The Mechanism of NaBH4 Addition to Aldehydes: A Labeling Experiment

In order to determine the sources of hydrogens in NaBH4 reductions of aldehydes, a series of reductions were carried out using differentially deuterated reagents and solvents. Thus, benzaldehyde was subjected to four different reduction protocols: reaction with NaBH4 followed by HCl, reaction with NaBD4 followed by HCl, reaction with NaBH4 followed by DCl, and reaction with NaBD4 followed by DCl. Products were isolated and analyzed by GC-MS. The results showed four different compounds were produced differing in the number and/or position of deuterium atoms and indicated that hydrogens in the reduced product came from NaBH4 and the acid work up.