions of bands believed to arise from P-CI stretching in seven additional conipounds. In each case one band is observed between 475 and 540 mi.-' For chlorides of trivalent phosphorus the bands fall in the region from 485 to 525 cm.-l, while for the compoundE of higher-valent phosphorus they occur between 430 and 585 cm.-l Those compounds containing two or more P-CI bonds usually exhihit two hands within these regions.
Stretching Freqiiencies Formula PF3
PCFa
Position Cm. - 1 p 840,890 865.980
Figure
11.2,ll 2 11. i . 10 2
PSCIzF 400 (CH30)tPOF 860 ~ C ~ H K O ) ~ P880 OF
11 1 11.4
40 . 9 i
11.4
60
( C ~ H K ) ~ X - P 740,800 F~
13 5 . 1 2 . 5
58
type, but wit,h tm-o P-F bonds, have not beeii st.udieti. and may not always absorb within this region. The spectrum of only one fluoride of trivalent, phosphorus h a p been obtained (Table 111),so that for this type of compound it is known only that P-F frequencies as low as 740 cni.-' may occur. Until additional flucrides of trivalent phosphoru:: and higher-rrtle~itphosphorus compounds containing t'he PF? groups are st,udied. our knowledge of P-F frequencies will r r m i n inadequate. P-Cl Bond. According to previous results (6, IO) c~:ic~llof the inorganic compounds phosphorus trichloride, phosphoryl uichloride, a n d thiophoephoryl chloride has two frrquetic+- a r o u ~ i d
Table 1 \ . Compound
F-CI
Stretching Frequencies Formula
Phosphorus crichloride Phenyldichlorophosphine Et hyldichlorophosphine Phosphonitrilic chloride (trimer) Phosphoryl chloride Phenyldichlorophosphine oxide Diphenylchlorophosphine oxide Thiophosphoryl chloride Phenyldichlorophosphine sulfide Thiophosphoryl dichloride f l r i PSChF oride
4
WAVE
LENGTH- mu
Figure 4. Benzenephosphinic Acid (Naval Research Laboratory) Figure 5. Ethyl Benzenephosphinate (Naval Research Laboratory) Figure 6. Diethyl Benzenephosphonite (Naval Research Laboratory) Figure 7 . Diethyl Phosphonate (Naval Research Laboratory) Figure 8. Triethyl Phosphite (Monsanto Chemical C o . )
Position Cm. - 1 p 488,511 ,500
488, 302 488, 321 485, 581 488. 572 521 433 ,538 500.524
20.5, 19.6 20.0 20.5,19 2 20 5 , 19 2 20.6, 17 2 20 5, 1 7 . 5
~ i ure 28 38 4;
56 25
19.2 26 23.1, 18 6 20.0,19.1 2 i
476,366 21 O , l 7 7
40
~
-
ANALYTICAL CHEMISTRY
856
WAVE LENGTH
- mu
Figure 9. p-Toluenephosphinic Acid Figure 10. Naphthalenephosphinic Acid Figure 11. p-EthylbenzenephosphinicAcid Naval Research Laboratory
w
WAVE
LENGTH - m u
Figure 12. Benzenephosphonic Acid (Naval Research Laboratory) Figure 13. p-Chlorobeozenephosphonic Acid (Monsanto Chemical CO.) Figure 14. Diethyl p-Chlorobenzenephosphonic Acid (Monsanto Chemical Co.) Figure 15. Diethyl Benzenephosphonate (Naval Research Laboratory)
V O L U M E 23, NO. 6, J U N E 1 9 5 1
8ST
Phosphoryl Group. LVhen an oxygen atom is bonded only to +
-
a pliosphorus atom, the rrsulting group, =(P-O), will be called the phosphoryl group,. 1111 phosphoryl halides (OPX) exhibit R strong barid near 1280 c ~ i i . -due ~ to the strrtching vibration of this group (6, 10). Au intense band in this same region, a d having the same origin, has also been observed for other compounds containing the phosphoryl group, as listed in Table V. Compounds of trivalent phosphorus usually do not absorb strongly in this region.
TutJt 1'.
