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Infrared and Raman spectra of tetrahydrofuran hydroperoxide
VIBRATIONAL SPECTROSCOPY ELSEVIER
Vibrational Spectroscopy15 (1997) 137-146
Infrared and Raman spectra of tetrahydrofuran hydroperoxide H.F. Shurvell a,*, M.C. Southby b a Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6 b Shell Research and Technology Centre Thornton, P.O. Box 1, Chester CH1 3SH, UK
Received 31 March 1997; accepted 1 July 1997
Abstract
The hydroperoxide of tetrahydrofuran (THF) has been prepared from unstabilized THF by a simple procedure. It appears that there are no previous reports of vibrational spectra of THF hydroperoxide in the literature. Raman and infrared spectra of the compound are presented here. The prominent feature of the infrared spectrum is a very strong broad band centered at 3330 cm-1 attributed to the OO-H stretching mode. A strong Raman line at 884 cm-1 is assigned to the O-O stretching vibration. The corresponding infrared band is very weak. 300 MHz proton and 13C NMR spectra also have been recorded. The NMR spectra are consistent with the structure 2-hydroperoxytetrahydrofuran. Implications of the formation of the hydroperoxide during storing and handling of THF as a solvent for liquid chromatography and other applications are discussed. © 1997 Elsevier Science B.V. Keywords: Raman; Infrared; NMR; Tetrahydrofuranhydroperoxide
1. Introduction Tetrahydrofuran (THF) is a widely used solvent for organic compounds and its infrared [1-5] and Raman spectra are well known [5,6]. An important use of THF is in the preparation solutions of polymeric materials. Heating is often required to dissolve the polymers or copolymers in THF. Explosions have occurred in such procedures due to the presence of THF-hydroperoxide. Although the properties of THF-hydroperoxide are known [7], there do not appear to be any published spectra of this compound. It is well known that ethers slowly form hydro-
* Corresponding author. Tel.: (1-613) 545-2646; Fax: (1-613) 545-6669.
peroxides on standing in contact with air. These compounds are often dangerously unstable and suppliers usually add small amounts of inhibitors to prevent the formation of peroxides. For liquid chromatography (LC), pure solvents are required and unstabilized THF stored under an inert gas is commonly used as a solvent. A standard method for analyzing LC fractions involves removing most of the solvent by blowing dry air into a vial containing the solution. A thin film of the fraction is then cast on a KBr window and an infrared spectrum recorded. This procedure could lead to erroneous conclusions regarding the composition of the LC fraction, because it is probable that THF hydroperoxide is formed during the evaporation process.
0924-2031/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0924-203 1(97)0003 1-3
It.F. Shurvell, M.C Southby / Vibrational Spectroscopy 15 (1997) 137-146
138
In a recent experiment in our laboratory it was required to record the infrared spectrum of a preparative gel permeation chromatography (GPC) high molecular weight fraction in THF solution out to 180 cm -1. For this a CsI window was used. It was observed that a bright yellow color formed when a drop of the residue from the GPC fraction was placed on the window. The yellow color was assumed to be due to free iodine produced by the oxidation of the iodide ion of CsI. This was confirmed by the blue color produced by a drop of starch solution. It appears that the oxidation was caused by THF-hydroperoxide formed during the evaporation of the GPC fraction. It seems likely that the hydroperoxide may react with the compounds in an LC fraction, which may lead to an incorrect interpretation of the infrared spectrum of the fraction. It is therefore important to be able to detect the presence of THF-hydroperoxide from characteristic bands in the spectrum. A search of the literature failed to find a vibrational spectrum (neither infrared nor Raman) of THF-hydroperoxide and it was decided to prepare a sample of the compound and record the spectra for future reference. X-ray structure analysis [8], high resolution neutron powder diffraction studies [9] and a microwave spectroscopic study [10] have shown that THF has the symmetric twisted conformation (1) with symmetry C 2. Ab initio calculations at various levels indicate that the C 2 conformation is more stable than the planar C s or C2v forms [5]. The ring of THF-hydroperoxide is assumed to assume similar conformation (2). In the liquid phase, THF hydroperoxide is probably intermolecularly hydrogen bonded. Also, as indicated in the structure shown below (2), intramolecular hydrogen bonding is possible between the furan ring oxygen atom and the hydrogen atom of the hydroperoxide OH group.
Much work has been published on the parent compound THF. Detailed infrared and Raman spectra of the compound in gas, liquid and solid states were included in Ref. [5] and a complete vibrational assignment based on an ab initio calculation at the MP2 level was given. Descriptions of the 33 normal modes of vibration of THF were expressed in terms of contributions from symmetry co-ordinates. These assignments have been very valuable in the present discussion of the spectra of THF-hydroperoxide. In this paper we present the infrared and Raman spectra of THF-hydroperoxide, discuss the characteristic features of the spectra and suggest assignments of the major bands. The literature search failed to find any reference to an NMR spectrum of THF-hydroperoxide, so proton and 13C NMR spectra of the compound were recorded and interpreted and are included here.
2. Experimental 2.1. Samples and sample treatment For infrared spectroscopy, the volume of an LC fraction in THF solution is reduced by blowing dry air or nitrogen into a vial containing the solution. A drop of the concentrated fraction is then placed on a KBr window and when the remaining solvent has evaporated, the infrared spectrum is recorded. It appears that during this procedure, THF hydroperoxide may be formed. A small quantity of THF hydroperoxide was prepared by blowing dry air into a vial containing unstabilized THF until all that remained was an oily viscous liquid. The infrared spectrum of this material showed no bands that could be attributed to THF. The pure hydroperoxide appears to be quite stable.
2.2. Infrared spectra Infrared spectra were recorded on a Perkin-Elmer Model 983G spectrometer interfaced to a model 7700 data station. Spectra were stored on floppy disks and subsequent handling of the spectra was carried out using the GRAMS-386 software package [11]. TM
(1)
(2)
H.F. Shurvell, M,C. Southby/ Vibrational Spectroscopy 15 (1997) 137-146
2.4. NMR spectra
Tetml~t~nm
T
4000
3!
