Phys. Rev. 90, 153 (1953). (32) Tailor, I’. I., Havens, W. \V,-Jr., “Physical hlethods in Analytical Chemistry,” Vol. 3, pp. 539-601, Academic Press, Yew York, 1956. (33) Theuerer, H. C., Trans. Am. Inst. iMznzng Met. Enyrs. 206,1316 (1956). (34) Theuerer, H. C , Whelm, J. AT., Bridgers, H. E., Buchler, E., J . Electro-
chem. SOC.104, 721 (1957). (35) Tiller, W. A., Trans. Am. Inst. Mining Met. Enyrs. 209, 847 11957). (36) Tiller, W. A,, Trans. Met. SOC.A I J f E 215,555 (1959). (37) Trumbore, F. A,, Bell System Tech. J . 39, 205 (1960). (38) Vigdorovich, V. G., Nashel’skii, A.
Ya., Russ. J . Inory. Chem. 4 (9), 922 (1969). (39) Yue, A. S., Clark, J. B., Trans. M e t . SOC.A I M E , to be published. RECEIVEDfor review July 21, 1960. Accepted September 14, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
Zone Melting and DifferentiaI Therma I An a lysis of Some Organic Compounds MICHAEL J. JONCICH’ and DELLA RUTH BAILEY2 Department o f Chemistry, University o f Tennessee, Knoxville, Tenn.
b Techniques of zone melting were applied to systems of organic compounds using a simple apparatus which allowed the passage of 18 molten zones through the sample during a single run. Spectrophotometric analysis indicated that the methyl violet concentration in naphthalene could be lowered to 1 p.p.m. by a single passage through the 18-zone column. Similarly, combustion of samples followed by counting of the CO? in an ionization chamber showed that the concentration of carbon-1 4labeled naphthalene in benzoic acid could b e lowered to less than one part per 10 million using this zone refiner. A differential thermal analysis apparatus, using thermistors as the temperature sensing element, was constructed for use with organic compounds. Zone melting and differential thermal analysis were used on phenanthreneanthracene mixtures to determine the phase diagram of this two-component system. A tentative phose diagram is proposed based on these two types of measurements.
A
the majority of the work in zone melting has been in the fields of metallurgy and solid-state physics (fd), the technique may be considered an extension of the work of Schwab and Wichers (19) on the purification of benzoic acid and acetanilide. One of the techniques they used involved the lowering of a fused impure sample through a heating coil, allowing the freezing process to start a t the bottom of the tube and progress upwards as the sample emerged from the heater. The final liquid, containing a larger concentration of impurities, was then siphoned off. 1 Present address, National Science Foundation, Washington, D. C. 4 Present address, E. I. du Pont de Nemours &a Co., Aiken, S. C . LTHOUGH
1578
ANALYTICAL CHEMISTRY
Since the development of the zone melting technique by Pfann (23) in 1952, a number of organic compounds have been purified by the simple process of allowing one or more molten zones to pass through an impure sample (5-7, 25-18, 24). -4 large part of this work has involved the design and construction of zone refiners. I n tne testing of zone melting apparatus, usually only qualitative results were obtained. The authors were interested in carrying out quantitative experiments on organic systems using several methods of analysis, particularly in the possibility of zone refining equimolar mixtures of compounds and in using this technique for the determination of phase diagrams. This technique, therefore, coupled with results obtained from differential thermal analysis (DTA), was used to obtain a phase diagram for the phenanthrene-anthracene system. Z O N E MELTING APPARATUS
