Step nonisothermal method in kinetics studies of captopril oxidation under compressed oxygen.

ABSTRACT

A step nonisothermal experiment under high oxygen pressure and a computation with optimization for a step nonisothermal experiment on a stability study of drugs are introduced. The kinetics parameters of captopril oxidation in aqueous solution were determined with this method. It is reported that the reaction of captopril solution occurs under either aerobic or anaerobic conditions, giving different products. Then the total rate constant k(total) can be expressed as k(total)=k(anaerobic)+k(aerobic)=A(anaerobic) exp (-E(a, anaerobic)/RT)+A(aerobic) exp (-E(a, aerobic)/RT)p(O(2)), where k(anaerobic) and k(aerobic) are the rate constants of anaerobic and aerobic degradation, respectively. The results indicate that the parameters obtained in the step nonisothermal experiment are comparable to those obtained in isothermal-isobaric experiments.