addition, the absorption at the 250, mp wave length point is a more definite peak for glyceraldehyde than for acetol and dihydroxyacetone. The aldehyde carbonyl gives a sharper absorption at this point than the ketone carbonyl. The infrared absorption curves (Figure 2) did not show any highly significant differences for these compounds. I n the 3- and 9-micron region the dihydroxyacetone curve shows additional absorption bands which differentiate it from acetol and glyceraldehyde. The acetol curve shows a much more significant band a t 13.8 microns than those for glyceraldehyde or dihydroxyacetone. Semicarbazones. Only two semicarbazide derivatives were made and characterized from the five compounds-Le., the acetol and methylglyoxal semicarbazones. These have distinctly different physical properties and furnish an excellent means of differentiating acetol and methylglyoxa!. As shown in Table I, the melting points of the two compounds are 192--4O C. for acetol semicarbazone and 256-7' C. for methylglyoxal disemicarbazone. The ultraviolet absorption curves (Figure 3) have absorption maxima a t widely different points, acetol a t 225 mp and methylglyoxal a t 286 mp.
Osazones. T h e five compounds produce just two osazones which are usually designated as the pyruvaldehyde dinitrophenylosazone and the hydroxypyruvaldehyde dinitrophenylosazone. T o have the compounds involved in this study distinctly different in name, the alternate term methylglyoxal has been used for pyruvaldehyde. The osazone derivative does not contribute much toward the identification of the five carbonyls because the methylglyoxal dinitrophenylosazone may be formed from any of them. However, the hydroxypyruvaldehyde derivative can be made from only three-those containing two hydroxyl groups (glyceraldehyde, dihydroxyacetone, and hydroxypyruvaldehyde). As the melting points of the two osazones are significantly different, a partial separation of the five carbonyls can be made on this basis. ACKNO WLEDGMENl
The authors express their appreciation to B. il. Brice for interpretation of the ultraviolet absorption data, to Anne Smith for making the ultraviolet measurements, t o Carl Leander and Roland Eddy for obtaining and interpreting the infrared data, and to Ruth Kelly
for the elemental analyses of the compounds. LITERATURE CITED
(1) Allen, C. F. H., J. Am. Chem. SOC. 52, 2955 (1930). (2) Brady, 0. L., J. Chem. SOC.(London) 1931, 756. f3) Coulson. D. M..Anal. Chim. Acta 19, 284 (1958). ' (4) Davison, W. H. T., Cristie, P. E., J , C h m . SOC.(London) 1955,3389. (5) Eistert, B., Haupter, F., Chem. Ber. 91, 2703 (1958). (6) Kamm, Oliver, "Qualitative Organic I
,
Analysis," 2nd I
(8) Neuberg, C., Strauss, E., Arch. Bzochem. 7,211 (1945). (9) Kodzu, R., Matsui, K., Bull. Chem. SOC.Japan 10, 122 (1935). (10) Reich, H., Samuels, B. K., J . Ow. Chem. 21, 68'(1956). (11) Strain. H. H.. J . Am. Chem. SOC. . 57, 758 (1935). ' (12) Underwood, J. C., Lento, H. G., Jr.. Willits. C. 0.. Food Research 21. 589 (195G).' '
'
RECEIVED for review February 5, 1960. Accepted June 23, 19GO. Fifteenth paper in a series on maple sirup. The mentior of commercial names in this paper does not constitute a recommendation Of these items over others of similar nature.
Absorption Spectra of Molten Fluoride Salts Solutions of Praseodymium, Neodymium, a n d Samarium Fluoride in Molten Lithium Fluoride J. P. YOUNG and J. C. WHITE Analytical Chemisfry Division, Oak Ridge National laboratory, Oak Ridge, Tenn.
b Spectra are presented for solutions of praseodymium, neodymium, and samarium fluoride in molten lithium fluoride a t a temperature of approximately 900" C. These data are discussed and compared to similar resul?s which have been obtained in other molten salts and aqueous sobtions. Molar absorptivities for selected major absorbance peaks of these rareearth spectra are also given.
I
shown. These spectra were obtained using the Cary recording spectrophotometer, Model 14M, equipped with the high-temperature cell assembly as described in a previous report (6). The molten salts were confined in the form of a pendent drop. The ability t o obtain these spectra demonstrates the capability of this technique for confining corrosive solutions such as molten fluoride salts at very high temperatures in a windowless container.
