A Microdistillation Apparatus With Receiver for Distilling under Reduced Pressure S. A. SHRADER AND J. E. RITZER The Dow Chemical Co., Midland, Mich.
An all-glass apparatus combining a re-
The internal projections made by punching indentations in the column act as baffles to arrest accidental spray and reduce the volume of the column to a minimum. The receiver is constructed for easy removal of the fractions when the distillation is completed. The all-glass receiver has the advantage that no contamination from rubber stoppers is possible, and the desired amount of distillate can be estimated for each fraction before collecting the succeeding portion. The apparatus shown in Figure 1, designed for volumes of 0.5 to 2.0 grams of material, is easily cleaned and assembled and relatively easy to manipulate. It has a holdup (weight of material in apparatus when the distilling flask has become dry) of approximately 0.08 to 0.12 gram of liquid, the column being 7 to 15 cm. in length and approximately 5 111111. in inside diameter. The receiver (Figure 1) contains small glass cups, each having a capacity of 0.10 ml. These cups are arranged in a circle of nine or more, so that each succeeding fraction distilled can be collected by rotating the entire receiver around joint f. The number of cups is variable with the thickness of the glass tubing used and the size of the glass joint, m. The details of the unassembled apparatus are shown in Figure 2.j,A condenser was not necessary for most of the liquids distilled in this laboratory. When low-boiling liquids are distilled, the side arm e may be wrapped with a cloth containing powdered solid carbon dioxide.
ceiver of new design with a microdistilling column for the distillation of high-boiling liquids is described. The receiver allows several fractions of the distillate to be collected without interrupting the pressure under which the distillation is performed. Design and method of constructing the apparatus for 0.5 to 2.0 grams of material are given. The apparatus is easily cleaned and assembled, and shortens the time required for a distillation.
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INCE their introduction in industrial laboratories, microprocedures have constantly required improvements to reduce further the mechanical manipulations, thus broadening the field of application of some of the micromethods already familiar to industry. Although several devices for microdistillation under reduced pressure ( 2 , s ) have been reported, no attempt has been made to complete the distillation without interruption of the pressure under which the distillation is performed. This laboratory was confronted with the need for an apparatus for distilling small quantities of substituted benzene compounds. These compounds for the most part boiled a t 225" to 325" C., and the apparatus here described seems an improvement justifying a communication a t this time, although the work is still in progress.
Constructional Details
Design of Apparatus The flask and column of the apparatus are similar to that of Clarke and Hermance (1). The design of the sidearm delivery tube and that of the receiver for collecting the distillate were perfected in this laboratory during the past 2 years. The flask has a greatly flattened bottom; the size may be varied to suit special conditions or particular liquids. When a thin layer of 30-mesh silicon carbide or clean sea sand is used in place of boiling chips, as is customary in macrodistillations, evaporation takes place without active ebullition, thus eliminating bumping. An extremely small holdup becomes necessary, and this requirement can be fulfilled by using a Vigreux column.
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FIGURE1. DIAGRAM OF APPARATUS 54
The distilling flask, a, is a flatbottomed bulb of 4-ml. capacity having neck with stopper to fit. The neck and stopper are made from a T 7/25 ground joint. Onto the top of the flask is sealed a 6.5mm. tube, c, which is approximately 0.75 mm. in wall thickness and contains as many internal projections (4 to 5 mm. from center t o center) as is convenient. The column has an outside jacket, d, 15 mm. in outside diameter, evacuated with a mercury vapor pump. The jacket is wrapped with alummum foil further t o insulate column c. A 5-mm. tube is sealed to the top of the column and bent downward to form side arm e. The lower end of the tube has a T 7/25 glass joint to which is sealed a 5mm. tubing, g. The latter is ground on a wheel to an angle, the long side being 9 mm. and the short side 4 mm. from the small end of the male part of the ground joint, f. To the long side of tube g is sealed a 1.0-mm. glass rod, tapering to 0.8 mm. The length of the glass rod varies with the distance the receiving cups, j, are placed from
JANUARY 15, 1939
ANALYTICAL EDITION
55
high-boiling liquids. The latter was used in those cases where the liquid did not wet the glass surface. A short ground-glass joint was placed between the flat-bottomed flask and the column used by Craig to facilitate introduction of the resistance wire and the inner part of the column.
