Adsorption Mechanisms of Imazamethabenz-Methyl on Homoionic Montmorillonite

A. Pusino1, A. Gelsomino1 and C. Gessa2
1 Dipartimento di Agrochimica e Agrobiologia, Università di Reggio Calabria Piazza San Francesco di Sales 4, 89061 Gallina (RC), Italy
2 Istituto di Chimica Agraria, Università di Bologna Via Berti Pichat 11, 40127 Bologna, Italy

Abstract: The adsorption of the herbicide imazamethabenz-methyl, a mixture of the two isomers methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4-methylbenzoate (para isomer) and methyl (±)-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methylbenzoate (meta isomer), from water onto Al3+-, Fe3+-, Ca2+-, K+- and Na+-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 Fe3+- and Al3+-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 Ca2+-, K+- and Na+-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.

Key Words: Adsorption • Hydrolysis • Imazamethabenz-methyl • Infrared spectroscopy • Interlayer cations • Montmorillonite • Pesticides

Clays and Clay Minerals; June 1995 v. 43; no. 3; p. 346-352; DOI: 10.1346/CCMN.1995.0430309
© 1995, The Clay Minerals Society
Clay Minerals Society (www.clays.org)