139
The spectra were recorded on a Bruker AC300 instrument operating at 300.13 MHz for IH. A QNP 5 m m probehead was used and the spectra were acquired at 297 K. The operating parameters for ~H were: spectral width 20 ppm, total relaxation time 12.7 s, acquisition time 2.72 s, 16 scans. The solvent was CDC13 with 1% TMS. For ~3C the parameters were: spectral width 250 ppm, total relaxation time 2.9 s, acquisition time 0.8885 s, 1000 scans, 2.4 kHz decoupling using WALTZ-16. The solvent was CDC13 with added Fe(acac) 3 at 8 m g / g and TMS at
~
1% (w/w). 1068
3. Results and discussion
2961
3000
2000 1000 Wavenumber (cm 1)
500
Fig. 1. Infraredspectraof THF and THF-hydroperoxide. 2.3. Raman spectra Samples for Raman spectroscopy were contained in glass spheres blown at the ends of melting point capillary tubes. Details of the experimental arrangement for Fourier transform Raman spectroscopy have been given in a previous publication [12]. The excitation source was a cw Nd:YAG laser operating at 1064.1 nm (9397.6 c m - l ) . The laser beam was focused to a 1 mm diameter spot at the sample, which was placed at one focus of an ellipsoidal mirror. The scattered radiation was collected by this mirror and directed into the Jacquinot stop of a Perkin-Elmer Model 1760 near-IR spectrometer. Laser powers of 200-300 mW (at the sample) were used and 100 scans at a nominal resolution of 4 cm-1 were collected. The nitrogen-cooled germanium detector covered the spectral range 9400-6200 cm -1, which is equivalent to a Raman shift range of 0-3200 cm -1. The 0 - 2 0 0 cm -1 region, however, was obscured by the filters needed to remove any unscattered laser radiation. The detector response was not linear and was very low in the CH stretching region of the Raman spectrum near 3000 cm-~ and the OH stretching region could not be observed. The Raman spectra of Fig. 2 have not been corrected for detector response.
The infrared spectrum of THF hydroperoxide is shown in Fig. 1 with a spectrum of THF for comparison. A similar comparison of the Raman spectra of the two compounds is shown in Fig. 2. Table 1 lists the wavenumbers (cm -1) observed in the infrared
Tetrahydrofuranhydroperoxide
I I~I
I | 7 I~ III
416 J
n"
T~rahydrofumn
3000
2000
1500
1000
500
Wavenurnber (cm "~) Fig. 2. Raman spectra of THF and THF-hydroperoxide.
140
H.F. ShurveU, M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
Table 1 R a m a n a n d i n f r a r e d w a v e n u m b e r s ( c m - 1) a o f T H F a n d T H F h y d r o p e r o x i d e THF
THF hydroperoxide
A s s i g n m e n t b,c
Raman
infrared
Raman
infrared
--
--
--
3 3 3 0 v v s , br.
OO-H
--
2975 vs
--
2 9 8 2 sh
a s y m . C H 2 stretch a s y m . C H 2 stretch
stretch
2940 m
2960 vs
2955 m
2961 v s
2875 s
2891 s
2900 m
2892 vs
sym. C H 2 stretch
--
--
1491 m
1486 sh
CH 2 deformation
1484 sh
1460 m
1466 sh
1458 s
CH 2 deformation
1451 m
1 4 5 0 sh
1446 s
1441 s
CH 2 deformation
--
--
--
1402 s, br.
H - b o n d e d O H def.
--
1365 w
1371 w
1368 s
--
--
--
1345 s
a-CH 2 wag ot-CH w a g
--
--
1328 w
1323 s
fl- C H 2 w a g
--
--
1292 w
1290 sh
/3- C H 2 w a g
1240 w
--
1240 m
1237 v w
CH 2 twist
--
1182 m
1200 sh
1192 s
C-O-C
--
--
1126
1122
C - O O H stretch
--
1068 v s
1040 m
1068 v s
r i n g stretch
1027 w
1032 sh
--
1038 v s
r i n g stretch
--
--
--
965 v s
r i n g stretch
--
--
926 vs
928 vs
C-O-C
913 vs
910 s
--
--
ring 'breathing'
--
--
884 s
881 v w
O - O stretch
865 s h
8 6 7 sh
851 m
848 s
CH z rock
657 v w
658 w
--
754 w
CH 2 wag
.
.
.
w
.
s
6 1 0 sh
a s y m . stretch
sym.stretch
H - b o n d e d O H def.
591 v w
581 v w
--
565 m
i n - p l a n e r i n g def.
--
--
416m
--
i n - p l a n e r i n g def.
a R e l a t i v e i n t e n s i t i e s are d e n o t e d by: v = v e r y , s = s t r o n g , rn = m e d i u m , w = w e a k , sh = s h o u l d e r , b r = broad. b A s s i g n m e n t s b a s e d o n t h o s e g i v e n f o r c o r r e s p o n d i n g m o d e s i n T H F [5]. c sym = symmetric, asym = antisymmetric, def = deformation.
and Raman spectra of THF and THF hydroperoxide. An assignment of the observed wavenumbers in the hydroperoxide spectra is included in Table 1. Figs. 3 and 4 show the 300 MHz proton and 13C NMR spectra and Table 2 lists the positions and assignments of the observed resonances. 3.1. Vibrational spectra The dominant feature of the infrared spectrum of THF-hydroperoxide is the very strong broad band centered at 3330 cm -1, which is assigned to the O O - H stretching mode. Other groups of strong absorptions are observed near 2900, 1400, 1060 and 940 cm -1. Single sharp bands are seen at 1192, 1122, 848 and 565 cm-1. The strongest line in the Raman spectrum occurs at 926 cm -x. Other strong
Raman fines are observed at 1446, 1240, 1040, 884 and 416 cm -1. 3.1.1. The 0 - 0 stretching mode It is reported in the literature that the O - O stretching vibration of peroxides gives rise to an intense Raman line between 700 and 950 cm -1 [13], while the corresponding infrared absorption is very weak. Recently a narrower range of frequencies, 845-875 cm-I has been observed for this vibration in the spectra of 23 organic peroxides [14]. The only hydroperoxide mentioned in this recent study was tert-butylhydroperoxide for which the stretching frequency was listed as 848 cm-1 in the Raman spectrum and 845 cm -1 in the infrared. Gigu~re [15] assigned a very strong Raman line at 877 cm-1 and a weak infrared band at 880 cm -I to the O - O
H.F. Shurvell, M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
-CH2-O-
-O-CH-O-
141
-CH2-CH2-
singlet at 9.7 ppm (-O0-H)
IL 6
5
4
3
2 PPM
Fig. 3. The 300 Mhz proton NMR spectrum of THF-hydroperoxide.
stretch in the spectra of hydrogen peroxide. For THF-hydroperoxide the strong Raman line at 884 c m - 1 , which has a weak infrared counterpart at 881 cm-~ can be attributed to the O - O stretching mode. An alternate assignment would be the weaker Raman band at 851 cm -1. This is very close to the frequency of 848 cm-1 assigned to the O - O stretch in the Raman spectrum of tert-butylhydroperoxide [14], but the infrared counterpart is relatively strong. It is tempting to attribute the very strong Raman line at 926 c m - ~ in the Raman spectrum of THF-hydroperoxide to the O - O stretching vibration, but in view of the recent work on organic peroxides [14], the frequency seems to be too high. Also, in the Raman spectrum of THF a very strong line at 914 cm-1 was assigned to a vibration described as the ring 'breathing' mode by Dollish et al. [16], or a mode involving the Ct3-C ~ stretch and in-phase stretching of the two C~-Ct3 bonds by Cadioli et al.
