An Undergraduate Thin-Layer Chromatography Experiment Olfactory Delights Mary Anne Lynch, Wendy Gloffke, and Richard A. ~auner' Cedar Crest College, Allentown, PA 18104
Undergraduate instructors are continually challenged to incorporate technical experience, deductive reasoning, and relevance into their freshman chemistry laboratories. We have designed a n experiment for a second-semester course for nonmajors that addresses these concerns. An exercise in qualitative organic analysis was developed previously in our laboratory and discussed in this Journal (1).We now look a t the occurrences of these functional groups i n flavors and fragrances. These two chemical families provide an especially useful example of "real life" chemistry because both are substances with which every student is familiar. Asurvey of articles in this Journal shows that while many have used thin-layer chromatography a s a vehicle for the introduction of seoaration techniaues and conceots. none of them use as thei; focus the separHtion of flavor i n d fraerance comDonents a s described in this article (2-71. A portion of the pre-laboratory session t h a t provides some insight into the olfactory process can be used to "whet the appetite". I t also reinforces the importance of molecular structure a s it relates to chemoreceptors in the nose and on t h e tongue (8).Representative compounds found in this laboratory exercise are well illustrated and discussed by Atkins (9). Students are given a four-component standard to analyze and a two-component unknown to identify After development of the TLC sheet, visualization of the spots is iicc~mpl~.shcd usmg porasiinm pt:rmanganntc I K M ~ O J , 12.4-1)NI'H . Hrnrti\.ity and %.4-dinitrt1ph~~n\~lhsdraz1ne . . . toward reagents is noted, Rfvalues are calculated for each component, and unknown components are identified by name and structure. In addition, a tracing of the chromatogram is included in the report along with comments on the relative rates of migration a s a function of the groups . . present within e;icll con~pound. Students also are able to pla!. a "sniff-and-guess" game Small numbered vials of vako;s compoundsare o n h a n d for the student to smell in order to identify the odor. Alist of their chemical formulas, names, and identifying scents is given to the students after all samples have been identified (10, 11).I t should be noted that some students have exhibited a n allergic-type reaction, especially when sniffing floral scents.
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Reagents Baker-flex silica gel IB2 sheets were obtained from VWR Scientific, Bridgeport, NJ. Gelman Science Chromist reagent spray units were obtained from Baxter Healthcare Corp., Edison, NJ. Chemical reagents and solvents were purchased from Aldrich Chemical Company. Potassium permangauate was prepared by dissolving 1.6 g KMn04 and 15 ganhydrous NazC03 in 100 mL distilled water (12). Watch for the appearance of MnOz a s a brown solid. Discard if this occurs.
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Figure 1. Spotting template: UK = unknown; S =standard; not drawn to scale. Standardsa Used in Olfactory Delights Experiment
Group
Compound ~ , ~ - D N R1(lOO)C PH~ 1RI-(+I-citronellal + 72 . . ,, piperonal (+/-)-menthol (R)-(+)-pcitronellol 4-allylanisole linalyl acetate (R)-(-)
