Protonation−Dissociation Reactions of Imazamethabenz-Methyl and Imazamethabenz-Acid in Relation to Their Soil Sorption and Abiotic Degradation

• Published in: Journal of agricultural and food chemistry 2009-12, Vol.57 (23), p.11292-11296
• Main Authors: Pintado, Sara, Ruiz Montoya, Mercedes, Rodríguez Mellado, José Miguel
• Format: Article
• Language: English
• Subjects: Adsorption; Biological and medical sciences; dissociation; Environmental Chemistry; Food industries; Fundamental and applied biological sciences. Psychology; herbicide residues; Herbicides - chemistry; imazamethabenz; imazamethabenz-acid; imazamethabenz-methyl; Imidazoles - chemistry; Kinetics; photolysis; polluted soils; protonation-dissociation reactions; soil physical properties; Soil Pollutants - chemistry; soil quality; soil treatment; sorption
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf902845h

This paper present ultraviolet−visible absorption spectra of imazamethabenz-methyl (IMBM) (mixture of the isomers methyl 6-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-m-toluate, m-imazamethabenz, and methyl 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-p-toluate, p-imazamethabenz) and the corresponding carboxylic acid, imazamethabenz-acid (IMBA). The spectral characteristics are determined as functions of the pH. The appreciable absorbance in the visible (or near-ultraviolet) region of the spectra indicates that the natural photolytic degradation is possible. From variations of the maximum absorbances of the bands, the pK values of 3.4 ± 0.2 and 9.4 ± 0.2 were obtained for protonation of the imidazol (N−) nitrogen and dissociation of the NH imidazol nitrogen of IMBM, respectively. For IMBA, the dissociation pK of the carboxylic group is very close to that of the imidazol (N−) nitrogen, both being close to 3.3. The dissociation pK of the NH imidazol nitrogen for IMBA is 9.6 ± 0.2. The role of the acid−base reactions on the sorption on soils of these herbicides is discussed.