Chiral symmetry breaking in stirred crystallization of 1,1′-binaphthyl melt

As a supercooled melt at 150 degrees C, the chiral compound 1,1'-binaphthyl racemizes rapidly. The melt solidifies as a conglomerate of crystals, each consisting exclusively of either R-(-)- or S-(+)-enantiomer. We find that crystallization performed with a 2.00 g sample with constant stirring produces a large enantiomeric excess (mean 77%) in almost every crystallization, The predominance of R-(-) or S-(+) was random. Unstirred 2.00 g samples of binaphthyl produce a much lower enantiomeric excess (mean 20%) with optical activity centered around zero similar to an earlier report.(1) Thus, chiral symmetry breaking can be realized in crystallization from a melt by the mere act of stirring, as it can be in crystallization from a solution.