[5]. It is likely that the 926 cm-1 line in the hydroperoxide spectrum is due to a similar ring stretching vibration.
3.1.2. Vibrations of the C H 2 groups The strong infrared band at 2960 cm-~ and the shoulder at 2982 c m - ] are assigned to stretching of the f l - C H 2 groups and the band at 2891 crn -] to stretching of the a-CH 2 groups by analogy with the spectra of THF [5]. A Raman line at 1491 cm -~ and infrared bands at 1457, 1441 and 1400 cm -1 are attributed to CH 2 bending (scissors) modes and absorptions at 1368, 1348 and 1323 cm -~ and a Raman line at 1292 cm -~ are assigned to CH 2 wagging modes. Again the assignments are based on those of the same modes in the spectra of THF [5]. The strong Raman line at 1240 c m -1 and the shoulder at 1200 c m -1 carl be assigned to CH 2 twisting modes. The corresponding frequencies in
H.F. Shurvell, M.C. Southby/ Vibrational Spectroscopy 15 (1997) 137-146
142
-CH2-O-CH2-CH2-
-O-CH-OCHCI3
Ill
tl ...t...i...,,....i..,. , .... 100
80
60
40
2O PPM
Fig. 4. The 13C NMR spectrum of THF-hydroperoxide.
the Raman spectrum of THF are 1244 and 1227 cm -1. The sharp infrared absorption band at 1192 cm-1 could correspond to a band at 1182 cm-1 in the spectrum of THF, which was attributed a mixed mode.
3.1.3. C-O-C, C-O(OH) and C - C stretching vibrations One of the strongest bands in the infrared spect_rum of THF-hydroperoxide is observed at 1065 cm -~. This is assigned to the antisymmetric C - O - C Table 2 NMR spectra of tetrabydrofuran hydroperoxide Chemical shift (ppm)
Assignment
IH spectrum
t3C spectrum
1.83-1.89 multiplet 1.96-2.08 multiplet 3.96-4.00 quartet 5.60-5.62 quartet 9.7 singlet
24.0 29.2 67.8 108.0
-CH 2 -CH 2 (•) -CH 2 -CH 2 (fl) -CH2-O- (a) -O-CH-O-OO-H
stretch. This mode gives rise to a very strong infrared band in the spectrum of THF [5]. The symmetric C - O - C stretch in THF is observed as an infrared band of medium intensity at 896 cm -1, but there is no band in this region in the spectrum of the hydroperoxide. A strong infrared band at 1122 cm -1 is assigned to the C-O(OH) stretching vibration. The corresponding Raman line is weak. The 926 cm-1 Raman line and its infrared counterpart at 927 cm-1 are assigned to ring C - C stretching as discussed above.
3.1.4. Ring bending and other modes Frequencies of 657 and 591 cm-1 were attributed to ring bending modes and 286 cm -1 to the ring puckering mode in the Raman spectra of THF [5]. Corresponding infrared frequencies were 658, 581 and 290 cm -1. In the hydroperoxide molecule it appears that the heavy O - O - H substituent on the a carbon atom has the effect of lowering the frequencies of the ring bending and ring puckering modes.
H.F. Shurvell, M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
An infrared band at 565 cm-~ and a Raman line at 416 cm -] are assigned to ring bending modes, but no Raman band attributable to the ring puckering mode has been observed.
3.1.5. Vibrations of the hydrogen bonded OH group The very strong broad infrared band at 3330 c m - ~ is typical of a hydrogen bonded OH stretching mode. Two other absorptions in the infrared spectrum can be attributed to hydrogen OH deformation modes. These features are shown in Fig. 5. The absorption between 1460 and 1320 cm-1 consists of a series of sharp peaks and shoulders superimposed on a broad band centered at 1402 cm - l . This can be assigned to the hydrogen bonded in-plane OH deformation mode. A weak broad shoulder near 610 c m - 1 on the high frequency side of the 565 cm-1 band can be attributed to the hydrogen bonded out-of-plane OH deformation vibration. None of these features are observed in the Raman spectrum. 3.2. NMR spectra The proton and 13CNMR spectra of THF are very simple [17]. The proton spectrum contains only two triplets arising from the two identical /3-CH 2 groups at 1.85 ppm and the two identical a-CH 2 groups at 3.75 ppm.. The corresponding 13C resonances occur
1450
t350
6OO
500
Wavenurnber (cm "~) Fig. 5. Details of Infrared spectra in t h e r e g i o n s o f O H d e f o r m a fionrnodes.
143
at 25.69 and 67.96 ppm, respectively [17]. In the hydroperoxide molecule there is only one ot-CH 2 group which gives rise to a quartet near 4.0 ppm in the proton spectrum of Fig. 3. The two fl-CH 2 groups are no longer identical and they give rise to two complex multiplets near 2.0 ppm. The corresponding resonances in the 13C spectrum of Fig. 4 occur at 67.82 ppm for the a-CH z group and 29.19 and 23.98 ppm for the two different fl-CH 2 groups. Resonances attributable to the CH group at carbon atom 2 are observed as a quartet centered at 5.61 ppm in the proton spectrum and at 67.82 in the 13C spectrum. The hydrogen atom of the - O - O H group gives rise to a singlet at 9.7 ppm. Both proton and 13C NMR spectra are entirely consistent with the structure of tetrahydrofuran-2-hydroperoxide.
3.3. Products of reaction of THF-hydroperoxide Fig. 6a shows the infrared spectrum of a preparative GPC high molecular weight fraction (fraction 2) on a KBr plate. The original sample was a dialysis residue obtained from a lubricating oil. The spectrum contains several bands due to oil components. For example, the weak band at 1729 c m - 1 is assigned to an ester group and the weak bands at 1601, 1492, 757 and 700 cm - I are assignable to styrene-diene copolymers [18]. However, it is clear from the very strong broad band at 3330 cm -1 that the main component of the residue is THF-hydroperoxide. In addition, all bands from 1458 to 848 c m -1 a r e present in the infrared spectrum of THF-hydroperoxide shown in Fig. 1. When the same fraction was placed on a CsI plate, the sample turned bright yellow and the resulting spectrum is shown in Fig. 6b. This spectrum is completely different from that recorded from the sample on a KBr plate. The very strong band at 3330 c m - I has broadened and the maximum has shifted to 3250 cm -i. The very broad absorption now observed between 3500 to 2500 cm-1 resembles that normally observed for an aiiphatic carboxylic acid. Other evidence for the presence of a carboxylic acid is the shoulder at 1720 c m -1 due to the C = O stretching mode. A very strong band is observed in the spectrum of Fig. 6b at 1765 cm -~. This can be attributed to stretching of the carbonyl group of
144
H.F. ShurvelL M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146 100
a.
