Abstract
The kinetics of the degradation of cinnarizine in aqueous solution at various pH values and four different temperatures were investigated. The degradation of cinnarizine was observed as a pseudo first-order reaction. By determining the degradation rate of cinnarizine at various pH values, it was found that the degradation rate of cinnarizine increased with decreasing pH within the range from pH 3.0 to 1.0. The rate remained unchanged at below pH 1.2, and cinnarizine was stable at above pH 3.0. The pseudo first-order rate constants in aqueous solution (pH 1.20) at 60, 70, 80 and 90°C were 1.85×10-5, 1.05×10-4, 4.07×10-4 and 1.94×10-3 min-1, respectively. The activation energy of degradation in aqueous solution (pH 1.20) was calculated to be 36.8 kcal/mol from an Arrhenius plot.
