Optically Active Seleninic Acid

Each optical isomer of methaneseleninic acid (1a) was isolated as chiral crystals by recrystallization from methanol/toluene. The absolute configuration of one of the enantiomers was determined by X-ray crystallographic analysis, and the relationship between the absolute configuration and the circular dichroism spectra of 1a was clarified. The optically active seleninic acid (R)-1a was stable toward racemization in the solid state, although it racemized very rapidly in solution. Each enantiomer of 1a was obtained in bulk by chiral crystallization in the presence of a seed crystal or chiral solvents. The absolute configuration of optically active methanesulfinic acid (4) was also assigned by comparing its circular dichroism spectra with those of 1a.