The infrared spectra of organophosphorus compounds in the CsBr region

Spectrochimica Acta,1963, Vol.19,pp.811to 817.Pergamon PressLtd. Printed inNorthern Ireland

The infrared spectra of organophosphoruscompounds in the CsBrregion* J. R. FERRARO, D. F. PEPPARD and G. W. MASON Argonne National Laboratory,

Argonne, Illinois

(Received 10 October 1962) Abstract-The infrared absorption spectra of organophosphorus compounds of the type GOG’PO(OH), (GO),PO(OH), (GO),G’PO and (GO),POt have been investigated from 275 to 650 cm-l. Absorption in the 600 cm-l region appears to be associated with the P-OQ, group and absorption in the 530 cm-l region with the PHI group.

INTRODUCTION A LONG-RANGE program investigating

various phosphorus compounds in the 275-650 region has been initiated. This paper reports on a preliminary investigation of the families GOG’PO(OH), (GO),PO(OH), (GO),G’PO and (GO),PO. The acidic compounds [l, 21 reported in this study have only recently been synthesized, and have not, been previously investigated in the CsBr region. The infrared spectra of the acidic compounds in the NaCl region have been reported [I, 21. Few infrared studies in the CsBr region have been reported with phosphorus compounds, and most of these have been made only to 450 cm-l. MEYRICK and THOMPSON [3] studied some organophosphites and neutral phosphonates, [(GO),G’PO] to 450 cm-l. The infrared spectrum of trimethyl phosphine oxide was investigated from 450 to 5000 cm-l in 1951 by DAASCH and SMITH [4]. They also studied a number of halogen containing phosphorus compounds in this region [5], and proposed a PC1 absorption in the region 430-585 cm-l. In 1954 DAASCH [6] investigated the infrared spectra of (PNCI,), and (PNCl,), down to 260 cm-l. CORBRID~E [7] also studied halogen containing phosphorus compounds, and proposed a PC1 stretching absorption at 440-580 cm-l and a PBr stretching absorption at 440-485 cm-l. MORTIMER [8] investigated the infrared spectra of trimethyl, triethyl and triphenyl phosphate to 450 cm-l. NYQUIST [9] studied several chlorine containing phosphorus cm-l

* Based on work performed under the auspices of the U.S. Atomic Energy Commission. Presented at the International Symposium on Far Infrared Spectroscopy, Cincinnati, Ohio, August, 1962. t G may be aryl, alkyl or mixed alkyl-aryl or a substituted variant thereof. [l] D. F. PEPPARD, J. R. FERRARO and G. W. MASON, J. Inorg. & Nuclear Chem. 16,246 [2] D. F. PEPPARD, J. R. FERRARO and G. W. MASON, J. Inorg. & Nuclear Chem. l&60 [3] C. I. MEYRICK and H. W. THOMPSON, J. Chem. Sot. 225 (1950). [4] L. W. DAASCH and D. C. SB~ITH,J. Chem. Phys. 19, 22 (1951). [KJ L. W. DAASCH and D. C. SMITH, Anal. Chem. 23, 853 (1951). [6] L. W. DAASCH, J. Am. Chem. Sot. 76, 3403 (1954). [7] D. E. C. CORBRIDUE,J. Appl. Chem. 6, 456 (1956). [8] F. S. MORTIMER, Spectrochim. Acta 9, 270 (1957). [9] R. A. NYQUIST, J. AppZ. Spectrosc. 11, 161 (1957). 811

(1961). (1959).

812

J. R.

FERRARO,D. F. PEPPARDand G. W. MASON

compounds and proposed a PC1 frequency at 430-585 CID-~. MCIVOR et al.[ 101 studied some sulfur and chlorine containing phosphorus compounds to 450 cm-l. A 1954 Army Chemical Corps report [llj lists some work done with several phosphorus compounds to 450 cm-l. THOMAS and CHITTENDEN[ 121 recently reported on some group frequencies found in the region 435-587cm-l for organophosphorus compounds. MOEDRITZERand IRANI [13] have investigated the tetra-ethyl methylene-diphosphonates and the methylene-diphosphonic acids through the KBr region.

