Solid-state hydrolysis of aspirin

Abstract

The hydrolysis of solid aspirin has been studied, using single-crystal material, over the temperature range 368–387 K at humidities varying between 7 and 24 kN m^–2. The reaction follows the Avrami–Erofeyev equation, indicating that nucleation-and-growth kinetics are rate controlling, rather than the through-solution processes suggested previously. The Arrhenius parameters increase with increasing water vapour pressure and a compensation effect seems to operate. Water sorption and microscopy have been used to aid to the kinetic analysis.