the microscale laboratory with an extraction of the 9-fluorenone. Extract this crude mixture two times, each with 2 mL hexane. Then wash the hexane extract with 1mL of 5% sodium bicarbonate solution to eliminate any acetic acid 2 mL water
. .
Dry the hexane extract with anhydrous sodium sulfate for a few minutes, and transfer the hexane extract to a previously tared vial. Rinse the sodium sulfate with 1mL of hexane. and add this to the hexane extract. Evaoorate the hexane'in a sand bath in a hood. This oxidation procedure is more efficient than the chmmic acid-amherlite procedure, which is a heterogeneous solid-liauid reaction that oroceeds ooorlv - due to the requirement of very efficient agitation.
-
Recrystaiiization
The dried crude oroduct has a meltinc point range of 7879 "C and is sufliciently pure for cha;akerizatioi by IR, NMR. and ketone derivatiration. IIowevcr, if a higher - -DUrity is desired, recrystallization from 1 m~ of hexane, as specified in Mayo et al. ( I ) , is recommended. Acknowledgment
Our thanks for proofreading and advice to Barbara Sawrey and Antonio Ochoa, whose work and enthusiasm are stimulating, and to teaching assistants and colleagues at UCSD, who it was a pleasure to work with. Literature Cited 1.Mayo. D. W:PiLe,R. M.; Butchsr, S. S. M I c ~ c ~ cOrgoniehbomtary. le 2nd ed.;Wiley, 1989.
A Microscale Rotary Evaporator Daivd F. Maynard
formaSlate Unlvers Iy San Bernara~no, CA 92407
Ca
tanks, and manifolds. To solve the ahove difficulties, we have developed a simple roto-vap-type apparatus using a 10-mL round-bottom flask and capped Hickman still a& tached to a water aspirator. A typical experimental procedure involves transferring product with solvent and washings to a preweighed 10-mL RB flask. (We have found that the heavy walled "V reaction vials are not as efficient for solvent removal.) The flask is then attached to a Hickman still stoppered with a rubber septum and threaded compression cap. The entire apparatus is connected to a water aspirator and trap through a thick-walled vacuum hose. With the water aspirator on, the student shakes the apparatus while warming the flask in the ~ a l mof the hand. This action inhibits bumping and expedites solvent evaporation. The Hickman still also acts as a solash euard. Heat transfer is verv effective, and the student can easily determine when the solvent is removed by noting the temperature of the RB flask. Once the flask remains at ambient temperature, the apparatus can be secured with a clamp for 1-2 min to allow for the last traces of solvent to be removed. The vacuum is released by unscrewing the Teflon septum. The aspirator is turned off, and weighing and analysis (IR, GC, RI, NMR, etc.) of the product is carried out. The above procedure has greatly improved the yields and purity of the products synthesized in the microscale lab. This apparatus allows for the rapid removal of low boiling solvents, such as diethyl ether (bp = 35 OC) and methylene chloride (hp = 40 'C). Even tetrahydrofuran (bp = 65 "C) can be removed, but this appears to be the boiling point limit for solvents that can be efficaciously removed within an undergraduate laboratory period using this procedure. Overall, yields are more accurate, and analyses of products are free of solvent impurities. Extra heating equipment is not required, thus reserving hood space for the dispensing of chemicals. Because students remain at their benches, their time is more effectively used for cleaning glassware, organizing equipment, and updating notebook records.
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The rapid removal of excess solvent from products is of critical importance in the microscale laboratory. L A Due to the small quantity of com~ o u n dsynthesized, incomolete sol- Threaded compression cap kent removal may result in-unrealis- Teflon-lined rubber septum +[/. tic reaction yields (>loo%) and extraneous peaks in the chromatographic analysis. Recommended means for solvent removal currently include the use of a stream of dry air or nitrogen, heating the reaction vial in a warm sand bath, or using a ruhber septum with a syringe needle a& tached to a vacuum. However, these methods often result in the removal Threaded compression cap of product along with solvent, resulting in low yields and insufficient 10-mL RE flask product for further chemical analysis. In all of the ahove methods, students have difficulties determining when the solvent is completely removed. These procedures also require hood space, heating apparatus, nitrogen Construction of the rotary evaporator
To water as~irator 4 with trap
+@
A272
Journal of Chemical Education
I
.I
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m with hands or h(lt water
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