Sulfonic acid support/activator

The new sulfonic acid support/activator was synthesized by the ring-opening reaction of a fluorinated sultone with an SBA-15 silica surface (Fig. 20.4). 

Resorcinol Derivatives. Aminophenols (qv) are important intermediates for the syntheses of dyes or active molecules for agrochemistry and pharmacy. Syntheses have been described involving resorcinol reacting with amines (91). For these reactions, a number of catalysts have been used / -toluene sulfonic acid (92), zinc chloride (93), zeoHtes and clays (94), and oxides supported on siUca (95). In particular, catalysts performing the condensation of ammonia with resorcinol have been described gadolinium oxide on siUca (96), nickel, or zinc phosphates (97), and iron phosphate (98). 

The ion pair mechanism initially suggested by Darwish and McLaren28 (equation 2) has received further support from related studies conducted by several other investigators38-42. For example, Fava and coworkers38 have reported that during isomerization in acetic acid, optically active benzhydryl p-toluenesulfmate loses optical activity at a rate which is about two and a half times faster than the rate of sulfone formation, thus indicating that return from an ion-pair species is occurring (equation 3). 

Polymer supported persulfonic acids can be prepared by treating polymer-bound sulfonic acids with H2O2 or K2S20g. The resulting resin was found to display an activity of 2.5 mole equivalents per gram of wet resin. This persulfonated resin was successively applied for the oxidation of carboxylic acids, ketones, olefins and for the cleavage of disulfide linkage and of A-formylamino acids. 

Spontaneous polymerization of 4-vinyl pyridine in the presence of polyacids was one of the earliest cases of template polymerization studied. Vinyl pyridine polymerizes without an additional initiator in the presence of both low molecular weight acids and polyacids such as poly(acrylic acid), poly(methacrylic acid), polyCvinyl phosphonic acid), or poly(styrene sulfonic acid). The polyacids, in comparison with low molecular weight acids, support much higher initial rates of polymerization and lead to different kinetic equations. The authors suggested that the reaction was initiated by zwitterions. The chain reaction mechanism includes anion addition to activated double bonds of quaternary salt molecules of 4-vinylpyridine, then propagation in the activated center, and termination of the growing center by protonization. The proposed structure of the product, obtained in the case of poly(acrylic acid), used as a template is ... 

Fig. 6. Polymer-supported IBX (resin 5) can be activated and recycled with monoperoxy sulfonic acid (Caro s acid). The polymer reagent is capable of alcohol oxidations, dehydrogenations, and radical cyclization reactions.

Saturation of a carbohydrate double bond is almost always carried out by catalytic hydrogenation over a noble metal. The reaction takes place at the surface of the metal catalyst that absorbs both hydrogen and the organic molecule. The metal is often deposited onto a support, typically charcoal. Palladium is by far the most commonly used metal for catalytic hydrogenation of olefins. In special cases, more active (and more expensive) platinum and rhodium catalysts can also be used [154]. All these noble metal catalysts are deactivated by sulfur, except when sulfur is in the highest oxidation state (sulfuric and sulfonic acids/esters). The lower oxidation state sulfur compounds are almost always catalytic poisons for the metal catalyst and even minute traces may inhibit the hydrogenation very strongly [154]. Sometimes Raney nickel can... 

As previously mentioned, one of the primary motivations for the development of site-isolated aminosilicas is to construct a better molecular-level understanding of immobilized catalysts through the use of a more uniformly reactive surface. Within the area of a-olefin polymerizations, another parameter that negatively affects the ability to study well-defined surfaces is the use of methylaluminoxane (MAO) as a catalyst activator. The exact structure of the MAO species has been postulated to exist in a number of different forms, which makes it difficult to elucidate the exact nature of its interactions with the surface [21]. To address this issue, a well-defined sulfonic acid organic/inorganic hybrid material was developed to serve as both a support and a catalyst activator for homogeneous a-olefin polymerization catalysts [22]. 

With differences in activity between crystal faces of only a factor of five or less for oxygen reduction in perchloric acid, the particle models of Kinoshita indicate that there would be little or no crystallite size effect for the ORR in a nonadsorbing acid, such as trifluoromethane sulfonic acid or closely related derivatives [44]. In KOH, because the (111) face is the most active, an increase in activity with the smallest particles (e.g., 1 nm)—ideally (uniform size, perfect geometry) would be predicted by the Vt hkl) data—would be by about a factor of five. With real catalysts, where all particles are neither uniformly sized nor perfectly facetted, the effect might be much less, perhaps only a factor of two or so. Unfortunately, we do not know of any studies of crystallite size effects for supported Pt catalysts in either KOH or... 

The vapor-phase nitration of benzene with NO2 was investigated by Suzuki et al. using polyorganosiloxanes bearing sulfonic acid groups and silica-supported benzenesulfonic acid catalysts [31]. Phenylsulfonic polysiloxane was the most active among the polysiloxanes tested, its activity was not related to the concentration of acid sites as determined by a titration method, however. From the partial pressure dependence of the reaction rate it was concluded that the formation of NO as the active species was the rate-limiting step [32]. 

The liquid composition of Nafion , approximately 5 wt% solution, was used to coat the calcined shot coke (10-20 mesh, 0.42m /gram). Loadings were varied up to 3 wt%. The oligomerization of isobutylene in toluene at 110°C was used to measure the activity of the sulfonic acid catalysts. Table 4 compares the activity of several supported and non-supported sulfonic acid polymers. The... 

In the recent drive to prepare mesoporous solid acid catalysts for liquid phase processes, a popular approach has been to tether sulfonic acid groups to mesoporous silica supports. The preferred method for functionalising has been to incorporate 3-mercaptopropylsilane in the synthesis gel for the mesoporous silica, and then, after precipitation and isolation, to oxidise the thiol group to sulfonic acid. These materials have exhibited relatively high catalytic activity and the approach is emerging as one of the most successful for preparing acid forms of porous silica. 

The objective of the present work is to discover whether the same sort of acidity/activity enhancements seen for polymer-supported sulfonic acids can be obtained on more rigid inorganic supports. Acid strengths of the two types of catalyst have been measured in both the absence of solvent as molar enthalpies of ammonia adsorption, and in the presence of water through molar enthalpies of neutralisation with aqueous NaOH solution. Catalytic activities have been measured in water for the hydrolysis of ethylethanoate. 

The results show clearly that, in the presence of water, the acid catalytic activity of supported sulfonic acid groups is essentially the same on polymer and silica supports, except where the level of polymer sulfonation is high, when the sulfonic acid exhibits significantly enhanced activity. The trend in molar enthalpies of neutralisation with aqueous NaOH is similar. On silica supports, and polymer supports with low sulfonic acid concentrations, these enthalpies are very similar to those of strong mineral acid solutions. In contrast, resins with high levels of sulfonation show significantly higher molar enthalpies of neutralisation. 

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