Isoxazoles. VII: Hydrolysis of 4-methyl-5-isoxazolylnaphthoquinone derivatives in aqueous solutions.
The kinetics for the degradation of 2-(4-methyl-5-isoxazolylamine)-N-(4-methyl-5-isoxazolyl)-1,4 -naphthoquinone-4- imine (1) in solution were investigated at 70 degrees C and at a constant ionic strength of 0.5 over a pH range of 1.75 to 12.85. The degradation rates were determined by absorption and second-derivative UV spectrometry. Two degradation products were identified in acidic and neutral pHs; they are 4-N-(4-methyl-5-isoxazolyl)-1,2-naphthoquinone (2) and 2-methyl-cyanoacetamide (5), respectively. In alkaline pH, two degradation products, 2-hydroxy-N-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine (3) and 5-amino-4-methylisoxazole (4), were isolated. The pathway for degradation of 1 in acidic and neutral pH followed consecutive first-order kinetics since 2 undergoes hydrolysis giving 2-hydroxy-1,4-napthoquinone (6) and 2-methylcyanoacetamide (5). No appreciable buffer effect on the degradation of 1 and 2 was observed for any of the buffer species in this study. The pH-rate profiles exhibited specific acid and specific basic catalysis for 1 and specific acid catalysis for 2. The maximum stability for 1 and 2 occurred in the neutral pH region.
Departamento de Farmacia, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Argentina.
M R
MR
Longhi
M M
MM
de Bertorello
M C
MC
Briñón
D002021:Buffers; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007555:Isoxazoles / Q000737:chemistry*; D007700:Kinetics; D009285:Naphthoquinones / Q000737:chemistry*; D009994:Osmolar Concentration; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013696:Temperature
D002021:Buffers; D007555:Isoxazoles; D009285:Naphthoquinones; C071673:2-(4-methyl-5-isoxazolylamine)-N-(4-methyl-5-isoxazolyl)-1,4-naphthoquinone-4-imine