1275
7
126.5
7 90
1265
7 90
1265
7 BO
1257
7.95
1236
8.10
1236
8.10
1190
8.40
1176
8.50
Kj
Deptmclerice of t'hosplior> 1 Frequency upon Electronepativit?of 5ui)stitueuts Position Cn-1 130.5
7.61
7 58
1309
J
7.75
1276
7 85
1M
WAVE
LENGTH - m u Figure 18. Figure 19.
Figure 16. Tri-n-butyl Phosphite Figure 17. Di-n-butyl Phosphonate Naval
Reattnish Laboratory
n-Butanephosphonic Acid Di-n-butyl n-Butanephosphonate
858
.
ANALYTICAL CHEMISTRY
The phosphoryl frequency occurs in a rather wide range estending from 1170 to 1310 cni.-l The position of the band within this range appears to depend neither upon the type of compound (as shown by the intermixing of phosphonates, phosphinates, and phosphine oxides in Table V) nor upon the size of the subst,ituents (as shown by the intermixing of compounds of different molecular weight). There is, however, a definite correspondence between the phosphoryl frequency and the electronegativity of the other subutituents on the phosphorus atom (as shown in Tahle V), the high frequencies always being associated with high electronegativities. This relationship is of considerable help in identifying the substituent groups, as illustrated by the examples cited below. .Icids have not been included in this correlation. I n the case of phosphonic acids (Figures 12, 13, and 18) and phosphinic acids (Figures 4,9,10, and ll), both the phosphoryl band and the hydroxyl band are displaced toward lower frequencies and YO broadened t h a t they are difficult to identify, particularly in the spectra of the solid samples. The effects are clearly due to hydrogen bonding between the acid hydrogen and the phosphoryl oxygen. I n dilute solutions t,he effects are greatly diminished, as shown by the spectra of benzeriephosphinic acid (Figure 4) in the 1200 crn.-' region. Thiophosphoryl Group. The valence vibration of the thio-
phosphoryl linkage appears a5 a medium to strong band a t 753 cm.-' in thiophosphoryl chloride and a t 718 cm. --I in thiophosphoryl immide (6). Thiophosphoryl dichloride fluoride (Figure 40) and phenyldichlorophosphine sulfide (Figure 27) each has a strong band in the 745 to 750 cm.? region, although in the latter case the ahorpt,ion would be expected from the presence of the phenyl group. Similarly, five compounds of the type SP(C,H,)(SR& (Figwes 42 to 46) have one band a t approximately 720 c m - ' , and another between 745 and 765 ern.-' One of these (probahly the former) is undouhtedly associated with the phenyl group, and the ot,her may be related to the thiophosphoryl group. The spectrum of the compound known as trimethyl thionophosphate (Figure 3) is peculiar in that the thiophosphoryl absorption is displaced, weak, or ahsent, n-hereas in other compounds it appears a s a medium to strong hand in the region 715 to 770 c i n - ' P-C (Aliphatic) Bond. I n trimethylphosphine the two vibrations which involve mainly a stretching of P-C bonds appear at, 653 and 708 cm.-l (14). In trimethylphosphine oside the corresponding vihrations appear at 671 and 756 crn.-' ( 5 ) . If characteristic frequencies for P-C' stret,chingvibration esist, they should appear in the approximate range 650 to 750 c i n - ' , although the size and structure of the alkyl groups and the identit.! of the
1
WAVE
LENGTH - m u
Figure 20. Benzenephosphinic . k c i d 4 (Naval Research Laboratory) Figure 21. Benzenephosphonic kcid-ds (Kava1 Research Laboratory) Figure 22. Phosphorus Pentoxide (J. T. Baker Chemical Co.) Figure 23. Triphenylphosphine Oxide (Naval Research Laboratory) Figure 24. Trimethylphosphine Oxide ( l a b al Research Laborator))
859
V O L U M E 2 3 , N O . 6, J U N E 1 9 5 1
y r c t i v e stiuctures,even though the ring is attached to ph hphoi us in each case. Presumably other polysubstituted aromatic groups having one phosphorus substituent will also exhibit the characteristic frequencies by which they may usually be identified. There are two additional frequencies near 1000 and 1440 c.ni.-' in the spectra of all compounds containing a phenyl group attached directly to phosphorus (Table VIII). The band a t 1000 cm.+ is usually stronger than observed for hydrocarbons :md the other always occurs below 1450 cm.-' in phosphorus compounds but above 1450 cm. -1 in hydrocarbons. Although one or both of these bands may arise from ring vibrations, they
