This experiment is a greener version of the classical benzoin condensation reaction, where students are shown a method for making C-C bonds and learn carbonyl chemistry. In this version, benzaldehyde is replaced by furfural and toxic sodium cyanide is replaced by sodium hydroxide and catalytic amounts of thiamine hydrochloride (vitamin B1). The use of thiamine hydrochloride represents one of the earliest examples of biologically derived reagents being used as a catalyst.
The reaction can be generally applied to other aryl aldehydes. Furfural (furan-2-carboxy aldehyde) is used in place of benzaldehyde to illustrate that heterocyclic aromatic compounds undergo condensations analogous to their benzene counterparts. Students will observe the formation of a light tan crystalline crude product. The crude product is vacuum filtered and recrystallized in ethanol to obtain a pure white material which is analyzed by infrared spectroscopy. Students are asked to interpret the IR spectrum of the product, determine its melting point, calculate the atom economy, and perform an economic evaluation of the process. The resulting product, furoin, can be easily oxidized under mild oxidation conditions to give furil (an alpha-diketone). The link to the laboratory procedure includes pre- and post-lab questions.
Summary prepared July 2005 by Joshua Pak, Department of Chemistry at Idaho State University and Scott W. Cowley, Department of Chemistry and Geochemistry at the Colorado School of Mines.
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 201-205.