Watch It Happen: Teaching Esterification and Hydrolysis with Fluorescein Diacetate

Classic esterification experiments often engage students through their characteristic aromas but typically lack a direct visual indicator of reaction progress. This experiment addresses that gap with a simple, rapid, and visually observable method for teaching both esterification and ester hydrolysis. By converting fluorescein into its nonfluorescent ester, students can visually track the reaction progress under UV light. The esterification is complete within approximately 10 min, making it well-suited for classroom or laboratory settings with limited time. The product, fluorescein diacetate, is obtained in high yield and good purity through simple precipitation and filtration. Subsequent basic hydrolysis demonstrates the reverse reaction, with the reappearance of fluorescence providing a vivid real-time indicator of ester cleavage.