N A PREVIOUS PUBLICATION ( 7 ) the
authors presented the absorption spectra of several metal fluorides dissolved in a molten lithium fluoridesodium fluoride-potassium fluoride mixture a t temperatures ranging from 500" t o 650" C. In this report the qpectra of praseodyniium, neodymium, and samarium fluorides dissolved in molten lithium fluoride (m. p. 848' C.) are 1658
ANALYTICAL CHEMISTliY
EXPERIMENTAL
Apparatus and Reagents. The hightemperature cell assembly (6) was used to obtain the spectra; the molten fluoride samples were contained as a pendent drop in a platinum tube, 1.0 cm. in length and 0.44-vm. diameter (6, 7 ) > a t approximately 999' C;. This temperatu:? wa5 obtained within 45
minutes by passing a current of 8 amperes a t a voltage of 40 volts to the heater circuit, which consisted of quartz plate5 wound with 20-mil platinum wire. The temperature of the pendent, drop of lithium fluoride was determined either by direct measurement of t'he drop with a platinum-platinum rhodium thermocouple (0' C. cold junction) w!iich v;ns spot-welded to the skin of the platinum tube sample container, or by e proportionality relationship in which the furnace block temperature, measured by a Chromel-Alumel thermocouple, was compared to the illensured tempcratuie of the drop. Ana!)-ticsl reagent-grade lithium fiuuride "as used in thP prepiratioi: of the samples. Tile pure rare-earth salts praseodymium fiuoride, neodyrniuni fluoride, and saniariuin fluoridc, wvrre prepared at the Oak Ridge Natiozal La!,oratory. Procedure. The melts w x e pre-
r
l
l
l
4c4
l
l
l
l
l
l
l
l
~
l
1 l
l
690
y)o
WAVE LQGlU. my
Figure 1. Spectrum of praseodymium fluoride in molten lithium fluoride Temperature, 896' C. Path length, 0.94 cm. Pr concentration, 2.5% (w./w.)
pared by heating weighed amounts of solvent and solute in a platinum crucible a t a temperature of about 950" C. until t h e melt was clear. T h e crucible and its contents were then placed in a desiccator, and transferred to a dry box. On cooling, t h e solid sample was removed from t h e crucible, pulverized, and then placed in a platinum cup for insertion into the high-temperature cell assembly. The spectra mere determined as described previously ( 7 ) . The concentration of the various rare earths was determined spectrophotometrically (2) after dissolving the melt in a minimal quantity of sulfuric acid. RESULTS AND DISCUSSION
The spectra of praseodymium, neodymium, and samarium fluorides in lithium fluoride a t a temperature of approximately 900' C. (exact temperatures are given with the spectra) are shown in Figures 1, 2, and 3, respectively. The apparent optical cut-off which can be observed in all the spectra at approximately 300 mp is postulated to be due t o the optical characteristics of a pendent drop of liquid. This effect is observed in pendent drops of any liquid, including aqueous solutions at room temperature. The drop, contained in a platinum tube, has the shape of a double concave lens. It may be assumed that as light of lower xave lengths passes through the lens-shaped liquid, a greater fraction of this light is scattered and lost. This effect is not particularly noticeable in the near-infrared and visible regions of the spectra, but becomes significant in the ultraviolet region. Molten lithium fluoride and the rareearth fluoride solutions that were prepared from this solvent were apparently very transparent liquids, as defined in terms of Kirchhoff's law (4),which relates absorptive and emissive power of materials as a function of temperature. Little, if any, black-body radia-
tion was observed to emanate from the molten solutions. Since these solutions are confined in a windowless container, no difficulty from thermal interference or noise originating from cell windows was encountered. Such problems would probably be associated with more conventional cells a t these temperatures. The noise level for the spectra obtained in the near-infrared region of the spectrum was less than 0.01 absorbance unit; in the visible region the noise level was slightly greater than 0.01 absorbance unit. This difference is probably due to the optical characteristics of the Cary spectrophotometer. I n the former case all thermal radiation emitted by the high-temperature cell assembly is passed through the monochromator before impinging on the detector. I n either case the noise level is not serious and probably could be entirely eliminated by suitable masking of the black-body radiation originating from the hot portions of the furnace itself. Praseodymium Fluoride. T h e principal absorbance peaks found in the spectrum of praseodymium fluoride in molten lithium fluoride are presented in Table I (see also Figure l ) , along with absorbance peaks which have been reported in other solvents.
Table I. Spectrum of Praseodymium in Various Solvents; W a v e Length of Maximum Absorbance, M p
LiF-NaFLiF, KF (71, 900" C. 550" C. 585 522 479 468 444
588 (522?) 479 467 444
LiNO, KNOt (I), 184 C.
25 C.
590
590
485 467 447
0.1M HClO,
(!I,
...
