Habit Modification of a Diastereomeric Salt with an Additive in Optical Resolution

Abstract

In the optical resolution of α-methylbenzylamine (1) with mandelic acid (2), the dimeric derivative of 1, bis(α-methylbenzyl)amine (4), caused a habit modification of the diasteromeric salt, (R)-1·(R)-2 (3). The habit modification was strongly influenced by the stereochemistry of 4. Amine (R,R)-4 changed the morphology of the crystal of the diastereomeric salt, even at a concentration of 0.007 mol% of 3; the shape of the crystal became a hexagonal plate from a long hexagonal plate, whereas its stereoisomer ((R,S)-4) changed the morphology less than (R,R)-4, and (S,S)-4 did not change at all. The habit modification of 3 by 4 is discussed on the basis of the crystal growth mechanism while considering the stereochemistry of 4.