A Laboratory Exercise for Organic Chemistry The first day of organic chemistry lahoratory at Alfred University the students get their hands on a gas chromatograph. They analyze a mixture of two unknown liquids, which as the semester progresses they are to separate, analyze, and identify. The gas chromatograph is used to determine the percent composition, (1)as received, (2) after simple distillation of a small sample, and (3) after complete separation by fractionation. Not only do the students have experience with, and learn the relative values of, simple distillation and fractional distillation, hut they are also expected to work at the fraetionation until the gas chromatograph shows both the low boiler and the high boiler to he at least 90% pure. The students are told that one component of each mixture is an alcohol and that the other is either s ketone or an alkyl halide. When the liquids have been separated, infrared spectra of each are made and used to determine which is the alcohol and whether the other component is a ketone or an alkyl halide. The students are encouraged to make tentative identifications from the spectra. If the alcohol is the higher boiling component, it is divided into three equal parts, each of which is to be the starting material for a preparation to be handed in. One part is converted to an alkyl bromide by displacement with hydrohromic acid; another is esterified with acetic acid: another is dehydrated with sulfuric acid. If the alcohol is the lower boiling component, it is divided into only two parts: one for esterification and the other for bromide formation. Ketones are reduced with lithium aluminum hydride. Some of the resulting alcohol is handed in and the remainder is dehydrated as above. Alkyl halides are converted to the methyl ethers hy the Williamson reaction. The unknowns are selected so that everyone does a dehydration, an esterification and a bromide formation; thwe who don't do a reduction, do the Williamson. A mixture of s high boiling alcohol and a ketone or a mixture of a low boiling alcohol and an alkyl halide are both avoided. The former would result in five preparations and the Latter in threa On his unknown, then, each student does a simple diatillation, a fractionation, infrared spectra, and four conversions to products to be handed in. Finally, he assembles the spectra, the boiling ranges of the two unknowns and of the various products he has farmed and identifies everything. This exercise is spread over the entire first semester of the organic laboratory where organic is a non-integrated, 4-hr course, devoting 3 hr to class and 4 to the laboratory each week. The chromatography, the four preparations, and the final identification constitute six of the ten maded exoeriments the students oerform. A t Alfred this program has been fulluwrd surc~sstullyfor the last four years. With no two students doing the same thing, they solve their uwn laboratory prublrrnr, they get to gas chromatography and spectroscopy early. and they seem to like it. ~~
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Alfred University Alfred. New York 14802
732 / Journal of Chemical Education
Richard D. Sands