1e01
GPC fraction 2 on a KBr plate
14M
.o_
.=_ E
m p.
1720sh
GPC fraction 2 on a Csl plate
t ~0-
V 15~t t 17116 50
40
3~
3000
25()0
2000
15~X)
1000
Wavenumber (cm-1) Fig. 6. Infraredspectraof the residuefromGPC fraction2: (a) on a KBr plate, (b) on a CsI plate.
3,-butyrolactone [19], which is an expected decomposition product of THF-hydroperoxide [20]. A second very strong band at 1585 cm -1 is in the region of the antisymmetric stretching mode of an aliphatic carboxylate group, which could be formed by opening of the lactone ring. Fig. 7 shows the progress of the decomposition reaction of THF-hydroperoxide present in the residue after evaporation of another GPC fraction (fraction W). This residue contained essentially only the hydroperoxide as may be seen in Fig. 7a, which shows the infrared spectrum of the residue on a KBr window. Fig. 7b is the spectrum of the bright yellow material that appeared when a drop of this residue
was placed on a CsI window. This spectrum is similar to that of Fig. 6b. Fig. 7c shows the spectrum of the residue on the CsI window after 18 h (overnight). The spectrum of Fig. 7b contains a very strong band due to T-butyrolactone (1764 cm-1). The strong broader band centered at 1572 cm-] in this spectrum could be due to a carboxylate salt [21] (caesium butyrate). The spectrum of the residue after 18 h (Fig. 6c) is completely different from the spectra of Fig. 7a and b. The prominent feature of Fig. 7c is the very strong band at 1574 cm -1 with a shoulder at 1602 cm -]. The 1574 cm -1 band is close in frequency to the very strong C = O stretching band
H.F. ShurvelL M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
145
a.
1-/114
,1572
2o1
Wavenumber (cm-1) Fig. 7. infrared spectra of the residue from GPC fractionW: (a) on a KBr plate, (b) on a Csl plate, (c) on a Csl plate after 18 h.
observed in the infrared spectrum of sodium butyrate [22]. It appears that the final product of the decomposition of THF-hydroperoxide on the CsI window may be a carboxylate salt (caesium butyrate).
4. Conclusions Raman and infrared spectra of tetrahydrofuran 2-hydroperoxide are presented for the first time, These spectra are useful for the identification and characterization of this compound. An assignment of the observed wavenumbers in the spectra is suggested. Proton and ~3C NMR spectra are also pre-
sented here. The spectra are consistent with the structure of 2-hydroperoxytetrahydrofuran. LC fractions without careful sample preparation could be contaminated with THF hydroperoxide. The infrared spectra of these fractions may contain an absorption band near 3300 cm-1 due to the O O - H stretching mode of the hydroperoxide. However, in some cases the hydroperoxide formed during the evaporation of THF may completely react with the compound(s) in the LC fraction and the characteristic band may be absent. In such cases the observed spectrum is unreliable for identification of the LC fraction, since it may contain absorptions due to oxidation products.
146
H.F. Shurvell, M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
The O-OH group of THF-hydroperoxide in the liquid phase is hydrogen bonded. The bonding is probably intermolecular. In dilute solution and in the vapor phase, intramolecular hydrogen bonding might exist. A study of the compound in dilute solutions in inert solvents should provide information on the nature of the hydrogen bonding. The infrared spectra of a sample of THF-hydroperoxide on a CsI window suggest that decomposition proceeds initially to y-butyrolactone and nbutyric acid and finally to caesium butyrate. The mechanisms of the reactions involved in these conversions are not clear and are perhaps worthy of further study.
Acknowledgements The authors are grateful to Dr. Barry Taylor for recording and interpreting the NMR spectra. We are also grateful to The Shell Research and Technology Centre, Thornton, for Sabbatical leave support for one of us (H.F.S.) and for permission to publish our results.
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H. Tschamler, H. Voetter, Monatsch. Chem. 83 (1952) 302. G.M. Barrow, S. Searles, J. Am. Chem. Soc. 75 (1953) 1175. A. Palme, E.R. Bessell, Spectrochim. Acta 16 (1960) 459. M.-T. Forel, J. Derouault, J. Le Calve, M. Rey-Lafon, J. Chim. Phys. 66 (1969) 1232.
[5] B. Cadioli, E. Gallinella, C. Coulombeau, H. Jobic, G. Berthier, J. Phys. Chem. 97 (1993) 7844. [6] K.W.F. Kohlrausch, A.W. Reitz, Z. Phys. Chem. B 45 (1940) 249. [7] L. Bretherick, Handbook of Reactive Chemical Hazards, 2nd ed., Butterworths, London (1975). [8] P. Luger, J. Bushmann, J. Angew. Chem. Int. Ed. Engl. 22 (1983) 410. [9] W.I.F. David, R.M. Ibberson, Acta CrystaUogr. C 48 (1992) 301. [10] G.G. Engerholm, A.C. Luntz, W.D.G. Winn, D.O. Harris, J. Chem. Phys. 50 (1969) 2446. [11] GRAMS/386 TM , Galactic Industries Corp., Salem, NI-I, 1991. [12] F.J. Bergin, H.F. Shnrvell, Appl. Spectrosc. 43 (1989) 516. [13] P.A. Budinger, J.R. Mooney, J.G. Graselli, P.S. Fay, A.T. Guttmann, Anal. Chem. 53 (1981) 884. [141 V. Vacque, B. Sombret, J.P. Huvenne, P. Legrand, S. Sac, Spectrochim. Acta 53A (1997) 55. [15] P.A. Gigu~re, J. Chem. Phys. 18 (1950) 88. [16] F.R. Dollish, W.G. Fateley, F.F. Bentley, Characteristic Raman Group frequencies of Organic Compounds, John Wiley and Sons, New York, NY, 1974. [17] C.J. Pouchert, J. Behnke, The Aldrich Library of 13C and ~H FT-NMR Spectra, vol. 1, The Aldrich Chemical Co., Milwaukee, WI, 1993, p. 381A. [18] J.P. Coats, L.C. Setti, Oils Lubricants and Petrochemical Products - - Characterization by Infrared Spectra, Marcel Dekker, New York, NY, 1985, p. 79. [19] D.P. McDermott, J. Phys. Chem. 90 (1986) 2569. [20] V.I. Stenberg, C.T. Wang, N. Kulevsky, J. Org. Chem. 35 (1970) 1774. [21] G. Socrates, Infrared Characteristic Group frequencies, 2nd ed., John Wiley and Sons, Chichester, 1994. [22] R.A. Nyquist, C.L. Putzig, M.A. Leugers, Handbook of Infrared and Raman Spectra of Inorganic Compounds and Organic Salts, vol. 3, Academic Press, San Diego, CA, 1997, p, 251.
