Interaction of Ammonium Fluoride Mulls and Deposited Films with Sodium Chloride Plates SIR: I n an investigation of the formation of complex fluorides such as NH4CuF3, it has been necessary t o obtain infrared spectra of mixtures of the complexes with ammonium fluoride, run as halocarbon mulls ( 2 ) . Anomalous absorption peaks found with identical mixtures led us to investigate the spectrum of ammonium fluoride itself, for a rapid exchange takes place between the fluoride ion of the ammonium fluoride and the chloride ion of the salt plate. This proved t o be the case not only when the ammonium fluoride was run as a mull, but also when i t was deposited as a film from anhydrous methanol. Plumb and Hornig (6) have pointed out a similar situation in explaining several anomalous absorption peaks reported by Bovey (1) in the spectra of sublimed films of ammonium fluoride on sodium chloride plates. Several groups of investigators (5-5) have shown that anion exchange takes place in KBr pellets. They show that moisture contributed significantly t o the exchange process. This has also been found in the case reported here. DISCUSSION OF RESULTS
I n Table I are listed the absorption peaks a t room temperature for ammonium fluoride and ammonium chloride as reported b y Plumb and Hornig (6) and Wagner and Hornig ( 7 ) , along with the results of a typical run in this investigation using C.P. ammonium fluoride directly from stock. It is
obvious t h a t the ammonium fluoride run, both as a mull and as a film deposited from methanol, gives only a spectrum comparable to ammonium chloride. This was further proved by the x-ray diffraction pattern of scrapings from the salt plate surface of the methanol deposited film. This showed ammonium chloride t o be the major species present. In the case of both mull and film, the surface of the salt plate was deeply etched, making i t necessary t o repolish the plates after each run. A fairly intense spectrum for ammonium chloride could be obtained by rerunning the etched plates which had been washed with CC14 but not repolished. The importance of surface moisture in the exchange process has been shown in the case of K B r disks ( S , 4 ) . T h a t i t is also important here is seen from the fact t h a t in order to get any indication a t all of the presence of ammonium fluoride it was necessary either t o precipitate the ammonium fluoride from anhydrous methanol solution with dry ether, or to dry the ammonium fluoride for extended periods of time at a temperature just below the sublimation temperature, and then to prepare the mulls in a dry box. Even under these conditions an appreciable amount of exchange takes place so that a considerable bulk of ammonium fluoride was required between the plates in order that a sufficient amount would remain unchanged. Since the mull has two surfaces at which to exchange,
3
WAVELENGTH MICRONS Figure 1 . nesses"
Spectrum of NH4F mull run a t different "thickDotted line: "Thick" mull 4 drops halocarbon oil Solid line: "Thin" mull 5 drops halocarbon oil
Table 1. Absorption Bands for NH4CI and NH4F a t Room Temperature
NHdF
Wagner and..
h'HaC1 [Plumb and Hornig, ( 6 ) ] ern.-'
This work, cm.-'
3138 3044 2810
3110 3035 2800
Homing, (7)]
em.-' 3310 3218 3065 2999 2969 2820 2590 2485 2261 2007 1489
2000'. poorly 1762 /characterized
it is not surprising that in many instances only the spectrum of ammonium chloride was obtained. This is illustrated in Figure 1 which shows a comparison of a single sample of ammonium fluoride precipitated from methanol, mulled in the dry box, and run as mulls of two different thicknesses. The thickness is changed by adding more halocarbon oil, thus decreasing the viscosity of the mull. The use of calcium fluoride plates offers further evidence of the exchange reaction. Figure 2 shows a single sample of ammonium fluoride mulled with halocarbon oil and divided into two parts. One run was on sodium chloride and the other on calcium
4
5
W AV E LENGTH Figure 2. plates
1440 1406
1445 1403
6
7
M IC RO NS
Spectrum of NHIF mull run on CaF2 and NaCl Dotted line: Halocarbon mull run on N a C l plates Solid line: Same sample run on CaF2 plates
VOL. 34, NO. 1 1, OCTOBER 1962
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fluoride plates. The spectrum run using sodium chloride plates clearly shows the spectrum of ammonium chloride superimposed on that of the ammonium fluoride. An attempt t o run the reverse exchange, using ammonium chloride mull on the calcium fluoride plate, gave no indication of en ammonium fluoride spectrum. There was also no etching of the calcium fluoride plate although the mull was in contact with it for over an hour. No care was taken to exclude moisture, and the ammonium chloride was used directly from a stock bottle.
