638
ANALYTICAL CHEMISTRY
vacuum of less than 0.1 micron for 2-1 hours. The basic aluminum acetate before drying showed a strong bonded band a t 3.00 microns caused by the presence of water. However, this band was absent in the dried eample, and the presence of the free OH band a t 2.70 microns was clearly evident. Hence, the presence WAVE
5000
2500
group. It has previously been shown that, only monosoaps or mixtures of mono- and disoaps show the presence of bonded hydroxyl groups. The strong band a t 6.28 microns can best be attributed to the -C=O stretching vibration in the carboxylate group of the aluminum soap. A comparison of the spectra of the fatty acids (see Figure 2) with the spectra of the aluminum soaps prepared from these acids shows that there is little similarity between the soap and the fatty acid from which the disoap was made. This evidence yields strong support to the idea that these aluminum soaps are distinct chemical compounds.
NUMBERS IN CM-’
1400
1000
800
ACKNOWLEDGMENT
Tht, authors are indebted to Henry Raich, Grant Rauscher, and the Ctieniical Corps Technical Command, h m y Chemical Centrr, ;\Id., for use for an infrared study of the aluminum soaps discussed in this report. The soaps were prepared, analyzed, and previously used by Henry Raich and Grant Rauscher for research conducted under contracts between the Chemical Corps Technical Command and Rensselaer Polykchnic Insfitute. LITERATURE CITED
(1) Alexander, A. E., and Gray, V. R., Proc. Roy. SOC.(Lomion), 200, 165 (1950). (2) Colthup, N. B., J . Optiral SOC.Am., 40,398 (1950). (3) Grav. V . R.. and Alexander. A. E.. J . Phlra. and Colloid Chem.. 53.37 (1949). (4) McB&in,’J.Ri., and McClatchie, W. L., J . Ant. C’hun. Soc., 54, 3266 (1932). ( 5 ) McGee, C. G., Ibid., 71,278 (1949).
WAVE LENGTH IN MICRONS
Figure 3. Infrared Absorption Spectra of Aluminum Disoaps Made from Various Fatty Acids
of water in the soaps may result in the concslusion that a bonded hydroxyl group i R present. Likewise, soaps made by the reaction between an aluminum alkoaide and fatty acid are likely to contain traces of alcohol, which also will show a strong bonded hydroxyl
RECEIVED for review July 23, 1951. Accepted January 21, 1952. Presented before Section 5, Fats, Soaps, Detergents, at the XIIth International Congress of Pure and Applied Chemistry, New York. N . Y., Segteinber 10, 1931.
Infrared Absorption Spectra of Tertiary Peroxides A. R. PHILPOTTS AND WILLIAM THAIN The Distillers Co., Ltd., Great Burgh, Epsom, Surrey, England It has been suggested that absorptions at 870 and M O cm.-’ are characteristic of peroxides and hydroperoxides, respectively. This work sets out to check the validity of these rules and to assess their usefulness in identifying the oxidation products of hydrocarbons in the case of tertiary compounds. The infrared spectra of tert-butll, tert-amrl, and phenyl dimethyl methyl peroxides, hydroperoxides, and alcohols are compared. The identification bands are useful for the CCand Cg compounds, but at higher molcular weights differentiation between alcohol and peroxide becomes difficult. It seems probable that these
C
1
absorptions are due to the C-C-0
I
grouping rather than the 44- link.
C Then possible, the spectra of the individual components of an oxidation mixture should be recorded so that the compounds can be “fingerprinted.”
T
H E increased interest in the oxidation of organic compounds has produced several papers on the identification and estimation of oxidation products by infrared absorption spectroscopy (2,6,10).In particular, mention has been made of the identification of peroxide bodies. I n these laboratories the authors have found the method very successful when dealing with specific compounds that have been prepared in a pure state, but they have also found that caution must be used when discussing types of peroxides.
