Structural aspects of optical resolutions. Optical resolution of (R,S)-mandelic acid. DSC and X-ray studies of the diastereoisomeric salts

Abstract

The diastereoisomeric salt pair formed during the resolution of mandelic acid (MA) using (R)-2-tert-butyl-3-methylimidazolidin-4-one (BMI) has been studied by DSC and X-ray crystallographic methods. Both diastereoisomers crystallize in a monoclinic system with space group P2₁; unit cell parameters for the less soluble R–R isomer: a= 11.484(1), b= 6.027(1), c= 11.951(1)Å, β= 98.77(1)°, V= 817.5(3)ų; for the more soluble R–S diastereoisomer a= 11.170(1), b= 5.975(1), c= 13.327(1)Å, β= 111.95(1)°, V= 825.0(3)ų. The structures were solved by direct methods and refined to a final R value of 0.044 and 0.057, respectively.