Dissolution Kinetics of Barbital Polymorphs

Abstract

The dissolution rate constants of barbital polymorphs in water were measured by rotating disk method. The phase transition took place by compression during preparing of the disk. Combining the Levich equation and the concept of consecutive process first proposed by Berthoud, the rate constant of interfacial chemical reaction and that of transport process were obtained separately, and the diffusion coefficient also was calculated. These values were reasonable compared with data found in many references, and the theoretical diffusion coefficient calculated according to the Wilke and Othmer equations. The activation energies of transport process and chemical reactionwere obtained from the temperature dependence. Furthermore, the solubility data obtained by the finite differences diagram method affordedthe heat of transition, transition temperature and entropy change between Phase I and Phase III.