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 degrees. The apparent first-order rate constants were evaluated from log absorbance versus time plots at lambda max 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 leads to products, where I- = mono-dissociated indomethacin species. Activation energies and other related parameters were calculated from Arrhenius-type plots.