Types of Solid Acid

The solid acids utilized for carbonless paper must meet the following requirements  

Both organic and inorganic solid acids are used. As organic acids, Bronsted acids such as condensed compounds of /Mira-substituted phenol with formaldehyde,and Lewis acids such as zinc salts of the above compounds and those of aromatic carboxyl acids are used. As inorganic acids, montmorillonite clays such as bentonite, fuller s earth, kaoline, chinaclay, and their chemically modified materials are used. 

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With this purpose, several different types of solid acid catalysts have been investigated for the acylation of aromatics, but the best performances have been obtained with medium-pore and large-pore zeolites (3-9). In general, however, the use of acylating agents other then halides, e.g., anhydrides or acids, is limited to the transformation of aromatic substrates highly activated towards electrophilic substitution. In a previous work (10), we investigated the benzoylation of resorcinol (1,3-dihydroxybenzene), catalyzed by acid clays. It was found that the reaction mechanism consists of the direct 0-benzoylation with formation of resorcinol monobenzoate, while no primary formation of the product of C-benzoylation (2,4-dihydroxybenzophenone) occurred. The latter product formed exclusively by... 

K Tanabe Solid Acid and Base Catalysts This chapter deals with the types of solid acids and bases, the acidic and basic properties, and the structure ofacidic and basic sites. The chemical principles of the determination of acid-base properties and the mechanism for the generation of acidity and basicity are also described. Howacidid and basic properties are controlled chemically is discussed in connection with the preparation method of solid acids and bases. 

Bentonite, whose main ingredient is montmorillonite, is one kind of layer structure clay mineral. It is an ideal material for preparation of pillared clays. If metal cations with high catalytic activity were intercalated in the interlayers of montmorillonite, a new type of solid acid catalyst can be obtained. The catalytic activity of the catalyst is closely associated with its porosity, specific surface area and surface total acidity. One of the effective ways to enhance catalytic activity is to prepare catalyst with appropriate metal cations and structure. 

The most widely used conventional chemical methods are pyrolysis [21-25] and catalytic cracking [13, 26-30], The latter yields products with a smaller range of carbon numbers and of a higher quality than products generated by the former method. Several types of solid acid catalysts, which are known to be effective for catalytic cracking (e.g. HZSM-5, HY and rare earth metal-exchanged Y-type (REY) zeolite and silica-alumina (SA)) were evaluated by catalyst screening tests and are listed in Table 6.1. The acidic... 

Not only do these acids present an economic advantage over conventional acid technology, but there are also frequent selectivity eidiancements and changes in reactivity associated with the use of these heterogeneous catalysts. A number of different types of solid acids have been involved in synthetically useful reactions. They range from the hydrogen forms of various ion exchange resins and the perflourinated resin sulfonic acid, Nafion-H, to the amorphous acidic oxides, silica and aluminum silicate,the crystalline zeolites > and the natural clays. -9... 

Many types of solid acid and base catalysts are known.11 Superacids are those that are at least as strong as 100% sulfuric acid.12 The acid strengths are measured using basic indicators and are assigned a Hammett acidity function, H0- Table 6.1 lists some superacids, with the strongest at the top. 

Of the solid electrophilic catalysts an acidic clay [13] and alumina were applied in the early history of the pinacol rearrangement. The last two decades, with the development of a variety of new classes of solid acid has, however, brought an upsurge in research activity. Almost all types of solid acid have been tested and found to have high catalytic activity in the transformation of vicinal diols, although selectivity is not always satisfactory. 

A general introduction to the subject is followed by a discussion of basic principles regarding types of catalyst and their preparation and characterization and types of catalytic reactors. Chapter 3 deals with the different types of solid acids. In the following chapters (4-6) various (solid) acid-catalyzed transforma-... 

Many types of solid acids, such as MCM-41 (21), Cs2 5H0.5PW12O40 (23), H+-ZSM-5 (24), M +-mont (25,26), and 864 /Zr02 (27) have been reported to promote acylation by carboxylic acids both in liquid and gas phases. 

Many of the d-block elements form characteristically colored solutions in water. For example, although solid copper(II) chloride is brown and copper(II) bromide is black, their aqueous solutions are both light blue. The blue color is due to the hydrated copper(II) ions, [Cu(H20)fJ2+, that form when the solids dissolve. As the formula suggests, these hydrated ions have a specific composition they also have definite shapes and properties. They can be regarded as the outcome of a reaction in which the water molecules act as Lewis bases (electron pair donors, Section 10.2) and the Cu2+ ion acts as a Lewis acid (an electron pair acceptor). This type of Lewis acid-base reaction is characteristic of many cations of d-block elements. 