I /

A t

l-l

n- Decyl

\

hydrogen

n - Decyl phorphonate Film-

(Liquid 0.03

mm)

I 2-ethylhexyl

\

hydrogen 0.03

phenyl

hydrogen

phenyl

phosphonote

mm]

phenyl

phosphonote

400

600 Frequency,

cm-’

Fig. 1. Spectra comparing various acidic organophosphonates in 275-650 cm-l region. EXPERIMENTAL The initial program was commenced using a Beckman IR-4 equipped with cesium bromide optics, and later the IR-4 was converted to a Beckman IR-7 equipped with CsI optics. Solid-state spectra were obtained with CsBr and KBr pellets. Liquid spectra were made with cells having polyethylene windows, and in sealed cells using CsI windows and platinum spacers of 0.03 mm thickness. [lo] R. A. McIvox, G. A. GRANT and P. E. HUBLEY, Can. J. Chem. 34, 1611 (1956). [ll] Chemical and Radiological Laboratory Report CRLR 310. 11 February (1954). [l2] L. C. THOMAS and R. A. CHITTENDEN, Chew+. & 1nd. (hndon) 1913 (1961). [13] K. MOEDRITZER and R. R. IRANI, J. Inorg. & Nuclear Chem. 22, 21’7 (1961).

The infrared spectra of organophosphorus

compounds in the cesium bromide region

813

The spectra shown in Figs. 1 and 2 are presented as obtained by the IR-7. The overlap region (450-500 cm-l) occasionally appears to disagree. However, all spectra had been obtained with the IR-4 prior to conversion, and the results in this region are reported on the basis of the IR-4 scans. The acidic organophosphorus compounds were synthesized as previously reported [ 1, 21. The neutral compounds were obtained from commercial sources such as : Victor Chem. Co., Aldrich Chem. Co., Delta Chem. Works, Monsanto Chem. Co., Virginia Carolina Corp., KaK Laboratories and Eastman Org. Chemicals. The results reported in this investigation were obtained on 19 acidic organophosphonates, 18 acidic organophosphates, 20 neutral organophosphonates, 20 neutral organo-

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A

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500

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Fig. 2. Comparison of spectra of acidic and neutral alkyl phosphates and phosphonates.

phosphates, 5 phosphonic acids, 5 phosphonic acids, 4 phosphine oxides and 6 miscellaneous compounds. As more compounds become available through synthesis or from commercial sources their spectra will be obtained. The inferences made in this paper on characteristic frequencies must thus be considered as tentative. The absorption at about 530 cm-l, and probably due to the Pv group, is based on 28 compounds. The absorption at about 600 cm-l, and probably due to the POP, group, is based on 23 compounds.