Vibrational Spectroscopy15 (1997) 137-146
Infrared and Raman spectra of tetrahydrofuran hydroperoxide H.F. Shurvell a,*, M.C. Southby b a Department of Chemistry, Queen's University, Kingston, Ontario, Canada K7L 3N6 b Shell Research and Technology Centre Thornton, P.O. Box 1, Chester CH1 3SH, UK
Received 31 March 1997; accepted 1 July 1997
Abstract
The hydroperoxide of tetrahydrofuran (THF) has been prepared from unstabilized THF by a simple procedure. It appears that there are no previous reports of vibrational spectra of THF hydroperoxide in the literature. Raman and infrared spectra of the compound are presented here. The prominent feature of the infrared spectrum is a very strong broad band centered at 3330 cm-1 attributed to the OO-H stretching mode. A strong Raman line at 884 cm-1 is assigned to the O-O stretching vibration. The corresponding infrared band is very weak. 300 MHz proton and 13C NMR spectra also have been recorded. The NMR spectra are consistent with the structure 2-hydroperoxytetrahydrofuran. Implications of the formation of the hydroperoxide during storing and handling of THF as a solvent for liquid chromatography and other applications are discussed. © 1997 Elsevier Science B.V. Keywords: Raman; Infrared; NMR; Tetrahydrofuranhydroperoxide
1. Introduction Tetrahydrofuran (THF) is a widely used solvent for organic compounds and its infrared [1-5] and Raman spectra are well known [5,6]. An important use of THF is in the preparation solutions of polymeric materials. Heating is often required to dissolve the polymers or copolymers in THF. Explosions have occurred in such procedures due to the presence of THF-hydroperoxide. Although the properties of THF-hydroperoxide are known [7], there do not appear to be any published spectra of this compound. It is well known that ethers slowly form hydro-
* Corresponding author. Tel.: (1-613) 545-2646; Fax: (1-613) 545-6669.
peroxides on standing in contact with air. These compounds are often dangerously unstable and suppliers usually add small amounts of inhibitors to prevent the formation of peroxides. For liquid chromatography (LC), pure solvents are required and unstabilized THF stored under an inert gas is commonly used as a solvent. A standard method for analyzing LC fractions involves removing most of the solvent by blowing dry air into a vial containing the solution. A thin film of the fraction is then cast on a KBr window and an infrared spectrum recorded. This procedure could lead to erroneous conclusions regarding the composition of the LC fraction, because it is probable that THF hydroperoxide is formed during the evaporation process.
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It.F. Shurvell, M.C Southby / Vibrational Spectroscopy 15 (1997) 137-146
138
In a recent experiment in our laboratory it was required to record the infrared spectrum of a preparative gel permeation chromatography (GPC) high molecular weight fraction in THF solution out to 180 cm -1. For this a CsI window was used. It was observed that a bright yellow color formed when a drop of the residue from the GPC fraction was placed on the window. The yellow color was assumed to be due to free iodine produced by the oxidation of the iodide ion of CsI. This was confirmed by the blue color produced by a drop of starch solution. It appears that the oxidation was caused by THF-hydroperoxide formed during the evaporation of the GPC fraction. It seems likely that the hydroperoxide may react with the compounds in an LC fraction, which may lead to an incorrect interpretation of the infrared spectrum of the fraction. It is therefore important to be able to detect the presence of THF-hydroperoxide from characteristic bands in the spectrum. A search of the literature failed to find a vibrational spectrum (neither infrared nor Raman) of THF-hydroperoxide and it was decided to prepare a sample of the compound and record the spectra for future reference. X-ray structure analysis [8], high resolution neutron powder diffraction studies [9] and a microwave spectroscopic study [10] have shown that THF has the symmetric twisted conformation (1) with symmetry C 2. Ab initio calculations at various levels indicate that the C 2 conformation is more stable than the planar C s or C2v forms [5]. The ring of THF-hydroperoxide is assumed to assume similar conformation (2). In the liquid phase, THF hydroperoxide is probably intermolecularly hydrogen bonded. Also, as indicated in the structure shown below (2), intramolecular hydrogen bonding is possible between the furan ring oxygen atom and the hydrogen atom of the hydroperoxide OH group.
Much work has been published on the parent compound THF. Detailed infrared and Raman spectra of the compound in gas, liquid and solid states were included in Ref. [5] and a complete vibrational assignment based on an ab initio calculation at the MP2 level was given. Descriptions of the 33 normal modes of vibration of THF were expressed in terms of contributions from symmetry co-ordinates. These assignments have been very valuable in the present discussion of the spectra of THF-hydroperoxide. In this paper we present the infrared and Raman spectra of THF-hydroperoxide, discuss the characteristic features of the spectra and suggest assignments of the major bands. The literature search failed to find any reference to an NMR spectrum of THF-hydroperoxide, so proton and 13C NMR spectra of the compound were recorded and interpreted and are included here.
2. Experimental 2.1. Samples and sample treatment For infrared spectroscopy, the volume of an LC fraction in THF solution is reduced by blowing dry air or nitrogen into a vial containing the solution. A drop of the concentrated fraction is then placed on a KBr window and when the remaining solvent has evaporated, the infrared spectrum is recorded. It appears that during this procedure, THF hydroperoxide may be formed. A small quantity of THF hydroperoxide was prepared by blowing dry air into a vial containing unstabilized THF until all that remained was an oily viscous liquid. The infrared spectrum of this material showed no bands that could be attributed to THF. The pure hydroperoxide appears to be quite stable.
2.2. Infrared spectra Infrared spectra were recorded on a Perkin-Elmer Model 983G spectrometer interfaced to a model 7700 data station. Spectra were stored on floppy disks and subsequent handling of the spectra was carried out using the GRAMS-386 software package [11]. TM
(1)
(2)
H.F. Shurvell, M,C. Southby/ Vibrational Spectroscopy 15 (1997) 137-146
2.4. NMR spectra
Tetml~t~nm
T
4000
3!