Fig. 14.—Schematic Representation of the Fragmentation Observed in the Positive F.a.b.-Mass Spectrum of a Permethylated Ganglioside Isolated from Granulocytes. [Other glyco-sphingolipids fragment in a similar way. Major cleavages are shown with solid lines, and minor cleavages with dotted lines. The masses of ions resulting from cleavages (a), (b), and (c) define the type of sphingosine and the type of fatty acid. In this example, (a) is 548, (b) is [M + H] minus 238, and (c) is [M + H] minus 533.]...

Parallel Synthesis We start the reaction by using two sets of building blocks, amines (A) and carboxylic acids (B). The amines are first attached to solid supports, normally polystyrene beads coated with linking groups, in separate reaction vessels for each amine. After the amines have been attached, excess unreacted amines are washed off. Next, the carboxylic acids are added to the amines to form the desired amides. We illustrate these steps in Fig. 3.8. Assuming there are 8 amines to react with 12 carboxylic acids in a 96-well plate with 8 rows and 12 columns of tiny wells, the amines, A1 to A8, are added across the rows to each well containing the polystyrene beads. Different types of carboxylic acids, B1 to B12, are added to the wells in each column. 

Although the specific role of each type of center (acid or base) in each process (dehydration-dehydrogenation) is still only incompletely elucidated, many authors have correlated the initial rates of dehydration and dehydrogenation with the acidity and basicity, respectively, of the solid. Thus, the number of basic sites has been correlated with the rate constants for dehydrogenation or with the ratio of the rate constants for dehydrogenation and dehydration (74,80,89,90,94). 

Many types of solid catalysts have been tested in esterification and transesterification reactions of fatty acids, TG feedstock and simple esters. Nonetheless, it is possible to group most catalysts in three general categories metal, base, and acid catalysts. The following sections deal with these three groups accordingly. 

These sulfuric acid particles become less concentrated as the temperature decreases or the water vapour increases. Under very cold stratospheric conditions, these liquid aerosols may take up water and HNO, forming ternary solutions H,S0/HN0,/H,0, which eventually freeze [19,24,26], Below 192 K, HNO, becomes the dominant condensed acid, and H,S04 drops to below 3 wt %. The thermodynamics and freezing nucleation of ice and H,S04 or HNO, hydrates from such solutions are however not well understood [27,28]. Other types of solid particles, such as the less stable nitric acid dihydrate (NAD, HN0,.2H,0) [29], sulfriric acid tetrahydrate (SAT, H S04.4H,0) [18,30], sulphuric acid hemihexahydrate (SAH, H2S04.6.5H20) [18], nitric acid penta-hydrate (NAP, HN03.5H,0) [31] and more complex sulfuric acid/nitric acid mixed hydrates [32] may also be a key to understanding Type IPSC nucleation and evolution [28],... 

We would expect peculiarities (1) and (2) to be also inherent in carbenium-ion-type intermediates of other reactions (such as the cracking, alkylation, and isomerization of hydrocarbons) occurring in the pores of solid acid catalysts. 

The acidic sites of solid acids may be of either the Brpnsted (proton donor, often OH group) or Lewis type (electron acceptor). Both types have been identified by IR studies of solid surfaces using the pyridine adsorption method. The absorption band at 1460 cm 1 is assigned to pyridine coordinated with the Lewis acid site, and another absorption at 1540 cm 1 is attributed to the pyridinium ion resulting from the protonation of pyridine by the Brpnsted acid sites. Various solids displaying acidic properties, whose acidities can be enhanced to the superacidity range, are listed in Table 2.6. 

The enhanced diffusivity of polynuclear compounds in sc C02 has been utilized to enhance catalyst lifetimes in both 1-butene/isoparaffin alkylations (Clark and Subramaniam, 1998 Gao et al., 1996). The former may be catalyzed using a number of solid acid catalysts (zeolites, sulfated zeolites, etc.), and the use of sc C02 as a solvent/diluent permits the alkylations to be carried out at relatively mild temperatures, leading to the increased production of valuable trimethylpentanes (which are used as high-octane gasoline blending components). The enhancement of product selectivity in the latter process is believed to result from rapid diffusion of ethylbenzene product away from the Y-type zeolite catalysts, thus preventing product isomerization to xylenes. 

This review summarizes the recent works on syntheses of solid superacids and their catalytic action, including Lewis acids and liquid superacids in the solid state, as discussed in Sections Il-IV. Sections VI and VII describe new types of solid superacids we have studied in this decade sulfate-supported metal oxides and tungsten or molybdenum oxide supported on zirconia. Perfluorinated sulfonic acid, based on the acid form of DuPont s Nafion brand ion membrane resin, is also gaining interest as a solid superacid catalyst Nafion-H-catalyzed reactions are reviewed in Section V. 

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