An Optimization Exercise for Organic Chemistry Although optimization methods are used extensively in industrial chemistry, they are given little attention in undergraduate chemistry courses. Many students will later find themselves required to make on-the-job decisions regarding selection of substances and praeess conditions. I t is desirable that students gain some experience in the use of optimization methods in their undergraduate courses. The present exercise was devised to give students an initial experience in optimization in organic chemistry. The task involved is the selection of a solvent to replace benzene for dehydration of ethanol by azeotropic distillation I t can be used in conjunction pith a laboratory distillation of azeotropes, or as a separate exercise in either the lecture or the lab course. Preliminary discussion includes an explanation of azeotropes in general and the removal of water from ethanol by distillation of a ternary azeotrope (X/EtOH/H20) followed by removal of X as a binary azeotrope with ethanol. The historical use of benzene as X and reasons for avoiding benzene in the laboratory are highlighted. Toxicity, flammability, offensive odor, formation of explosive peroxides, and cast are presented as major factors to consider in the selection of X. Students are given,the assignment to identify a preferred organic liquid, X, and the following strategy is suggested. First, find those compounds that form minimum bailing azeotropes with ethanol and water. Then, those that form the ternary azeotropes are examined to determine which form minimum boiling binaryazeotropes with ethanol. This basic list of about 30 compounds is then reduced to asmaller number by consideration of a number of safety factors, offensiveness of odor, and cost. References, which supply data on carcinogenicity, threshold limit value, flash point, odor, and tendency to farm explosive peroxides upon exposure to air, are provided.'-5 Costs are obtained from current catalogs. The student report includes alist of the substancesremaining at each stage of the optimization process and the reasons for exclusion of substances from further consideration. A list of the five "finalist"rnmpounds is submitted, listed in order of preference, with a table of significantproperties. For comparison, comparable data for benzene are included in the table. Fina1ly.a single compound is reported as the preferred substance to use, together with reasons for the choice. Documentation is presented for all data used.
Horsley, L. H. Adv. Chem. Ser. 1973, 116,130. National Research Council Committee on Hazardous Substances in the Laboratory. "Prudent Practices for Handling Hazardous Substances in Laboratories"; National Academy: Washington, DC, 1981. "ax. N. I. Dangerous Properties of Industrial Materials; Van Nostrand: New York, 1979. Tatken, R. L.; Lewis, R. J.. Eds. Registry of ToxicEffectsof ChernicalSubstances; US. Department of Health and Human Services: Cincinnati, OH. 1983. Windholtz, M., Ed. The Merck Index, 10th ed.; Merck and Co., inc.: Rahway, NJ. 1983. Martln M. Anderson University of Portland Portland. OR 97203
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Volume 6 5
Number 1 January 1968
77
