Superacids properties

Acid—Base Chemistry. Acetic acid dissociates in water, pK = 4.76 at 25°C. It is a mild acid which can be used for analysis of bases too weak to detect in water (26). It readily neutralizes the ordinary hydroxides of the alkaU metals and the alkaline earths to form the corresponding acetates. When the cmde material pyroligneous acid is neutralized with limestone or magnesia the commercial acetate of lime or acetate of magnesia is obtained (7). Acetic acid accepts protons only from the strongest acids such as nitric acid and sulfuric acid. Other acids exhibit very powerful, superacid properties in acetic acid solutions and are thus useful catalysts for esterifications of olefins and alcohols (27). Nitrations conducted in acetic acid solvent are effected because of the formation of the nitronium ion, NO Hexamethylenetetramine [100-97-0] may be nitrated in acetic acid solvent to yield the explosive cycl o trim ethyl en etrin itram in e [121 -82-4] also known as cyclonit or RDX. 

Hydrogen Fluoride-Trifluoromethanesulfonic Acid. The acidity of this binary Brpnsted acid system has not been measured, but the superacidic properties are mentioned in numerous patents concerning fluorination, olefin alkylation, and hydrocarbon conversion. 

The natural clay minerals are hydrous aluminum silicates with iron or magnesium replacing aluminum wholly or in part, and with alkali or alkaline earth metals present as essential constituents in some others. Their acidic properties and natural abundance have favored their use as catalysts for cracking of heavy petroleum fractions. With the exception of zeolites and some specially treated mixed oxides for which superacid properties have been claimed, the acidity as measured by the color changes of absorbed Hammett bases is generally far below the superacidity range. They are inactive for alkane isomerization and cracking below 100 °C and need co-acids to reach superacidity. 

III. ACIDIC AND SUPERACIDIC PROPERTIES OF TRICHLOROGERMANE A. Chemical Examples and Determinations... 

The superacidic properties of trichlorogermane are clearly manifested in the properties of its etherates (vide infra) and the ability of DGeCl3 to participate in a deuterium-hydrogen exchange reaction with methylbenzenes32 (Section VIII.E). 

The unusual superacidic properties of trichlorogermane are clearly manifested in its reactions with aromatic compounds. Here, the hydrogermylation of the aromatic nucleus is the basic pathway of the reaction between trichlorogermane and aromatic compounds. In many cases the reaction is accompanied by processes of protodegermylation, alkylation, trans-cis isomerization of the trichlorogermyl derivatives of cyclohexane and formation of some organic salts with GeCl3 counterion. 

We conclude that there is no evidence for WZ catalysts having superacidic properties or sites with the acidic character that would be necessary for initiation of catalysis by alkane protonation. In as much as WZ catalysts are some four orders of magnitude more active than zeolites for alkane isomerization,26 it is clear that there is no one-to-one correlation between acid strength of WZ and its catalytic activity. We therefore infer that although the acidity of WZ catalysts is important in alkane conversion catalysis, the reaction is most likely initiated by a reaction other than protonation of the alkane by the catalyst or a species formed from it. 

The method of incipient wetness has one major drawback, which is the destruction of structured support materials. Immobilisation on zeolites or MCM-41 leads to the decomposition of the carrier when a highly acidic ionic liquid is added directly. The reason for this seem to be superacidic properties of HCI in ionic liquids. Especially the MCM-41 materials, which are mesoporous aluminosilicates with a very high surface area, are interesting carrier materials. Alternatives to the method of incipient wetness have been developed and will be presented elsewhere. 

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