of the technique. the information obtained on the orientation of the hydroxyl groups within the molecule is of value in studies of the reactivity of phenols slid phenolic antioxidants. LITERATURE CITED
(1, Bmi:ird. D.. Hargrave, K . R., Higgins. G . 11.C.. J . Chetn. SOC.1956, 2845. (2) Comeshall. S U , , J . -4m.Chem. SOC. 69,
l%20 (19471
13) ~, Unviea. 11 31.. Truns. Faradav SOC.
36, 11 14’(1O40‘1, (4) Flett. 31. Pt. C., Spectrochim. Acta 10, 21 ( 1 9 5 7 , ( 5 ) Fox, J. J.. Martin! A . E., Proc. Roy. SOC. (Loridon) A162, 419 (1937). (6) Gp_ddri. R . F.. ASAL. CHEX.29. 1770 (19or).
( 7 ) Goddu, R. F., Pittsburgh Conference
on A4nalytical Chemistry and Applied Spectroscopy. 3Iarch 1958. (8) Goddu. R . F., Delker, D. A., ANAL. CHEY.30, 2013 (1958,. (9, Kuhn. 1,. P.. J . -4m.Chem. SOC. 74, 2492 ( 19L52\.
Table 111. Near-Infrared Absorption Data on Other Hydroxyl-Containing Compounds Absorbing in 2.7- to 3.0-Micron Region
Av. Molar Region of AbsorpAbsorption tivity, Functional Maxima, e, Liter/ Group c1 Mole-Cm. Acids (monomer) 2.82-2 84 10-100~ 50 .4lcohols 2.74-2 78 .. Hydroperoxides Aliphatic 2.81 85 Aromatic 2.82,2.84 40,30 Oximes 2.77-2.78 200 a Molar absorptivity of acids a t 2 83 microns is a strong function of concentration. (IO) Lord, R . C., Merrifield, R. E.. J . Chem. Phys. 21, 166 (1953). (11) Luttke, W.,Mecke, R., 2. physik. Chem. Hoppe-Seyler’s 196, 56 (1950).
Determination of Terminal Epoxides N e a r-Inf ra red Spect ro photo metry
(12) Pauling, Linus, “Sature of the Chemical Bond,’’ 2nd ed., p. 316 ff., Cornel1 Univ. Press, Ithaca, S. I-., 1948. (13) Sears, W. C., Kitchen, J. J., J . A m . Chem. SOC.71, 4110 (1949). (14) Stone, P. J., Thompson, H . W., Spectrochlm. Acta 10, 17 (1957). (15) Whetsel, Kermit, Roberson, K.E., Krell, M. W.,ASAL. CHEM.29, 1006 (1957). (16) Ibid., 30, 1594, 1598 (1958). (17) Whetsel, Kermit, Roberson, W. E., Krell, M. W., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 1958, (18) Wulf, 0. R., Jones, E. J., J . Chem. P h y s . 8 , 745 (1940). (19) Wulf, 0. R.: Jones, E. J.! Deming, L. S..Ibid.. 8. 753 11940) (20) \T;ulf, 0. R.,Liddel, Urner, J . A m . Chem. Soc. 57, 1464 (1935). (21) Wulf, 0. R., Liddel, Urner, Hendricks, s. B., Ibid., 58, 2287 (1936). RECEIVED for review l f a y 8, 1958. Accepted July 28, 1958. Presented in part a t the Pittsburgh Conference on -4nalytical Chemistry and iipplied Spectroscopy, March 1958.
by
ROBERT F. GODDU and DOROTHY A. DELKER Research Center, Hercules Powder Co., Wilmington 99,Del.
,Terminal epoxides have sharp absorption bands in the near-infrared region at 1.65 and 2.20 microns. The latter are several times more intense than the former. These bands are useful for the rapid determination of epoxides in a variety of mixtures. In particular, both terminal epoxides and terminal olefins may be simultaneously determined in the same sample. Other oxygen rings d o not interfere. The range covered b y the method is from 10 y per ml. of
’ ‘C-CH:
to pure epoxides.
The
\o.
accuracy and precision over most of the range are to =!=l to 2% of the amount present. If suitable standards are available, near-infrared can often replace chemical procedures which usually require more sample and more time, and in some instances, d o not give appreciably better accuracy or precision. Also, preliminary work indicates that it may be possible to improve the accuracy and precision of this method to *0.570 b y using high absorbance reference techniques and a 0.0- to 0.1-absorbance slidewire.
