This experiment provides a rare example of a solventless reaction. Students mix together two solids, an aldehyde and a ketone, that form a low-melting eutectic mixture. Addition of a small amount of powdered sodium hydroxide to the liquid initiates an aldol condensation between the two components, forming a solid product. A brief rinse of the solid with dilute aqueous HCl affords the product in high yield and purity. A video clip is available to highlight the features of this rapid and convenient synthesis.
The solventless aldol condensation provides lessons on several key topics. Given that nearly all chemical transformations carried out in undergraduate teaching laboratories rely on solvent to bring the reactants together, this exercise provides a unique opportunity to discuss the role of solvents and reexamine the need for solvents. The exercise also provides an excellent opportunity to discuss and illustrate melting points, eutectic mixtures, and melting point depression. Finally, the condensation is an example of a reaction with high atom economy. The link to the laboratory procedure includes post-lab questions.
Summary prepared July 2006 by James E. Hutchison, Department of Chemistry at the University of Oregon.
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 115-119.