Heteropolyacid compounds

It was concluded from chemical and physicochemical studies that the anions of these heteropolyacid compounds consist of phosphate ions and ions of octavanadic acid HaofVsQBS aq.) in varying molecular ratios [G. Jander and K. F. Jahr, Kollold-Beihefte 324 (1935)]. Other authors obtained compoxmds which they classify as salts of a 12-vanadic-l-phosphoric acid HrlPVisOae aq.] [A. Rosenheim and M. Pieck, Z. anorg. allg. Chem. 98, 223 (1916) P. Souchay and S. Dubois, Ann. Chimie (12) 3, 88 (1948)]. 

The brownish-red heteropolyacid compounds of this class, rich in vanadic acid, are designated in the older literature as purpureophosphovanadates. ... 

Heteropolyadd compounds. Some anions react with molybdate and other ions in solution, yielding heteropolyacids of definite chemical composition. These heteropolyacid compounds are then usually extracted into an organic phase. The metal of the compound is determined by AAS either in the organic phase or in aqueous solution after back-extraction. 

Isopropanol was used as a probe molecule to characterize the acidity of heteropolyacid compounds because the product s distribution upon reaction depends on the nature of the surface active sites. Strong Brdnsted (H ) and Lewis acid sites catalyze the dehydration of isopropanol to propylene (di-isopropyl ether over weak Lewis acid sites), and redox/basic sites lead to the dehydrogenation of the alcohol to acetone. 

The scientific interests of Anatoly K. Babko ranged widely, especially in regard to fundamental aspects of analytical chemistry, applications of organic reagents in inorganic analysis, chemistry of complex compounds (including heteropolyacids), analytical applications of complex compounds in photometry, luminescence and chemiluminescence, ion chromatography, and liquid-liquid extraction. 

Heteropolyacids (HPA) are the unique class of inorganic complexes. They are widely used in different areas of science in biochemistry for the precipitation of albumens and alkaloids, in medicine as anticarcinogenic agents, in industry as catalysts. HPA are well known analytical reagents for determination of phosphoms, silica and arsenic, nitrogen-containing organic compounds, oxidants and reductants in solution etc. 

Although platinum is the metal of choice for PEM fuel cell cathodes, Paul Matter, Elizabeth Biddinger, and Umit Ozkan (Ohio State University) show that nonprecious metals will have to be developed for this type of fuel cell to become practical and widely used. Although few materials have the electrochemical properties needed to replace platinum, this review discusses candidates such as macrocycle compounds, non-marcrocyclic pyrolyzed carbons, conducting polymers, chalcogen-ides, and heteropolyacids. 

Two types of insoluble triarylcarbonium compounds are used industrially as pigments. Both are salts of these basic dyes. So-called Alkali Blue type triarylcarbonium pigments are inner salts of sulfonic acids, while the second group comprises salts of complex inorganic anions of heteropolyacids. 

Reducing agents, such as zinc dust or sodium dithionite, convert heteropolyacids into deeply colored blue compounds consisting of heteropolyacids with four hydrogen atoms to be substituted. This makes it possible to precipitate more dye with the same heteropolyacid to produce an insoluble pigment. 

The present study focused on the structure elucidation of heteropolyacid salts named Zirconium Antimonoarsanotungstate Zr[SbAsW] salt synthesised at variable pH using sol-gel route. Instrumental technique, IR was used to assign the structural aspects to the compound. Physical characterisation... 

Heterogenous reactions, Sh/Nu ratio, 27 64 Heteroligand complex, 32 260-262 Heteropolyacids defined, 41 117 heteroatoms, 41 118, 120, 121 Prins reaction, 41 156 supported, 41 149-150 Heteropolyanions, 41 113, 117, 119-121 Heteropoly blues, 41 191 Heteropoly compounds absorption, 41 179-180, 190-191 acid-catalyzed reactions heterogeneous, 41 161-178 liquid phase, 41 150-161 acidic properties in solid state, 41 141-150 in solution, 41 139—14] catalysis, 41 114, 116-117, 190-191 as catalyst, 41 113-116, 117, 223-232... 

Prins reaction, heteropolyacid catalysis, 41 156 Probe molecules, 42 119 acidic dissociation constant, 38 210 NMR solid acidity studies, 42 139-140 acylium ions, 42 139, 160 aldehydes, 42 162-163 alkyl carbenium ions, 42 154-157 allyl cation, 42 143-144 ammonia, 42 172-174 arenium ions, 42 150-154 carbonium ions, 42 157-160 chalcogenenonium ions, 42 161-162 cyclopentenyl cations, 42 140-143 indanyl cations, 42 144-147 ketones, 42 162,163-165 nitrogen-containing compounds, 42 165-170... 

Heteropolyacids and related compounds have attracted increasing interest in catalysis owing too their ability to catalyze both acidic and red-ox processes. 

Heteropolyacids are frequently used to modify proton-conducting composites,or they are just dispersed in inert matrixes.However, because the proton conduction mechanism of such hydrated salts is similar to those of hydrated polymeric sys-tems, these composites show qualitatively similar transport properties. The same is true for organically modified inorganic layered compounds such as titanium phosphate sulfophenylenphosphonate, the conductivity of which is dependent on the RH value, in a manner similar to that observed with Nafion. ... 

In this section, these influences will be described. Besides the acidic properties, the absorption properties of solid heteropolyacids for polar molecules are often critical in determining the catalytic function in pseudoliquid phase behavior. This is a new concept in heterogeneous catalysis by inorganic materials and is described separately in Section VI. With this behavior, reactions catalyzed by solid heteropoly compounds can be classified into three types surface type, bulk type I, and bulk type II (Sections VII and IX). Softness of the heteropolyanion is important for high catalytic activity, although the concept has not yet been sufficiently clarified. 

Similar types of nucleophilic substitutions have also been carried out when PIFA is activated by two equivalents of Lewis acids such as trimethylsilyl triflu-oromethanesulfonate (TMSOTf) and BF3 Et20 or heteropolyacid in standard solvents such as CH2C12 and MeCN. These reactions were applied to intramolecular reactions by the same authors leading to biaryls (49) [54-57], quinone imine derivatives (50) [58], and dihydrobenzothiophens (51) [59], which are important structures of bioactive natural products [Eqs. (7)-(9)]. Dominguez and co-workers have expanded the above biaryl coupling reaction to the syntheses of benzo[c]phenanthridine system (52) [60] and heterobiaryl compounds (53) [61] [Eqs. (10,11)]. 

Supported hcteropoly compounds, where heteropoly compounds are dispersed on the surface of porous solids, are important for applications, since the surface area of heteropolyacids is usually low. The structure, stabil-... 

The solid superacids of the second group which have a possibility of leaching or evaporating of halogen compounds seem to be environmentally undesirable as catalysts. These superacids and Nafion-H have been extensively reviewed [1-5]. H-ZSM-5 and heteropolyacids are discussed in Sections 2.3.3 and 2.1.7 of this handbook, respectively. Therefore, the superacids of the first group for which many papers have been contributed recently and the industrial application of which is promising, are mainly described here and the other superacids are dealt with only briefly. 

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,... 

In the literature (and here) the term "polyoxometalate" (POM) is used exchangeable with the term "heteropoly compounds" or heteropolyacids - abbreviated as HPA. 

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