Crystal Growth of Salicylic Acid in Organic Solvents

The crystal growth rate of salicylic acid has been determined by seeded isothermal desupersaturation experiments in different organic solvents (methanol, acetone, ethyl acetate, and acetonitrile) and at different temperatures (10, 15, 20, and 25 °C). <i>In situ</i> ATR-FTIR spectroscopy and principal component analysis (PCA) were employed for the determination of solution concentration. Activity coefficient ratios are approximately accounted for in the driving force determination. The results show that the dependence of the growth rate on the solvent at equal driving force varies with temperature; <i>e.g.</i>, at 25 °C, the growth rate is highest in ethyl acetate and lowest in acetonitrile, while at 15 °C the growth rate is highest in acetonitrile. The growth rate data are further examined within the Burton Cabrera Franck (BCF) and the Birth and Spread (B+S) theories, and the results point to the importance of the surface diffusion step. Interfacial energies determined by fitting the B+S model to the growth rate data are well-correlated to interfacial energies previously determined from primary nucleation data.