Probing Crystal Nucleation of Fenoxycarb from Solution through the Effect of Solvent

Induction time experiments, spectroscopic and calorimetric analysis, and molecular modeling were used to probe the influence of solvent on the crystal nucleation of fenoxycarb (FC), a medium-sized, flexible organic molecule. A total of 800 induction times covering a range of supersaturations and crystallization temperatures in four different solvents were measured to elucidate the relative ease of nucleation. To achieve similar induction times, the required thermodynamic driving force, RT ln S, increases in the order: ethyl acetate < toluene < ethanol < isopropanol. This is roughly matched by the order of interfacial energies calculated using the classical nucleation theory. Solvent-solute interaction strengths were estimated using three methods: solvent-solute enthalpies derived from calorimetric solution enthalpies, solvent-solute interactions from molecular dynamics simulations, and the FTIR shifts in the carbonyl stretching corresponding to the solvent-solute interaction. The three methods gave an overall order of solvent-solute interactions increasing in the order toluene < ethyl acetate < alcohols. Thus, with the exception of FC in toluene, it is found that the nucleation difficulty increases with stronger binding of the solvent to the solute.