Metal sulfates reactions catalyzed

Tanabe el al. studied in detail the catalytic action and properties of metal sulfates most of the sulfates showed the maximum acidity and activity by calcination at temperatures below 500°C, with respect to the surface acidity and the acid-catalyzed reaction (118, 119). Other acid-catalyzed reactions were studied with the FeS04 catalyst together with measurement of the surface acidity of the catalyst the substance calcined at 700°C showed the maximum acidity at Ho s 1.5 and proved to be the most active for the polymerization of isobutyl vinyl ether, the isomerization of d-limonene oxide, and the dehydration of 2-propanol (120-122). It is of interest that the catalyst calcined at a slightly higher temperature, 750°C, was completely inactive and zero in acidity in spite of the remarkable activity and acidity when heat treated at 700°C. 

In 1950, Walling (I) discovered that the solid surface of some metal sulfates changes the color of Hammett indicators, suggesting a new series of solid acids, but did not consider their usage as a possible catalyst. In 1957, Tanabe et al. 2,3) were able to affirm that the solid acidity of the metal sulfates is an intrinsic one, not arising firom any impurities, and they found that it increased remarkably on heat treatment, attained a maximum value, and then decreased at higher temperatures. Since then, many of the metal sulfates heat-treated at optimum temperatures have been used as solid catalysts for various acid-catalyzed reactions. Among those reactions are the depolymerization of paraldehyde, the polymerization of propylene and of aldehydes, the hydration of propylene, the formation of formaldehyde from methylene chloride,... 

The measurement of the acidic property of metal sulfates is a prerequisite for the investigation of their catalytic activity, since many reactions are known to exhibit strong dependence on the acid strength and the acidity of the acid catalyst. These properties have an important bearing on what type of reactions will be catalyzed by metal sulfates. 

Since the metal sulfate catalyst has both Bronsted and Lewis acid sites, it is expected that many n bases with nonbonding electrons such as —O— and —Cl and tt bases hke olefin will undergo acid-base equilibria, thus initiating carbonium ion or carbonium ion-like reactions. Table II summarizes the acid- catalyzed reactions on metal sulfate catalysts and shows the versatility of these systems. Although this table includes some examples of industrial work, our results and others clearly show the general trend in the strength of acid sites required for each specific reaction. But detailed discussion of correlation between the catalytic activity and the acidic property is reserved for the next section. 

Before we discuss characteristic features of a metal sulfate catalyst, it is to be noted that the model reaction should be one which has as straightforward a mechanism as possible, preferably in a homogeneously catalyzed reaction. This is the only way we can critically evaluate the efficiency of the present solid catalyst system. The depolymerization of paraldehyde was most extensively studied in view of the foregoing criterion. For the homogeneous acid catalysis of the depolymerization of paraldehyde, there are ample data given by Bell and his associates in nonaqueous solvent (by proton acid as well as Lewis acid) and also in aqueous solution (55,56). Since most Hammett indicators change their color when adsorbed on the surface acids of both Bronsted and Lewis type, it is fortunate that this depolymerization proceeds easily by acids of both types. Evidently the dotted line in Fig. 2 shows excellent... 

We have attempted to present an integrated picture on the acid property of solid metal sulfates as used in various heterogeneously catalyzed reactions, with some view presented on the surface structure. We saw some unusual catalytic activity and selectivity exhibited by these solid sulfates in diversified reactions which may surpass in some aspects those of a more universal catalyst represented by silica-alumina and its related oxides. 

Reaction (22.21) is the key step in the process, but it occurs very slowly unless catalyzed. The principal catalyst is V2O5 mixed with alkali metal sulfates. The catalysis involves adsorption of the 802(g) and 02(g) on the catalyst, followed by reaction at active sites and desorption of 8O3. 

Complexes of DMAC and many inorganic haHdes have been reported (20). These complexes are of iaterest because they catalyze a number of organic reactions. Complexes of DMAC and such heavy metal salts as NiBr2 exert a greater catalytic activity than the simple salts (21). The crystalline complex of SO and dimethylacetamide has been suggested for moderating the reaction conditions ia sulfation of leuco vat dyestuffs (22). 

