AL-143 Mineral Adsorbents, Filter Agents and Drying Agents
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VI. MONTMORILLONITES AND OTHER MINERAL ADSORBENTS

An extensive series of catalysts has been prepared by the chemical processing of the mineral montmorillonite (Al₂O₃•4SiO₂•xH₂0),³one of the major components of bentonite and Fuller’s earth.

Characterized by high catalytic activity, these products have shown the ability to promote reactions that usually require Brönsted or Lewis acid catalysis. Advantages include easy handling, chemical inertness (noncorrosiveness) and high economy.

A. Applications

In 1980, Professor Pierre Laszlo introduced a versatile catalyst for heterogeneous organic reactions termed clayfen [K 10/ Fe(NO₃)₃], consisting of iron(III) nitrate dispersed on K 10 clay.⁴ The catalyst is prepared⁵ by thorough mixing of an acetone solution of Fe(NO₃)•9H₂O with the clay followed by solvent removal on a rotary evaporator at 50°C. Note that, in a recent review,⁶ Laszlo points out that prolonged heating or bath temperatures > 50°C in the preparation of the catalyst can lead to an unstable reagent which decomposes in a vigorous exothermic reaction. Furthermore, clayfen should be used freshly prepared and never stored in closed containers.⁶

Applications of the catalysts include oxidation of alcohols⁴ and thiols,⁷ oxidative cleavage of thioacetals⁸ and N, N-dimethylhydrazones,⁹ conversion of hydrazines to azides,¹⁰ nitration,¹¹ Diels-Alder catalysis,^12,13 dehydration, esterifications, synthesis of enamines and selective halogenations.

^aml/g at nm range by CCI₄
^bml/g at nm range, Hg porosimeter