Although a number of rather elegant systems were constructed (fd),a simple apparatus gave best results. An 18-zone system was constructed by providing 18 heated regions and 19 cold regions (alternating hot and cold) surrounding a 20-mm. outer diameter borosilicate glass tube clamped in a vertical position. The heated regions were 14 mm. in length; the cold regions \vere 35 mm. long. To provide the hot zones, aluminum disks (40-mm. outer diameter) with 20-mm. holes bored in the center to fit the column were used. Insulated Xichrome wire was wound on each flat side of each disk in thr form of a spiral and the Lvire attached to the disks using asbestos and Sauercisen. If the Xichrome wiring of all 18 aluminum disks was connected in series, then to a Variac power supply, the length of the molten zones did not remain constant, but fluctuated $18 the laboratory voltage fluctuated. In the extreme case, the molten zones became so narrow
(or so wide) that the liquid-solid interfaces moved in the wrong direction. To avoid this difficulty the two sides of the aluminum disks were wired separately and two separate circuits were used. The Nichrome wires a t the bottom end of each disk were connected in series, and finally to a Variac which was used to control the voltage. This formed the constant heater circuit. The wires a t the top of each disk were connected in series and were used as part of an intermittent circuit, controlled by a mercury thermoregulator placed a t the bottom of the column. I n this way the heating zones were essentially a t constant temperature and the widths of the molten zones were maintained constant during a run. Instead of using aluminum disk heaters around the thermoregulator, faster response of the thermoregulator was possible by wrapping Nichrome wire directly around the glass tube in this part of the system. The cold zones between the aluminum heaters were formed by coils of natercooled copper tubing which surrounded the glass tube. A continuous and rapid flow of cold water t.hrough the copper tubing provided sufficient cooling for all systems studied, although use of a refrigeration system may be desirable in some cases. A11 cold zones were in series and the copper tubing was looped to avoid close contact with the aluminum heating disks. During zone melting, the sample, placed in a tube of approximately 7 mm. outer diameter and usually 15 em. in length, was drawn up through the 20-mm. glass tube, causing the sample to pass through 18 heated regions. Glass twine attached to the top of the sample tube was connected to the shaft of a 1 r.p.m. electric clock motor, mounted above the large glass tube. The winding of the glass twine on the shaft of the motor caused the sample to be raised a t the rate of 2.5 rm. per hour. I n all work described here the column was mounted in a vertical position. If clamped in a horizontal position, huhblea occasionally formed which
caused separation of the sample. This was particularly true for organic compounds with rather high vapor pressures. To contain the sample it was found best to use Teflon tubing with a glass plug a t each end. This avoided any shattering (which was encountered occasionally when glass tubing was used) and had the additional advantage that the sample could be removed easily after purification. The tube and sample could be sliced with a razor, allowing easy separation of different fractions. METHYL VIOLET-NAPHTHALENE SYSTEM
-
of the tetralone by the method of Linstead and Michaelis (IO), using the palladium on charcoal catalyst described by Linstead and Thomas ( 1 1 ) . This naphthalene had a specific act'ivity of 179.9 millicuries per mole.
- 1.0 -
W
z W
-2.0-
r
In.
a -3.0-
z
dI;- 4 0 > 0
i
2 -5.0 -
2 z 8 -60y. 0 c)
5 -7.0 I n this initial experiment the dye, methyl violet, was removed from naphthalene by the use of this apparatus, The efficiency of the zone refining apparatus was demonstrated quantitatively using s~~ectrophotometric means of analysis. Solutions of methyl violet in 95% ethyl alcohol were prepared in concentrations ranging from 2 to 120 x 10-5 gram per liter. These solutions were examined a t 576 mp using a Ueckman D L spectrophotometer. h linear relationship was found between the log per cent transmittance and the methyl violet concentration, indicating that. Beer's lniv is valid for these solutions. Upon the addition of 2, 10, and 30 grams per liter of