As super acid

The dehydration of 1-hexanol to hexene was conducted over heterogeneous sulfated zirconium oxide catalyst [19, 138]. The zirconia was treated with sulfuric acid and is known as super acid catalyst, having well documented performance for many reactions [19]. The reaction conditions are notably milder as for other acid catalysts, such as silica-alumina. 

Bronsted acids stronger than pure (100%) sulfuric acid Hq = —11.9) are classified as super acids [131, 132]. Thus, perchloric acid (HCIO4), fluorosulfonic acid (F—SO3H), and trifluoromethanesulfonic acid (CF3—SO3H) are considered as super acids. Even exceedingly weak basic solvents e.g. carbonyl compounds aromatic, ole-finic, and saturated hydrocarbons) are protonated by these super acids to give the corresponding carbocations [131]. 

Metal ions could play an important role in many electro transferring systems, which was frequently used as super acid catalyst and had directional function. Thus, metal ions were introduced into analogue enzyme model in order to increase its catalyzing efficiency. The earliest CD and metal complex was carboxypeptidase... 

Many metal ions are essential to living cells. They are Na, K, Mg, Ca, Mn, Fe, Co, Cu, Mo, Zn and constitute about 3% of the human body weight. Na(I), K(I), and Ca(II) are particularly important in the 30-called ion pump mechanism where active transport of metabolites and energetic processes are taking place. Transitions metals such as Zn(II) and Co(II) are found in various metalloenzymes where they coordinate with amino acids and enhance catalysis at the active site (214). They act as super acid catalysts having a... 

Super Lewis Acids. Acid systems stronger than anhydrous AlCl ate classified as super Lewis acids (211). By this definition, Lewis acids such as SbF, NbF, AsF, andTaF ate so categorized. 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

The aromatic ring has high electron density. As a result of this electron density, toluene behaves as a base, not only in aromatic ring substitution reactions but also in the formation of charge-transfer (tt) complexes and in the formation of complexes with super acids. In this regard, toluene is intermediate in reactivity between benzene and the xylenes, as illustrated in Table 2. 

The major disadvantage of the alkylation process is that acid is consumed in considerable quantities (up to 100 kg of acid per ton of product). Hence, solid acids have been explored extensively as alternatives. In particular, solid super acids such sulfated zirconia SO/ IZr02) show excellent activities for alkylation, but only for a short time, because the catalyst suffers from coke deposition due to oligomerization of alkenes. These catalysts are also extremely sensitive to water. 

The carbeniiun ion so formed then reacts in the ICC 1 manner except perhaps for not abstracting a hydride ion from another alkane. Although initial views that zeolites in general were super acids have come into question, definite super acids have been found such as calcined H2S04 Zr(0H)4 which catalyze the isomerization of alkanes at low T. 

However, an atom somewhat heavier than H might well be less susceptible to the perturbations that may disturb the latter as, for example, 13C which also generates an n.m.r. spectrum. Thus the 2-arylpropyl(cumyl) carbocations (56 produced from the corresponding tertiary alcohols in super acid —S02ClF/FS03H/SbF5— solution, cf. p. 181),... 

The first carbocation in this series - (cw-1,2-dimethylvinyl)-9,l 0-dimethyl-phenanthrenium ion (la) was formed as a result of rearrangement of 1,2,2a, 10b-tetramethyl-2a,10b-dihydrocyclobuta[/]phenanthrene (2) in super-acids (Scheme... 

Protonated amides and carboxylic acids have also been shown to activate adjacent electrophilic centers. Although protonated carboxylic acids and amides are not typically considered stable cationic groups, in superacidic media they can be readily generated and many have been observed by spectroscopic studies.16 As an example of electrophilic activation by a protonated carboxylic acid, P-phenylcinnamic acid (35) is diprotonated in super- acid to give the dication (36, observable by NMR) which then reacts with benzene and gives the indanone (37) in good yield (eq 12).17 It is known that the 1,1-diphenylethyl... 

A Some of the most interesting and informative experiments in this field were done by Pepper s group and then at Keele and elsewhere with anhydrous perchloric acid as the initiator. It is therefore historically important that in the present super-cautious, safety conscious era, few, if any, workers are ever likely to follow Pepper s pioneering work with this hazardous material, to test the reproducibility of these classical findings. The same applies of course to our studies on the polymerisation of various 1,3-dioxacycloalkanes, most of which were also done with anhydrous HC104, see Chapter 7. There is no substitute for it, as every acid behaves differently and in particular the lazy worker s substitute aq. HC104 + acetic anydride, is a very different initiator system. 

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