IJther substituents on th(, phosphorus atom may be esperted t o have some effect. In addition t.o the two compounds already mentioned, four other compounds with 1'--C (aliphatic) bonds have been studied (Table VI). All have bands in the region of 750 cm.-', but I)ecausr absorption appears i n this region for practically all phosphorus compounds, the oi,igin of the bands is uncertain. 111 the case of methyl group substituents, further investigation niay establish some correlations of value, but it does not appear likely that organophosphorua molecules in general can be recogriized by characteristic infr:rred absorption involving vibrations of the P-C (aliphatic) bond. Phenyl-Phosphorus Group. It is knovin from previous work :it this laboratory and elsewhere (3, 4,1.5) that the aromatic ring i i i hytlrocarbons produces a number of characteristic absorption I)aiids which not only c o n h n i the presence of the ring but also indicate the number and positions of t,he substituents. It' is celear t,hat. if the aromatic ring in :I phosphorus compound is Ijonded only to carbon, these same correlations ill apply. In the prescmt work it has been found that they also apply when the aromatic ring is bonded directly to phosphorus. Thus, all the compounds containing R phenyl group (Table VII) or a psubstituted benzene ring (Figures 9, 11, 13, and 14) exhibit the cliarncteristic aromatic fr6,quencies corresponding to the re-
Position Compound
Formula
Trimethylphosphine Triinethylphosphine aside Di-n-butvl n-butaneuhosphonatk Diethylphenyl phosphine Ethyldichlorophosphine Diethyl trichloromethanephosphonate
-
WAVE LENGTH mu Figure 25. Phenyldichlorophosphine Oxide (Xaval Research Laboratorj) Figure 26. Diphenylchlorophosphine Oxide (Naval Research Laboratorj ) Figure 27. Phenyldichlorophosphine Sulfide (Victor Chemical Works) Figure 28. Phenyldichlorophosphine (Naval Research Laboratory) Figure 29. Triphenylphosphine (Naval Research L2boratory)
Cm
-1
#
~ i ure
6.53, 708 fi71,756
I 5 , : j , 11 1 14.9, 13.4 24
735, 7 5 2
13.6.13.3
Z$!
I-.).
758
13 B 13 8, 1 3 . 2
19 39 38
R5
~
-
860
ANALYTICAL CHEMISTRY
appear to be useful for the identification (Jf' the 1,~icil~l-phodpIiorus group. In previous R-ork a t this laboratory, characteristic bands a t approximately these same positions have been observed for compounds containing a phenyl ring bonded to a silicon atom. The origin of these bands, believed to be the sanic for the two groupings, may be related to the fact that the phosphorus and silicon single bonds have about the same force constants, at least, for bonds to halogen (18) or b aliphatic carboii atoms ( 7 ) . Hydroxyl Group. I n the present work no evidenct: of a free hydroxyl group in phosphorus compounds has been found. Such groups should have characteristic absorption due to the stretching vibration of the OH bond a t about 3620 ern.-' (8,,$, 15). In every case where it was sought to identify free hyc1roxyI absorption in an acid supposedly containing trivalent phosphorusthat is, containing no polar phosphoryl groups anti consequently having the possibility of free hydroxyl groups-there was observed, instead, the characteristic absorpt,ion of the phosphoryl group, an indication that the acid contained a phosphorus atom in its higher valent state. In the presence of these highly polar groups, any hydroxyl groups may he expected to show hydrogenbonding effects. The stretching frequency could be expected in the 3000 em. region, which is partially masked by the absorption of petrolatum used in the preparation of the solid samples. However, one compnund, benzenephosphinic acid, n-hich was soluble enough to be studied in carbon disulfide solution, showed (Figure 4) a strong, broad band a t approximately 2680 em.-' Absorption at, about this same position vias also observed for several other compounds studied as solids. It is believed to be due to bondcd hydroxyl gpnups, especially as other compounds n-hich
~~
Table 1 I I .
