Isoxazoles. 10. Degradation and enolization kinetics of 4- aminoisoxazolyl-1,2-naphthoquinone in basic aqueous solution

Article abstract of DOI:10.1002/jps.2600840623

The kinetics of enolization and degradation of N-(5-methyl-4-isoxazolyl)- 4-amino-1,2-naphthoquinone (1) was investigated in aqueous solutions over a pH range of 7.30 to 12.25, at 35 °C and at constant ionic strength (μ = 0.5) using reversed-phase HPLC. Pseudo-first-order kinetics was observed throughout the pH range studied. The rate of enolization (k(e)), the keto- enol equilibrium constant (K(t)), and specific base catalysis rate constant (k(OH)) were determined. Good agreement between the theoretical pH-rate profile and the experimental data supports the proposed transformation process. The average recovery for 1 and its tautomerization product 2- hydroxy-N-(5-methyl-4-isoxazolyl)-1,4-naphthoquinone 4-imine (2) from mixtures of different composition was evaluated.