A Simple Photochemical Experiment for the Advanced Laboratory Stualt M. Rosenfeld Smith College, Northampton, MA 01063 At Smith College, Advanced Laboratory is a year-long course. taken in the iunior or senior year, that encompasses all disciplines of chemistry. The ~ d i a n c e dLab course consists of two lecture hours and six lab hours per week but students are free to work outside normal lab-hours with a partner. Advanced Lab provides a vehicle for introducing sophisticated techniques and for discussing topics that lie outside the scope of earlier courses. The experiment described below was developed to provide advanced lab students with 1) an introduction to photochemical techniques and theory, 2) an experience with semimicro techniques and especially chromatography on preparative plates. 3) an application of 13CNMR, and 4) a lab with some of the qualities of a genuine experiment. For practical reasons, we sought an experiment that would not require expensive or delicate photochemical equipment. All of these criteria are met in the photooxidation of 9,lOdiphenylanthracene. Ba~kground'.~ Condensed aromatic compounds, such as anthracene, have long been known to undergo oxidation in the presence of air and visible light. The oxidation proceeds by formation of an electronic excited state of 02 (singlet oxygen, l02) throughenergy transfer (sensiti7ationl from an excitedstate oi the aromatic hydrocarbon. Often, a m a l l amount of a sensitizer that absorbs light strongly or over a brond rangeof visihle wa\,elengrhs is added LO the reartion mixture to enhanre the eiiiriencv of sinelet - oawen .- formation. Howe\w, the substrate to be oxidized can also function as the sensitizer. Singlet oxvaen reacts with anthracenes to form endoper~xides.,'e.~.. I; which are generally stableenough to be isolated though this depends upon the nature of the subsrituenti on the anthracene ring. lhdoperuxides undergo thermal decompositiun n t moderate temperatures, a cnmmon pathway involves loii of (singlet) 0?and refmnation of rhr original aromatic hydrocarbon.
184
Journal of Chemical Education
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Detailed discussions of this material, as well as hackground on photochemistry and 13CNMR spectroscopy, were presented prior to beginning the experiment. Instructions to the Student We will synthesize, purify, and identify an endoperoxide of 9,lO-diphenylanthracene.Since the starting hydrocarbon is rather exoensive. we will perform all operations on asmall (100-mg) scale. This is a convenient scale for running exploratory reactions since i t not only conserves expensive reageits, solvents, and chromatog