Hitherto, useful information has been obtained by comparing the strength of the hydroxyl absorption with iodine titration figures, although when alcohols, peroxides, and hydroperoxides are present together the analysis is not possible. A method of measuring total hydroxyl absorption and deducting acidity and hydroperoxide values to give alcohol by difference ( 2 ) is not of general application, since both the extinction and frequency of a hydroxyl band vary with the concentration of hydroxyl group, nature of hydroxyl group, and constitution of the medium. It
V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2
639
would therefore be of considerable advantage if one could use group. absorption bands characteristic of the -0-0The first problem (an academic one) is the assignment of the observed frequencies in peroxide spectra to vibrations involving or C-0-0-H groupings. There 1'. niainly the C - 0 4 - C promise of the necessary experimental information in the near future (6). Then we must consider whether any of these f r e quencies give 8 sufficiently specific identification of the -0-Olinkage to be useful in practical problems. In general, no very strong specific absorption bands would be expected from the -0-0grouping in peroxides and hvdroperoxides. The vibrations which thew compounds do not share Rith the corresponding ethers arid alcohols involve both ouvgen
atoms, so that the great intensities of absorptions associated with the C-0 linkage are reduced by symmetry (9). Again the mass of an osyyen atom is so similar to that of a -CHor -CHzgroup that "structural" modes involving the oxygen atoms will have frequencies similar to tliose due to the carbon skeleton. Recent. commun,ications (5, 8-10) give 800 to 900 cin. as the most useful region for establishing the presence of hydroperoxides and peroxides in oxidation mixtures. Minkoff (6) said that while bands in this region are given by primary peroxides arid hydroperosidw, they are weak relative t'o the rest of the spcetrum; but the lert-hut\-l compounds give strong bands. Shreve el al. (10) give sievr:ral examples, but again only the spectra of tertiayy comporind.: have strong and specific bands. This present work gives
t -BUTYLHYDROPEROXIDE 2 0
t-AMYL ALCOHOL
DI[t-AMYL]PEROXIM
30 'le
20
t-AMYLHYDROPEROXIDE
30
PHENYLDIMETHYLCARBINOL
30
DI[KOPROPYLBENZENE]PEROXlDE
IO
)O
ANALYTICAL CHEMISTRY
640 further evidence for the empirical rule that compounds contain-
C ing the C-A-0-0
I
grouping have strong bands in this region of
solvent trace as 100yo transmittance. Lithium fluoride and glass shutters were used for zero determination where appropriate; no other correction has been made for scattered radiation. The cell used was approximately 0.1 mm. thick and the solvents were cyclohexane and carbon tetrachloride.
C
PURE SUBSTANCES
the spectra. I t seems, however, that these ba,ntis are associated
c
' I I
with the C-C-0
group rathcr than the tertiary ptlroside link,
c
and the espcrimental results below are set out to demonstrate this (Figure 1). EXPERI3IENTA L
The infrared spectra were recorded with a Perliin-I*;hner 12H spectrometer Ivith General Motors amplifier and Brown recorder. The percentage transmittance curves were calculated using the
IO0
ierl-Amyl Hydroperoxide was prepared by the method of Alilas and Surgenor ( 4 ) . The sample used boiled a t 53" C. and 17 mm., n'," = 1.4160,96 ure by iodine titration. ' Di-( ferf-amyl) Peroxid prepared from the hydroperoxide by the method of )Mas enor (3). The sample used boiled a t 63.5' C. and 25 mm. ai refractive index n 2 , O = 1.4082 agreed with the value of Kaley, , and Vaughan (Y),although the iodine titration, by a modification of the nwthod of Vaughan and Rust ( I S ) , gave a purity of 90% only. tert-Amyl Alcohol was obtained commercially, n2,o = 1.4050. Isopropylbenzene Hydroperoxide was obtained by extraction from the oxidation products of isopropylbenzene. The method (which involves the preparation and purification of the sodium
t-AMYL ALCOHOL
n
1100
900
700
900
700
100
t-AMYLHYDROPEROXIDE 006 040 -
20 W
O' Figure 2.
1700.
