Dissolution kinetics of carboxylic acids II: effect of buffers.

The dissolution behavior of 2-naphthoic acid from rotating compressed disks into aqueous buffered solutions of constant ionic strength (mu = 0.5 with potassium chloride) at 25 degrees was investigated. A model was developed for the flux of a solid monoprotic carboxylic acid in aqueous buffered solutions as a function of the solution pH and the physicochemical properties of the buffer. The model assumes a diffusion layer-controlled mass transport process and simple, instantaneously established reaction equilibrium between all reactive species (acids and bases) across the diffusion layer. Using intrinsic solubilities, pKa values, and diffusion coefficients, the model accurately predicts the dissolution of 2-naphthoic acid as a function of the bulk solution composition. The concentration profiles of all species across the diffusion layer are generated for each buffer concentration and bulk solution pH, including the pH profile within the microclimate of the diffusion layer and the pH at the solid-solution boundary.