Crystal growth rates of paracetamol in mixtures of water + acetone + toluene

Crystal growth rates of paracetamol (4-hydroxyacetanilide) have been determined by seeded isothermal desupersaturation experiments at 16°C in 23 different solvent mixtures of water + acetone + toluene. Parameters of different growth rate equations have been estimated by direct nonlinear optimization. At equal thermodynamic driving force, the growth rate depends on the composition of the solvent mixture. In the surface diffusion spiral growth model, this dependency can be described in terms of the interfacial energy between the solid and the solution. A reasonable prediction of the influence of the solvent composition on this interfacial energy is obtained if a proper estimation of the enthalpy of dissolution is done. For the case of paracetamol crystals growing in water + acetone + toluene mixtures this estimation needs to include an estimation of the entropy of fusion at the temperature of growth as well as of the nonideal entropy of mixing.