Chiral Symmetry Breaking and Deracemization of Sodium Chlorate in Turbulent Flow

The chiral symmetry breaking and deracemization of sodium chlorate were investigated when varying the agitation speed and cooling rate in cooling crystallization. At a low agitation speed, almost zero crystal enantiomeric excess occurred at the induction period. When increasing the agitation speed, the crystal enantiomeric excess at the induction period (called the “initial CEE”) increased due to the promotion of chiral symmetry breaking. The chiral symmetry breaking at the induction period (called the “initial chiral symmetry breaking”) also varied with the cooling rate. At a low cooling rate of 0.0738 °C/min, the initial CEE reached up to about 90% and was rapidly reduced when increasing the cooling rate. The experiments also showed enhanced deracemization of the chiral crystals when increasing the initial CEE. Thus, complete deracemization was achieved when the initial CEE was over 60%. The influence of the agitation speed and cooling rate on the initial CEE originated from secondary nucleation depending on the supersaturation at the induction period (called the “induction supersaturation”). Using a nucleation rate equation, the initial CEE was found to correlate well with the induction supersaturation. Also, varying the final setting temperature and agitator confirmed that secondary nucleation was significantly involved in the chiral symmetry breaking at the induction period