A Simple Apparatus for Continuous Steam Distillations
Steam distillation, a useful method for separating volatile compounds from plant parts or other complex mixtures is often associated with annoying practical problems. Among these are the periodic requirement of adding water to the distillation flask and the need to extract often voluminous quantities of the condensed water repeatedly with organic solvents. Both of these procedures result in the expenditure of time and solvents. A solution to the above problems is to use a circulatory continuous steam distillation apparatus. Unfortunately, only a few versions of this apparatus are commercially available1, and their cost ("$250) often prevents many laboratories from purchasing them for only occasional usage. Most laboratories possess, however, a continuous heavier-than-water liquidliquid extractor2 (see figure) that can he easily utilized for continuous steam distillations. The material to be steam distilled is placed into the distilling flask (A) of the liquid-liquid extractor and is covered with water. The extraction flask (B) is filled with water and a small amount (2-10 mL) of a suitable solvent is added t a t h e neck (C)of the extractor. Ethyl acetate is ideal because it is easily removed by rotoevaporation but is not so volatile so as to evaporate, as more volatile solvents such as diethyl ether will, during the steam distillation. During the steam distillation, volatiles, after condensing along with the steam, are extra&ed by theethyl acetate while the water condensate is recycled into the distilling flask. After the steam distillation is complete, the ethyl acetate is most easily reinoved by means of a disposable pipet. The advantages of this procedure are that exhaustive steam distillations can be done with little supervision, using negligible amount of solvents, and the need for time-consuming extractions is removed. 1 Kontes Scientific Glasswareflnstruments offers a continuous steam distillation apparatus (catalog # k-523010) for $257.30. Kontes Scientific Glassware/Instruments offers a heavier-than-water continuous extractor identical to the one described here (catalog # k-584100) for $139.00. Thomas P. Clausen
Unlvenity of Alaska Fairbanks. AK 99775
92
Journal of Chemical Education
