Air-Free Distillation and Multifraction Sealing Apparatus M. D. Cagle, T. T. Denton, J. M. Lucas, and E. J. ~isenbraun' Oklahoma State University, Stillwater, OK 74078
Protection from air is essential in maintaining the integrity of high-purity (99.9+ %) samples used in thermodynamic studies. This is best realized by sealing the samples in glass ampoules once purification is complete. The apparatus (116 scale) was designed to enable vacuum distillation of organic com~oundswith rieomus exclusion of air until the h i l l e d material is perm&ently sealed in glass ampoules. The fimre shows a short-oath distillation aooarat& intended f& final distillation bf organic compogds that usually have previously received rigorous purification by other means. This distillation is primarily intended to remove trapped air, solvent, and nonvolatile residue. Notable improvements have been introduced. The splash arrester b, c contains spray and boiling surges and thus reduces column flooding, the magnetically operated fraction cutter l-r permits precise and convenient selection of collection port, and the fdling adapter s-v allows isolation of a fdled ampoule from the main vacuum system. For description, the apparatus is divided into four parts: the still (a-k), the magnetically operated fraction collector (1r), the filling adapter with needle valve (5-v), and ampoule (w-2). The column d includes Vigreux indentations, placed in a spiral pattern. Except for the lower tier, these have been omitted from the drawing. More efficient distillation is realized with longer columns containing a spiral tantalum wire, Stainless Steel saddles or glass helices as column packing. If loose packing is used, the column can be fitted with a perforated glass basket, installed at the junction of c and d. The number and size of these perforations should be carefully selected to ensure good drainage and thus avoid a focus for flooding. Column floodingis a major source of reduced distillation efficiencyand for this reason a large diameter (29142) was selected for the standard-taper, o-ring, inner joint a (Ace Glass Inc., Vineland, NJ 08360, no. 7648-141, relative to the length of column d. The spray trap b, c was designed to reduce column flooding. This trap intercepts surging liquid or spray from the distillation flask and diverts it through the holes a t the top of b to the wall of bulb c where the liquid impinges and then drains to the distillation flask via the holes a t the base ofb. Thus, the expansion ofvapor and liquid spray into bulb c smooths out surges and greatly decreases flooding in the column. The Vigreux column d is enclosed in vacuum jacket e to provide insulation. Insulation is further improved by wrapping the column with aluminum foil. The vacuum jacket is not silvered heeause all of the elassware is heated in an annealingown at 560°C before each use to eliminate possible organic impurities. The dixtillation temoerature is monitore2 a t f wiZh thermometer or thermocoiple. The distilled liquid, cooled by the water-cooled condenser g, next passes through needle valve h2 (Ace No. 8195-04). Valve h is kept open during distillation. It is used to exclude air from the distilling compound in the event that it becomes necessary to release the vacuum during distillation. The larger needle valve i2was added to provide pres-
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'Corresponding author. he Teflon plug was omitted from the drawing--see Ace Glass Inc. catalog forthis item. 168
Journal of Chemical Education
Design of the short-path disilllation apparatus. sure control during start up and as a cut-off valve in the event of power failure to the vacuum pump. Vacuum in the system may be released by admitting air through the hole a t the base of needle valve j.' The needle valve was installed a t this point to serve as a structural brace.
The 50130, o-ring, ball joint k, and the corresponding 50130 socket serve to connect the still a-k to the fractioncollection assembly 1-r. The latter was designed to ensure smooth fraction collection without disturbing the distillation or the pressure within the system. Fraction collection is accomplished through rotation of the glass funnel m to the various ports (5-6 in number) shown as standardtaper, 19/38, o-ring, inner joints r (Ace no. 7648-10). Rotation of funnel m is controlled by moving the horseshoeshaped magnet q. This magnet, in turn, controls the movement of the Teflon-coated, bar magnet p attached with a hinge to shaft n. The faces of the magnet q is circled with plastic tape to minimize the possibility of breaking glassware during handling of q. ARer tape has been added, magnet q may be hung with wire circling the neck of the apparatus 1-r. Glass funnel m is supported by aluminum block o (29 mm in dia.). This aluminum block is slotted to permit insertion of funnel m, and it also has a 20-mm cavity that contains the funnel. In turn, the aluminum block is attached to 114in. stainless steel shall n. The tip of shall n rests in a slight depression of the domed under portion of the fraction-collection apparatus 1-r. This dome, shown as a dotted line in the figure, was included to provide a curved surface as a protection against implosion. The shaR n is fitted with a Nylon tip to provide frictionless rotation and thus eliminate the possibility of metal scratching the glass wall. 3 ~ hthermochemical e studies are carried out by personnel of the National institute for Petroleum and Energy Research, Barllesville,
The filling adapter s-v consisting of a standard-taper, 19138, outer joint s, needle valve t, and threaded connector u (Ace no. 7644-18)with Nylon bushing v (Ace 110.7506-08) serves to connect the ampoule w-z to the fraction-colleetion assembly 1-r. To attach the ampoule w-z to the filling adapter s-v, part w of the ampoule is fed through bushing v and an o-ring (supplied with the bushing) is then added to w projecting through v. The bushing is then threaded into v until w passes over the drip tip of needle valve t. The Nylon bushing v compresses the o-ring to form an effective, airtieht vacuum seal. The small amooule. shown attached to u; is used to contain analytical samples; whereas, the large ampoule w-z, constructed from a 250-mL, round-bottomed flask, contains 70-100 g of sample. Both size am~ o u l euse s 15mm O.D. tubing w and v selected to fit Nylon bushing v. After the sample-has been distilled, theamooules are chilled in a dry ice-acetone bath and are flamesealed under vacuum at.; The remaining side tube y of the large ampoule is later used to attach the filled ampoule to a vacuum system. In this operation, a cylindrical magnet is first inserted into y for later use in fracturing the breakoffseal z. This permits vacuum transfer of the k p l e fmm the large ampoule to a calorirnete~.~
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Care should ~~-~~ be taken in handline a flame in the vioinity of acetone. However, the evaporating carbon dioxide i s effective in blanketing the areain which the flame sealing is taking place. ~~
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Acknowledament We thank the National Institute for Petroleum and Enerm Research, Bartlesville, OK 74005 for financial sup-
OK 74005.
Volume 70 Number 2 February 1993
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