All spectra were run using a Beckman I-R5 spectrophotometer. The x-ray powder photograph of the surface scrapings from NaCl plates was taken using CuK, radiation. LITERATURE CITED
( 1 ) Bovey, L. F. H., J. O p t . SOC.Am. 41, 866 (1951). (2) Crocket, D. S., Haendler, H. M., ANAL.CHEM.31, 626 (1959). (3) Ketelaar, J. A. A., Haas, C., van der Elshen, J., J . Chem. Phys., 24, 624 (1956). (4) Kutaelnigg, W., Nonnenmttcher, G., Mecke, R., Chem. Ber. 93, 1279 (1960). \ - - - - I .
(5) Meloche, V. W., Kalbus, G. E., J . Inoro. Nucl. Chem. 6. 104 (1956). (6) PlGmb, R. C., Hornig, D.'F., J. Chem. Phys. 23, 947 (1955). (7) Wagner, E. L., Hornig, D. F., Zbid., 18, 296 (1950). DAVIDS. CROCKET ROBERTA. GROSSMAN Department of Chemistry
Lafayette College Easton, Pa. THISwork waa supported part by the National Science Foundation Grant No. G14180, by the National Science Foundation Undergraduate Research Participation Program, and by the Lafayette College Research Fund.
A General Microqualitative Technique.
Combination of Ring Oven, Cation Exchange Paper, and Emission Spectrograph
SIR: The emission spectrograph is an excellent qualitative tool for very small samples; however, with conventional spectrochemical techniques the nonmetals 0, N, C, S, F, C1, Br, I, and the inert gases are not detected. Frequently the entire sample is consumed and none of the above elements can be identified. Many of the nonmetals exist in solution as anions, whereas the spectrographically detectable elements are cations, with some exceptions such as the permanganate ion. A combination of the Weisz ring oven (6) and cation exchange paper (4is useful in running a complete qualitative analysis on a single drop of solution.
air-dried. The disk is then placed in the center of a filter paper circle, and the anions are washed to the ring with distilled water. The disk and a portion of the ring zone are analyzed spectrographically by placing the paper directly in a graphite electrode for the d.c. arc method. Alternatively, the disk and ring zone may be leached with 6N nitric acid and the solution analyzed by the copper (3) or graphite (2) spark technique. The remaining portion of the ring is sectioned and tested for anions ( 5 )' The cations can be identified with the ring oven also. The cation exchange paper disk is transferred to a fresh filter paper circle and the cations are washed out to the ring with 3N nitric, where ring oven qualitative tests are made. Cation Capacity. Aliquots of a nickel chloride solution were dried on disks and washed on the ring oven.
EXPERIMENTAL
Apparatus and Procedure. Ring oven, Il'ational Appliance Co., Portland, Ore. Whatman CbI50, carboxymethylcellulose cation exchange paper. Nine-mm. disks c u t with a No. 4 cork borer. Whatman 41H filter ~. paper, 5.5-em. circles. Spectrograph, ARL 1.5-meter Quantograph, 2400-4600 A. Kodak S.A. 2 film. The sample is placed on a disk and
Figure 1 .
Separation and elution A.
of nickel chloride
0.04 p o l e
B
0.08 pmole C. 0.4 pnole D. 0.8 pmole E. 0.08 pmole (eluted)
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ANALYTICAL CHEMISTRY
T h e filter paper circles were cut in half, and a silver nitrate ring test for chloride on one semicircle was positive in every case. T h e other semicircle and the disk were tested for nickel with dimethylglyoxime and are shown aa A , B, C, and D of Figure 1. The faint nickel ring in C shows that breakthrough had occurred, although the disk is not saturated. The capacity of CM50 as listed by the manufacturer is 0.5 meq. per gram. Sample C contained 0.4 pmole of nickel, which is about 25y0 of theoretical capacity for the 6-mg. disk. When the sample was transferred to the disk on the ring oven without prior drymg, breakthrough occurred a t a much lower level. Elution of Nickel. A sample identical to B in Figure 1 was eluted b y washing with 3 N nitric. T h e resultant dimethylglyoxime test on t h e disk and semicircle, E of Figure 1, shows complete transfer t o the ring.
0 1
1
1
1 1 1
