INDUSTRIAL AND ENGINEERING CHEMISTRY
736
and press gently on the rod. The upper end of the bearing is flared a trifle in order to eliminate undue friction. A drop of glycerol lubricates and improves the seal. This device is practically the reverse of the well-knonm bearing with the rubber seal at the top, used often for stirring at reduced pressures. The seal a t the top is not tight enough t o permit use of the apparatus in preparation of organosodium compounds. That at the bottom has given entire satisfaction. The device is particularly good in place of a mercury seal because it offers less drag in stirring and spills no tiny particles of mercury. The seal should be a little distance above the flask, a change easily made with an adaptor, in order to reduce the softening action of organic solvents on rubber. Neoprene has proved better in this respect than ordinary rubber. A single rubber piece has been used
Vol. 14, No. 9
in as many as ten or twelve runs in the preparation of organosodium compounds before it was necessary to replace it.
Literature Cited (1) Huber, F. C., and Reid, E. E., IXD. ENG.CHEM.,18, 535 (1926). (2) Morton, 4 . A., Davidson, J. B., and Kewey, H. N., J. Am. Chem. Soc., 64, to be published (1942); Morton, -4.A., Davidson, J. B., and Hakon, B., Ibid., 64, to be published (1942). (3) Morton, A. A,, and Knott, D. M.,IND.ENG.CHEM.,ANAL.ED., 13 --, A49 " - , (1441) --, \--
CONTRIBUTION from the Research Laboratory of Organic Chemistry, l\.lassachusetts Institute of Technology, N O . 270.
Apparatus for Crystallization and Filtration at Low Temperatures F. W.QUACKENBUSH
AND
H. STEENBOCK, University of Wisconsin, Madison, Wis.
B
ECAUSE of the technical difficulties involved, fractional
crystallization has seldom been employed for t h e purification of lowmelting substances. Brown and his co-workers ( I , @ surmounted these difficulties b y carrying out the necessary operations in a special room a t a constant temperature of -20°, and were able t o demonstrate the effectiveness of low-temperature fractionation as a means of separating unsaturated fatty acids. Wheeler and Riemenschneider (4) employed the method successfully in the preparation of pure oleic acid. I n this laboratory, the method has been adapted t o a relatively small unit which permits both crystallization and filtration at temperatures as low as -75" C. The unit consists of a suitable assembly within a well-insulated chamber. The chamber is provided with means for external control, thus
I,
p FIGURE 1 . LARGECRYSTALLIZATION CHAMBER
eliminating discomfort t o the operator, and the apparatus is sufficiently simple t o be practicable in any laboratory. Two units were constructed which differed chiefly with respect t o size and means of effecting filtration. I n the larger unit t h e solvent with suspended crystalline material was forced onto the funnel b y means of air pressure. In the smaller unit transference of the funnel was effected b y manually rotating t h e crystallization flask and its supporting shaft.
Construction of the Larger Apparatus The apparatus consisted of an insulated chamber (Figure 1) the interior of which was divided into three compartments: A , for crystallization and filtration; B, for collection and removal of the filtrate; and C, a reservoir. The chamber (outside dimensions 62.5 X 40 X 75 cm., 25 X 16 X 30 inches high) was constructed of galvanized sheet iron and wood and insulated with a 7.5-cm. (3-inch) thickness of packing-box paper and rock wool. An observation window (17.5 X 22.5 cm., 7 X 9 inches, triply glazed) permitted visibility of operations. Compartment A contained the cooling liquid in which t h e crystallization flask and Buchner funnel were partially submerged. I t was provided with a mechanical stirrer and a chute, F (2.5 X 7.5 em., 1 X 3 inches), through which dry ice was introduced to produce the cooling. Circular openings, 1.25cm. (0.5inch) in diameter, a t the lower end of the chute were covered with a sliding door to aid in controlling the rate of cooling. The crystallization flask (5-liter, round-bottomed) was set on the floor in a rigid steel collar (12.5 cm., 5 inches, in diameter X 2.5 cm., 1 inch, high), and was held in position by a removable wooden collar which was fitted over the neck of the flask and was anchored to the walls of the compartment. Two glass tubes extended into the flask from the exterior of the chamber. The smaller tube, D (14 mm.), which terminated in the neck of the flask, served for the introduction of the solution to be fractionated, for the insertion of the thermometer, and as an inlet for air during filtration. The T-tube, E (16 mm.), which extended to within 1.25 cm. (0.5 inch) of the bottom of the flask, served both as a bearing for a mechanically-driven glass stirrer and as a conduit for transferring the contents of the flask to the approximate center of a 20-cm. (&inch) Buchner funnel. The stem of the funnel was held by a rubber stopper within a conical collar which extended from the floor of A into B. Compartment B , which was accessible through a door a t the end of the chamber, contained a &liter flask into which the stem of the Buchner funnel extended. A small glass tube, I, connected the flask to an aspirator. Compartment C (25 x 25 x 20 cm.,.lO X 10 X 8 inches, high) was gas-tight and served as a reservoir for the cooling medium from A during the removal of a solid fraction from the funnel. A tube (1.25-cm., 0.5-inch steel pipe) originating a t the deep end of A extended to within 1.25 em. (0.5 inch) of the floor of compartment C. A glass tube, H , connected the top of compartment C with a compressed-air line. I t served for the admission or removal of air to transfer the cooling medium from one compartment to the other. A drain pipe extended from the bottom of C to the exterior.