I'heii) I-Phosphorus Group Frequenc? Frequencies, C m . 3
Compound
Benzenephosphinio acid Ethyl bensenephosphinate Diethyl benzenephosghonite Benzenephosphonic acid Diethyl benzenephosphonate Benzenephosphinic acid-dr Benzenephosphonic a c i d 4 Triphenylphosphine oxide Phenyldichlorophosyliine oxide Diphenylchlorophosphine oxide Phenyldichlorophosphine sulfide Phenyldiohlorophospliine Triphenylphosphine Diphenyl benzenephosphonate Benzenephosphonic dianilide Benzenephosphonic diphenylhydrazide Diethylphenylphosphine .V,.V-Dimethyl benzenethiophosphonic diamide S,N-Diethyl benzenethiophosphonic diamide Y,N-Di-n-butyl benzenethiophosphonic diamide .V,.V-Diisobutyl benzenethiophosphonic diamide S,.Y--Didecyl beneenethiopho~plionicdiainide
1442 1413 1441 1440 1450 1443 1440 1440 1441 1443 1440 1436 1435 1450 14iO" 1440 1440 1440 1440 1435 143s
1002 1000 1000 998 1000" 1003 998 996 998 997 999 999 999 1005 1000 1000" 1000 995'1 1002[L 1oooa 995a 990"
I'ieilr
6 12 15 20 21 23 25 26 .>i 28
-
?!I :?A 96
37 39
42
43 44 4.-1 46
Weak band.
cwinot contain hydroxyl groups are considerably more trms-
parent iii this region. The data itre summarized in Table irIII, Although the frequency range is somewhat lower than that usually observed for hydrogen-bonded hydroxyl groups in alcohols, aliphatic acids. phenols, etc., it is not much lower than t,hat reported for benzoic acid (16). P-0-R Linkage. Organic esters have a characteristic band a t about 1110 em.-' which has been ascribed to the G O - - c ' linkage (3, 4,1.5). Substitution of phosphorus for carbon in an
I
14
WAVE
e
4 5
LENGTH
15
16
17
-ma
Figure 30. Tetraethyl Pyrophosphate (Victor Chemical Works) Figure 31. Tetra-n-but>-lPyrophosphate (Victor Chemical Works) Figure 32. Methyl Ethyl Phosphate (Victor Chemical Works) Figure 33. Triphenyl Phosphate (Eastman Kodak Co.)
18
19
20
21
V O L U M E 23, N O . 6, J U N E 1 9 5 1
861
ester group will normally shift the absorption band toward lower frequencies. Indeed, in the twenty phosphorus esters Position ~ i ~ listed in Table I X there was found near 1050 cm.-l a strong, Cm.-1 p ure Formula Compound moderately broad band envelope which was absent in each of Benzenephosphinic acid 3 73 4 CsHsPH(0) OH 2680 pToluenephosphinic acid CHs-CaH4PH(O)OH 2640 3.79 9 four parent acids studied and which is believed to be characNaphthalenephosphinic linkage in alkyl esters. The frequencies teristic of the P-0-R CiaHiPH ( 0 ) O H 2550 3 92 10 acid pEthylbenzenephosphinic C I H ~ - C ~ H I P H ( O ) O H 2640 3.79 11 given in the table are the estimated centers of the band envelopes acid CaHsPOH (0) OH 2690 3 72 12 Benzenephosphonic acid which sometimes have rather sharp absorption peaks superpChlorobenzenephosphonic acid Cl-CsH4POH(O)OI-I 13 imposed on them. 25503'9218 n-Butanephosphonic acid C I H ~ P O H ( O ) O H When the R group is methyl 2800 3.57 Methyl ethyl phosphate CHsO(CaHaO)P(O)OH 2650 3.77 32 ( F i-w e s 1, 2, 3, 32, and 49) the P-0-R absorption a p pears as a single, well-defined, Linkage Table IX. Characteristic Absorption Bands of the P-0-C strong band, and there is obA4pproximate Position of served, in addition, a weak but Center of Band Figtire sharp band a t about 1190 Envelope CornParent Compound Formula Cm.-i p pound acid rm.-I Furthermore, the 19 Di-n-butyl n-butanephosphonate 9.65 18 methyl g r o u p a b s o r p t i o n 15 Diethyl benzene hoaphoniate 12 9.5 (which appears a t 1379 em.-' Diethyl p-chlorogenzenephosphonate 13 9.6 9.5 Ethyl benzenephosphinate 4 in hydrocarbons) is not ob6 9.6 Diethyl benzenepbosphonite 59 9.5 Dimethyl fluorophosphate served at its usual position. 60 Diethyl fluorophosphate 9 5 When the R group becomes Trimethvl Dhnsnhate 1 9,6 TctrarnGh;4 pirrophosphatc 2 9.4 ethyl (Figures 5, 6, 7, 8, 14, Trimethyl thionophoeghate 3 9.7 Diethyl phosphonare 9.5 7 30, 32, 35, 50, and 5 5 ) the 9.i Triethyl phosphite 8 P-0-R band becomes some16 9 7 Tri-n-butyl phosphite 9.63 31 Tetra-n-but 1 pyrophosphate what broadened and frequently 35 9.7 Diethyl tricgloromethanephosphonate 9.6 Methyl phosphonitrilate (trimer) 49 shows subsidiary maxima, the n-ProDvl Dhnsohonitrilate (trimer) 9.65 ;1 02 9 7 Isopropyl'phosphqnitrilate (trimer) methyl group (in GH,) absorbs 53 9.6 Ootyl phosphonitrilate (trimer) posinear its usual 1379 9.7 55 Ethyl phosphonitrilate (polymer). tion (but as a sharp halid a t
