Olaf Runquirt Hamline University St. Paul, Minnesota 55101
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The Essential Oils A serie s of laboratory experiments
The essential oils offer an interesting set of "research type" laboratory problems for students in organic chemistry. A variety of projects are possible ranging from relatively simple isolation and structure determinations to more sophisticated research, such as the identification of minor constituents, rate and equilibrium studies, rearrangements, strncture proofs of conversion products, or the development of quantitative analytical methods for various components. Most of our students develop a very strong interest in problems associated with these oils. Because of the strong motivation developed, they become less dependent upon the instructor for the design, execution, and interpretation of their work and rely more heavily upon the literature, the experience of other students, and their own resourcefulness. The fact that a considerable amount of the published work on the essential oils and their constituents is old and of questionable validity greatly enhances student interest. Following are some illustrations of the ways in which we have made use of the essential oils. I n the second term of the introductory organic course, each pair of students selects an essential oil from approximately twenty that are availab1e.l Each pair of students separates two components from their oil and then each student purifies and identifies one of the isolated components. I n the process of solving his problem, the student engages in a literature search, an isolation by vacuum fractional distillation, a purification by column chromatography, and an analysis of purity by gas and/or thin layer chromatography. Each student obtains the nmr, ir, and uv spectra of his constituent and analyzes the spectral data. The only "formal" instructions given for the project are: (a) a list of reference books useful in initiating a literature search (given below), (b) very brief (2 min) instructions on how to use Chemical Abstracts, (c) indication that a vacuum fractional distillation followed by chromatography on alumina is a desirable isolation and purification procedure, (d) programmed materials on the use of Beilstein's Handbueh and the spectroscopic analysis of organic compounds,2 and (e) audio tapes on the use of the spectrometer^.^ The laboratory instructor and Obtained from Fritzsche Brothers, Ino., 76th Ninth Avenue, New York, New York 10011. RUNQUIST, 0.)"A Programmed Guide to Beilstein's Handbuch," Burgess Publishing Company, Minneapolis, Minnesota, 1966. CRESWELL, C., AND RUNQUIST, O., "Spectroscopic Analysis of Organic Compounds," Burgess Publishing Company, Minneapolis, Minnesota, 1970. T h e s e tapes were prepared in our laboratories. BOCHE, J., AND RUNQUIST, O., 3. 079. Chetn., 33, 4285 (1968). WUNQUIST, A., PI~RSON, G., AND RUNQUIST, O., J. 018. Chen., 34, 3192 (1969).
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journal o f Chemical Education
assistants are available as consultants. Somc assistance is given to students'who desire translations of articles writkn in languages other than German, French, or Russian. Our advanced students have found that the essential oils offer a wide variety of challenging problems. Several students have isolated, purified, and identified minor constituents of an oil. This work usually requires the student to obtain molecular weights and elemental analysis, and prepare derivatives in addition to obtaining and interpreting spectral data. One student made a kinetic study of the thermal rearrangement of ascaridole, the major constituent of Wormseed oil. His work is reported el~ewhere.~Other students reacted amines with the thermal rearrangement product of ascaridole and determined the strncture of the resulting materials! (The structures reported in the literature for these addition products were shown to be incorrect.) There are many advantages to using the essential oils as research type problems for undergraduates. The cost of the oils is relatively low as can be seen from the approximate prices of some representative oils (see table). The experiments are "open-ended." Thus, .an isolated major constituent might be used in an equilibrium or rate study or converted to some other compound of interest. Furthermore, the residue from an oil provides the starting material for the isolation of a minor constituent. The older literature dealing with the essential oils and their constituents abounds with interesting and highly instructive reactions which can be profitably restudied with modern research techniques. However, the most compelling reason for using the essential oils in the undergraduate laboratory is the abiIity of these intriguing materials to motivate the student toward independent study and research. We wish to acknowledge the financial assistance of the Louis W. and Maud Hill Family Foundation. Cost o f Some Representative Oils Essentid Oil
Approximate Price per Pound'
Fir Reedla Siberian Bitter Almond Anise Citronella Lime Chenopodium Pennyroyal Pinus Sylvestris Tangerine Tansey Petitgrain
3.00 3.50 4.00 1.00 8.00 6.00 2.50 4.50 3.00 10.00 3.00
Fritzsche Brothers, Inc., 76 Ninth Avenue, New York, N. Y. 10011.
Initial Reference Sources "Merok Index," (8th ed.), Merck and Company, Inc., Rahway, New Jersey, 1968. "Pharmacopoeia of the United States," (17th ed.), Mack Publishing Co., Easton, Pennsylvania, 1965.
POCRER, W. A,, "Perfumes, Cosmetics, snd Soaps," (3 Vols.) Van Nostrand, Princeton, New Jeney, 1959. J. L., BARTON, D. H. R. AND OWEN,L. N., "The SMONSEN, Terpenes," Cambridge University Press, Cambridge, England, 1949. GUENTHER, ERNEST,"Essential Oils," (3 Vals.) Van'Nostrand, New York, 1948.
Volume 46, Number 12, December 1969
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