Isoxazoles V: chemical stability of diisoxazolylnaphthoquinone in aqueous solution

The hydrolytic degradation of 2-(3,4-dimethyl-5-isoxazolylamine)-N-(3,4-dimethyl-5-isoxazolyl )-1,4- naphthoquinone-4-imine (1) was investigated over a wide range of pH values and at different temperatures. The degradation rates were determined by reversed-phase HPLC and were observed to follow pseudo-first-order kinetics with respect to the concentration of 1. The pH-rate profile was linear with slopes -1 and +1 in acid and alkaline pH, respectively, becoming pH independent in the region of maximum stability from pH 4.5 to 10.0. Neither primary salt effects nor buffer catalysis was observed due to the buffer species employed.