139
The spectra were recorded on a Bruker AC300 instrument operating at 300.13 MHz for IH. A QNP 5 m m probehead was used and the spectra were acquired at 297 K. The operating parameters for ~H were: spectral width 20 ppm, total relaxation time 12.7 s, acquisition time 2.72 s, 16 scans. The solvent was CDC13 with 1% TMS. For ~3C the parameters were: spectral width 250 ppm, total relaxation time 2.9 s, acquisition time 0.8885 s, 1000 scans, 2.4 kHz decoupling using WALTZ-16. The solvent was CDC13 with added Fe(acac) 3 at 8 m g / g and TMS at
~
1% (w/w). 1068
3. Results and discussion
2961
3000
2000 1000 Wavenumber (cm 1)
500
Fig. 1. Infraredspectraof THF and THF-hydroperoxide. 2.3. Raman spectra Samples for Raman spectroscopy were contained in glass spheres blown at the ends of melting point capillary tubes. Details of the experimental arrangement for Fourier transform Raman spectroscopy have been given in a previous publication [12]. The excitation source was a cw Nd:YAG laser operating at 1064.1 nm (9397.6 c m - l ) . The laser beam was focused to a 1 mm diameter spot at the sample, which was placed at one focus of an ellipsoidal mirror. The scattered radiation was collected by this mirror and directed into the Jacquinot stop of a Perkin-Elmer Model 1760 near-IR spectrometer. Laser powers of 200-300 mW (at the sample) were used and 100 scans at a nominal resolution of 4 cm-1 were collected. The nitrogen-cooled germanium detector covered the spectral range 9400-6200 cm -1, which is equivalent to a Raman shift range of 0-3200 cm -1. The 0 - 2 0 0 cm -1 region, however, was obscured by the filters needed to remove any unscattered laser radiation. The detector response was not linear and was very low in the CH stretching region of the Raman spectrum near 3000 cm-~ and the OH stretching region could not be observed. The Raman spectra of Fig. 2 have not been corrected for detector response.
The infrared spectrum of THF hydroperoxide is shown in Fig. 1 with a spectrum of THF for comparison. A similar comparison of the Raman spectra of the two compounds is shown in Fig. 2. Table 1 lists the wavenumbers (cm -1) observed in the infrared
Tetrahydrofuranhydroperoxide
I I~I
I | 7 I~ III
416 J
n"
T~rahydrofumn
3000
2000
1500
1000
500
Wavenurnber (cm "~) Fig. 2. Raman spectra of THF and THF-hydroperoxide.
140
H.F. ShurveU, M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
Table 1 R a m a n a n d i n f r a r e d w a v e n u m b e r s ( c m - 1) a o f T H F a n d T H F h y d r o p e r o x i d e THF
THF hydroperoxide
A s s i g n m e n t b,c
Raman
infrared
Raman
infrared
--
--
--
3 3 3 0 v v s , br.
OO-H
--
2975 vs
--
2 9 8 2 sh
a s y m . C H 2 stretch a s y m . C H 2 stretch
stretch
2940 m
2960 vs
2955 m
2961 v s
2875 s
2891 s
2900 m
2892 vs
sym. C H 2 stretch
--
--
1491 m
1486 sh
CH 2 deformation
1484 sh
1460 m
1466 sh
1458 s
CH 2 deformation
1451 m
1 4 5 0 sh
1446 s
1441 s
CH 2 deformation
--
--
--
1402 s, br.
H - b o n d e d O H def.
--
1365 w
1371 w
1368 s
--
--
--
1345 s
a-CH 2 wag ot-CH w a g
--
--
1328 w
1323 s
fl- C H 2 w a g
--
--
1292 w
1290 sh
/3- C H 2 w a g
1240 w
--
1240 m
1237 v w
CH 2 twist
--
1182 m
1200 sh
1192 s
C-O-C
--
--
1126
1122
C - O O H stretch
--
1068 v s
1040 m
1068 v s
r i n g stretch
1027 w
1032 sh
--
1038 v s
r i n g stretch
--
--
--
965 v s
r i n g stretch
--
--
926 vs
928 vs
C-O-C
913 vs
910 s
--
--
ring 'breathing'
--
--
884 s
881 v w
O - O stretch
865 s h
8 6 7 sh
851 m
848 s
CH z rock
657 v w
658 w
--
754 w
CH 2 wag
.
.
.
w
.
s
6 1 0 sh
a s y m . stretch
sym.stretch
H - b o n d e d O H def.
591 v w
581 v w
--
565 m
i n - p l a n e r i n g def.
--
--
416m
--
i n - p l a n e r i n g def.
a R e l a t i v e i n t e n s i t i e s are d e n o t e d by: v = v e r y , s = s t r o n g , rn = m e d i u m , w = w e a k , sh = s h o u l d e r , b r = broad. b A s s i g n m e n t s b a s e d o n t h o s e g i v e n f o r c o r r e s p o n d i n g m o d e s i n T H F [5]. c sym = symmetric, asym = antisymmetric, def = deformation.
and Raman spectra of THF and THF hydroperoxide. An assignment of the observed wavenumbers in the hydroperoxide spectra is included in Table 1. Figs. 3 and 4 show the 300 MHz proton and 13C NMR spectra and Table 2 lists the positions and assignments of the observed resonances. 3.1. Vibrational spectra The dominant feature of the infrared spectrum of THF-hydroperoxide is the very strong broad band centered at 3330 cm -1, which is assigned to the O O - H stretching mode. Other groups of strong absorptions are observed near 2900, 1400, 1060 and 940 cm -1. Single sharp bands are seen at 1192, 1122, 848 and 565 cm-1. The strongest line in the Raman spectrum occurs at 926 cm -x. Other strong
Raman fines are observed at 1446, 1240, 1040, 884 and 416 cm -1. 3.1.1. The 0 - 0 stretching mode It is reported in the literature that the O - O stretching vibration of peroxides gives rise to an intense Raman line between 700 and 950 cm -1 [13], while the corresponding infrared absorption is very weak. Recently a narrower range of frequencies, 845-875 cm-I has been observed for this vibration in the spectra of 23 organic peroxides [14]. The only hydroperoxide mentioned in this recent study was tert-butylhydroperoxide for which the stretching frequency was listed as 848 cm-1 in the Raman spectrum and 845 cm -1 in the infrared. Gigu~re [15] assigned a very strong Raman line at 877 cm-1 and a weak infrared band at 880 cm -I to the O - O
H.F. Shurvell, M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
-CH2-O-
-O-CH-O-
141
-CH2-CH2-
singlet at 9.7 ppm (-O0-H)
IL 6
5
4
3
2 PPM
Fig. 3. The 300 Mhz proton NMR spectrum of THF-hydroperoxide.
stretch in the spectra of hydrogen peroxide. For THF-hydroperoxide the strong Raman line at 884 c m - 1 , which has a weak infrared counterpart at 881 cm-~ can be attributed to the O - O stretching mode. An alternate assignment would be the weaker Raman band at 851 cm -1. This is very close to the frequency of 848 cm-1 assigned to the O - O stretch in the Raman spectrum of tert-butylhydroperoxide [14], but the infrared counterpart is relatively strong. It is tempting to attribute the very strong Raman line at 926 c m - ~ in the Raman spectrum of THF-hydroperoxide to the O - O stretching vibration, but in view of the recent work on organic peroxides [14], the frequency seems to be too high. Also, in the Raman spectrum of THF a very strong line at 914 cm-1 was assigned to a vibration described as the ring 'breathing' mode by Dollish et al. [16], or a mode involving the Ct3-C ~ stretch and in-phase stretching of the two C~-Ct3 bonds by Cadioli et al.
