NOTES INTERACTIONS OF MONTMORILLONITE WITH p-NITRO- AND p-METHOXYANILINES

Clay minerals are known to interact with a wide variety of organic molecules by adsorption, intercala-tion, cation exchange, and catalysis. In soil science and environmental engineering these interactions should be better known in order to describe and predict the transport of organic compounds through soil. Studies on the binding and transformation f well-defined or-ganic compounds on pure clay minerals can provide models for interpreting the behavior of organic ma-terials in soil. However, additional variables must be considered when dealing with the natural environment in soil. Among the clay minerals, montmorillonite (smectite) is an important component of many soils and shows interesting behavior in clay-organic inter-actions because it has unusual intercalation properties that afford opportunities to catalyze a wide variety of organic reactions (Ortego et al., 1991). Aniline and its substituted erivatives are compo-nents of numerous herbicides and many pesticides. They can be readily liberated by partial degradation to free aromatic amines in soil environments. In partic-ular, nitroanilines are residues of herbicides bound as butralin (Helling and Krivonak, 1978), trifluralin (Sei-beret al., 1975; Golab et al., 1979), and benefin (Golab et al., 1970). Interactions of organic compounds with montmo-rillonite depend on the composition and the structure of the organic molecules and the kinds of metal cations located on exchange sites of clay. Therefore, it seemed interesting for us to study the interactions ofp-nitroan-iline and p-methoxyaniline with montmorillonite as a function of different exchangeable cations. EXPERIMENTAL The organic reagents (p-nitroaniline and p-meth-oxyaniline) were analytical-grade chemicals from Al-drich and were used without further purification. The solvents (n-hexane and methanol) were HPLC-grade from Aldrich. Cu 2+-, Fe 3.- and A13+-montmorillonites w re pre-pared by suspending 10g of K- 10 montmorillonite (from Aldrich) in 300 ml of freshly-prepared aqueous olu-tions of the metal chlorides (2 • 10 2 mol liter ~) and stirring for 24 hours. The particular ion-exchange