A review by Brandt and van Eldik provides insight into the basic kinetic features and mechanistic details of transition metal-catalyzed autoxidation reactions of sulfur(IV) species on the basis of literature data reported up to the early 1990s (78). Earlier results confirmed that these reactions may occur via non-radical, radical and combinations of non-radical and radical mechanisms. More recent studies have shown evidence mainly for the radical mechanisms, although a non-radical, two-electron decomposition was reported for the HgSC>3 complex recently (79). The possiblity of various redox paths combined with protolytic and complex-formation reactions are the sources of manifest complexity in the kinetic characteristics of these systems. Nevertheless, the predominant sulfur containing product is always the sulfate ion. In spite of extensive studies on this topic for well over a century, important aspects of the mechanisms remain to be clarified and the interpretation of some of the reactions is still controversial. Recent studies were... 

While the Lewis acid-catalyzed aldol reactions in aqueous solvents described above are catalyzed smoothly by several metal salts, a certain amount of an organic solvent such as THF had still to be combined with water to promote the reactions efficiently. This requirement is probably because most substrates are not soluble in water. To avoid the use of the organic solvents, we have developed a new reaction system in which metal triflates catalyze aldol reactions in water with the aid of a small amount of a surfactant, such as sodium dodecyl sulfate (SDS). 

Moreover, the efficiency of these catalysts could be modihed by tailoring the nature of the metal oxide support and/or reaction conditions (especially the reaction temperature). In this way, interesting conclusions can be obtained when comparing the isobutane/2-butene alkylation catalyzed on two of the most studied catalysts, that is, beta zeolite and sulfated zirconia, when operating at different reaction temperatures. (Table 13.2). ... 

Isomerization of olefins or paraffins is an acid-catalyzed reaction that can be carried out with any number of strong acids, including mineral acids, sulfated metal oxides, zeolites and precious metal-modified catalysts [10]. Often the catalyst contains both an acid function and a metal function. The two most prevalent catalysts are Pt/chlorided AI2O3 and Pt-loaded zeolites. The power of zeoHtes in this reaction type is due to their shape selectivity [11] and decreased sensitivity to water or other oxygenates versus AICI3. It is possible to control the selectivity of the reaction to the desired product by using a zeoHte with the proper characteristics [12]. These reactions are covered in more detail in Chapter 14. 

Reaction with amorphous silicon at 900°C, catalyzed by steam produces cadmium orthosilicate, Cd2Si04. The same product also is obtained by reaction with sdica. Finely divided oxide reacts with dimethyl sulfate forming cadmium sulfate. Cadmium oxide, upon rapid heating with oxides of many other metals, such as iron, molybdenum, tungsten, titanium, tantalum, niobium, antimony, and arsenic, forms mixed oxides. For example, rapid heating with ferric oxide at 750°C produces cadmium ferrite, CdFe204 ... 

Oxidation to Phenols. Direct hydroxylation of benzene to phenol can be achieved in a free-radical process with H202 or 02 as oxidants.739-744 Metal ions [Fe(II), Cu(II), Ti(HI)] may be used to catalyze oxidation with H202. Of these reactions, the so-called Fenton-type oxidation is the most widely studied process.742 Oxidation in the presence of iron(II) sulfate was reported in early studies to yield phenol. Since phenol exhibits higher reactivity than benzene, varying amounts of isomeric dihydroxybenzenes were also formed. 

The cyclopropanation of alkenes, alkynes, and aromatic compounds by carbenoids generated in the metal-catalyzed decomposition of diazo ketones has found widespread use as a method for carbon-carbon bond construction for many years, and intramolecular applications of these reactions have provided a useful cyclization strategy. Historically, copper metal, cuprous chloride, cupric sulfate, and other copper salts were used most commonly as catalysts for such reactions however, the superior catalytic activity of rhodium(ll) acetate dimer has recently become well-established.3 This commercially available rhodium salt exhibits high catalytic activity for the decomposition of diazo ketones even at very low catalyst substrate ratios (< 1%) and is less capricious than the old copper catalysts. We recommend the use of rhodium(ll) acetate dimer in preference to copper catalysts in all diazo ketone decomposition reactions. The present synthesis describes a typical cyclization procedure. 

The reaction is catalyzed by divalent heavy metal ions, especially by Cu2+ and Co2+. It follows zeroth order, so it is independent of the concentration of the reactants Na2S03 and 02( ) but only depends on the rate of mass transfer. The remaining sulfite is oxidized to sulfate by the addition of iodine and the iodide generated is back-titrated with thiosulfate [Eqs. (8.37), (8.38)]. 

Cyclic sulfates provide a useful alternative to epoxides now that it is viable to produce a chiral diol from an alkene. These cyclic compounds are prepared by reaction of the diol with thionyl chloride, followed by ruthenium-catalyzed oxidation of the sulfur (Scheme 9.26).166 This oxidation has the advantage over previous procedures because it only uses a small amount of the transition metal catalyst.167168... 

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