Table VlII. Possible Bonded Hydroxyl Group Frequencies
?
WAVE
LENGTH
-mu
Figure 34. Diphenyl Benzenephosphonate (Naval Research Laboratory) Figure 35. Diethyl Trichloromethylphosphonate (Rlonsanto Chemical Co.) Figure 36. Benzenephosphonic Dianalide (Naval Research Laboratory) Figure 37. Renzenephosphonic Diphenylhydrazide (Naval Research Laboratory)
ANALYTICAL CHEMISTRY
862 1388 with a weaker branch a t 1370 em.-'), and in addition there appears a sharp band of medium intensity a t 1165 em.-' Only three compounds (triphenyl phosphite, triphenyl phosphate, and diphenyl benzenephosphonate) have been studied xbsorp in which R is aromatic. The characteristic P-0-R tion does not appear in the spectra of these aromatic esters (Figures 33, 34, and 41) a t the sanie position as for the alkyl esters. Additional data are required to determine whether the band has shifted toward lower (875 to 950 c m - l ) or higher (1200 to 1250 cm.-l) frequencies. Phosphites and Phosphonates. report ( 2 7 ) that phosphites and phosphonates could be quantitatively analyzed according to type by two characteristic bands a t 870 and 940 em.-' has recently been withdrann (11). Absorptiou data in the 825 to 1000 cm.-' for typical compounds of several types here irivestigated are shown in FigurP 61. Xo basis for the proposed analytical procedure is evident, However, all four phosphites of higher molecular weight (above ethyl) have a band between 870 and 880 cm.-l, in which region other classes of phosphorus compounds are usually transparent and which, therefore, may be of some use for qualitative analysis. Phosphonates have a band betweeii 940 and 990 cm.-lrather than a t exactly 940 cni.-l, but this knowledge is of little use, even for qualitative analysis, because many compounds o f other types (including phosphites) also absorb in this region. Phosphinic Acids. All five acids of the type RPO(H)OH showed definite spectral similarities (Figures 4, 9, 10, 11, and 20), some of which are due to the characteristic absorption of P-HI OH, and P-0, and of the aromatic ring which was present in each compound. In addition, each has a broad band of medium or low intensity a t 1665 c 1 n - 1 which is not observed in other classes
of compounds and lyhich has been useful for identification of phosphinic acids. DISCUSSION
In Figure 62 are summarized in graphical form probable characteristic frequency ranges for several molecular groups, as derived from the data presented. Because these correlations are based upon a limited number of compounde, they must be applied with due reserve, especially in cases where other than organophosphorus compounds are considered. Those of a particularly tentative nature are indicated by broken-line boxes. The ranges given for P-€I and phosphoryl group frequencies are in agreement with the correlations of Chlthup ( 4 ) and data cited by Thompson (11). Thompson has also suggest.ed that t,he P-0 link in P--0-C produces ii harid :It 795 cm.-l, but this is not particularly evident in t,he authors' curves and does not, appear to be as useful as the I050 cm.-' absorption. The latter probably arises from the 0--C part of the P--o--C group. Application of these correlations to determination of molecular structure is most fruitful in the case of pure materials, for in this case the minimum number of different groups is present in the sample. To illustrate, Figures 15 and 25 are chosen, assuming for present purposes that, these are the spectra of unidentified phosphorus compounds.