'
I500
1300 C M - ~ 1100
Spectra of tert-Amyl Alcohol (30% Solution), Di-(tert-amyl) Peroxide
(2094 Solution), and tert-Amyl Hydroperoxide (30% Solution)
V O L U M E 2 4 , N O . 4, A P R I L 1 9 5 2
641
salt. then regeneration ant1 niolecular distillation) will lie dc~ 1.5240. scril-)ed elsewhere (12). 1 ~ 1 ,= Di-(isopropylbenzene) Peroxide \vas isolated from the products of the cata1yt)icdecompoiition of the hydroperoxide by dist'illatioii ( 1 2 ) . It \\-as cryst,allizetl to constant melting point (39.8" C.) froni absolute methanol. Phenyldimethylcarbinol. Thc~prtwnt sample !vas obtained hy thp electrolytic rwluctioii of the h>-droperoside ( I d ) , although niatei~ialof '3970purit!. mn lie o1)tained by other reductions-e.g., with triethanolamine ( 1 ). Ethyl tert-Butyl Ether \ v w pwpared ky the method of Sorris nncl Ilighy (6). TIIC-:3rnplc Iioiled fit 73 and 751 nun. and nLo =
earlier one has impurity bands not girtfin i n tli latter. The spectrum in Figure 2 is in good agreement uit,h S o . 756, although the shoulder a t 865 cm.-' was riot found. The absorption curve of isopropylbenzene hydroperoxide (Figure 3) is in good agreement with that reported b?- Shrew el al. (IO). The spectra of fertbutanol, tert-butyl hydroperositle, antl di-(/ert-butyI) peroxide have been recorded and agreed n-it11 those of Yhreve et al. The spectra of the ROH, ROR, anti ItOOIl types for the three different radioals (It = lert-butyl, tert-amyl, or cuniyl) are compared in the liri(3 diagram (Figure 1). 1.4101. The thrre h\-droperoxides absorb a t 845,840, and 835 cni. -1 and ~ ~ ~ ti-Decane sec-Hydroperoxide. .\ sample (purit,p ! K I . hy the prrosides a t 875, 860, itnd 558 cm. This is good corroboraiotlirita titration) was rupplicd by ,J, I,. Bentori of this company. This gave a mixture ot' approsi!nately equal amounts of 2-, 3-, 4-, tion for the generalization of Yhreve et al., who suggest 847 and and 5-tlccaiiols on hytil,ogc.il:tt,loIl. 577 cm.-I for the characteristic absorptions of the two types. I)ISCCSS1ON OF SPECTR.4 The three alcohols absorb at 915, 882, and 863 crn.-'-i.e., the slcohol frequency changes more with the It group than the Two different ?pwtra for lert-amyl alcohol are i n c l u d d iri the perositlc~fitquency. On the other hand, for d l three groups the Sat ioiiitl Hur~au'or5tan(I:wls catalog (Sos. 437 antl 756). The
.
,7---
\
r r
tLo4YLDIMETHYLCARBINOL
i 1760
O'
w
1300
CM-'
I100
900
700
I
U
sc
1500
80-
bo-
U
e
40-
u
20
q
n5.
DI[ISOPROPYLBENZENE]PEROXIDE
0
I700
b
1500
1300
I100
900
700
1500
1300 C M - ~ 1100
900
700
CM-i
IO0
80
60
40 20 0
1700
e
Figure 3. Spectra of Pheiirldiniethplcarbinol (30% Solution), Di(isopropy1benzene) Peroxide (10% Solution), and Isoprop?lbenzene Hydroperoxide (30% S o l u t i o n )
642
ANALYTICAL CHEMISTRY
magnitudes of the characteristic frequencies are in the order not been completely investigated. I t seems, however from the alcohol > peroxide > hydroperoxide. work cited here, that tertiary alcohols, peroxides, and hydroThese differences in frequency are clearly sufficient to make peroxides all have strong bands in the region 915 to 830 cm -1 I n identification and estimation of the three types possible in oxidathat case it is more logical to associate these absorptions with the tion niixt,ures in the cams of R = tert-butyl and R = tert-amyl, C but it has been found difficult to analyze ternary mixtures when C-4-0group than with the - 0 4 1 group. Tertiary R = cumpl, since the peroxide and alcohol bands arc too close to separate. This tendency for the closing together of the three c characteristic frequencies in higher molecular weight compounds ethers and the esters of tertiary alcohols should therefore absorb in will limit the usefulness of the method, as well as the ever-present this region. Figure 4 shows that ethyl tert-butyl ether has a band chance of accidental coincidence of frequencies due to different Phenyl(dimethy1 phenyl methyl) ether also has a a t 847 cm.