ISOXAZOLES .6. ASPECTS OF THE CHEMICAL-STABILITY OF A NEW NAPHTHOQUINONE-AMINE IN ACIDIC AQUEOUS-SOLUTION

Some aspects of the chemical degradation of N‐(3, 4‐dimethyl‐5‐isoxazolyl)‐4‐amino‐1, 2‐naphthoquinone were investigated as a function of pH and temperature. In acid and neutral pH, four main degradation products were identified: 2‐hydroxy‐1, 4‐naphthoquinone, 2‐butanone, ammonia, and hydroxylamine. No significant buffer effects were observed for the buffer species used in this study. The pH–rate profile exhibited a specific acid catalysis which is important at pH values <3.5, and an inflection point at pH 1.10 corresponding to a pKa value. From Arrhenius plots, the activation energy was found to be 17.8 ± 0.3 kcal/mol. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company