Stability determination of 3-bromo-2-hydroxy-N-(3,4-dimethyl-5- isoxazolyl)-1,4-naphthoquinon-4-imine in ethanol by first-derivative spectrophotometry

Article abstract of DOI:10.1002/jps.2600831118

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-napthoquinon- 4-imine (1). A simple, rapid, and stability-indicating method for the determination of 2 in the presence of 1 using '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 of 2, obtained from linear plots of the residual concentration logarithms vs time, the calculated activation parameters E(a), ΔH((+)) and ΔS((+)) were similar under room-light and light-protected conditions. The in vitro antibacterial activity of 2 was also evaluated.