814

J. R. FERRARO,D. F. PEPPARDand G. W. M&ON RESULTS and DISCXJSSION

A. Acidic organophosphorus

compounds

The acidic organophosphorus compounds reported in this paper are of the phosand of the hydrogen phosphonate type, GOG’PO(OH). phate type, (GO),PO(OH); When G or G’ are aryl or an aryl derivative, a rich CsBr spectrum is to be expected. If one views these compounds as substituted benzene derivatives, then the reduction in symmetry that has occurred in going from benzene to mono-substituted benzene allows certain ring frequencies to become active in this region. In addition, bending modes involving the G-P, GOP and P-O atoms are also to be expected in the CsBr region. Where G or G’ are alkyl, a considerably less rich spectrum is to be expected because all of the aryl ring vibrations will be missing. The results for all series of compounds indicate that the absorptions between 500-650 cm-l are more significant than the absorptions at lower frequency. These absorptions are generally strong and sharp. The region between 300-500 cm-1 This region is less characteristic, and in some shows weak to medium absorptions. compounds these absorptions can be missing. 1. Hydrogen phosphonates (GOG’POOH). The hydrogen phosphonates studied included the types where G and G’ respectively were: (a) substituted aryl and aryl, (b) aryl-(CH,),-and aryl, (c) alkyl and aryl, (d) alkyl and alkyl. The richest spectra are shown whenever the hydrogen phosphonates have G and The region between 450-600 cm-1 has several G’ = aryl or any aryl derivative. Strong absorption occurs at about 570-605 cm-l, 535-550 strong sharp absorptions. medium absorption at 485-495 cm-l and 460-465 cm-r; and weak absorptions om-l ; at 420-430 cm-l, 350-370 cm-l and 290-315 cm-l. As G becomes aryl(CH,),-or alkyl, the spectrum in this region reduces to two strong peaks at about 530 cm-1 and 570 cm-l and weak absorptions at about 430 cm-i, 350-360 cm-l and 310 cm-l. When G and G’ are alkyl, the spectrum has degenerated into just two medium broad peaks at about 450-500 cm- l, 540-570 cm-l and weak absorption at about 300-320 cm-l. Several typical spectra are shown in Fig. 1. Within the GOG’PO(OH) series, it appears possible to distinguish between the types where G and G’ are both alkyl and where they are both aryl or where G is alkyl and G’ is aryl. On the basis of the results obtained for the compounds containing a POT and a Pg, link in this series, and also for the other series reported in this paper, it appears that the region of 600 cm-l is probably associated with the POg, group and the absorption at about 530 cm-l associated with the P----g) group. The absorption at 530 cm-l appears to be invariant, and in all compounds with P-v links varied only about &20 cm-l from 530 cm-l. 2. Acidic phosphates (GO),POOH. The phosphates investigated included the types where G is aryl and where G is alkyl. The diary1 phosphates can be very quickly differentiated from the dialkyl phosphates because of their very rich spectra in the 500-600 cm-l region. Four strong and sharp absorptions appear at about 580-600 cm-l, 535-565 cm-l, 500-515 cm-l and 470-490 cm-l in the diary1 phosphates. The dialkyl phosphates have very broad absorptions from 460-590 cm-l. Both aryl and alkyl phosphates show very weak absorptions from 300-450 cm-l, but these are less characteristic. Weak absorption at about 380-400 cm-l is present in

The infrared spectra of organophosphorus

compounds in the cesium bromide region

815

the phosphates, but apparently absent in the phosphonates. The aryl phosphates produce a richer spectra because of the ring associated vibrations. The strong band at 580-600 cm-l appears in most all of the phosphate compounds having a P-Oaryl link. However, this band in the acidic phosphates appears to be sensitive to the position of the substituent on the phenyl ring and can shift (e.g. p-tolyl phosphate shows its absorption in this region at 640 cm-l). B. Neutral phosphorus compounds The neutral phosphates and phosphonates were also studied. Although several compounds from each family have been examined to 450 cm-l, no extensive investigation has been done. 1. Neutral phosphates (GO),P 0. When G = aryl, strong sharp absorptions were found at about 578-625 cm-l, 540-570 cm-l, and 490-510 cm-r. A medium Table 1. Characteristic frequencies in NaCl and CsBr regions used to differentiate between POP and 9P groups in acidic organophosphorus compounds Acidic organophoaphorus compound

G

G’

Aryl

(GO)G’PO(OH)

NaCl region

CsBr region

(1) Absorption at -1170 cm-‘* (v((pO)P) stretching; 1440 cm-’ (2) Absorption at 9661000 cm-’ due to @(PO&)&. Main absorption shifts to -930 cm-’ on sodium salt formation

(1) Absorption at ~600

cm-’

(2) Absorption at ~530 (sharp and strong)

cm-’

ArYl

Alkyl

(1) Absorption at -1170 cm-’ (v(qO)P) stretching (2) Absorption at 966-1000 cm-’ due to (v(PO)cp)st. Shlfts to -930 cm-’ on sodium salt formation

Absorption at -600

cm-’

Alkyl

Aryl

(1) No absorption at -1170 cm-’ (2) Sharpening up of spectrum in 900-1000 cm-’ ropion on salt formrttmn, but no shift to lower frequency. (3) Ahsorption in 1000-1050 region (broad and very intense); 1440 cm-’

Abeorption et -630 (sharp and strong)

cm-1

Absorption at 1440 WI-~

G,PO(OH) GHPO(OH) GPO(OH),

ArYl

(GO),PG(OH)

A+

-

Arpl

Sharpening up of spectrum in 900-1000 cm-’ region on salt formation, but no shift to lower frequency.

