Unexpected Synthetic Outcomes from a Traditional Separations Laboratory

The introduction of 1H NMR analysis into a trusted separation experiment in an undergraduate Organic Chemistry laboratory has yielded a revelatory unexpected outcome. When students extract acetylsalicylic acid (aspirin) from dichloromethane using a sodium hydroxide solution followed by precipitation with acid, the separated sample collected is not aspirin but instead the saponified salicylic acid product. Faculty investigated the experiment to determine the conditions under which the hydrolysis reaction occurred. In response to the failed separation experiment, students were guided through a discussion of carbonyl reactivity along with an experiment in which they converted the collected salicylic acid into acetylsalicylic acid. Faculty investigated modifications to the separation experiment that prevent the unwanted hydrolysis reaction in future iterations. The experience underscores the importance of product characterization along with adequate testing of published laboratory experiments for both faculty and undergraduate students.