taining 0.2 p.p.m. of phosphorus. These samples give a mean absorbancy value of 0.420 .ivith a standard deviation of 0.006, or 1.4%. The solutions are stable for weeks and adjustment Of the is not Exact duplication of technique in ex-
traction and washing of extract is important. LITERATURE CITED
(1) Berenblum, I., Chain, E., Biochem*J . 32, 287 (1938).
(2) Boltz, D. F., Mellon, M. G., ANAL. CHEM.19, 873 (1947).
(3) Huckel, JV., “Structural Chemistry of Inorganic Compounds,” p. 183, Elsevier, New York, 1950. (4) Radelin, C., blellon, M. G., ANAL. CHEM.2 5 , 1668 (1953). (5) WU, H., J . Bd.Chem. 43, 189 (1920). RECEIVEDfor review May 3, 1956. Accepted October 11, 1957.
Determination of 1,l ’-Ferrocene Dicarboxylic Acid in Presence of Ferrocene Monocarboxylic Acid by Infrared Spectroscopy EUGENE F. WOLFARTH’ Materials laboratory, Wright Air Developmenf Center, Air Research and Developmenf Command, Wright-Patterson Air Force Base, Ohio
A method is described for obtaining quantitative infrared absorption data for highly insoluble materials using potassium bromide disks. The preparation of the disks and treatment of the data is given, along with an example using ferrocene carboxylic acids.
F
E~;~;c,
(dicyclopentadienyl because of the resonance between the iron and the conjugated ring, shows a high degree of aromaticity and consequently, a high degree of stability. I n the course of studying the chemistry of ferrocene compounds, it was of interest to determine the amount of ferrocene dicarboxylic acid in a mixture of both the mono- and dicarboxylic acids. A spectrometric method of analysis \vas desired because of the inherent speed and accuracies of absorption methods, and the small amounts of sample available (usually 3 to 7 mg.). I n a scan of the entire spectral region from 0.2 t o 35 microns, only two bands were found which would be suitable for quantitative measurements. Both were infrared bands associated with the unsubstituted cyclopentadiene ring. The first band, at 9.02 microns, was assigned (1-5) to an antisymmetrical ring breathing vibration and the second band, at 9.98 microns, to a C-H bending vibration. Both bands are very strong in the spectrum of the unsubstituted ferrocene molecule. I n monosubstituted ferrocenes, the two bands are still present but of diminished intensity ( 5 ) . Both bands are completely absent in 1,l’-disubstituted E NC
Present address, Ohio State University, Columbus, Ohio.
ferrocenes ( 4 ) . As can be seen in Figure 1, the ferrocene carboxylic acids follow these generalizations. Because ferrocene dicarboxylic acid is insoluble in the solvents useful in infrared absorption nwasurements, the potassium bromide disk technique was investigated. A method was devised to obtain semiquantitative data. MATERIALS A N D APPARATUS
Both the ferrocene mono- and dicarboxylic acids were prepared in the laboratory. Elemental analysis indicates they are of high purity. The potassium bromide was an infrared spectral grade reagent supplied by Harshaw Chemical Co.; it was dried a t 120’ C. for 2 days prior to USP. The potassium bromide disks, 0.5 inch in diameter, were prepared in a PerkinElmer wmium die. The die \vas pressed in a 20-to11 Carver laborntory press t o approximately 23,000 pounds per square inch. Weighings ryere made on a Sartorius Dial-0-matic analytical balance to an accuracy of 50.05 mg. Absorbance measurements were made on a Perkin-Elmer Model 112 doublepass infrared spectrometer equipped with sodium chloride optics. The instrument was calibrated to AO.01 micron using atmospheric water and carbon dioxide bands and ammonia vapor. The absorbance values were measured directly using the Model 112 densitometer attachment, applying the “sample in, sample out” technique. The values are accurate t o +0.02 absorbance unit. PROCEDURE A N D DISCUSSION O F RESULTS
