Montmorillonite

Montmorillonite clay's are layered silicates and are among the numerous inorganic supports for reagents used in organic synthesis. They can be used as an efficient and versatile catalyst for various organic reactions. In Montmorillonite clay one octahedral aluminate layer is sandwiched between two octahedral silicat layers. These are non-toxic, non-corrosive, economical and recyclable. In Montmorillonite clay both Brønsted and Lewis acidic catalytic sites are available, hence its natural occurrence as well as its ion exchange properties allow it to function efficiently as a catalyst. The interlayer cations are exchangeable, thus allowing alteration of the acidic nature of the material by simple ion-exchange procedure. In recent years Montmorillonite particularly Montmorillonite K-10 emerges as an efficient acidic catalyst in organic chemistry. This can be prepared by calcination of Montmorillonite. Montmorillonites are modified by simple cation exchange process to give more effective Montmorillonites such as Fe⁺ Montmorillonite, clayfen, claycop. Most of the nitrates are deposited on K 10, i.e. Iron (II) nitrate-K 10, Montmorillonite clay and copper (II) nitrate K 10 Bentonite clay. These are used in oxidation and nitration reactions. K 10 is sometimes misunderstood by name or its uses with other clay based acidic catalysts (KSF, K10F, H⁺-exchanged Montmorillonite, clay). The activation of K 10 clay is carried out by thermal activation. Its acidic character is enhanced by cation exchange, i.e. by Fe (II), Zn (II) or by deposition of Lewis acids such as Zn (II) or Iron (III) chlorides. Recent reports on K 10 focus on some important reaction and various transformations. K 10 is used as catalyst in the synthesis of dimethyl acetals, enamines, γ-lactones, enolthioethers, α,β-unsaturated aldehydes and porphyrin synthesis etc.