Tests on a Synthetic Mixture Although the apparatus described has been used primarily for determining the boiling range of organic liquids obtained in small amounts, actual tests on the separation of synthetic mixtures were made to be sure of the value of the apparatus.
FIGURE 2. DETAILSOF UNASSEMBLED APPARATUS the exit end of the side arm, the most convenient length being 225 to 290 mm. Several different arrangements have been tried for conducting the drops of liquid from the side arm into the receiving cups, the one described above proving the most satisfactory. The only requirements for continuous transfer of the liquid from the side arm to the cups are: the glass rod, h, must be smoothly sealed to the lower end of the side arm with the end of the rod extending directly over the cups; and the apparatus must be entirely free from grease. The receiving cups, j, for collecting the distillate are made from 4-mm. thin-walled glass tubing which is sealed to 4-mm. glass rod k. The rods with the cups are sealed to a 10-mm. glass rod, I, and the latter is made a part of the removal male glass joint, n. This latter operation is performed by closing the small end of the male joint and sealing the 10-mm. glass rod to the center of this closure. A 6-mm. hole (Figure 2) is then blown opposite this connection to permit evacuation of the apparatus by attaching tubing to vacuum pump at 0. The distilling flask is heated by means of an oil bath, which is stirred mechanically by a small air-driven stirrer. A thermometer in the oil bath is the only means of measuring the temperature. A 1-mm. layer of clean sea sand or 30-mesh silicon carbide is placed on the bottom of the flask and the liquid is inserted wibh a pipet through neck b. The flask is connected to the receiver and the apparatus evacuated to the desired pressure. The temperature of the oil bath is then slowly raised until a steady reflux is maintained in the column. To do this it is necessary to adjust the temperature of the oil bath to i-1.0" C. to permit only one or two small drops of the liquid to be distilled during 3 minutes. If a large amount of liquid is driven over, the column floods and the efficiency of the apparatus is impaired. A uniform reflux is essential for best results. Arhitrary fractions are collected by rotating the receiver containing the glass cups around joint f, rather than at m, there being less resistance, especially when a high vacuum is maintained. When the distillation is complete, air is allowed to enter the apparatus at o, and the lower part of receiver n is removed. The refractive index, boiling point, and chemical analysis, if desired, are determined on the separate fractions by well-known micromethods. The receiver described here has been used with the Vigreuxtype column, and the column described by Craig for
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FRACTiON D I S T I L L E D
FIGURE3. TESTS ON 50-50 MIXTUREOF ISOAMYL SALICYLATE AND CAPRYLIC ACID 0 Separation obtained by Craig's column
0 Vigreux column with evacuated jacket and receiver A Vigreux column without evacuated jacket but with receiver
The curves (Figure 3) represent graphically a comparison of the results obtained with a 50-50 mixture (per cent by weight) of caprylic acid and isoamyl salicylate. The analyses were made by the refractive index method. Curve 1 represents the separation given by the column described by Craig but without the receiver. Curve 2 is the separation obtained with a 15-em. column and the receiver as described in this paper. Curve 3 represents the results obtained with an apparatus similar to the one described, but without the evacuated jacket surrounding the Vigreux column. I n each case 1 gram of the mixture was used and the distillation was done under 1-mm. pressure.
Literature Cited (1) Clarke, B. L., a n d Hermance, H . W., Mikrochemie, 18, 289
(1935). (2) Craig, L. C., IND.ENO.CHEM.,Anal. Ed., 9, 441 (1937) (3) Peakes, L. V., Jr., Mikrochemie, 18, 100 (1935).
RECEIVEDSeptember 26, 1938. Presented before the Microchemical Section a t the 96th Meeting of the American Chemical Society, Milwaukee, Wis., September 5 to 9, 1938.
