This convenient, effective and inexpensive liquid CO2-based extraction of a natural product (D-limonene) provides an engaging example of natural products extraction using an alternative solvent (liquefied CO2). Because the procedure can be carried out in a polypropylene centrifuge tube and uses crushed dry ice as its CO2 source, it provides an inexpensive alternative to the equipment-intensive extraction with supercritical CO2. A short video clip is available that illustrates the features of this convenient extraction.
The procedure offers a number of benefits. It provides opportunities to discuss phase behavior and to visualize a seldom-observed (liquid) phase of CO2. It is rapid and easy, leaving time during a laboratory period for thorough characterization of the natural product by, for example, 1H NMR, GC (or GC-MS) and IR. The purity of the product can be compared to that of products isolated by traditional steam distillation or solvent extraction methods. Finally, the method of liquefying CO2 is amenable to demonstrations in the classroom (at all levels) or in outreach activities.
Summary prepared July 2006 by James E. Hutchison, Department of Chemistry at the University of Oregon.
McKenzie, L. C.; Thompson, J. E.; Sullivan, R.; Hutchison, J. E. Green Chem., Print 2004, 6, pp 355-358.