Issue in Honor of Prof. Sándor Antus ARKIVOC 2004 (vii) 53-59 ISSN 1424-6376 Page 53 © ARKAT USA, Inc Time dependent efficiency of optical resolution of aminooxiranes with O,O'-dibenzoyl-(R,R)-tartaric acid Ferenc Faigl * a,b , Angelika Thurner b , Ferenc Farkas a , Ágnes Proszenyák a , Michela Valacchi c , and Alesandro Mordini c a Department of Organic Chemical Technology, Budapest University of Technology and Economics, H-1521 Budapest, Hungary b Research Group for Organic Chemical Technology, Hungarian Academy of Sciences, H-1521 Budapest, Hungary c Istituto di Chimica dei Composti Organometallici, Dipartimento di Chimica Organica “U. Schiff”, Via della Lastruccia 13 I-50019-Sesto Fiorentino, Firenze Italy E-mail: ffaigl@mail.bme.hu Dedicated to Professor Sándor Antus on his 60 th birthday (received 03 Oct 03; accepted 04 Dec 03; published on the web 06 Dec 03) Abstract Crystallization time dependent efficiencies of optical resolutions of two aminooxirane derivatives have been investigated. Time-scaled experiments demonstrated that efficient chiral discrimination of aminooxirane enantiomers by the resolving agent develops in slow, diffusion controlled exchange of the enantiomers between the solution and the precipitated salt of an enantiomeric mixture and the resolving agent. Comparison of the determined absolute configurations of the resolved aminooxiranes showed that quasi enantiomers of the structurally similar two model compounds crystallized with the same resolving agent from ethyl acetate. Keywords: Optical resolution, chiral amino oxiranes, chiral discrimination, diastereoisomeric salt formation Introduction Optical resolution via diastereoisomeric salt formation is known as a thermodynamically controlled process. 1 It means that the enantiomeric excess found in the crystallized salt has been determined by the solubility and dissociation constants of the two diastereoisomeric salts and the initial concentrations of the racemate and the resolving agent. 2 There are two classical methods to increase the enantiomeric excess of a diastereoisomeric salt: (a) recrystallization of the salt or (b) repeated resolution of the non racemic enantiomeric