Diethyl Phosphite: A Solvent you wouldn’t easily think of -Miscible both with Water and Ordinary Organic Solvents

 

Diethyl Phosphite is variously called diethyl phosphonate, diethyl hydrogen phosphite, diethyl phosphonite. 

According to Fieser & Fieser Organic Reagents Vol. 1 pg. 252 “Diethyl phosphonate {diethyl phosphite/diethyl phosphonite/(EtO)₂P(=O)H} is miscible with water and with ordinary organic solvents and has remarkable solvent power.” Diethyl phosphite may be just the trick when all the ingredients for a reaction cannot be dissolved together!

 It is also recommended for the preparation of phenyl hydrazones and 2,4-dinitrophenylhydrazones in the short communication: Maynard, J.A. Australian Journal of Chemistry, 1962, vol. 15, p. 867 - 868. These latter reactions drive the equilibrium by removing water by reaction while generating a useful strong acid as catalyst. It is also important that diethyl phosphite readily dissolves both the reagent and substrate. Dr. Maynard points out that the addition of an acid catalyst to the mixture is unnecessary because the solvent reacts with any water initially present and all that is formed in the reaction to produce the strong acid ethyl hydrogen phosphate. Thus the needed acid is produced and the by-product water is scavenged. Many of the phenyl hydrazones made using this solvent precipitated directly; others required mixing with water equal in volume with the solvent. Recrystallizations were from methanol, ethanol, benzene, or acetone as the solubilities directed.

This trick of binding up by-product water and generating useful acid may apply to other reactions.