A
publication ( 2 ) described some advantages of near-infrared spectrophotometry n-hen applied to the determination of unsaturation-in particular, terminal unsaturation-in organic compounds. I n extending the uses of the near-infrared region (1.0 to 3.1 microns), another functional group method, similar to that described, has been developed. This concerns the determination of epoxides. It iq also applicable to the analysis of olefin-epoxide mixtures. Bearing in mind certain similarities between epoxides and olefins, the marinfrared region was investigated as a tool for the determination of epoxides. The spectrum of a typical terminal epoxide, epichlorohydrin, is shown in Figure 1. The sharp bands a t 1.65 and 2.20 microns are very similar to those usually found in terminal olefins ( 2 ) . The work reported here is based on the use of these bands to determine epoxides and differentiate them from terminal olefins. To the best of the authors’ knowledge, these bands have not been studied previously. Other ouygen rings such as those in oxetanes, furans, and dioxane do not absorb in this region. RECEXT
EXPERIMENTAL
Beckman Model DK-2 Spec’rophotometer. For qualitative s c m ning, t h e instrument was set u p as described ( 2 ) . For quantitative n-ork, it was desirable to operate a t a conqtant nominal slit rather than a t a constant sensitivity, because of the large varintions in nominal slit which occur as a function of both the fluctuations of room temperature during the qummer and the aging or replacement of the lead sulfide cell. Otherwise the instrument was set up as described prrvioiisly ( 2 ) . The effect of variations in nominal slits is more pronounced n-ith the DK-2 than with the Cary Model 14 because of the latter’s narrov-er spectral slits a t all operating conditions. A variable nominal or spectral slit may lead to a variable molar ahsorptirity. The slit width data are in Table I. Cary Model 14M Spectrophotometer. T h e Carv n a s used for quantitative work. The settings were: slit height o u t : speed 10 A . per second; and sensitiritv such t h a t t h e slit widths in Table I n e r e obtained. -4 -0.0 t o 0.1, 0.1 t o 0.2-absorbance slide-wire was used n.hen necessary. 3latched 1-em. cells !{-ere used for most of t h e work reported. Longer cells m a p be used t o obtain greater sensitivity and either fused silica or VOL. 30, NO. 12, DECEMBER 1958
2013
Corex cells may be used in this region. Background corrections mere used for the calculation of all spectral data. For example, in Figure 2 the tangent to the curve was drawn between 1.61 and 1.66 microns. I n Figure 3, tangents were drawn between 2.08 and 2.13 microns, and 2.17 and 2.25 microns. The sources of epoxides used and their purities are in Table 11. Other chemicals used were 1-octene, Phillips Petroleum Co., research grade 99% and carbon tetrachloride, reagent grade, dried over magnesium perchlorate.
I
i
1.65-MICRON OVERTONE BAND
The band a t 1.65 microns in Figure 1 is the first overtone of the fundamental C-H stretching vibration of the terminal epoxide group. The fundamental band occurs a t 3.28 to 3.36 microns and has recently been studied by Henbest et al. ( 3 ) . Resolution of this band from neighboring bands in the 1.65micron region appears to be better than that reported a t 3.3 microns with a calcium fluoride prism (5'). This band is located a t a shorter wave length than the first overtones of the methyl and methylene stretching vibrations a t about 1.70 microns. These methyl and methylene bands are sufficiently well resolved from the epoxide band that they seldom cause interference. Previous work ( 2 ) showed that the first overtones of terminal methylene bands occurred at 1.64 to 1.61 microns. It would not be expected to interfere with this terminal epoxide band. The only common hydrocarbon absorption which occurs in the 1.65-micron region is that due to aromatic C-H vibrations at 1.66 microns, and this does interfere with the use of the 1.65-micron band for epoxides. The wave lengths of the absorption maxima and the corresponding molar absorptivities in the 1.65-micron region of several representative compounds with terminal epoxide groups are listed in Table 111. Data from both the Beckman Model DK-2 and Cary RIodel 14 are included. No band could be resolved for styrene oxide or 112-epoxy3-phenoxypropane because of interfering bands from the aromatic nuclei. For the other compounds, the wave length of the absorption maximum is quite constant, 1.650 =t0.006 microns, and the molar absorptivity is of the order of 0.2 liter per mole-em. This absorptivity is somewhat less than that reported for terminal methylene groups (about 0.3), but is of the same order of magnitude. Thus, this region would be useful for the analysis of mixtures which contain roughly equivalent amounts of both types of functional groups. The spectrum of a compound containing both terminal unsaturation and terminal epoxide, butadiene monoxide, is shown in Figure 2. In the case of butadiene monoxide, the terminal methylene band is at 1.627 microns and 2014
ANALYTICAL CHEMISTRY
l
I
> 1 0
1 2
1 4
1 6
I 8
2 0 2 2 MICRONS
2 4
2 0
2 8
Figure 1 . Near-infrared absorption spectrum of epichlorohydrin in carbon tetrachloride
---
1% solution
the molar absorptivity is 0.384 liter per mole-cm. on the DK-2, and 0.457 liter per mole-cm. on the Cary Model 14. This large discrepancy in molar absorptivity between the instruments (see also Table 111) is due to the sharpness of the terminal methylene band and the better resolution of the Cary Model 14 in this region. Data in Table IV indicate a slight dependence of molar absorptivity on concentration in this region. The precision of duplicates in the same absorbance range is good, indicating that both accurate and precise results can be expected if calibration curves are used.
