the
edited bv ~, ZlPP SUNY-Cortland Cortland. NY 13045 ~~
~~
ARDEN P.
Design of a Microscale Sublimator Anthony Winston West Virginia University, Morgantown. WV 26506 One of the problems associated with microscale preparations is obtaining enough product to carry out a final purification step before characterization. In the caseof liquids, the quantity of product is seldom sufficient for that final step, distillation. Solids are normally purified by recrystallization, but on the microscale level they are often isolated simply by evaporating the solvent. In some cases, sublimation for ourification. . - -is -~ -recommended ~ Sublimation is particularly useful when unfavorable solubility properties may lead to high losses of material during crystallization. If a compound has sufficient vapor pressure, sublimation. with or without vacuum, is often possible with little material loss. There is, however, no convenient sublimation aDparatus for use with microscale equipment. Current text; describe arrangements using such equipment as a filter flask, a test tube, and rubber stopper' or a combination of test tubes and rubber s t ~ p p e r . ~ The convenient low-cost microscale sublimation adapter (see figure) described here consists of a 14/10 inner joint fitted with a collection tube of sufficient length to reach the cone a t the bottom of a 5-mL vial. The bottom of the collection tube is flat so that the sublimed material can be removed easilv. A hose connection to vacuum is provided, with sufficient distance between i t and the 14110-joint to allow easv attachment of the screw cap and O-ring. This adapter difiers from those available com&ercially in that continuous water flow has been eliminated by putting ice water in the collection tube, which suffices for the small amounts of material involved, (e.g., up to 150 mg). In a synthesis where the product is to be sublimed, the final evaporation step should be conducted in the 5-mL vial. After the solvent has been removed, the sublimation apparatus is connected to the vial with the joint and screw cap. Ice water is placed in the collection tube, vacuum is applied if necessary, and the sample is heated on a hot plate. When the sublimation is complete, the vacuum is broken, the adapter is removed carefully, to prevent dislodging any material, and the solid is collected. If the sublimation takes longer than a few minutes, fresh ice water can be added. Although . a water aspirator is asatisfactory source of vacuum, a vacuum pump is often preferred, and a vacuum manifold may be desirable for large numbers of students. In our laboratories we have installed a nitrogen supply system of copper tubing with needle valves at each student desk and hood. When vacuum sublimations are to be conducted, a vacuum pump connected to one of the needle valves provides vacuum at each work station. The following products described in footnote 1have been sublimed under vacuum using the adapter described here: caffeine, 2,4-dichloro- and 2,4-dihromonitrobenzene, 4-tert~
~
~
~
~
162
~
Journal of Chemical Education
Mlcmsublimation a d a e tor use in wmbinatian with a 5-mL conical vial wnh 14/10 ground glass joint.
hutylcyclohexanol, ferrocene, acetylferrocene, diacetylferrocene, and 9-fluorenone. I t is likely that many other compounds can be purified in this manner, thus broadening the applicability of microscale methods. Acknowledgment The author appreciates the assistance of Ace Glass Inc. for fabricating several prototypes of the sublimation adapter and that of John Penn for critique of the manuscript.
'
Mayo, D. W.; Pike, R. M.; Butcher, S. S. Microscale Organic Laboratory: Wiley: New York. 1986. Williamson, K. L. Microscale Organic Experiments: Heath: Lexington, MA. 1987.
