Adsorption and Degradation of Fenarimol on Montmorillonite

Abstract

The importance of the non-biochemical reactions in decomposing organic molecules adsorbed on clay surfaces has been emphasized in recent years (Mortland, 1970;Theng, 1974;Crosby, 1976). The nature of the interlayer exchangeable cation is one of the most important factors in the adsorption and transformation of the organic molecules on the clay surface. The higher the charge, the greater is the polarizing effect of the cation on coordinated water molecules which promotes their dissociation and leads to an increase in surface acidity. Moreover, on heating, as the water content decreases, polarization forces become more concentrated on the fewer remaining water molecules causing an increase in hydrolysis and in their proton donating abilities (Farmer and Mortland, 1%6;Mortland and Raman, 1968).The formation of carbonium ions has been demonstrated when triphenylcarbinol is adsorbed on montmorillonite surface. These ions result from the acidity present in the interlayers of the montmorillonite (Fripiat et al., 1964;Helsen, 1970;Helsen et al., 1975). Once adsorbed, this compound transforms into its respective carbonium ions (Ph3-C +) by heating at 100~ as a consequence of the reaction with proton from the solvation water of the exchange cations. Rehydration results in the formation of the triphenylcarbinol.The transformation of the fungicide Fenarimol adsorbed on montmorillonite saturated with different cations was investigated to ascertain whether the substitution of a pyrimidine for a benzene ring affects the nature of the reaction products. EXPERIMENTAL MaterialsHomoionic montmorillonites were prepared from <2-tzm equivalent spherical diameter fraction of a bentonite from Upton, Wyoming, by treatment with I N solutions ofAICl3, CaCIz, BaCI~, MgCI2, CuClz, KCI, and NaCI. The excess salt was eliminated by repeated washings until a test for C1-was negative.The Fenarimol [c~-(2-chlorophenyl)-t~-(4-chlorophenyl)-5-pyrimidinemethanol] was supplied by Elanco (Italy). The melting point of the pure compound (99.8%) was I 18 ~ I 19~ Infrared (IR) analysisThe IR spectrum of the Fenarimol was recorded in a KBr disk. The adsorption of the product on the clay surface was achieved by immersing self-supporting films of the clay in a saturated solution of Fenarimol in CC14. These films were washed with CC14 and air dried. IR spectra of the Fenarimolclay systems were recorded at room temperature on a Model 283B Perkin-Elmer spectrophotometer from: (1) the original sample, (2) the sample after heating at 100~ for 8 hr, (3) sample (2) after equilibration at I00% RH for 5 hr, (4) sample (3) after heating at 100~ for 30 hr, and (5) sample (4) after equilibration at 100% RH for 5 hr. Ultraviolet (UV) analysisUltraviolet spectra of the films of the Fenarimol-clay complexes were recorded on a Model DB-GT Beckman spectrophotometer by placing a pure clay film in the reference beam and wetting the sample with Nujol to avoid scattering. Thin-layer chromatographyFixed amounts of the Fenarimol-clay complexes (original, heated, and humidified) we...

Interactions between Small Organic Chemicals and Soil Colloidal Constituents

“…Weiss, 1969;Theng, 1974Theng, , 1982Rupert et al, 1987;RausseII-Colom and Serratosa, 1987) and Table 11.6 provides a brief resume of so me of the studies of organic reactions catalyzed by clays. et al (1978) montmorillonitic soil day weaker catalysts Lahav et al (1978) Weakest catalyst is montmoril-Solomon and Rosser (1965) lonite Fusi et al" (1983) ;:- Discussions in Section 12.3, and 11.4.1 emphasize the important role of the exchangeable inorganic cations in the binding of organic moleeules at clay surfaces. However, the nature of the clay surface, as weIl as the inorganic cation is important for the transformations which take place.…”

“…The unstable carbocation structures can then act as intermediates in subsequent transformations. Carbocation formation is likely to arise from protonation of the olefinic bonds with protons arizing from dissociation of the solvation water of the exchangeable cations (Fusi et al, 1983). Carbocation formation by surface protons can catalyse (and in some cases inhibit) oligomerization and polymerization reactions (Theng, 1974.…”