For each pure acid, a mixture of potassium bromide and the acid was prepared consisting of 0.0111 gram of ferrocene carboxylic acid per gram of pure potassium bromide. The resulting
mixtures were thoroughly ground, mixed in a carbide mortar, and placed in a desiccator. They contained exactly 4.830 X loes mole per gram of ferrocene monocarboxylic acid and 4.054 X mole per gram of ferrocene dicarboxylic acid, respectively. A weight of exactly 0.3000 gram !vas selected as the standard disk size. Varying amounts of the two mistures were combined for a total weight of approximately 0.3 gram to give a series of niixturcs ranging from 0 to 100% ferrocene dicarboxylic acid. These final mixtures n-ere again ground and mixed, the disk was prepared by the usual procedures, and the finished disk weighed. To determine the absorbance value. the Perkin-Elmer Mode1 112 was set at the desirfd m v e length, the slits set a t 0.9 mm., and the gain set at 0.02 pv. full scale. The absorbance value for each disk was then read directly from the densitometer scale. T o refer these absorbance values to a common point, the standard 0.3000gram disk. a weighted absorbance value was calculated as follows: W.A. =
0.3000
disk weight in grams X measured absorbance This procedure can be justified b y considering Beer’s law. A = kml where A is the absorbance, k is the extinction coefficient, m is the number of moles of sample, and 1 is the path length. Because the diameter of the disk and the ratio of organic material to potassium bromide (the density) remain constant, the only significant variable is 1. The path length is directly proportional to the amount of material present and, therefore, to the disk weight. I n Figures 2 and 3, these weighted absorbances were plotted against the VOL. 30, NO. 2, FEBRUARY 1958
185
WAVE NUMBERS IN CM
WAVE NUMBERS IN CM
r CL
--02
3
5000 4000 3000 100 ( 1 -
4
250C
5 WAVE
LENGTH
!
I
b 7 IN MICRONS
8
WAVE NUMBERS IN CM 2000 ,
,-L
15001400 1
,
I
1300
1200
1
I /
-
~
1
P
1100
IO
IO00
II
lP 12 WAVE LENGTH IN MICRONS WAVE NUMBERS IN CM
900
- ___
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'
FERROCENE ,f-,
DICAREYOXYLIC
r
-
0 I6
1
700
800
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15
4
b25 I00
J ,?
/'
i
0
Figure 3. Weighted absorbance of 9.98-micron band of ferrocene monocarboxylic acid vs. mole fraction of ferrocene dicarboxylic acid
Figure 2. Weighted absorbance of 9.02-micron band of ferrocene monocarboxylic acid vs. mole fraction of ferrocene dicarboxylic acid
mole fraction of ferrocene dicarboxylic acid. Both plots give a linear curve except for the slight divergence in Figure 3 a t the higher dicarboxylic acid concentration. This departure from linearity is probably due to the overlap of the 9.70-micron band as it increases in intensity. The spread of points indicates that this method will give a concentration value accurate to * 5 % *
An unknown sample is analyzed by weighing out 0,0111 gram of sample per 186
ANALYTICAL CHEMISTRY
gram of potassium bromide, preparing a disk, obtaining its weighted absorbance, and then reading the per cent composition from the curve. All of the samples studied were known t o be essentially mono- and dicarboxylic acid mixtures with no other interfering materials present. ACKNOWLEDGMENT
The author wishes to thank D. W. Mayo for the pure samples of ferrocene mono- and dicarboxylic acids used in this study.
LITERATURE CITED
(1) Kaplan, L., Kester, L., Katz, J., J . A m . Chenz. SOC.74, 5531 (1952).
(2) Lippincott, E. R., Nelson, R. D., Ibid., 77, 4990 (1955). (3) Lippincott, E. R., Nelson, R. D., J . Chem. Phys. 21, 1307 (1953). (4) Pauson, P. L., J . A m . Cheni. SOC. 76, 2187 (1954). (5) Rosenblum, M.,Ph.D. thesis, Harvard University, Cambridge, Mass., 1953. RECEIVEDfor review July 22, 1957. Accepted October 10, 1957.
