Degradation Kinetics and Aqueous Degradation Pathway of Cloxacillin Sodium

Abstract The degradation kinetics of cloxacillin sodium (CS) under real production conditions was determined using high‐performance liquid chromatography (HPLC). Degradation in methanol (MeOH) follows zero‐order kinetics. The introduction of water kept the degradation order but decreased the rate constant, while butyl acetate (BA) accelerated the degradation and shifted the kinetics to first order. In the MeOH/BA system, the pH‐dependent degradation rate generally increased when increasing the pH, except for a distinct drop at about pH 6.5. In aqueous solution, the effect of temperature was determined and the apparent activation energy of degradation was found to be 80.34 ± 5.88 kJ mol–1. The degradation products were analyzed using HPLC, mass spectrometry, and infrared spectroscopy, and a pathway toward cloxalloic acid via cloxacilloic acid as intermediate is proposed.