naphthalene to the above solutions the same straight iine was obtained, indicating that the presence of naphthalene has no effect on the absorbance of the solutions. After the passage of 1s nioltcn zones through a niixture of methyl violrt and naphthalene which contained gram of methyl violet per gram of naphthalene, the sample was removed from the apparatus, the Teflon tube cut a t various positions along the tube, and the various samples lvere analj,zrd sl~ectrophotometricall~.. The results (Figure 1) were given in terms of the logarithm of th(a mt8thyl violet concentration as a function of the length of the bar in zone lcngths (14). The rise in impurity concentration (dye) a t the front end of the bar is believed
0
1 2 3 4 5 6 LENGTH OF BAR IN ZONE LENGTHS
7
I
Figure 1. Distribution of methyl violet in naphthalene after passage of 18 zones through sample
to be due to supercooling of the melt followed by rapid refreezing. The extremely low concentration of methyl violet in the center portion of the sample (10-6 to 10-7 gram of dye per gram of naphthalene) indicates the effectiveness of the zone refiner. NAPHTHALENE-BENZOIC ACID
SYSTEM
Tagged naphthalene containing a carbon-14 atom in the alpha position was prepared b>- standard procedures. The Grignard reagent, y-phenylpropylmagnesium bromide, was prepared and reacted with radioactive CO, (obtained by treating labeled BaC03 with acid) according to the procedure described by Fort (4).The reaction product was hydrolyzed with 10% HC1, neutralized, and tiic product, ?-phenylbut>-ric acid, isolated. This was treated -:,i'h J olyphosphoric acid by the method c: Kkinberg and Xudrieth (8)to give the a-labeled a-tetralone. Tile alabekd naphthalene \vas prepared by catalytic dehydration-dehydrogenation
Mixtures of carbon-14-labeled naphthalene and benzoic acid were prepared by melting together measured amounts of the two compounds and grinding the crystalline mixture. Figure 2 shows the concentration distribution obtained after passing one molten zone through the mixture. Figure 3 shows the resulting concentrations after the passage of 18 zones through a second sample. The logarithm of the average naphthalene concentration in milligrams of naphthalene per gram of benzoic acid is plotted as the ordinate. The distance measured in zone lengths from the end of the bar that was first to melt is plotttd as thc abscissa. Concentrations of less than one part of naphthalene per 10 million parts of benzoic acid could not be measured. .Ipproxiniately 0. I-gram samples were used for the analysis. The samples \\ere burned in a combustion train >imilnr to that uwd for carbon and hydrogen nn:iiysia (20) except the usual copper oside was replaccd by broken quartz t o avoid tiic earimn-~4dioxitir. "nicmory" effect a w r i a t e d v-it11 copper osidc ( 2 3 ) . T h e C 0 2 \{:is swept into a 1600-ni1. ionization chambcr construe trc! accordirg to t'he design of norkowki ( 1 ) and the radioactivity determined using :i Cary ;\Iode! 31 vibrntii?g reed elect,rom&cr. The r;itc of drift miithod \vas uscd (23; to rl(ctcrniine the nc'tiyity of the eamples. DIFFERENTIAL THERMAL ANALYSIS
A major portion of this reseereh was to involve zonc w-lting of nearly equimolar mixtures of compounds and to dran- anaiogic.9 h h w n the processes of zone mplting :ind distillation as ii means of separating mistures. A twocomponent systcm whibiting ccmplete __.
1
1.0, 0.0
0.0-
-1.0
w \
t
~~
.
0.
e
ORIGINAL CONCN.
ci 5
0 V
0
ORIGINAL CONCN-
.
J
-2.01
- 3 0 t =-.
' F ' T
- 4.0 I
00
'0 20 30 LENGTH OF BAR IN ZONE LENGTHS
Figure 2. Distribution cf naphthciene i:, benzoic acid after passage of one zone
.,
-cn ! "GO
I IO
1
20
30
40
50
60
70
80
90
LENGTH OF BAR IN Z W f LEWGTHS
Figure 3. Distribution of naphthalene in benzoic acid ofter passage of 18 zones
2 . 0 1 52.94%
I
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**-p--
91 92 93 94 95 96 97 98 99 100 101 102
90 100 110 120 130 140 150 160 170 180 190 i x)
SAMPLE TEMPERATURE 'C Figure 4.