-' vibrational modes of the molecule. band in this region Lyith a maximum a t 889 cm-1 and a n intensit.y Some idea of the amount the alcohol frequencies move to longer similar to t,he 864 em. -' band in phenyldimethylcart)iI~ol. ledwave lengths can be obtained from the work of Smith and Creitz Butyl acetate absorbs strongly at 841 c m - ' , but this is only nega(11). Although fully reasoned assignments are not attempted, tive evidence, since other acetates absorli here. Xgaiii, the specthe spectra of the six tertiary alcohols presented in their work totrum of t,he secondary peroxides of n-dwane (Figure 5 J slio~vsno gether with those of the three discussed here do follon- the Sitme vistrong bands in this rcgion. This implies that any -0-0pattern. hrational frequency occurring bet\vc.en 800 atid 900 cm. -1 gives tert-Butanol has two strong absorptions only in thc region 700 rise to a \Teak band. The authors would like to repeat the )Tarnto 1300 em.-', a strong single band a t 915 cm.-l, and a partially resolved group of maxima centering near 1200 em.-' I n the ing of Minkoff (5) (based on the spectra of several perosides and higher tertiary alcohols the group near 1200 cm-1 remains while hydroperosides): "The characteristic frequency is not strong; it the 915 cm.-' band splits into two bands or groups of bands ma!- be hidden by or confused with skeletal frequencies of comcentering in the regions 950 t o 1000 and 850 to 910 c m - ' It is parable intensities." -4s the peroxide link alone cannot give rise clearly the last group which will interfere with the identification to the strong bands reported here for the tertiary compounds, it is of peroxides in oxidation mixtures Of the eight substituted tertprobable that this is a case where this characteristic frequency is butanols quoted, six (2,4-dimethyl-3-ethyl-3-pentanol,2,2,4trieither masked by a much stronger absorption due to another mode methyl-3-ethyl-3-pentanol, 2,2,4-t~rirnethyI-3-isopropyl-3-pen- or is modified greatly by t'he tertiary group. tanol, 2,2,4,i-tetramethyl-3-n-propyl-3-pentanol,2,2,4,4-tetramethyl-3-isopropyl-3-pentanol, and phenyldimeth~.lcarbinol)have COKCLU SIos absorptions in the region 850 t o 870 em.-' strong enough to be It seems probable that these strong absorptions in the 800 t o mistaken for or interfere with the use of the 855 to 875 em.-' hand quoted above for the peroxides. Only tertamyl alcohol and 3methyl-3-pentanol are free from this difficulty. On the other hand, only 2,2,4,4-tetramethyl-%n-propyl-3-pentanol with an absorpt.ion a t 830 cm.-' is likely to interfere Ivith the hydroperoxide band. Casual application of the characteristic frequency identifications might cause this last pure alcohol to be described as a ternary mixture of alcohol, peroxide, and h5-droperoside! J I700 1,500 I300 I 100 900 ' 700 It seems likely, then, that these CM" characteristic frequen$ies are useful for distinguishing tertiary hyFigure 4. Spectrum of Ethyl tert-Butyl Ether (20% Solution) droperoxides from peroxides and alcohols, hut arc capable of resolving t,he ternary mixture for only the compounds of lower molecular weight. This is rather a severe limitatioxi on the application of the spectroscopic method especially as the hydroperoxide can alnays be recognized by iodine titration. If all three substances are available in a pure state for a required radical R, then the nornial method of "fingerprinting" by the infrared spectra is clearly more reliable than using the generalizations. The problem of the origin of Figure 5. Spectrum of Decane Hydroperoxide (30% Solution) these strong absorption bands has
i I
V O L U M E 2 4 , NO. 4, A P R I L 1 9 5 2
643 LITERATURE CITED
C !I20 cin
-1
range are associated with the C-C-0
group rather
C than nith the - G O link. Nevertheless, the modifications imposed upon this vibrational mode (whatever it may be) by the rest of the molecule in alcohols, peroxides, and hydroperoxides alter its frequency sufficiently to differentiate among the three types in oxidation mixtures nhen the molecular weight is low. A t higher niolecular weights it is difficult to distinguish between the alcohol and peroxide. It is preferable to identify the individual coniponents of oxidation mixtures by fingerprinting with the spectra of the isolated compounds \Thenever possible. ACK\OW LEU