Cm. -1
:HI00 1480
_-
For Figure 16
Observation
Strong band Strong band
InterpretatioiiC-H C'-H
present present
I
e
3
4
5
WAVE
LENGTH-mu
Figure 38. Ethyl dichlorophosphine (Naval Research Laboratory) Figure 39. Diethj-lphenylphosphine (University of Chicago Toxicological Laboratory) Figure 40. Thiophosphoryl Dichloride Fluoride (University of Chicago Toxicological Laboratory) Figure 41. Triphenyl Phosphite (Eastman Kodak Co.)
V O L U M E 23, NO. 6, J U N E 1951 -
Cm-1
863
For Figure 15 (Contznued)
Observation
greater than methyl (probably ethyl) and X is an electronegative group. -0 OCzHs
Interpretation
2665 -4bsorption weak 2350- Y o sharp band 2450 1260 Iiitriise band
S o 0-H;
not an acid
+I /
Actual compound. Diethyl benzenephosphonate, CsHs-P,
SOP-H
I’hosphoryl group present, probably with two or three electronegative substituents 1050 lirgion of intt~tisc~ :iIiwiyitioii P-0-R present, an ester (alkyl) s o band Xot a methyl ester; probably 1200 1166 Sharp band I :in ethyl ester Strong sharp band \ 700 750 Strong sharp band 1030 Strong sharp band \ Phenyl KI oup prearnt 1605 Strong sharp band I Sharp band I 3050 1450 Strong sharp band ’, Phenyl group attached to 1000 Weak sharp band phosphorus Iritensc absorption Many phosphorus compounds 980 absorb here Conclusioii. The compound is probably a phosphonate of structure CsHaP(O)(OR)z where R is greater than methyl, probably ethyl; it
1
\
OCiHs
3000 2665 23502460 690 760 1030 1605 3050 1450 1000 1275
-0
+I
could also he a phoxphinate of atrurtiire CnHs-P--X
I
where H is
For Figure 25 Interpretation
Observation
CUI-’
N o band Absorption weak S o sharp band
Strong band Strong band Sharp band Strong band Sharp band
S o paraffinic C-H KO *H, not an acid No P-H
1
1 J
Phenyl group present
}
sharp band Phenyl group attached to phosphoius Sharp band Intense band Phosphoryl group present, with two or three electronegative substituents (since one substituent is phenyl, remaining two must be electronegative) Stlong
(Continued on nert page)
OK
I
WAVE Figures 42 to 46.
LENGTH
N,N-Dimethyl-, N,N-Diethyl-, N,N-di-n-butyl-, N,N-Diisopropyl-, and N,N-Didecylbenzenethiophosphonic Diamides Naval Research Laboratory
ANALYTICAL CHEMISTRY
864 Cm.-’ 1050 1 1 10 9iO
i50 570
For Figure 25 (C‘ontznued) Obseivation Interpretation Wo intense band Not an estei Intense band ? Broad band hlany phosphoius tompourids dbsorb here Intense absorption Possibly P-F Broad band Possibly P--ri
Conclusion
Compound must he a p h o s p h i n ~oxide u i t h
atiul t u l e
x
-0
+I / CsHs-P \
Y
where both X and Y are electronegative, possibly fiuol 1111’ 01 Actual compound. Phenyldichlorophosphine oxide. -0
+I /
When other information-for example, the method of preparation or the physical and chemical properties of a material-is available, those data should also be taken into consideration. As a case in point, the spectrum of benzenephosphinic acid is readily interpreted in terms of t h e simple structure shown on Figure 4, except that here (and in all acids studied) hydrogen bonding is observed. It has been found independently by iiiolecular weight determinations in benzene solution (8) that the acid exists in trimeric or higher polymeric form. Thus, the w t u a l structure probably consists of cyclic (or possibly linear) jn~lyrnersi I i which the monomers &re joiued by hydrogen honds. :IC I I I the structurt.
