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Acid hydrolysis of 1,6-dihydro-4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one (1,6-dihydrometamitron)

Author:
Ludvik, J., Jirkovsky, J., Urban, J., Zuman, P.
Source:
Journal of agricultural and food chemistry 1999 v.47 no.9 pp. 3879-3885
ISSN:
0021-8561
Subject:
metamitron, degradation, hydrolysis, reduction, pH
Abstract:
Metamitron (1) does not undergo hydrolysis at pH 1-8 and up to 5 M H2SO4. The product of its two-electron reduction, 1,6-dihydrometamitron (2), on the other hand, undergoes at pH <3 relatively fast hydrolysis. The dependence of the measured rate constant on acidity indicates that the completely protonated form (AH2 2+) predominating in strongly acidic media undergoes hydrolysis slower than the species bearing one less proton (AH+). The latter most reactive species is present in highest concentration in solutions of pH between 0 and 2. This species is protonated on the 2,3-azomethine bond and yields as final products 2-hydrazino-2-phenylacetic acid (4) and acethydrazide (5). Kinetic, polarographic, and spectrophotometric measurements indicated for the first dissociation an average value pK(a) = -0.8, for the second pK(a) = 0.95. These observations together with the easy reduction of the 1,6-bond in metamitron (1) indicate that in nature the cleavage of metamitron may be preceded by its reduction to 1,6-dihydrometamitron (2), which is then hydrolyzed. Thus, anaerobic, reductive conditions are likely preferable for the total microbial degradation of metamitron.