Montmorillonite-asulam interactions: I. Catalytic decomposition of asulam adsorbed on H- and Al-Clay

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Abstract
The adsorption of the Asulam herbicide (4-aminobenzensulphonyl-methyl-carbamate) by Al- and H-montmorillonite has been studied by IR spectroscopy, thin layer chromatography and chemical analysis. This compound is adsorbed from CCl4solution at room temperature through protonation of the NH2functional group by the ‘acidic’ water coordinated to the interlayer cation of the clay. After heating the complex at 75°C for 20 h, a hydrogen-bond between the C=O group of the Asulam and the water is established and the organic molecule decomposes to sulphanilic and carbamic acids. If the complex is equilibrated at 100% relative humidity, the carbamic acid becomes unstable, and the IR spectrum shows only the bands typical of the acidic montmorillonite-sulphanilic acid complex. The catalytic properties of the clay surface are demonstrated by comparison with the transformations occuring in the organic molecule on heating in concentrated mineral acids.

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