Adsorption mechanisms of imazamethabenz-methyl on homoionic montmorillonite
Adsorption mechanisms of imazamethabenz-methyl on homoionic montmorillonite
Clays and Clay Minerals (June 1995) 43 (3): 346-352
- adsorption
- alcohols
- cation exchange capacity
- chemical properties
- clay mineralogy
- clay minerals
- experimental studies
- hydrolysis
- infrared spectra
- mechanism
- methanol
- montmorillonite
- organic compounds
- pesticides
- physicochemical properties
- pollutants
- pollution
- sheet silicates
- silicates
- soils
- spectra
- imazamethabenz-methyl
The adsorption of the herbicide imazamethabenz-methyl, a mixture of the two isomers methyl (+ or -)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4-methylbenzoate (para isomer) and methyl (+ or -)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methylbenzoate (meta isomer), from water onto Al (super 3+) -, Fe (super 3+) -, Ca (super 2+) -, K (super +) - and Na (super +) -montmorillonite was studied by analytical (HPLC) methods. The adsorption from an organic solvent was also investigated by spectroscopic (IR) and X-ray diffraction measurements. It was observed that, depending on the acidic properties of the exchangeable cations, two different mechanisms may take place. The first one, acting on Fe (super 3+) - and Al (super 3+) -clays, involves the protonation of the more basic nitrogen atom ofimidazolinone ring of the herbicide because of a proton transfer from the acidic metal-bound water, followed by adsorption on the clay surfaces. In this case, the clay surfaces have greater affinity for the meta than the para isomer, due to the extra-stabilization of the meta protonated form by resonance. The second mechanism, taking place on Ca (super 2+) -, K (super +) - and Na (super +) -clays, is hydrogen-bond formation between the ester carbonyl group of the herbicide and hydration water metal ions and is not affected by the structure of the isomers.