Kinetics of Indomethacin Degradation I: Presence of Alkali

The kinetics of indomethacin degradation were followed in alkaline aqueous solutions at various temperatures between 20.1 and 40.7°. The apparent first‐order rate constants were evaluated from log absorbance versus time plots at λmax 318 nm. The primary salt effect was positive. The rate constant‐hydroxide‐ion concentration profile was linear with a positive slope, suggesting the following rate law. kobs= k1 [OH−]. The experimental data fit the proposed reaction of degradation, I− + OH− k1 →k1products, where I− = mono‐dissociated indomethacin species. Activationenergies and other related parameters were calculated from Arrhenius‐type plots.