Optical resolution and racemization of areneseleninic acids

Abstract

Various optically active areneseleninic acids (ArSeO₂H; Ar = 4-Me-C₆H₄; 4-MeO-C₆H₄; 2-MeO-C₆H₄; 2-MeOCO-C₆H₄; 2,4,6-Me₃-C₆H₂; 2,4,6-Et₃-C₆H₂; 2,4,6-ⁱPr₃-C₆H₂; 2,4,6-^tBu₃-C₆H₂; 2,4-^tBu₂-6-MeO-C₆H₂) were obtained as solutions by optical resolution on a chiral column using medium-pressure liquid chromatography. Concentration of the eluate by evaporation under reduced pressure yielded completely racemized seleninic acids. Optically active seleninic acids with low-acidity were more stable against racemization than those with high-acidity. The bulky substituents at the ortho position on the benzene ring of the areneseleninic acids were also found to be effective for retarding the racemization. The mechanism for the racemization was clarified to proceed via seleninate anion with the extrusion of a proton under dilute conditions.