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Scott D. Murray and Peter J. Hansen[1] Northwestern College, Orange City, IA 51041
For at least three decades a common undergraduate organic chemistry experiment has consisted of the extraction of caffeine from tea leaves. The caffeine is extracted from the tea leaves using hot or boiling water, extracted from this aqueous solution using an immiscible organic solvent, isolated in crude form by evaporating off the organic solvent, and purified by recrystallization or sublimation. During the 60's and 70's the organic solvent of choice was chloroform (1-3), while more recent organic laboratory manuals have specified the use of dichloromethane (4-7).
Both chloroform and dichloromethane generally are recognized as having significant toxicity. Chlorofonn is a "confirmed carcinogen" and dichloromethane is a "suspected human carcinogen" (8). A recent article reported increasing concerns about "chlorinated organics as a class and human health" (9). These potential hazards prompted the authors to seek a more suitable organic solvent for use in this experiment.
The initial set of criteria used in selecting an alternative organic solvent included:
1. immiscibility with water;
2. low toxicity;
3. low cost;
4. high stability (especially with respect to peroxide formation); and
5. appreciable caffeine solubility.
The reasons for the first four are apparent, while the last is necessary for a favorable caffeine partition coefficient between the organic solvent and water. Unfortunately, we were unable to identify a common organic solvent that met all five of these criteria. Leggett, et al., howeve reported that the salting-out effect can be employed to reduce dramatically the solubility in water of some normally water-miscible organic...