Clays ether formation

Acidic clays are widely applied in the dehydration of alcohols [38]. Although similar to zeolites in their capacity to induce the formation of both alkenes and ethers, selective alkene synthesis is possible. Various layered materials (clays, ion-exchanged montmorillonite, pillared layered clays) are very active and, in general, selective in transforming primary, secondary, and tertiary aliphatic alcohols to 1-alkenes [39-43]. Al -exchanged montmorillonite, however, induces ether formation from primary alcohols and 2-propanol [41]. Substituted 1-phenyl-1-ethanols yield the corresponding styrene derivatives at high temperature (653-673 K) [44]. 

In the presence of Japanese acid clay ethanol decomposes mainly into ether at 200° C. with formation of only traces of aldehyde and ester. At 300° to 400° C. ethylene is the main product, alcohol and ether being almost absent in the liquid product which comprises 92-96 per cent water.470 With a clay catalyst, Hisamura47b has obtained a yield of ethylene of 83 per cent in a product that was 98 per cent pure ethylene at 400° C. 

Selectivity in the dehydration of olefins is improved with pillared clays. Clays with aluminum oxide or mixed aluminum and iron oxide pillars converted isopropyl alcohol to propylene with more than 90% selectivity.256 A small amount of isopropyl ether was formed. When zeolite Y is used, the two products are formed in roughly equal amounts. A tantalum-pillared montmorillonite converted 1-butanol to butenes at 500°C with 100% selectivity at 41% conversion.257 The product contained a 17 20 16 mixture of 1 -butene/c/s-2-butene/fra/ s-2-butene. No butyraldehyde or butyl ether was formed. A pillared clay has been used for the alkylation of benzene with 1-dodecene without formation of dialkylated products.258 The carbonylation of styrene proceeded in 100% yield (6.50).259... 

The alkoxyalkylation reaction of carbonyl compounds can be considered as an orientated cross-aldol condensation between two masked carbonyl compounds, an acetal and a silyl enol ether. The key step involves the formation of an electrophilic species by reaction of the acetal with catalytic amounts of a Lewis acid and the right catalyst can lead to excellent diastereo- and enantio-selectivities. Clays are satisfactory catalysts in these reactions, with the acid-treated clay K10 performing better than the more powerfully acidic clay KSF,... 

Layer Inclusion-compounds In this type of complex formation, the layer structure of the host is made use of. Certain clays, such as montmorillonite and halloysite, have a sandwich or layer structure that will readily include organic compounds of a polar nature. Alcohols, ethers, nitriles and amines are among the guests included by these clays. The layer width may vary, depending upon the compound included. Ionic attraction and van der Waals forces are involved in this type of inclusion. 

Metal-exchanged KIO clays were studied as catalysts in the acylation of benzo crown ethers 36 with AC (Scheme 4.25). The best catalyst is SnKlO, which affords product 37 in 90% yield after 1 h. The activity of SnKlO is about three times higher than that of clayfen. Product 37 is accompanied by a minor by-product ( 5%) due to the opening of the polyether ring followed by O-acetylation. The cafalysf acfivify is lowered upon recycling. The redox mechanism depicfed in Scheme 4.26 can represenf an alternative pathway for the formation of an acyl cation fhaf can accounf for the high activity of SnKlO. 

The Claisen rearrangement of substituted allyl phenyl ethers in benzene solution to 2-allylphenols has been effected by montmorillonite clays employed in equal weight to the reactant (ref. 12). A short reaction time at ambient temperature favours the allylphenol but longer period at a higher temperature results in formation of a chroman or, exceptionally, a coumaran. 

Acid-catalyzed organic reactions by using clays continue to attract attention, and many reports on acetalization have appeared. The formation of C-glycosides by the reaction of glycals with enol silyl ethers, acetates, and allylsilanes is efficient (53-97%). ... 

Thermoset polymers like polyimide, crosslinked sulfonated poly(ether ether ketone) and polyacrylate can be used for membrane applications. The presence of nanoparticle nucleates the nanopore formation with the assistance of an agent. The nanopore is responsible for the solvent separation and transportation. Membranes such as solvent filters, filters for bacteria and virus, and membrane for gas separation can be developed using clay-polymer nanocomposites [118-119]. 

An interesting comparison of catalytic activities of synthetic beidellite and montmorillonite and PILCS prepared from them was recently reported [69]. The reactions examined included secondary amine formation from cyclohexylamine, ester production from 1-hexene and acetic acid and ether synthesis from pentanol. In all cases, the reactivity of the PILCS was much lower than that of the unpillared clays, whereas the montmorillonite was generally more effective than the beidellite. These results are not surprising in that all of the reactions are Br<(Jnsted-acid-catalyzed and the observed decreased activity of the PILCS may derive from a greater loss of protons to the layers by the pillared clays. This is also in keeping with the findings of Occelli and Tindwa [5] that the PILCS are mainly Lewis acids after heat treatment. 

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