title: Isoxazoles. 9. Degradation kinetics of 4-(isoxazolylamino)-1,2-naphthoquinone in acidic aqueous solution.
abstract: The degradation kinetics of N-(5-methyl-4-isoxazolyl)-4-amino-1,2-naphthoquinone (1) was studied in aqueous solution over a pH range of 0.65-7.50, at 35 degrees C and at a constant ionic strength of 0.5. The degradation rates were determined by high-pressure liquid chromatography and were observed to follow pseudo-first-order kinetics with respect to the concentration of 1. The pH-rate profile was linear with slope -1 under acidic pH, becoming pH independent from 3.50 to 7.50. Good agreement between the theoretical pH-rate profile and the experimental data supports the proposed degradation process. The catalytic rate constants for hydrogen ion and water were kH = 0.901 M-1 h-1 and k0 = 1.34 x 10(-3)h-1, respectively. These data are appropriate to develop a stable dosage form of 1. The accuracy, peak sharpness, and asymmetry factor for the analytical method were determined.
authors.affiliation: Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
authors.forename: C S
authors.initials: CS
authors.lastname: Ortiz
authors.forename: M M
authors.initials: MM
authors.lastname: de Bertorello
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007555:Isoxazoles / Q000737:chemistry*; D007700:Kinetics; D009285:Naphthoquinones / Q000737:chemistry*; D012015:Reference Standards; D015203:Reproducibility of Results; D012996:Solutions; D013411:Sulfadiazine / Q000737:chemistry; D013696:Temperature; D014867:Water / Q000737:chemistry*
chemical_list: D007555:Isoxazoles; C092440:N-(5-methyl-4-isoxazolyl)-4-amino-1,2-naphthoquinone; D009285:Naphthoquinones; D012996:Solutions; D014867:Water; D013411:Sulfadiazine