Multiple-Batch, Wolff−Kishner Reduction Based on Azeotropic Distillation Using Diethylene Glycol

Abstract

The Huang−Minlon (Wolff−Kishner) procedure for deoxygenating aldehydes and ketones is improved by recycling excess hydrazine hydrate instead of distilling to increase the reaction temperature. This procedural change provides lower reaction and distillation temperatures and a short reaction time. It is applicable to those examples which are compatible with a refluxing mixture of diethylene glycol, hydrazine hydrate, and alkali and yield a product forming an azeotropic bilayer with diethylene glycol and hydrazine hydrate. The apparatus essential to these operational changes is described. Multibatch runs reusing reagents (alkali, diethylene glycol, and some retained hydrazine hydrate) show that high yields and product purity remain unchanged throughout this repetitive process and that accumulation of nonvolatile residue is minimal over a series of multiple runs applied to 2‘-acetonaphthone and dimethoxybenzaldehydes. This suggests that a continuous process, utilizing these techniques, could be developed.