Crystal Size Deracemisation Lab Report

To resolve this and to design an ultrasound-enhanced process that would lead to homochirality in the absence of glass beads, we employed seeding during ultrasound-enhanced deracemization. We theorized that by introducing larger seed crystals to the system after the establishment of the monodispersed sized crystals (~2 hours), we would broaden the crystal size distribution and thus allow the deracemization process to resume. To test this idea we performed seeded experiments using ultrasound, in which we introduced 2.5 g of large seed crystals (~200 µm, e_0= 40%) after sampling of the 2nd hour. Obviously, the addition of extra mass of a particular e to the system has a direct effect on the total e in the suspension. To separate the effect of
Just before seeding, the e of the system was measured to be 50%, hence the addition of 2.5 g of e_0 = 40% would in fact decrease the total e to approximately 46%. Remarkably, one hour after the seed addition, e is still measured at 50% and after two hours it increases further to 62%. Pictures of this experiment, displayed in Figure 8, show that one hour after the addition of the seeds, crystal size distribution is much broader compared to the ultrasound experiment without the addition of seeds. This crystal size dispersion gives rise to further ultrasound-enhanced attrition, allowing the system to overcome the stagnation in the e evolution; a significant e increase is observed over the next hours. However, after prolonged times of ultrasonication, a leveling in e is again observed and the attainment of homochirality is again hindered, indicating the need of additional seeding events. We performed a second seeded experiment in which seeding was applied after the sampling of both 2nd and 5th hour (2.5 g and 4 g respectively), using homochiral (e_0 = 100%) seeds. The results of this experiment in comparison with the glass bead experiment at the same conditions are presented in Figure