A SUBLIMATION APPARATUS FOR RAPID SEPARATIONS LEWIS N. P I N 0 and WINPIELD S. ZEHRUNG I11 Allegheny College, Meadville, Pennsylvania
Smm distillation or fractional crystallization is commonly used to separate mixtures of ortho-para isomers. If the ortho isomer is chelated, steam distillation is the usual means of separation. However, steam distillation in the laboratory is a lengthy process if large quantities of a pure isomer are desired. If the isomers involved have reasonable thermal stability, separation hy sublimation should work well. If higher temperatures than those obtained in steam distillation can be used without damage to the nonvolatile isomer, much more rapid separation should result. Experiments with 20 to 60-g. mixtures of 2amino-3-nitropyridine and 2-amino-5-nitropyridine showed that rapid, nearly quantitative separations could be made using temperatures around 120°C. We used in this work our own macrosublimation apparatus which was designed to allow accurate temperature control and ease of recovery of the residue. Most sublimators (1-7) were designed with purification of the sublimate in mind rather than preservation of the nonvolatile material. The apparatus shown in the fignre is easy to construct and to use. Changes in scale would allow its use on micro or semimicro samples. I n preparing the apparatus for use, a Pyrex wool plug F is placed in one end of the sublimation chamber and the chamber filled with the dry mixture. The drying tube is inserted into the end of the sublimation chamber. This assembly is then placed in the air jacket into which the condenser has already been fitted and sealed with two turns of asbestos cloth E. F
E
An aspirator is connected to the condenser to provide an air current to transport the vapors of the sublimate. The sublimation area is gradually brought to the correct temperature by the heating coil. A variable autotransformer is nsed to control the power supplied to the heating coil and thus control the temperatnre. A thermometer may be placed in the sublimation chamber for calibration runs. If the proper temperature is used, little or no decomposition of the nonvolatile isomer results. For ezsily oxidizable materials a dry nitrogen atmosphere could be used. Upon completion of the separation the residual material may be shaken into a beaker for recrystallization. The sublimate may be extracted from the condenser and recrystallized in one step with an appropriate solvent. We have reported this apparatus in the hope that others may find it useful as a device for separating isomeric mixtures now separable only by steam distillation or fractional crystallization. LITERATURE CITED (1) CAROTHERS, W. H., A N D J. W. HILL,J . A m . Cham. 8% 1557 (1932). (2) MOREY,G. W., ibid., 34, 550-2 (1912). (3, pmBA, J., J. E ~ ~23,~403. (1946). ,
cHEM. A N D c. A.
(4) HEUN, A. F.,
54,
VANDERI%-ERF, Anal. Chern., 21,
1284-5 (1949). ( 5 ) MORTON,A. A., J. F. MAHONEY,A N D G. ibid., 11, 460-1 (1939). (6)NELSON, O. A,, ihid,, 14, 153(1912).
(7) ROBINSON, G. R.,
AND
T.
RICHARDSON,
w.DEAKERS, J. CBEM.EDIJC.,9,
1 i l i (1932).
,B
C
A. Condenser tube: 72.5 cm. X 3.2 cm. B. Heater tube: 61 em. X 4.2 om. wound with 25 ft. of No. 22 Chrome1 wire. C. Sublimation chamber: 52 om. X 2.6 cm. D. Drying tube withindicating drierite: 58 om. X 2 em. E. Asbeetar cloth, 1 in, wide. F . Pyrex wool.
