Bronsted acid inorganic acids

At first sight, this may seem like a very simple question with a simple answer, yes. The problem is, of course, that many organic and inorganic ions are in chemical equilibrium with neutral species. Depending on the position of this equilibrium -and the latter is a function of temperature and pressure - even a pure ionic liquid may contain significant amounts of neutral molecules. Of course, this will greatly infiuence all properties of the substance. Volatility, viscosity, chemical reactivity etc. will greatly differ from the hypothetical mixture of the individual ions if free molecular species such as amines, phosphines, Bronsted-acids or acid esters form as neutral molecules in an equilibrium reaction under the conditions of the ionic liquid application. 

Cas/liquid reaction 28 [CL 28] Acid-base reaction between ammonia and Bronsted inorganic acids... 

Although the discussion to this point has been concerned with the explanation of the behavior of Bronsted acids as catalysts, there is an enormous range of reactions in which catalysis by acids and bases occurs. Many of the important types of organic reactions involve catalysis by acids or bases. In this section, several reactions will be mentioned, but the mechanistic details will not be presented in this book on inorganic chemistry. The discussion is intended to show the scope of catalysis by acids and bases. 

The abiotic hydrolysis of triazines in soil environments is catalyzed by acidic sites on the surfaces of both organic and inorganic soil constituents. The surfaces of soil constituents have both Lewis acid sites (which accept electron pairs) and Bronsted acid sites (which donate protons). However, triazines are not competitive with water and OH groups for complexation with Lewis acid sites, so in soil environments hydrolysis is catalyzed primarily by Bronsted acid sites. Four types of Bronsted acid sites are found on soil surfaces (Mortland, 1970) ... 

Low-temperature CO adsorption measurements indicate that the strength of Bronsted acid sites on reduced catalysts are lower than those characteristic of the oxidized catalyst.27 This finding is not unexpected, as it is well known that the acid strength of inorganic oxyacids depends on the oxidation state of the central atom.30... 

Polyoxometalates (POMs), also known as heteropolyacids (HPA),3 are a class of compounds formed from negatively charged inorganic metal-oxygen building blocks. When charge-balanced with cationic species, POMs self-assemble into unusual 3D structures with specific topological and electronic properties.214 POMs are commonly formed from polyanions of early transition metals such as W, Mo or V. These anions can be substituted with other transition metals. The diversities in POMs composition and structure make them attractive for many applications, particularly as Bronsted acid and redox catalysts. For example,... 

Such observations lead to the designation of reactions as acid- or base-catalyzed. When the catalysis is limited to the species H+ (or OH ), the reaction is spoken of as being subject to specific ion (or OH ion) catalysis. Many reactions of both organic and inorganic chemistry fit such a designation. However, very early work on such systems soon showed that the catalysis was not limited to or OH but did extend to other species which could be subsumed under the category of what are now called Bronsted acids and bases. 

Further variation of the stmctural and catalytic properties of four-coimected tetrahedral frameworks is obtained by the substitution of silicon or metal cations,giving materials known as SAPO s and MeAPO s, respectively. More than twenty metal aluminophosphate frameworks have been identified with Mg, Mn, Fe, Co, or Zn substituents. These give the possibility of framework redox activity (e.g. Fe +/Fe +) in catalysis as well as the usual Bronsted acidity. For further information about zeolitic and microporous phosphate frameworks see Porous Inorganic Materials and Zeolites) and recent reviews. ... 

Pillaring would be expected to inqrrove the Bronsted and Lewis acidity of the materials due to increasing the access to these sites within the layers. Pillaring with inorganic oxides has been examined. Alumina and chromium(III) oxide, for example, can be used as suitable props resulting in materials with good surfiice area, porosity and thermal stability 123-126 stability to 400°C have been reported. ... 

Drummond et al. [54] synthesized protic ionic liquids by combining Bronsted acid/base pairs where the primary amine cations were of the form RNH3 and R(OH) NH3 combined with organic anions of the form RCOO, R(OH)COO or with an inorganic anion. They studied physicochemical properties of synthesized PILs at nominally equimolar ratio of anion and cation (1 1 stoichiometry) and in the presence... 

The acidic properties of mesoporous molecular sieves rely on the presence of active sites in their framework. In the case of MCM-41 active sites are generated by the introduction of heteroatoms into the structure. In particular, Bronsted acid sites are introduced by isomorphous substitution of A1 for Si which is achieved by hydrothermal synthesis in which charged quaternary ammonium micelles are used as the template for charged alumino-silicate inorganic precursors. 

Hydroxyalkylations are catalyzed by Lewis-type acids, like AICI3, and by mineral Bronsted acids. Some papers and patents have appeared in recent years, where zeolitic materials are described as catalysts for this reaction [1-4,7]. Solid acid materials are highly desirable catalysts, since the environmental impact of the process benefits fi-om easier separation of the catalyst, the absence of liquid wastes containing inorganic salts, and less severe corrosion problems. 

The synthesized zeolite ZSM-35 disc was calcinated at 873k for 12 hours to remove ethylenediamine and water. Because inorganic ions Na", was not used in synthesis process, the synthesized zeolite ZSM-35 disc was a zeolite H-ZSM-35. The surface acidity of zeolite H-ZSM-35 was tested by pyridine adsorption IR. From the data in fig. 4, the synthesized zeolite H-ZSM-35 had Bronsted acid site at 1549 cm and Lewis acid site at 1443 cm [24]. Certainly, zeolite ZSM-35 disc from Al203-Si02-EDA-H20 had good acidity and would be a good acid catalyst. 

The present effort in many acid-catalyzed reactions with zeolites is to substitute inorganic Bronsted and Lewis acids by solid acids. The first step in the fine tuning of zeolite properties is usually the isomorphous substitution of metals other than AI into the zeolite framework. The modified product selectivity and conversion are due to the induced changes in the zeolite acidity. 

The use of homogeneous Bronsted and Lewis acids and bases was one of the main reasons for the production of high amounts of inorganic salts as byproducts in industrial syntheses. The ratio of mass unit by-product per mass unit of product is explained as an E-factor by Sheldon for several industry segments. For example, in the fine chemical industry and for the production of pharmaceuticals, sometimes 50-150 kg of by-products per kg desired product are formed. Therefore, new processes in the production of fine chemicals in order to reduce the high numbers of by-product formation are needed. 

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