Absorption at 630 cm-1 (sharp and strong)

(1) Absorption at 1170 cm-l (2) Absorption at 966-1000 cm-l shifts to -930 cm-’ on sodium salt formation

Several 450-650 636665 470-490

sharp absorptions cm-‘, 68&600 cm-l cm-‘, 60&516 cm-l. cm-’

* The peek at ~1170 cm-’ may not be diagnostic, since 80x1118 compounds have their P0 absorption in this vicinity. Absorptions presented in thig table except those involving salt formation can also be used in differentiating between FOP and pP groupe in the neutral organophosphorus compounds.

816

J. It.

D. F.

FERRARO,

and G. W. MASON

PEPPARD

to weak absorption occurs at 430-460 cm-l. absorptions occur at 520-595 cm-l and 465-495 430 cm-l and 360-395 cm-l. In all compounds

Where G is alkyl, medium broad and weak absorptions at 415-in this series containing aryl groups cm-l

(GO)2G’P-0 G

G’ methyl methyl methyl ethyl ethyl n-butyl

methyl ethyl n-propyl ethyl n-propyt n-b&y1

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I’

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I (GOI

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P-O

G methyl I

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Ii

!-ethyl haxyl

I

I’ tGO)G’PO(OH)

G n-butyl

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n-hexyl

1 n-hexyl

II

1

I-ethylheryl

2-ethylhexyl

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1 I

I

I G n-hdxyl

I

O.5012

PO(OHI

I I

2, 6-dimethylheptyl-4

700

600 Frequency,

500

450

cm-l

Fig. 3. Tabulated absorption bands from 500-600 cm-l for various alkyl organo-

phosphorus compounds ~ndicati~ shift toward higher frequenciesas the C chain lengthens. absorption was found in the 600 cm-l region. In the CsBr region, the neutral alkyl phosphates resemble the acidio alkyl phosphates, and the similarity between neutral and acidic alkyl phosphorus compounds is shown in Fig. 2. 2. ~e~~~~Z ~hos~~nu~es (GO),G’P - 0. Where G and G’ are aryl, sharp and generally medium absorption was found at 600-618 Cm-l, and sharp and strong Very weak absorption occurs at 480-500 cm-l and absorption at 515-535 cm-l.

The infrared spectra of organophosphorus

compounds in the cesium bromide region

817

Where G = alkyl and G’ aryl, strong absorptions were found at 565-585 cm-l and 520-530 cm-l, and weak absorption at 420-435 cm-l and 310-320 cm-l. Where G and G’ are alkyl, broad medium absorptions were found at 460-490 cm-l and 500-570 cm-l and weak absorption at 400-440 cm-l. In all compounds in this series where G’ is aryl absorption was found in the 530 cm-l region. 415-425 cm-l.

Characteristic frequencies in the NaCl and the CsBr regions used to differentiate between cpOP and p1P groups in acidic organophosphorus compounds It is recommended that the CsBr region be used in combination with results obtained in the NaCl region to distinguish between ~JOP and VP groups in acidic organophosphorus compounds, as is illustrated in Table 1. The absorption in the 530 cm-l region in compounds having a VP link is not as definitive as the peak at about 1440 cm-l, because compounds having only plOP links also show absorption in the same general region. However, the results of the CsBr region when used with those obtained in the NaCl region, are much more conclusive than if the results of either region are used alone. Determination

of chain length in alkyl organophosphorus

compounds

In all four families of organophosphorus compounds reported it appears that the alkyl chain length can be determined up to a limit of n = 10 where n = number of C atoms in the chain. The results are shown in Fig. 3. As the alkyl chain lengthens, the absorption maximum in the region of 500-600 shifts to higher frequency. BENTLEY [ 141 reported similar result’s with aliphatic hydrocarbons. [14] F. F. BENTLEY and E. F. WOLFAFLTH,Spectrochim. Acta 15, 165 (1959).