Oxides heteropoly acids

In addition to CuCfi, some other compounds such as Cu(OAc)2, Cu(N03)2-FeCl.i, dichromate, HNO3, potassium peroxodisulfate, and Mn02 are used as oxidants of Pd(0). Also heteropoly acid salts comtaining P, Mo, V, Si, and Ge are used with PdS04 as the redox system[2]. Organic oxidants such as benzo-quinone (BQ), hydrogen peroxide and some organic peroxides are used for oxidation. Alkyl nitrites are unique oxidants which are used in some industrial... 

Acetoxybenzene is prepared by the reaction of benzene with Pd(OAc)2[325,342-345], This reaction is regarded as a potentially useful method for phenol production from benzene, if carried out with only a catalytic amount of Pd(OAc)2. Extensive studies have been carried out on this reaction in order to achieve a high catalytic turnover. In addition to oxygen and Cu(II) salts, other oxidants, such as HNOi, nitrate[346,347], potassium peroxodisulfate[348], and heteropoly acids[349,3S0], are used. HNO is said to... 

In a biotechnology-based approach, Japanese workers have reported on the microbial conversion of 2-methylnaphthalene to both 2-methyl-1-naphthol and menadione by Jiodococcus (64). The intermediate 2-methyl-1-naphthol can readily be converted to menadione by a variety of oxidizing agents such as heteropoly acids (65) and copper chloride (66). A review of reagents for oxidizing 2-methylnaphthalene and naphthol is available (67). 

Under microwave irradiation and applying MCM-41-immobilized nano-iron oxide higher activity is observed [148]. In this case also, primary aliphatic alcohols could be oxidized. The TON for the selective oxidation of 1-octanol to 1-octanal reached to 46 with 99% selectivity. Hou and coworkers reported in 2006 an iron coordination polymer [Fe(fcz)2Cl2]-2CH30H with fez = l-(2,4-difluorophenyl)-l,l-bis[(l//-l,2,4-triazol-l-yl)methyl]ethanol which catalyzed the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as oxidant in 87% yield and up to 100% selectivity [149]. An alternative approach is based on the use of heteropoly acids, whereby the incorporation of vanadium and iron into a molybdo-phosphoric acid catalyst led to high yields for the oxidation of various alcohols (up to 94%) with molecular oxygen [150]. 

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Melting a mixture of germanium dioxide and metal oxides produces ortho-and metagermanates of the corresponding metals. Aqueous solutions of ger-manate react with molyhdic and tungstic acids forming heteropoly acids of varying compositions. 

Heteropoly acid, tungstate-based, 496, 497 Hexacoordinate silyl peroxides, 808-10 , -Hexa-2,4-diene, photooxidation, 254-5 Hexamethyldisiloxane, oxidation, 806-7 Hexamethylene triperoxide diamine (HMTD) enthalpy of formation, 166 explosive, 707-8... 

Studies with sulfated zirconia also show similar fast catalyst deactivation in the alkylation of isobutane with butenes. It was found, however, that original activities were easily restored by thermal treatment under air without the loss of selectivity to trimethylpentanes. Promoting metals such as Fe, Mn, and Pt did not have a marked effect on the reaction.362,363 Heteropoly acids supported on various oxides have the same characteristics as sulfated zirconia.364 Wells-Dawson heteropoly acids supported on silica show high selectivity for the formation of trimethylpentanes and can be regenerated with 03 at low temperature (125°C).365... 

An important drawback of the original Wacker process is the highly corrosive nature of the aqueous acidic PdCl2—CuCl2 system. Attempts were made to apply electrochemical reoxidation of palladium,513,514 and to use other oxidants,495 such as Fe(III) salts, Mn02, quinones,514-516 peroxides,517,518 and more recently, heteropoly acids.516,519"522... 

Highly selective formation of phenyl acetate was observed in the oxidation of benzene with palladium promoted by heteropoly acids.694 Lead tatraacetate, in contrast, usually produces acetoxylated aromatics in low yields due to side reac-tions. Electrochemical acetoxylation of benzene and its derivatives and alkoxylation of polycyclic aromatics789 790 are also possible. Thermal or photochemical decomposition of diacyl peroxides, when carried out in the presence of polycyclic aromatic compounds, results in ring acyloxylation.688 The less reactive... 

In new studies heteropoly acids as cocatalysts were found to be very effective in combination with oxygen in the oxidation of ethylene.1311 Addition of phosphomo-lybdic acid to a chloride ion-free Pd(II)-Cu(II) catalyst system results in a great increase in catalytic activity and selectivity.1312 Aerobic oxidation of terminal alkenes to methy ketones can be performed with Pd(OAc)21313 or soluble palladium complexes. Modified cyclodextrins accelerates reaction rates and enhance selectivities in two-phase systems under mild conditions.1315 1316... 

Methyl chloride and methanol are similarly formed in oxidation of methane with air with the Pt(IV)-Pt(II) pair in the presence of a heteropoly acid (120°C, 60-100 atm).223 The reaction is catalytic with respect to both platinum and the... 

In addition to large-scale industrial applications, solid acids, such as amorphous silica-alumina, zeolites, heteropoly acids, and sulfated zirconia, are also versatile catalysts in various hydrocarbon transformations. Zeolites are useful catalysts in fine-chemical production (Friedel-Crafts reactions, heterosubstitution).165-168 Heteropoly compounds have already found industrial application in Japan, for example, in the manufacture of butanols through the hydration of butenes.169 These are water tolerant, versatile solid-phase catalysts and may be used in both acidic and oxidation processes, and operate as bifunctional catalysts in combination with noble metals.158,170-174 Sulfated zirconia and its modified versions are promising candidates for industrial processes if the problem of deactivation/reactivation is solved.175-178... 

This compound is considered to be a complex salt of a heteropoly-acid formed from stannic oxide and vanadium pentoxide, and it is therefore comparable with the vanadoselenites and vanadotellurites.2... 

Y. Ishii and M. Ogawa, in Hydrogen Peroxide Oxidation Catalyzed by Heteropoly Acids Combined with Cetylpyridinium Chloride, Vol. 3, MYU, Tokyo, 1990, p. 121. 

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