P. Joseph-Nathan y
Centro de lnvestigoci6n de Estudios Avonzodos del I.P.N. Me'xico 14, D.F., Me'xico
I 1 I
Liquid-Liquid EX~III~~~OII
Liquid-liquid extraction provides a good laboratory method for the separation of many organic mixtures.' We would like to show how this can be done in a simple manner using commercially available substances and an apparatus of small dimensions that still allow the experiment to be followed visually. The experiment is designed to introduce students to laboratory techniques which are not usually taught in general chemistry courses. The equipment used in the experiment is schematically represented in the figure, and works as follows: The extracting solvent is placed in flask a, which is heated. The vapors pass through the broad branch of the distillation-extraction head, b, to the condenser, c; the condeusate drips through a tube to the bottom of flask d, in which the solution to be extraced is placed. Since the density of the extracting liquid is lower than that of the solution, it flows to the surface, extracting part of the solute during its ascendent course through the solution. When the level of the extracting liquid reaches the narrower branch of the extraction head, b, it begins to return to flask a where the extracted compound accumulates progressively. I n this way a constant flow of fresh extracting solvent passes through the solution placed in flask d. I n order to follow easily the course of the experiment, we have chosen a system with a nearly ideal behavior, since the solubilities and, therefore, the partition coefficient of the compound to he extracted favor the extracting liquid much more than the solvent in which it is initially dissolved. The experiment is carried out as follows: a solution of 5 mg of azulene (Aldrich Chemical Co.) in 7 ml of ethanol is diluted with 3 ml of distilled water, and the resulting blue liauid transferred t o the 25-ml flask d. ' CRAIG,L. C., AND CRAIG, D., "Technique of Organic Chemistry," (Edilor: WEISSBERGER, ARNOLD),Vol. 111, Interscience Publishers (division of John Wiley & Sons, Inc.), New York, 1950.
176 / Journol of Chemical Education
The distillation-extraction bead, b, and the condenser, c, are mounted. A boiling granule and 60 ml of cyclohexane are placed in the 100-ml round bottomed flask, a, equipped with a heating mantle and a Variac operated a t 90 v. The apparatus is then assembled and the operation is started. After 10 min the cyclohexane solution in flask a begins to turn blue, and 20 min later only a pale color remains in the ethanolic solution. Finally, after a total time of 45 min, no azulene can be detected in the ethanolic solution even by scanning an ultraviolet spectrum.
Apporobr for liquid-liquid extraction