482 469 444
The wave lengths of maximum absorbance of praseodymium ion at 900" C . in fluoride melt and at 25" C. in acidic aqueous solution are quite comparable considering the large ditference in temperature. A small b u t significant blue shift in the 590-mr peak is observed &s the temperature increases. A new absorption peak at 522 mp in molten lithium fluoride can also be noted. The presence of this peak is also indicated in the spectrum of praseodymium in lithium fluoridesodium fluoride-potassium fluoride (7); no mention of this peak was made in the latter melt since the absorbance was extremely weak. Whether the 522mp peak is due to a thermal or solvent effect is not definitely known at this time. Neodymium Fluoride. T h e absorbance peaks found in the spectrum of neodymium fluoride in molten lithium fluoride are presented in Table I1 (see also Figure 2), along with a comparison of peaks which have been reported for neodymium in other solvents. Again the absorption peaks found in molten lithium fluoride and 0.1M HCIOl compare, in general, quite closely. Sundheim and Harrington (3)note that some of the detail of the aqueous spectrum of neodymium is nqt observed
Table II. Spectrum of Neodymium in Various Solvents; W a v e Length of Maximum Absorbance, Mp
LiCIKC1
LiNOr KNO,
LiF, (a, ( I ) , 900OC. 373' C. 184" C. 874 885 871 803 810 801 747
755
683
...
654
...
582
590
532s 523 512s
520
474
...
...
... ...
460
...
43 1
...
383 356s 350
...
... ...
... ...
...
0.1M HClOi
.I!(
25 C. 868 803s" 797 739 742 7355 675 685s 679 ... 636b 628b 623 585 575 578s ... 532s 526 522 513 512 509s ... 480 476 ... 469 ... 46 1 ... 433b 430 427 418b (No published 380b data in UV region)
360
...
...
...
... 0 8 = shoulder. Very weak absorbance peak.
VOL. 32, NO. 12, NOVEMBER 1960
354 351 347 340b 329
1659
4
-
-
-
02
00
1
1
1
1
1
1
l
I
400
I
I
I
I
ILK)
i L - 1 rm
I
1
I
1
m
I
!
/&LA
em
I
I
1
1
900
WCIM L E r n H , m y
Figure 2.
Spectrum of neodymium fluoride in molten lithium fluoride
I
Table 111. Spectrum of Samarium in Various Solvents; W a v e Length of Maximum Absorbance, Mp
LiF,
900"
c.
4ss ...
460 4 1 419
... 399 390 373 358
340
...
... ... a
0.1M HClO4 (2), 25" C. 489" 479 464 451" 442 418 416 415 407 402 390 375 362 354" 344 332 318 306
Very weak absorbance peak.
Table IV.
Rare Esrth
Temperature, 873' C. Path length, 0.85 cm. Nd concentration, 2.8% (w./w.)
in molten salt spectra. Some peaks which are absent, however, from the spectra of neodymium in the lower meIting chloride salt mixtures are observed in molten lithium fluoride. It would appear, therefore, that thermal effects are not entirely responsible for the altered spectra of neodymium in lithium chloride-potassium chloride. As is the general case with the spectra of rare earths in molten salts, the absorption peaks of neodymium in lithium fluoride, although relatively sharp, exhibit some degree of broadening as compared with aqueous spectra of the same rare earth. Most of the very insensitive peaks of neodymium in aqueous solution (molar absorptivity index of less than 0.1) are not found in the lithium fluoride solvent. To determine if these peaks are present in this molten salt, the spectrum of a solution which contains a greater concentration of neodymium would be required.
Molar Absorptivities for Selected Absorbance Peaks of Several Rare Earths Mob Absorptivities Index Wave LiF-NaF-KF LiCl-KC1 0.1M Length, HC104 (21, LiF, 900" 550 c. 25" C. 373 MP"
c.
q, c.