737
ANALYTICAL EDITION
September 15, 1942
10 X 10 X 7 inches) for the cooling medium, and a mechanical stirrer. Three glass tubes entered the chamber through the cover: tube D (14 mm.) led to the crystallization flask, tube E (10 mm.) to the Buchner funnel, and tube F (40 mm.) to the bottom of the tank. From the Buchner funnel a glass tube, H , extended through a larger tube, I , to the suction flask underneath the chamber. The joints were made leakproof with tight-fitting rubber connections. A 500-cc. crystallization flask was used with a 10-cm. (4-inch) Buchner funnel. For smaller amounts of solution these were replaced with correspondingly smaller equipment. Capillary tube holders, M , provided convenient means for determining melting points during operation of the chamber. Fractionations were performed much as with the larger unit. The solution was introduced into the crystallization flask through tube D, 5 liters of alcohol were poured into the tank, and sticks of dry ice were added through tube F. To cool the bath to -70", 1.8kg. (4 pounds) of dry ice were required. At the lower temperatures, cooling was hastened by raising F from the bottom of the tank. To effect filtration, support S was rotated manually, thereby pouring the contents of the crystallization flask into the funnel. The flask was rinsed with fresh solvent and, after proper cooling, the latter was poured over the precipitate. As with the larger apparatus, the filtrate was returned to the crystallization flask and warm solvent was used to remove the solid mass from the funnel. Since the funnel remained in contact with the cooling medium during all operations, quantitative removal of the solid material required relatively large amounts of hot solvent.
Applications An application of the apparatus is shown in a typical experiment on the concentration of linoleic acid from a mixture of the fatty acids from corn oil (Table I). The fatty acids from 450 grams of corn oil (Mazola) were dissolved in 4.5 liters of freshly distilled aretone and the solution allowed to cool in the chamber. After discarding a fraction obtained a t -20°, crystalline fractions w r e collected at 10" intervals between -40" and -70". Prior to each filtration the temperature was held constant for a minimal period of 30 minutes.
FIGURE 2.
SMALL CRYSTALLIZBTION CHAMBER
A small funnel, G , the neck of which extended through the top of the chamber to the Buchner funnel, served for the introduction of a warm solvent to dissolve solid fractions.
Operation To perform a fractionation, tube H was clamped shut and alcohol sufficient to reach the neck of the crystallization flask (16 liters) was introduced into compartment A. A filter paper was fitted into the Buchner funnel, and the cover placed on the chamber. The solution to be fractionated was run into the crystallization flask through tube D and a thermometer then inserted through the tube. The stirrers were set in motion and dry ice was introduced throueh the chute, F , until the desired temperature was obtained. To loner the temperature to -75", 5.4 to 6.7 kg. (12 to 15 pounds) of dry ice were required. To effect a filtration, the thermometer was removed, an atomizer bulb attached to D, and the contents of the flask were forced through the side arm of tube E into the funnel. Meanwhile, tube I was attached t o an aspirator. The crystallization flask was rinsed with a small portion of solvent and when properly cooled the latter was forced into the Biichner funnel to n-ash the precipitate. The clamp was removed from H and the liquid from the bath allon ed to flow into reservoir C. The flask containing the filtrate in B was replaced by a rlean flask and the filtrate was returned to the crystallization flask. Warm solvent was introduced through tube G to a a s h the crystalline fraction from the funnel. The cooling medium in C was I hen forced back into A and more dry ice v a s added to produce the temperature desired for the next fraction.
Smaller Apparatus The smaller chamber (Figure 2) (outside dimensions 40 X 40 X 50 cm., 16 X 16 X 20 inches, high) was constructed of wood and insulated mith a 5-em. (2-inch) thickness of packing-box paper. An observation window (15 x 15 cm., 6 X 6 inches) was triply glazed. The chamber was provided with a crystallization flask which was mounted on a rotatable support, S , a Buchner filtering apparatus, a steel tank (26 X 26 X 17.5 cm.,
Assuming oleic acid t o be the sole contaminant in the crystalline fractions, the iodine numbers indicated that the concentration of linoleic acid in the separating crystals reached a maximum of 88 per cent at -60". These results compare favorably with those obtained by Brown and Stoner (1) in a room held a t -20'. The apparatus has also been applied effectively in the separation of isomers of linoleic acid (3) and in the preparation of oleic, linolenic, and arachidonic acids. It should be found useful in the purification of other types of compounds crystallizable only a t low temperatures.
TABLE
I.
CRYST.ILLIZ.4TION O F CORX O I L -4CETOXE
Temperature
c.
- 10 - 50 - 60
-70 -70
(filtrate)
Weight of Fraction
FATTYA C I D S
Total
Iodine Value (Wijs, 1 Hour)
Linoleio
17.0 23.2 21.2 7 2 8.4
116.0 143.3 169.9 169.2 162.3
28 58 88 87
of
70
Grams 71.0 97.0 88.5 30.1 35.0
FROM
..
Acknowledgment T h e aut'hors are indebted to Lever Brothers Company for a grant in support of this work.
Literature Cited (1) Brown, J. B., and Stoner, G. G., J . Am. Chem. Soc., 59, 3 (1937). ( 2 ) Natthews, N. L., Brode, W. R., and Brown, J. B., Ibid., 63, 1064
(1941).
(3) Quackenbush, F. W., Platn, B. R., and Steenbock, H., J . Nutrition,17, 115 (1939). (1) Wheeler, D. H., and Riemenschneider, R. W., Oil & Soap, 16,207
(1939). PUBLISHED with the approvrtl of the director of the Wisconsin Agricultural Experiment Station.