[5]. It is likely that the 926 cm-1 line in the hydroperoxide spectrum is due to a similar ring stretching vibration.
3.1.2. Vibrations of the C H 2 groups The strong infrared band at 2960 cm-~ and the shoulder at 2982 c m - ] are assigned to stretching of the f l - C H 2 groups and the band at 2891 crn -] to stretching of the a-CH 2 groups by analogy with the spectra of THF [5]. A Raman line at 1491 cm -~ and infrared bands at 1457, 1441 and 1400 cm -1 are attributed to CH 2 bending (scissors) modes and absorptions at 1368, 1348 and 1323 cm -~ and a Raman line at 1292 cm -~ are assigned to CH 2 wagging modes. Again the assignments are based on those of the same modes in the spectra of THF [5]. The strong Raman line at 1240 c m -1 and the shoulder at 1200 c m -1 carl be assigned to CH 2 twisting modes. The corresponding frequencies in
H.F. Shurvell, M.C. Southby/ Vibrational Spectroscopy 15 (1997) 137-146
142
-CH2-O-CH2-CH2-
-O-CH-OCHCI3
Ill
tl ...t...i...,,....i..,. , .... 100
80
60
40
2O PPM
Fig. 4. The 13C NMR spectrum of THF-hydroperoxide.
the Raman spectrum of THF are 1244 and 1227 cm -1. The sharp infrared absorption band at 1192 cm-1 could correspond to a band at 1182 cm-1 in the spectrum of THF, which was attributed a mixed mode.
3.1.3. C-O-C, C-O(OH) and C - C stretching vibrations One of the strongest bands in the infrared spect_rum of THF-hydroperoxide is observed at 1065 cm -~. This is assigned to the antisymmetric C - O - C Table 2 NMR spectra of tetrabydrofuran hydroperoxide Chemical shift (ppm)
Assignment
IH spectrum
t3C spectrum
1.83-1.89 multiplet 1.96-2.08 multiplet 3.96-4.00 quartet 5.60-5.62 quartet 9.7 singlet
24.0 29.2 67.8 108.0
-CH 2 -CH 2 (•) -CH 2 -CH 2 (fl) -CH2-O- (a) -O-CH-O-OO-H
stretch. This mode gives rise to a very strong infrared band in the spectrum of THF [5]. The symmetric C - O - C stretch in THF is observed as an infrared band of medium intensity at 896 cm -1, but there is no band in this region in the spectrum of the hydroperoxide. A strong infrared band at 1122 cm -1 is assigned to the C-O(OH) stretching vibration. The corresponding Raman line is weak. The 926 cm-1 Raman line and its infrared counterpart at 927 cm-1 are assigned to ring C - C stretching as discussed above.
3.1.4. Ring bending and other modes Frequencies of 657 and 591 cm-1 were attributed to ring bending modes and 286 cm -1 to the ring puckering mode in the Raman spectra of THF [5]. Corresponding infrared frequencies were 658, 581 and 290 cm -1. In the hydroperoxide molecule it appears that the heavy O - O - H substituent on the a carbon atom has the effect of lowering the frequencies of the ring bending and ring puckering modes.
H.F. Shurvell, M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
An infrared band at 565 cm-~ and a Raman line at 416 cm -] are assigned to ring bending modes, but no Raman band attributable to the ring puckering mode has been observed.
3.1.5. Vibrations of the hydrogen bonded OH group The very strong broad infrared band at 3330 c m - ~ is typical of a hydrogen bonded OH stretching mode. Two other absorptions in the infrared spectrum can be attributed to hydrogen OH deformation modes. These features are shown in Fig. 5. The absorption between 1460 and 1320 cm-1 consists of a series of sharp peaks and shoulders superimposed on a broad band centered at 1402 cm - l . This can be assigned to the hydrogen bonded in-plane OH deformation mode. A weak broad shoulder near 610 c m - 1 on the high frequency side of the 565 cm-1 band can be attributed to the hydrogen bonded out-of-plane OH deformation vibration. None of these features are observed in the Raman spectrum. 3.2. NMR spectra The proton and 13CNMR spectra of THF are very simple [17]. The proton spectrum contains only two triplets arising from the two identical /3-CH 2 groups at 1.85 ppm and the two identical a-CH 2 groups at 3.75 ppm.. The corresponding 13C resonances occur
1450
t350
6OO
500
Wavenurnber (cm "~) Fig. 5. Details of Infrared spectra in t h e r e g i o n s o f O H d e f o r m a fionrnodes.
143
at 25.69 and 67.96 ppm, respectively [17]. In the hydroperoxide molecule there is only one ot-CH 2 group which gives rise to a quartet near 4.0 ppm in the proton spectrum of Fig. 3. The two fl-CH 2 groups are no longer identical and they give rise to two complex multiplets near 2.0 ppm. The corresponding resonances in the 13C spectrum of Fig. 4 occur at 67.82 ppm for the a-CH z group and 29.19 and 23.98 ppm for the two different fl-CH 2 groups. Resonances attributable to the CH group at carbon atom 2 are observed as a quartet centered at 5.61 ppm in the proton spectrum and at 67.82 in the 13C spectrum. The hydrogen atom of the - O - O H group gives rise to a singlet at 9.7 ppm. Both proton and 13C NMR spectra are entirely consistent with the structure of tetrahydrofuran-2-hydroperoxide.
3.3. Products of reaction of THF-hydroperoxide Fig. 6a shows the infrared spectrum of a preparative GPC high molecular weight fraction (fraction 2) on a KBr plate. The original sample was a dialysis residue obtained from a lubricating oil. The spectrum contains several bands due to oil components. For example, the weak band at 1729 c m - 1 is assigned to an ester group and the weak bands at 1601, 1492, 757 and 700 cm - I are assignable to styrene-diene copolymers [18]. However, it is clear from the very strong broad band at 3330 cm -1 that the main component of the residue is THF-hydroperoxide. In addition, all bands from 1458 to 848 c m -1 a r e present in the infrared spectrum of THF-hydroperoxide shown in Fig. 1. When the same fraction was placed on a CsI plate, the sample turned bright yellow and the resulting spectrum is shown in Fig. 6b. This spectrum is completely different from that recorded from the sample on a KBr plate. The very strong band at 3330 c m - I has broadened and the maximum has shifted to 3250 cm -i. The very broad absorption now observed between 3500 to 2500 cm-1 resembles that normally observed for an aiiphatic carboxylic acid. Other evidence for the presence of a carboxylic acid is the shoulder at 1720 c m -1 due to the C = O stretching mode. A very strong band is observed in the spectrum of Fig. 6b at 1765 cm -~. This can be attributed to stretching of the carbonyl group of
144
H.F. ShurvelL M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146 100
a.