c hioi
ii~e.
c1 Speclral uietliuds, M Y illustrated, liave proved very useful im the course of work for the identification of other types of phosphorw compounds, including most of t h o v listed in Table 1 Many
CsHa-P
\
(‘1
A7
2
,3
4
5
6
7
8
IO
9
II
12
13
14
15
6
51
I
J
\
/\
(PN
3
4
5
6
7
8
9
IO
WAVE
II
I2
LENGTH
G3t$&
n
‘ 1
n
2
21
I7
13
14
15
-mu
Figure 47. Phosphonitrilic Chloride ‘I’rimer Figure 48. Phosphonitrilic Chloride Tetramer Figure 1.9. Methyl Phosphonitrilate Trimer Figure 50. Ethyl Phosphonitrilate Trimer Figure 31. n-Propyl Phosphonitrilate Trimer Y a w l Rracilrch Caburaiur.
16
I7
le
19
20
21
V O L U M E 23, NO. 6, J U N E 1 9 5 1
865
heen ancvuntered i n which a reaction product tlws riot h a w the structure expected 011 the basis of c,hemical considerations alone, or in which t,mo or more structures were possible. In such caves identification hy chemical met.hods can undoubtedly l h made, h u t spectral methods appear tL1 he much simpler, faster, and sometimes more relia.ble, pert,icwl:iI,ly in connection \\-iththe prepa.ration of new compounds. For r w m p l e , tjhe acid ohtaiiied by hydrolysir of phenyldi~ ~ h 1 ~ 1 ~ 1 ~ (C',H,PCI,) ~ ~ ~ 1 ~ ~ ~is ~not ~ 1 the 1 i iexpected ~ e henzenephosphntioii?; sri(1, C6H6P(Of4)?, hiit rxt.her t,he monolwsir henzerie phosphi tiir- a [,id, r a s w have
In I hc j ~ i ' e s ; c ~ ror i c ~J)yi,itiiiiethe phosphonite is ohtitined (Figure ci), wherrtis reaction of t,he pure materials yields the phosphinnte, ;is shon-n (*lrwdy hy t,he j~resenceuf P-H arid phosphoryl group iwqurnc.ies in thc spectrum (Figure 3). Similarly, t h r w differriit csters may be ob1,;linetl from t l i i t iwc%ion of phosphorun trichloridr and nlcohul in the presence of riyrirlinr (!/), R S iiit1ic:ited by t>hefollowing equations:
kiy the presmce oi characteristic !?-0 ( p h ~ ~ p l i ( 1I ,t ~ j ~ 1 OH, PH, and GHbP frequencies in its spectrum (Figure 4). I n fact., in this ioveat,igation no acids of trivalent phosphorus have h e m found! In every care where it was sought to identify II :IC S h J T l l
phosphorous or phosphonous acid there was foonnti. instead, t h e mrrespmding phosphonic or phoephinir, acid. Again, two different, esters can be formed by t h e reaction of ethyl alcohol -4th phen~1.ldichlorophosphine. depending upon how the reartinn is cairierl oiit :
The > l w f r : r of the. li-l)utyI eaters prepared by 1tc:tction; I I1 t i w shruwii in Figures 16 and 17, respectively. M'hile I yielded tributyl phosphiw, a s expect,ed, I1 yielded dibutjyl phosphonate, a s ~1inw-nby the spectral differences in thc regions of arid
52 1
WAVE
LENGTH -mu
Figure 52. Isopropyl Phosphonitrilate Trimer Figure 53. Octyl Phosphonitrilate Trimer Figure 54. Phosphonitrilic Chloride Polymer Figure ri5. Ethyl Phosphonitrilate Polymer \ a > nl
HCSPHrrh 1.a horator?
866
ANALYTICAL CHEMISTRY
P-H and phosphoryl absorptions near 2400 and 1275 e m - ’ , respectively. These differences are again illustrated in the ethyl esters in Figures 7 and 8. Reaction I11 has not yet been studied, but the spectrum of the ester should readily show whether the or the more likely alkyldihydrogen phosphite, RO-P-(OH)*, OH alkyl hydrogen phosphonate, RO-(PO)< , is obtained.
