How Do Most Stable Racemic Crystals Transform into Metastable Chiral Crystals by Grinding?

Abstract

An experiment [Viedma, C.; Ortiz, J. E. Isr. J. Chem. 2021, 61, 758] has been reported in which stable racemic crystals of aspartic acid are converted to metastable chiral crystals without any external bias. In order to reproduce this surprising result, we propose a rate equation model with a cluster reaction. Our result shows that even if the initial amount of metastable crystals is equal to that of stable crystals in a solution, only metastable chiral crystals survive when the crystals are continuously ground. This mechanism of chirality conversion by crystal grinding is effective even if there is an energetic disadvantage compared with the competing phase. The extinction of the most stable phase crystals may occur if the number of their components exceeds those of the competing metastable phase crystals.