SAMPLE TEMPERATURE O C
DTA of three samples of phenanthrene
l o p curve. Eastman White Label Middle curve. Chemically purifled samples Battom curve. Zone refined sample
Figure 5. Differential thermal analysis of mixtures of phenanthrene and anthracene
per minute were used in all DTA experiments. solubility in both the solid and liquid phase would be ideal for this purpose. The phenanthrene-anthracene system baa been studied and reported (2) to have such a phase diagram. Preliiinary experiments indicated that this may not be correct and it became of interest to determine the actual phase diagram of this system. The previous determinations of the phase diagram baaed on visual (2) and microscopic (9) observations appeared to give questionable results.. It was felt that accurate measurements of heat effects. associated with phase transformations (DTA), coupled with zone melting experiments, would be more fruitful (22).
A Veco 41All thermistor was used as the temperature sensing element for the sample. The reference temperature was the temperature of the aluminum block (a cylinder 7.5 cm. in length and 7 cm. in hameter) as measured by a thermometer graduated in tenths of a degree. The aluminum block was wound with insulated Nichrome wire, then covered with insulation. A hole from the top of the block was drilled to fit the thermometer. A glass sample holder having a volume of 1 ml. was constructed of 7-mm. borosilicate glass tubing and contained the tiny thermistor. This was introduced into the block through a hole drilled from the bottom. Before a run was started the glass tubing containing the sample was sealed with a small flame to prevent loss of sample by sublimation. The resistance of the therrrjstor and there1580
0
ANALYTICAL CHEMISTRY
fore, the temperature of the organic sample was determined by use of a k e d s & Northrup decade bridge. Since the reciprocal temperature is directly proportional to the logarithm of the thermistor resistance, small temperature changes of the sample could be detected. The resistance of the thermistor was calibrated in terms of temperature to 0.02" C. by the use of seven secondary standard liquids (%'I), boiling in the range 79" to 211" C. Initially it was necessary to determine the purity of the phenanthrene and anthracene. Figure 4 shows the results obtained by DTA of three samples of phenanthrene. The top curve represents the results obtained using Eastman White Label phenanthrene. The middle curve shows the results obtained on a sample of Eastman White Label phenanthrene which had been chemically purified by the method of Feldman et al. (5). The bottom curve shows results obtained using a sample of chemically purified phenanthrene which was then passed through the zone reh e r . Considerable improvement is noted for each stage of purification. Similar DTA curves were obtained for anthracme, although pure samples of this compound were more easily obtained. Eastman White Label anthracene after passage through t h p zone refiner showed a very sharp peak in the DTA curvp. Heating rates in tbe range of 1' to 4'
PHENANTHRENE-ANTHRACENE SYSTEM
Intimate mixtures of purified phenanthrene and anthracene were prepared having the following compositions in per cent anthracene by weight: 3.06, 4.19, 11.57, 19.03, 31.84, 38.93, 52.94, 61.67, 73.09, 80.46, 89.50, 93.06, and 95.45. Each sample was subjected to DTA Figure 5 shows typical results obtained. The difference in temperature between the sample and the block is plotted as a function of the sample temperature for samples containing 19.03, 31.84, 38.93, and 52.94% anthracene. I n all cases, endothermic changes in the organic system resulted in an increase in temperature difference between the sample and the block. Points of idection are designated by arrows. From the DTA data, a phase diagram could be postulated. To verify the presence of a peritectic in the phase diagram, a sample contabing 48% by weight anthracene was zone refined by a single pass through the 18zone apparatus. The samples were analyzed by determining the temperature a t which melting was complete and finding the concentration corresponding to this temperature from the liquidus curye in the phase diagram. The results are shoivn in Figure 6. A typical peritectic jump IS indicated on this diagram ( 1 4 ) verifying the peritectic suspected from the DTA data. From the combined results of the