1e01
GPC fraction 2 on a KBr plate
14M
.o_
.=_ E
m p.
1720sh
GPC fraction 2 on a Csl plate
t ~0-
V 15~t t 17116 50
40
3~
3000
25()0
2000
15~X)
1000
Wavenumber (cm-1) Fig. 6. Infraredspectraof the residuefromGPC fraction2: (a) on a KBr plate, (b) on a CsI plate.
3,-butyrolactone [19], which is an expected decomposition product of THF-hydroperoxide [20]. A second very strong band at 1585 cm -1 is in the region of the antisymmetric stretching mode of an aliphatic carboxylate group, which could be formed by opening of the lactone ring. Fig. 7 shows the progress of the decomposition reaction of THF-hydroperoxide present in the residue after evaporation of another GPC fraction (fraction W). This residue contained essentially only the hydroperoxide as may be seen in Fig. 7a, which shows the infrared spectrum of the residue on a KBr window. Fig. 7b is the spectrum of the bright yellow material that appeared when a drop of this residue
was placed on a CsI window. This spectrum is similar to that of Fig. 6b. Fig. 7c shows the spectrum of the residue on the CsI window after 18 h (overnight). The spectrum of Fig. 7b contains a very strong band due to T-butyrolactone (1764 cm-1). The strong broader band centered at 1572 cm-] in this spectrum could be due to a carboxylate salt [21] (caesium butyrate). The spectrum of the residue after 18 h (Fig. 6c) is completely different from the spectra of Fig. 7a and b. The prominent feature of Fig. 7c is the very strong band at 1574 cm -1 with a shoulder at 1602 cm -]. The 1574 cm -1 band is close in frequency to the very strong C = O stretching band
H.F. ShurvelL M. C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
145
a.
1-/114
,1572
2o1
Wavenumber (cm-1) Fig. 7. infrared spectra of the residue from GPC fractionW: (a) on a KBr plate, (b) on a Csl plate, (c) on a Csl plate after 18 h.
observed in the infrared spectrum of sodium butyrate [22]. It appears that the final product of the decomposition of THF-hydroperoxide on the CsI window may be a carboxylate salt (caesium butyrate).
4. Conclusions Raman and infrared spectra of tetrahydrofuran 2-hydroperoxide are presented for the first time, These spectra are useful for the identification and characterization of this compound. An assignment of the observed wavenumbers in the spectra is suggested. Proton and ~3C NMR spectra are also pre-
sented here. The spectra are consistent with the structure of 2-hydroperoxytetrahydrofuran. LC fractions without careful sample preparation could be contaminated with THF hydroperoxide. The infrared spectra of these fractions may contain an absorption band near 3300 cm-1 due to the O O - H stretching mode of the hydroperoxide. However, in some cases the hydroperoxide formed during the evaporation of THF may completely react with the compound(s) in the LC fraction and the characteristic band may be absent. In such cases the observed spectrum is unreliable for identification of the LC fraction, since it may contain absorptions due to oxidation products.
146
H.F. Shurvell, M.C. Southby / Vibrational Spectroscopy 15 (1997) 137-146
The O-OH group of THF-hydroperoxide in the liquid phase is hydrogen bonded. The bonding is probably intermolecular. In dilute solution and in the vapor phase, intramolecular hydrogen bonding might exist. A study of the compound in dilute solutions in inert solvents should provide information on the nature of the hydrogen bonding. The infrared spectra of a sample of THF-hydroperoxide on a CsI window suggest that decomposition proceeds initially to y-butyrolactone and nbutyric acid and finally to caesium butyrate. The mechanisms of the reactions involved in these conversions are not clear and are perhaps worthy of further study.
Acknowledgements The authors are grateful to Dr. Barry Taylor for recording and interpreting the NMR spectra. We are also grateful to The Shell Research and Technology Centre, Thornton, for Sabbatical leave support for one of us (H.F.S.) and for permission to publish our results.
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[5] B. Cadioli, E. Gallinella, C. Coulombeau, H. Jobic, G. Berthier, J. Phys. Chem. 97 (1993) 7844. [6] K.W.F. Kohlrausch, A.W. Reitz, Z. Phys. Chem. B 45 (1940) 249. [7] L. Bretherick, Handbook of Reactive Chemical Hazards, 2nd ed., Butterworths, London (1975). [8] P. Luger, J. Bushmann, J. Angew. Chem. Int. Ed. Engl. 22 (1983) 410. [9] W.I.F. David, R.M. Ibberson, Acta CrystaUogr. C 48 (1992) 301. [10] G.G. Engerholm, A.C. Luntz, W.D.G. Winn, D.O. Harris, J. Chem. Phys. 50 (1969) 2446. [11] GRAMS/386 TM , Galactic Industries Corp., Salem, NI-I, 1991. [12] F.J. Bergin, H.F. Shnrvell, Appl. Spectrosc. 43 (1989) 516. [13] P.A. Budinger, J.R. Mooney, J.G. Graselli, P.S. Fay, A.T. Guttmann, Anal. Chem. 53 (1981) 884. [141 V. Vacque, B. Sombret, J.P. Huvenne, P. Legrand, S. Sac, Spectrochim. Acta 53A (1997) 55. [15] P.A. Gigu~re, J. Chem. Phys. 18 (1950) 88. [16] F.R. Dollish, W.G. Fateley, F.F. Bentley, Characteristic Raman Group frequencies of Organic Compounds, John Wiley and Sons, New York, NY, 1974. [17] C.J. Pouchert, J. Behnke, The Aldrich Library of 13C and ~H FT-NMR Spectra, vol. 1, The Aldrich Chemical Co., Milwaukee, WI, 1993, p. 381A. [18] J.P. Coats, L.C. Setti, Oils Lubricants and Petrochemical Products - - Characterization by Infrared Spectra, Marcel Dekker, New York, NY, 1985, p. 79. [19] D.P. McDermott, J. Phys. Chem. 90 (1986) 2569. [20] V.I. Stenberg, C.T. Wang, N. Kulevsky, J. Org. Chem. 35 (1970) 1774. [21] G. Socrates, Infrared Characteristic Group frequencies, 2nd ed., John Wiley and Sons, Chichester, 1994. [22] R.A. Nyquist, C.L. Putzig, M.A. Leugers, Handbook of Infrared and Raman Spectra of Inorganic Compounds and Organic Salts, vol. 3, Academic Press, San Diego, CA, 1997, p, 251.