Organic reactions clay minerals

Birkel, U., Gerold, G., and Niemeyer, J. (2002). Abiotic reactions of organics on clay mineral surfaces. In Soil Mineral-Organic Matter-Microorganism Interactions and Ecosystem Health Dynamics, Mobility and Transformation of Pollutants and Nutrients. Violante, A., Huang, P. M., Bollag, J.-M. and Gianfreda, L., eds., Elsevier Science B.V., Amsterdam,The Netherlands, pp. 437 447. 

Solomon, D. H. (1968). Clay minerals as electron acceptors and/or electron donors in organic reactions. Clays Clay Miner. 16, 31-39. 

Because of their ubiquitous presence in natural materials and their strong surface reactions with cations and organic molecules, clay minerals are involved in many environmentally important phenomena (1). A nanoscale particle size with large specific surface area (ca. 750 m g ) is typical for clay minerals. Therefore, cation exchange and swelling processes occur readily, governed by the electrical double layer in the interlayers of the hydrated clay mineral. 

It is believed that clay minerals promote organic reactions via an acid catalysis [2a]. They are often activated by doping with transition metals to enrich the number of Lewis-acid sites by cationic exchange [4]. Alternative radical pathways have also been proposed [5] in agreement with the observation that clay-catalyzed Diels-Alder reactions are accelerated in the presence of radical sources [6], Montmorillonite K-10 doped with Fe(III) efficiently catalyzes the Diels-Alder reaction of cyclopentadiene (1) with methyl vinyl ketone at room temperature [7] (Table 4.1). In water the diastereoselectivity is higher than in organic media in the absence of clay the cycloaddition proceeds at a much slower rate. 

Carrizosa MJ, Hermosin MC, Koskinen WC, Cornejo J (2004) Interactions of two sulfonylurea herbicides with organoclays. Clays Clay Miner 52 643-649 Celis R, Hermosin MC, Cornejo J (2000) Heavy metal adsorption by functionalized clays. Environ Sci Technol 34 4593-4599 Chappell MA, Laird DA, Thompson ML, Li H, Teppen BJ, Johnston CT, Boyd SA (2005) Influence of smectite hydration and swelling on atrazine sorption behavior. Environ. Sci Technol 39 3150-3156 Chiou CT (1989) Theoretical considerations of the partition uptake of nonionic organic compounds by soil organic matter. In Sawhney BL, Brown K (eds) Reactions and movement of organic chemicals in soils. Soil Science Society of America, Madison, WI, pp 1-29... 

Zielke RC, Pinnavaia TJ, Mortland MM (1989) Adsorption and reactions of selected organic molecules on clay mineral surfaces. In Sawhney BL, Brown K (eds) Reactions and movement of organic chemicals in soils. Soil Science Society of America, Madison, WI, pp 81-97... 

The surfaces of clay minerals can catalyze the polymerization of organic compounds through a free radical-cationic initiation process. This type of reaction is believed to be initiated by the abstraction of an electron by Lewis acid sites on mineral surfaces however, Bronsted acidity has also been shown to be important in certain cases (see Chapter 22). 

Abiotic organic reactions, such as hydrolysis, elimination, substitution, redox, and polymerization reactions, can be influenced by surfaces of clay and primary minerals, and of metal oxides. This influence is due to adsorption of the reactants to surface Lewis and Br nsted sites. Temperature and moisture content are the most important environmental variables. Under ambient environmental temperatures, some reactions are extremely slow. However, even extremely slow transformation reactions may be important from environmental and geochemical viewpoints. 

The interest in mineral-promoted organic reactions stems from the need to understand the fate of pesticides in soils and pollutants in sedimentary environments (8), petrogenesis (20-27), humification (19, 28, 29), the origin and evolution of life (1, 30), the use of clays as catalysts in industrial processes (31-37), in pharmaceutical applications (3), and as pigments and fillers in paper, plastic, and rubber (37). 

Table II. Organic Reactions Affected by Surface Lewis-Acidity of Clay Minerals...

A heterogeneous natural system such as the subsurface contains a variety of solid surfaces and dissolved constituents that can catalyze transformation reactions of contaminants. In addition to catalytically induced oxidation of synthetic organic pollutants, which are enhanced mainly by the presence of clay minerals, transformation of metals and metalloids occurs with the presence of catalysts such as Mn-oxides and Fe-containing minerals. These species can alter transformation pathways and rates through phase partitioning and acid-base and metal catalysis. 

Clay minerals behave like Bronsted acids, donating protons, or as Lewis acids (Sect. 6.3), accepting electron pairs. Catalytic reactions on clay surfaces involve surface Bronsted and Lewis acidity and the hydrolysis of organic molecules, which is affected by the type of clay and the clay-saturating cation involved in the reaction. Dissociation of water molecules coordinated to surface, clay-bound cations contributes to the formation active protons, which is expressed as a Bronsted acidity. This process is affected by the clay hydration status, the polarizing power of the surface bond, and structural cations on mineral colloids (Mortland 1970, 1986). On the other hand, ions such as A1 and Fe, which are exposed at the edge of mineral clay coUoids, induce the formation of Lewis acidity (McBride 1994). 

Hassett IJ, Banwart WL (1989) The sorption of nonpolar organics by soils and sediments In Sawhney BL, Brown K. (eds) Reactions and movement of organic chemicals in soils Soil Science Society of America, Madison, Wl, pp 31 5p Hayes MHB, Malcom RL (2001) Considerations of compositions and aspects of the structure of humic substances. In Clapp CE, Hayes MHB, Senesi N, Bloom PR Jardine PM, Humic substances and chemical contaminants. Soil Science Society of America, Madison, Wl, pp 1-39 Herbillon AJ, Erankart R, Vielvoye L (1981) An occurrence of interstratified kaoUnite-smectite minerals in a red-black soil top sequence. Clay Miner 16 195-201 Horne RA (1969) Marine chemistry. Wiley, New York... 

Donors in Organic Reactions, in "Clays and Clay Minerals, Vol. 16, pp. 31-39, Pergamon, Oxford, 1968. 

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