q,
Wave lengths correspond to peaka in the spectrum in LiF; molar absorptivities are the maximumreported for wrresponding peaks in other solvents. 1660 *
ANALYTICAL CHEMISTRY
Samarium Fluoride. The absorbance peaks found in the spectrum of samarium fluoride in molten lithium fluoride are presented in Table I11 (see also Figure 3), along with the absorbance peaks which have been reported for samarium in 0.1M perchloric acid. As with the spectra of the other rare earths in this molten salt, the agreement of wave length of maximum absorbance for samarium in aqueous solution is quite close considering the differences in solvent temperature. As noted before, however, some small amount of detail is lost and the very insensitive absorption peaks are not observed. Because of the optical characteristics of a pendent drop of sample in the ultraviolet region of the spectrum, it is not possible to say whether absorption peaks in the region of 332 to 300 mp are present or absent in the lithium fluoride solvent. I n water the main absorbance peak for samarium is found at 402 mp; two much less intense peaks occur a t 407 and 390 mfi. I n the lithium fluoride solvent the broadened main peak of samarium, 399 mp, has apparently obscured the 407-mp peak; however, as ran be noted in Figure 3, a definite indication of a peak a t 390 mp can be observed. Molar Absorptivities. Molar absorptivities for selected major ahsorbance peaks of praseodymium, neodymium, and samarium in molten lithium fluoride are showii in Table IV. The density of 1it)hium fluoride was taken to be 1.7 in making these calculations. For comparison, correspond-
ing d a t a obtained with other solvents are also presented. A possible error of f10% is involved in all pendent drop data reported in Table 1V as a consequence of the difficulty in controlling accurately the quantity of a sample held as a pendent drop, and also on account of minor variations in the placement of the drop in the light path of the spectrophotometer that result in changes in the optical response of a sample of pure solvent. Based on various experimental evidence, a close approximation of the path length of a pendent drop of molten salt can be calculated by assuming that the pendent drop is a cylinder; hence, from a knowledge of the weight and density of the molten lithium fluoride pendent drop samples, the path length can be obtained. Errors involved in this calculation should be less than 3%. With respect t o the optical response of a sample of pure a reference absorbance solvent-Le.. spectrum-no way t o compare the absorbance of a sample directly with the absorbance of a solvent has been developed other than by extrapolation of the reference absorbance spectrum. Because of the relatively sharp peaks found in absorption spectra of rare earths, such an extrapolation of a reference absorbance under a peak should be subject t o only small errors. I n making the extrapolations of the reference absorbance curves, consideration was given to the regions of zero absorbance shown in aqueous rareearth spectra, since the molten salt spectra did agree well with corresponding aqueous spectra. The smallest errors are, therefore, probably involved in the neodymium spectra (Figure 2), and the largest error is involved in the praseodymium spectra (Figure 1) because of the occurrence of a new peak a t 522 mp. The two most logical approximations of the zero absorbance curve in the praseodymium spectra are shown in Figure 1 as dashed lines below the absorption spectrum. This figure shows that either choice would make only a slight difference in the absorbance of the 444-mp peak; some
WAVE
Lwaw. mP
Figure 3. Spectrum of samarium fluoride in molten lithium fluoride Temperature, 860’ C. Path length, 0.87 cm. Sm Concentration, 4.0% (w./w.)
errors are possible in determining the magnitude of the 479-mp peak; and gross errors could be involved in measuring the magnitude of the 522and the 585mp peaks. Neither base line affects the wave length of maximum absorbance that has been assigned to these peaks. Some rather interesting comparisons can be made from an inspection of the data shown in Table IV. I n all cases given in this table, the molar absorptivities for the various absorbance peaks of rare earths dissolved in molten salts are lower than similar data obtained from aqueous systems. From the praseodymium data a basis for comparing rare-earth spectra in similar molten salt solvent systeme a t widely separated temperature levels is available. As would be expected, the magnitude of the peak heights is less a t the higher temperature, at least in the case of the two that are shown. A basis for comparing rare-earth spectra in different molten salt solvent systems is provided from the neodymium data. Even though the lithium fluoride solvent was maintained at a much higher temperature than the lithium chloridepotassium chloride solvent, the magnitudes of the three peaks which are presented are lower in the latter molten salt solution. These peaks are also shifted to longer wave lengths, by about
7 mp, in the chloride solvent. From these data some type of solvent effect could be postulated which affects rareearth spectra, or at least affects the spectra more strongly, in the lithium chloridepotassium chloride eutectic as compared with lithium fluoride. ACKNOWLEDGMENT
The authors acknowledge the assistance of B. J. Sturm, Oak Ridge National Laboratory, who prepared the rareearth fluorides that were used in this study. LITERATURE CITED
(1) Gruen, D. M., J . Inorg. & Nuclear Chem. 4,74 (1957). (2) Stewart, D. C., U. S. Atomic Energy Comm., Rept. AECD-2389, Sept. 22, 1948. (3)Sundheim, B. R., Harrington, G., IW., Rept. NYO-7742,pp.30-2, 88-9, March 9, 1959. (4) Wood, R. W., “Physical Optics,” Chap. XXIII, Macmillan, New York, 1934. (5) Young, J. P., Oak Ridge National Laboratory, Oak Ridge, Tenn., unpublighed data, March 7, 1960. (6) Young, J. P., White, J. C., ANAL. CHEM.31,1892(1959). (7)Ibid., 32, 799 (1960).
RECEIVEDfor review May 2, 1960. Accepted August 10, 1960. Work performed under Contract No. W-7405eng-26 a t Oak Ridge National Laboratory operated by Union Carbide Corp. for the U. S. Atomic Energy Commission.
VOL. 32, N O . 12, NOVEMBER 1960
1661