---
10% solution
Table 1.
Slit Width Data" Beckman Cary hlodel Model
DK-2 14 Xominal slit at 1.650 H ~ - ~ ~ ~ s ~ ~ 0.030 . b a n 0.27 d
widthat 1.650 microns, A. Nominal slit a t 2.200
27
Hay-;!:2s?$m.band
0 040
b c
0.75
M-idthat 2.200 microns, A. 26 21 4 s Slit set with cell filled n-ith solvent in reference beam.
Table II. Data on Epoxides Used Epoxide Source Epichlorohydrin Redistilled Epibromohydrin Dist. Products, Eastman grade 1,2-Epoxy-3-phenoxypropane Dist. Products, Eastman grade 1,2-Epoxy-3-isopropoxypropane Dist. Products, Eastman grade 1,2-Diisobutylene oxide ( 1,2-epoxy-2,4,9 Union Carbide Chemicals Co. trimethylpentane) Butadiene monoxide (1,2-epoxy-3-butene) Columbia-Southern Cheni. Corp. Styrene oxide Dist. Products, Eastman grade a
8.9
Purity, % ' 98-9Qa 915 96" 93"
..
72" 926 l0lC
Analyzed by HC1 addition using modified CaC12 plus HC1 procedure. Analyzed selective catalytic hydrogenation. Direct oxygen determination (this value used in Table V). 2.2-MICRON COMBINATION BAND
The combination band for terminal epoxides a t 2.2 microns falls between the combination bands of the aliphatic methyl and methylene groups a t 2.3 and 2.4 microns and the terminal methylene band due to unsaturation a t 2.1 microns (Figure 3). This epoxide band is distinguishable from the aromatic C-H bands in this region and epoxide methylene may be easily detected and measured in aromatic compounds without interference.
Absorption maxima and molar absorptivities of some epoxides are listed in Table 111. The maxima occur a t 2.213 =t 0.004 microns on the Cary Model 14, which the authors believe to have the more correct ?\-are length calibration in this region. The niajority of the absorptivities are about 1.5 liters per mole-cm. Thus, the molar absorptivity of the terminal epoxide methylene group in this region is usually somewhat larger than that a t the 1.6-micron band. This increase in
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2 30
VOL. 30, NO. 12, DECEMBER 1 9 5 8
2015
per ml. of
C-CHo
from epichloro-
/, ‘\()/
hydrin in a carbon tetrachloride solution containing di-n-butyl ether (8 mg. per ml.) and 1-octene (110 y per ml.) has been detected, using this technique at 2.2 microns. I n this particular case, 10-cm. cells and the 0.0 to 0.1, 0.1 to 0.2 absorbance slide-nire on the Cary Model 14 were used. The detection limit is believed to be about 10 y per nil. of ‘C-CH?
\o/
Table V.
