Bernard Loev, Kenneth M. Snader, and Minema F. Kormendy Smith Kline & French Laboratories
Philadelphia, Pennsylvania
Apparatus for Molecular Distillation and Vacuum Sublimation
A simple, inexpensive, yet highly effective apparatus for laboratory scale purifications by molecular distillation or vacuum sublimation has been designed. The apparatus illustrated eliminates spattering due to residual traces of solvent or to snperheating, and minimizes exposure of the material to high temperatures since the heat is applied only to a thin film of the liquid. Quantities of material from 0.5 ml to 300 ml have been distilled using "hour-glass" flasks varying in size from 25 to 1000 ml. Larger flasks and quantities can also be used; however, these require some support at the constriction of the two flasks. We have found the Buckler Rotoevaporatnr Model PFE-1A to be a very convenient rotating device (as illustrated). The degree of vacuum attainable is limited only by the seal a t the rotating joint. Using Apiezon Grease N, we have been able to evacuate the rotating system to 10-20 microns. By the use of other more expensive sealed rotational systems, a lower vacuum could certainly be produced. The hour-glass flask can be used with other types of rotary
evaporators (Rinco, Lahline, Buchi, etc.); however, we found it difficult to obtain high vacuums with these. I n use, the material to be distilled is put into the bottom flask usiug a long-stemmed funnel. The apparatus is then assembled as illustrated; the flasks may be horizontal or sloped (left end raised slightly). Heat is conveniently applied by means of a heat or quartz lamp' and may be regulated by varying the distance from the flask. The temperature may he roughly measured by laying a thermocouple on top of the rotating flask. The flask may also be heated by means of an oil or steam bath, where prolonged direct heating of the material is not harmful. The condenser flask may be cooled by a stream of running water or an ice bath if air cooling is not snfficient. At the end of the distillation, the distillate can be removed using a long, bent dropper or pipet. I n addition to its use for the distillation of very high boiling substances, this apparatus is convenient for rapid purification by distillation of solvents and liquid reagents usiug a water aspirator as the source of vacuum. The apparatus is also useful for sublimation of large quantities of solid material. When used for this purpose, the sublimate can either he scraped nut of the condenser flask or dissolved and removed with a bent pipet. Another convenient heat source is a heat gun similar to Cole Farmer's #3024 which permits heating up to 350%
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Journal of Chemicnl Education
