Aluminum oxide reaction bonding

Many reactions are catalyzed by aluminum oxide, A1203, which is also known as alumina. In the solid, there are sites on the surface where a strongly acidic aluminum ion is available to bond to an electron pair donor. One such reaction involves the dehydration of alcohols to produce alkenes. This process can be represented as follows ... 

The reactions of the corresponding propargyl sulfoxides and sulfones now resemble the chemistry of the other acceptor-substituted derivatives such as ketones and aldehydes (see Section 1.2.4). Compared with the thioethers, here much milder bases are sufficient apart from aluminum oxide, often triethylamine or potassium carbonate are used. Sometimes even a spontaneous isomerization takes place. The selective isomerization of one triple bond in the presence of a second triple bond in 126 [313] (Scheme 1.56) or an allyl sulfone in 129 [314] (Scheme 1.57) are just two examples out of a whole series [178, 304, 313, 315-331]. When, on the other hand, the in situ oxidation of 126 was carried out in an aprotic solvent, no isomerization at all was observed. 

The above results show that post synthesis alumination of PSM with AlfNOjfi improves the hydrothermal stability of the resulting AMM material. Similar effect has been observed by Mokaya et al. [12], who reported that the hydrothermal stability of MCM-41 could be enhanced by reaction with chlorohydrate of aluminium. Moreover, from the study of high Si/Al ratio of Y zeolite, Lutz et al. [13] reported that the hydrothermal stability of Y zeolite was enhanced by an external introduction of non-structural aluminum species onto the surface of Y zeolite. The surface layer of Al-rich aluminosilicate or aluminum oxide was suggested to block the terminal OH groups and energy-rich =Si-0-Si= bonds on the surface of Y zeolite, hence minimizing the attack of water molecules on the framework. Due to these properties, the non-structural... 

Fig. 13.53. Mechanism of a Knoevenagel reaction with nitromethane. Alkaline aluminum oxide powder is sufficiently basic to deprotonate nitromethane. The small amount of the anion generated from nitromethane suffices for the addition to aldehydes to proceed. The elimination of water via an Elib mechanism follows quickly if a conjugated C=C double bond is formed, as in the present case.

Boer and co-workers examined the reaction of sterically hindered a-chloronitroso compounds with Me3Al [111]. The conspicuous reaction sequence is interpreted in terms of initial ring rupture, methane evolution and chlorine migration from carbon to aluminum intramolecular reaction of the carbon-carbon double bond with the rather electrophilic carbon atom from the nitrile oxide moiety leads to a seven-mem-bered ring with an exocyclic double bond as shown in Sch. 75. After hydrolysis, the corresponding oxime is obtained. 

ELECTRON SPIN RESONANCE SPECTROSCOPY Electron spin resonance (ESR) is a technique that can also be used on aqueous samples and has been used to study the adsorption of copper, manganese, and chromium on aluminum oxides and hydroxides. Copper(II) was found to adsorb specifically on amorphous alumina and microcrystalline gibbsite forming at least one Cu-O-Al bond (McBride, 1982 McBride et al., 1984). Manganese(II) adsorbed on amorphous aluminum hydroxide was present as a hydrated outer-sphere surface complex (Micera et al., 1986). Electron spin resonance combined with electron spin-echo experiments revealed that chromium(III) was adsorbed as an outer-sphere surface complex on hydrous alumina that gradually converted to an inner-sphere surface complex over 14 days of reaction time (Karthein et al., 1991). 

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