Molar Absorptivity of Epichlorohydrin in Various Solvents Using Cary Model 14 Spectrophotometer
1.6-1Iicron Region 2.2-Micron Region Molar A4bsorptivity Molar Absorptivity ___ Solvent X M ~ ~1.1. , E , liter/mole-cm. Xuax.,p e, liter/mole-cm. 2 207 1.65 1.644 0.214 Carbon tetrachloride 1.92 0.202 2 208 Heptane 1.645 1.35 0.196 ’7 207 Di-n-butvl ether 1 646 Methyl ethyl ketone 1.642 0.175 e Diethylcyanamide 1 642 0.182 Solvent absorbed too much in the 2.2-micron region to observe any bands. Q
in carbon
tetrachloride. I n hydrocarbon samples the limit is about 100 p.p,m. Some a o r k has also been done on the use of near-infrared to determine the purity of different c,po\id(.; To increase the accuracy over the i 1 to 27, which is usually typical of direct determinations in carbon tetrachloride, a high absorbance reference technique was used on the Cary Model 14 equipped 131th a 0 to 0.1. 0.1 to 0.2 absorbance slide-wire. Preliminary data indicate that determination of the purity of epoxides to *0.5% or better i; powble. ANALYSIS OF MIXTURES OF UNSATURATES AND EPOXIDES
It has been pointed out that both the 1.6- and 2.2-micron regions could be used to analyze mixtures of terminal epoxides and terminnl unsaturates.
Several synthetic mixtures of epichlorohydrin and 1-octene were analyzed using the Cary RIodel 14 spectrophotometer. Calibration curves for the analysis of binary mixtures, using the 2.2-micron region give good Beer’s law plots. Keither compound contributes to the absorption a t the maximum for the other in this region. The mixtures were also run in the 1.6micron region, but the two bands, epichlorohydrin a t 1.644 microns and 1octene a t 1.635 microns, overlap appreciably. Also, the molar absorptivities are lo^, indicating that a high concentration of sample is needed for analyqis. From previous work, it is evident that other types of compounds containing a terminal methylene group n-ould give better results than 1-octene when mixed Kith terminal epoxides, because most of them absorb a t shorter wave length; which are further from the epoxy band
at 1.65 microns. For instance, vinyl ethers have a band a t 1.615 microns, acrylic-type compounds a t 1.620 niicrons, and allyl acetate has a band a t 1.626 microns. Thus. it should be relatively simple to analyze mixtures of these olefins with epoxides in both the 1.6- and 2.2-micron regions. The determination of both functional groups in reaction mixtures and polyfunctional compounds by this technique should have many advantages over existing methods. LITERATURE CITED
(1) Durbetaki, A. J., A r a ~ CHEXI. . 29, 1666 (1957). (2) Goddu, R. F., Ibid., 29, 1790 (1957). (3) Henbest, H. B., Neakins, G. D.,
Xichols, B., Taylor, J. K., J . Chem.
SOC.1957, 1459.
RECEIVEDfor review January 10, 1958
A4cceptedJuly 16, 1958.
Spectrophotometric Determination of Iron, in Urine, Using 4,7Dipheny I- 1,lO- phe nunt hro Iine MARYIN
J. SEVEN’ and RALPH E. PETERSON
National Institute of Arthritis and Metabolic Diseases, Bethesda,
b A simplified procedure for the determination of iron in urine employs as a color agent the compound, 4,7diphenyl-1,lO-phenanthroline, which has a molar absorbancy index of 22,400 for the ferrous complex. The entire procedure is carried out in one flask. Extraction of the colored complex into isoamyl alcohol after wet ashing further increases the sensitivity and avoids interference from other ions commonly found in biological flJids. Spectrophotometric and radioactive iron recovery studies indicate that complete recovery of iron i s achieved when the proper proportions of reagents are used. For 1 to 4 y of iron, a precision to &2y0can be achieved.
2016
ANALYTICAL CHEMISTRY
Md.
iron determinations are beset TT ith problems. Some, inherent in trace metalanalyses,include the rendering large quantities of apparatus iron-free, the removal of contaminating iron from reagents, and the lack of sensitirity of color agents. Others are peculiar to iron determinations in biological materials, such as the adequate digestion of organic matter and the complete recovery of iron without interference by pyrophosphates Irhich may develop during digestion procedures (2-4, 6). The method detailed here overcomes these problems by a highly specific and simplified procedure employing 4,7-diphenyl-l,lO-phenanthroline (bathophenanthroline) as 3 color agent. Because the procedure is carRIXARY
ried out in one flask, large quantities of equipment are eliminated. Small amounts of urine are required. Reagents are readily made iron-free by redistillation or by extraction x i t h a reducing agent and the phenanthroline reagent in isoamyl alcohol. Spectrophotometric and iron-59 recovery studies indicate complete recovey of iron when the proper proportions of reagents are used. Interest has de\ eloped recently in the use of 4,7-diphenyl-1, 10-phenanthroline for iron determinations. This compound was introduced by Case (1) and shown by Smith, McCurdy, and Diehl 1 Present address, Hahnemann Medical College, Philadelphia, Pn.
