The Role of Triplet State Keto–Enol Tautomerism in the Photodeamination of Metamitron

Substituted 4-amino-1,2,4-triazin-5-ones undergo photodeamination through cleavage of the N–NH2 bond in the presence of oxygen and water. To elucidate the mechanism of this reaction, we investigated the photolysis of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5-one) by nanosecond laser flas...

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Bibliographic Details
Published in:The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2011-12, Vol.115 (50), p.14397-14406
Main Authors: Kouras-Hadef, Sofia, de Sainte-Claire, Pascal, ter Halle, Alexandra, Amine-Khodja, Amina, Richard, Claire
Format: Article
Language:English
Subjects:
A: Kinetics, Spectroscopy
Deoxygenation
Environment and Society
Environmental Sciences
Excitation
Lasers
Mathematical analysis
Nanostructure
Physical chemistry
Pulsed lasers
Solvents
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Summary:Substituted 4-amino-1,2,4-triazin-5-ones undergo photodeamination through cleavage of the N–NH2 bond in the presence of oxygen and water. To elucidate the mechanism of this reaction, we investigated the photolysis of metamitron (4-amino-6-phenyl-3-methyl-1,2,4-triazin-5-one) by nanosecond laser flash photolysis, steady-state irradiation, and ab initio calculations. Upon pulsed laser excitation of deoxygenated aqueous metamitron, two transient species are clearly detected. The predictions of ab initio results are consistent with experimental results: (i) it is proposed here that the transient species are, respectively, the keto and diradical forms of the metamitron keto–enol tautomerism in the triplet state, and (ii) in water, the activation free energy barrier of enolization is drastically decreased. Thus, the formation of the diradical triplet is enabled in aqueous solvent. A detailed analysis of the intermediate structures that lead to the final products (HNO2 and deaminometamitron) is provided.
ISSN:1089-5639
1520-5215
DOI:10.1021/jp208907f