The Resolution of 2-Hydroxy-5,5-dimethyl-4-phenyl-1,3,2-dioxaphosphorinan 2-Oxide (Phencyphos) by Preferential Crystallization

An inexpensive, reliable resolution method for the resolving agent, 2-hydroxy-5,5-dimethyl-4-phenyl-1,3,2-dioxaphosphorinan 2-oxide (phencyphos) was required. Anhydrous phencyphos is a racemic compound, but the hydrate is known to be a conglomerate. After examination of various solvent mixtures a preferential crystallization process in methanol/water solvent mixtures was chosen to deliver the pure enantiomers in good yields. The preferential crystallization process can be repeated up to 50 times without significant loss of efficiency.