Ion exchangers clays

The oxidative coupling of thiols catalyzed by Fem-exchanged montmorillonite in phosphate buffer (pH 7.2) has also been demonstrated (Scheme 3.48) [151]. This system gives the corresponding disulfide as the sole product, which is in contrast to a previous report [152], where oxidation of thiols catalyzed by ion-exchanged clay gave the sulfide as the major product. 

Intercalation of poly(ethylene oxide) into a lithium-ion exchanged clay gives an interesting class of layered silicate nanocomposites that are lithium-ion electrolytes. Componnds have been prepared by intercalation from methanol/water solutions and by melt intercalation. Melt intercalation typically gives samples with higher polymer contents than the solution method and with higher lithium-ion conductivity though the conductivity is probably stiU too low for practical applications. 

Use Ion-exchange clay-soil stabilizer, binder, and sealer (laboratory scale only). 

Cations based on substituted silsesquioxanes have also been intercalated [7]. On heating the ion-exchanged clay minerals water is evolved, but oxycation or oxide pillars keep the siliceous layers apart. These materials have enhanced thermal stability compared with clay minerals expanded with organic cations. Expanded clay minerals cover at least as wide a range of accessibilities to the interlamellar micropore spaces as the zeolites, but the pore characteristics of clay minerals with inorganic pillars need more detailed investigation. 

The Diels-Alder reaction has been shown to be subject to catalysis by a wide range of solid catalysts (see Chapter 4 for some examples). Acidic mesoporous aluminosilicates can be used to catalyse selective Diels-Alder reactions such as that between cyclopentadiene with methyl acrylate. The zinc-exchanged version of the material is particularly effective and compares well to other more established solid acids such as the ion-exchanged clay Zn2+-K10 as well as homogeneous catalysts such as boron trifluoride (Table 2.7).50... 

Many papers have been published on the catalytic activity of ion-exchanged clays. Ballantine et al. refluxed hex-l-ene with a Cu2+-exchanged montmor-illonite and produced a branched chain symmetrical ether (Reaction 3).21 The clay acted both as a Bronsted acid catalyst as well as providing water molecules for the reaction. 

Thanks to their low cost and easy availability, many metal-exchanged clays have been patented as efficient solid catalysts in Friedel-Crafts acylation reactions. A great number of arylketones is prepared by electrophilic acylation of arenes with anhydrides in the presence of ion-exchanged clays at 150°C-250°C. Thus, for example, aluminum-enriched mica promotes the reaction of BAN with mcto-xylene at reflux for 4 h in 99% yield. 

In 1999, an attempt was made to synthesize a polyolefin in clay gallery. Specifically, clay was ion-exchanged using tetradecylammonium ions, and this ion-exchanged clay and a paUadium-based complex of the Brookhart-type were mixed and conditioned in toluene to polymerize ethylene. The interlayer distance was initially 1.99 nm. This increased to 2.76 nm after a palladium catalyst was added. It was confirmed that the X-ray peak disappeared 24 hours after ethylene was introduced [40]. 

Potassium is abundant in all animal and plant cells. It is the most common intracellular ion in animal cells. It is therefore widespread in most foodstuffs [8] and potassium deficiency in animals from dietary causes is rare [9] in the absence of disease, malnutrition, or unusual dietary practices [10]. Anorectics [11], alcoholics, and those who consume significant quantities of ion-exchanging clays may show hypokalemia. 

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