Stability Determination of 3‐Bromo‐2‐hydroxy‐N‐(3,4‐dimethyl‐5‐isoxazolyl)‐1,4‐naphthoquinon‐4‐imine in Ethanol by First‐Derivative Spectrophotometry

The degradation kinetics of a new potential tripanocidal and antibacterial agent, 3‐bromo‐2‐hydroxy‐N‐(3,4‐dimethyl‐5‐ isoxazolyl)‐1,4‐naphthoquinon‐4‐imine (2), in 95% ethanol, was investigated between 35 and 50 °C under room‐light and light‐protected conditions. The decomposition product was isolated and identified as 2‐hydroxy‐N‐(3,4‐dimethyl‐5‐isoxazolyl)‐1,4‐naphthoquinon‐4‐imine (1). A simple, rapid, and stability‐indicating method for the determination of2in the presence of1using “zero crossing” first‐derivative spectrophotometry is reported. The validity of this method was proved using synthetic mixtures of the intact drug with its decomposition product and by statistical analysis of the calibration data. Pseudo‐first‐order constants for the degradation reaction of2, obtained from linear plots of the residual concentration logarithms vs time, the calculated activation parametersEa, ΔH#, and ΔS#were similar under room‐light and light‐protected conditions. Thein vitroantibacterial activity of2was also evaluated.