....... Kofler
I
0.0
220-
--
0
IO
Bradley and Marsh
,
1.0 2.0 3.0 4.0 5.0 LENGTH OF B A R IN ZONE LENGTHS
Figure 6. Concentration of phenanthrene and anthracene mixture after zone melting
DTA and zone melting experiments a phase diagram for the phenanthraceneanthracene system was drawn. This phase diagram is shown in Figure 7 . Also included in this diagram are the results obtained by Bradley and Marsh (9) as well as those of Kofler (9). Good agreement between all workers is noted for the liquidus line. Although Kofler designated 148’ C. as the peritectic temperature, our results indicate that 140’ C. is the peritectic temperature and that crystal rearrangements occur at 9 7 O , 148”, 170”, and 187’ C. Although the liquidus curve and the peritectic temperature for this system appear to be well established now, the remainder of the phase diagram must be considered as tentative and further work on this system is definitely indicated. Certainly it appears that the phase diagram is not simple and DTA at very low and constant rates of heating (and cooling) coupled with x-ray diffraction studies could be used to establish a phase diagram for this system. ACKNOWLEDGMENT
The authors are grateful to William G. Pfann for his comments on the theoretical and practical aspects of zone refining, to Edward Bailey for his aid in the interpretation of the DTA results,
20 30 40 50 60 70 80 90 100 % ANTHRACENE
Figure 7. Phase diagram ofphenanthrene-anthracene system
to Jerome F. Eastham for his aid in the organic chemistry aspects, and t o Ila Mae Poovey for typing the manuscript. LITERATURE CITED
(1) Borkowski, C. J., “Ionization Chamber for Carbon-14 Measurements,” USAEC, MDDC-1099, Oak Ridge, Tenn., 1947. (2) Bradley, G., Marsh, J. K., J . Chem. SOC.1933, 650. (3) Feldman, J., Pantages, P., Orchin, M., J . A m . Chem. SOC.73, 4341 (1951). (4) Fort, T., doctoral dissertation, Univerejty of Tennessee, Knoxville, Tenn., log;., ( 5 ) Hundley, R.
Herington, E. F. G.,
Chem. & Ind. ( h a d o n ) 1956,304. (6) Herington, E. F. G., Handley, .R., Cook, A. J., Ibid., 1956, 292. (7) Hesse, G., Schildknecht, H., Angew. Chem. 68, 641 (1956). (8) Kleinberg, J., Audrieth, L. F., “Organic Syntheses,” Vol. 3, p. 798, Wiley, New York, 1955. (9) Kofler, A., Monatsh. Chem. 86, 301 (1955). (10) Linstead, R. P., Michaelis, K. 0. A., J . Chem. Svc. 1940, 1134. (11) Linstead, R. P., Thomas, S. L. S., Ibid., 1940, 1127. (12) McKensie, D. R., M. S. dissertation, University of Tennessee, Knoxville, Tenn., 1958.
.--,
(13) Pfann. W. G.. Trans. AZME 194, 747 (1952). ’ (14) Pfann, W. G., “Zone Melting,” Wfley, New York, 1958. (15) Ronald, A. P., ANAL.CHEM.31, 964 (1959). (16) Riick, H., Nulurwissenschuften 43, 81 (1956). (17) Schildknecht, H., 2. Naturforsch. 12b, 23 (1957). (18) Schildknecht, H., Mannl, A., Angezu. Chem. 69,634 (1957). (19) Schwab, F. W., Wichers, E., J . Research Natl. Bur. Standards 32, 253 (1944). (20) Steyermark, A., “Quantitative Organic Microanalysis,” p. 92, Blakiston Co.; New York, 1951. (21) Timmermans, J., “Physico-Chemical Constants of Pure Organic Compounds,”Elsevier, New York, 1950. (22) Vold, M. J., ANAL. CHEM.21, 683 (1949). (23) Whitternore, I., Tolbert, B. M., Ludwigen, A., “Precision Assay for C14 in Organic Compounds,” UC? 3629, University of California Radiation Laboratory, Berkeley, Calif., 1956. (24). Wolf, H. C., Deutsch, P. H., Nuturunssenachaften 41, 425 (1954).
RECEIVEDfor review May 17, 1960. Accepted August 26, 1960. Division of Analytical Chemistry, 137th Meeting, ACS, Cleveland, Ohio, April 1960.
YOL 32, N3. 12.
NOVEMBER 1960
0
1581