H
Uncertainty as to the structure of esters also arises becaust’ of the possibility of rearrangement. For example, in the Arbusov transformation (1, 2 ) trialkyl phosphites are converted into dialkyl alkane phosphonates by alkyl halide according to the reartion:
-0
(RO),P
+I + RIX +RI-P-(OR),
+ RX (R, can be equal to I t )
Moreover, this conversion is reported to occur in certain instances w-ithout alkyl halide ( I d ) and to have the properties of a catalytic reaction (1, 2). It is frequently desirable, thrrefore,
to check the structure of an ester to determine whether rearrangement has occurred, and this is easily done by means of the phosphoryl frequency. I n the present work tri-butyl phosphite and tii-n-butyl n-butanephosphonate (Figures 16 and 17) have shown no tendency to rearrange a t room temperature. Finally, the characteristic group absorptions have been found useful in determining the purity of esters which tend to hydrolyze. For example, samples of pure triethyl phosphite, P(OC?H&, and diethyl benxenephosphonite, CsHsP(OC?H& (io not exhibit strong Characteristic absorption of phosphoryl, P---H, or OH (bonded), but most preparations of these compounds do have some absorption in these regions (Figures 6 and 8). Uthough these veak bands may he due to combination frequencies, it is more likely that they are caused by a small amount of hydrolytic impurity. When the samples were purposely Pxposed to the atmosphere for short periods of time, the intensity of these bands rapidly increased. ACKNOWLEDGMENT
The ituthors gratefully acknowledge the work of W.T . Dye, I,. €3. Lockhart, R. B. Fox, E:. J. Kohn, U. E. Hanninen, and
WAVE LENGTH m u Figure 56. Phosphoryl Trichloride (Naval Research Laboratory) Figure 57. Phosphoryl Tribromide (Naval Research Laboratory) Figure 58. N,N-DiethylaminophosphorusDichloride (University of Chicago Toxicological Laboratory) Figure 59. Dimethyl Fluorophosphate (University of Chicago Toxicological Laboratory) Figure 60. Diethyl Fluorophosphate (University of Chicago Toxicological Laboratory)
V O L U M E 23, NO. 6 , J U N E 1 9 5 1 Bernard Buchner. x h o svnthesized manv of the conwounds studied. Thanks are alsdextended to those organizatiois who contributed samples and to 111.~.E. J. Butler for her assistance in ulltaining some of the spectra. LITERATURE CITED
(1) Arbusov, .4., "Catalytic Phenomena in the Field of Phosphorus
Chemistry," dissertation. Kazan. 1914.
Rpectriiiii No.
867 (2) .Irbusov, -I.,J . Russ. Phys. Chem. SOC., 38 (ii), 687 (1906). (3) Barnes, R., Gore, R., Stafford, R., and Williams. v., ANII,. CHEW,20, 402 (1948). (4) Colthup, N., J . Optical SOC.Am., 40, 397 (1950). ( 5 ) Daasch, L., and Smith, D. C.. J. Chen. Phus., 19, 22 (1951). (6) Delwaulle, hl., and Francois, F., C o m p t . rend., 220, 817 (1945); 222, 1391 (1946); 224, 1422 (1947). (7) Duchesne, J., J . C h m . Phus., 7, 87 (1939). (8) Dye, W. T., Naval Research Laboratory, unpublished data
CM-' Phosphites
8
Triethyl phosjiliitr
16
Tributyl phosphite
41
Triphenyl IJhosphite
(17)
Tri-o-tolyl phosphitc
(17)
Di-o-tolylbutyl pliospliiti,
I'hosphonate? 7
Diethyl phosphonate
17
Dibutyl phos1)honate.
3 r,
Diethyl tricliloromethyl~,iioapliotiat~
1,s
Diethyl henzenephosphunate
14
Diethyl p-chlorobenzeneiilio~Iihot,iIt~
19
1)i-n-biityI-ii-butaneIrtioslilionate
34
Diphenyl henzenepiio-plionatc
(17)
Di-o-tolyl hutanephosphonute
(17)
Di-p-tolyl inethanel)hoslilionatr
I'houphonic acids 18
n-Butanephosplionic acid
12
Benoenephosphonic acid
21
Benaenephosphonic acid-dl
13
p-Ctilorohenzenepliosl,2lr,nir
a
