Assessing Basic Separatory Technique Skills in an Organic Experiment Based on an Incomplete Haloform Reaction

We present an experiment which was designed to assess the separation technique skills of the gifted high school students who attended the 50th International Chemistry Olympiad 2018. The procedure consists of two synthetic tasks and is also applicable for teaching undergraduates. The haloform reaction of 2-acetonaphthone with sodium hypochlorite in commercial bleach gave the corresponding carboxylate salt and some unreacted 2-acetonaphthone. This unreacted material is separated and then treated with in situ prepared Brady's reagent to give a near-quantitative yield of the hydrazone, while acidification of the carboxylate salt affords the corresponding carboxylic acid. The procedure includes several separation techniques: acid-base extraction, TLC analysis, and suction filtration. The grading of the student's work based on the combined yield of both products avoids having to account for the effects of temperature, reaction time, and reagent quality on the efficiency of the haloform reaction. The duration of the experiment is 3-4 h of working time, depending on the student's time management skills.