This pleasant-smelling reaction is a greener version of the classical borohydride reduction. The experiment utilizes a novel scenario to introduce reduction chemistry and to highlight the importance of experimental design. The vanillin is dissolved in a minimal amount of ethanol, reduced with sodium borohydride, and upon acidification, vanillyl alcohol precipitates from the resulting aqueous reaction mixture. This eliminates the need for an organic extraction, which is typically performed with this type of reaction. Students typically achieve excellent yields, with typical yield ranging from 65 to 95%. The exercise provides a good context for discussing pKas as the acidic phenol is deprotonated by the borohydride, generating hydrogen gas.
Summary prepared March 2007 by Carl S. Lecher, Department of Chemistry, Marian College.
Lecher, C. S. Sodium Borohydride Reduction of Vanillin: A Low Solvent Synthesis of Vanillyl Alcohol, Chemistry, Marian College, 2007