Application of Optically Active Phosphinothioic Acid as Chiral Shift Reagent to Determination of Enantiomeric Purity

Abstract

Phosphinothioic acid has tetrahedral structure in which the phosphorus atom becomes chiral center and the hydrogen oxide group has strong hydrogen bonding power. Fortunately, it is readily resolved into two enantiomers, which are stable to treat. The optically active phosphinothioic acids, especially phenyl-t-butylphosphinothioic. acid (1), can induce chemical shift non-equivalence of enantiomers in the ¹H NMR spectra of chiral compounds such as phosphinates, phosphonates, phosphine oxides, phosphinic amides, phosphinothioic acids, phosphonothioic acids, amines, and alcohols. The non-equivalence is due to the formation of diastereomeric complexes in which optically active acid is hydrogen bonded to the phosphoryl, amino, or hydroxy groups of the enantiomers.
Thus, the enantiomeric purities can be easily and accurately determined from the relative intensities (peak heights) of the two signals. Preparation of the thioacid (1) and recovery from the NMR solution are described in detail with the chemical shift non-equivalence data.