Stoichiometric metal oxidants

The results mentioned together with data outlined in Section 1.11 indicate that adsorption induced change in electric conductivity of sintered and partially reduced oxide is mostly dependent on adsorption related change in concentration of stoichiometric metal atoms which are responsible for dope electric conductivity rather than by charging of the surface of adsorbent due to transformation of radicals of O2 and O". 

More recently, the direct synthesis of methanol from methane, using metallic gold as catalyst, was reported, involving a purported CH3-Au intermediate. Selenic acid was used as a stoichiometric oxidant as it is known to oxidize gold metal. Moderate turnovers (30) were achieved (Equation (6)).14... 

SEGPHOS [271, 272]. Using this complex as a precatalyst, transfer hydrogenation of 1,1-dimethylallene in the presence of diverse aldehydes mediated by isopropanol delivers products of ferf-prenylation in good to excellent yield and with excellent levels of enantioselectivity. In the absence of isopropanol, enantio-selective carbonyl reverse prenylation is achieved directly from the alcohol oxidation level to furnish an equivalent set of adducts. Notably, enantioselective ferf-prenylation is achieved under mild conditions (30-50°C) in the absence of stoichiometric metallic reagents. Indeed, for reactions conducted from the alcohol oxidation level, stoichiometric byproducts are completely absent (Scheme 13). 

An Alternative Approach Anaerobic Oxidation with Metal Oxides in a Cycle Process (from an Oxidation Catalyst to a Reusable Stoichiometric Oxidant)... 

Both stoichiometric and catalytic reactions of allylic compounds via 7r-allyl complexes are known. Reactions of nucleophilic 71-allyl complexes with electrophiles involve oxidation of metals and hence constitutes stoichiometric reactions. 7i-Allyl complexes of Ni, Fe, Mo, Co and others are nucleophilic and undergo the stoichiometric reaction with electrophiles. However, electrophilic 71-allyl complexes react with nucleophiles, accompanying reduction of metals. For example, 71-allylnickel chloride (2) reacts with electrophiles such as aldehydes, generating Ni(II), and hence the reaction is stoichiometric. In contrast, electrophilic 7i-allylpalladium chloride (3) reacts with nucleophiles such as malonate and Pd(0) is generated. Thus repeated oxidative addition of allylic compounds to Pd(0) constitutes a catalytic reaction. 

The optimum combination of a tripropellant system is predictable through the systematic variation of the concentration of each of the propellants. The weight ratio of the oxidizer and metal components are always in stoichiometric proportion to produce the metal oxide or metal halide. The low molecular weight species is then added in an amount determined by the trade-off between decreasing molecular weight and decreasing temperature of the combustion products. The results of such calculations are reported in the literature (47). 

Trying to get the material by means of CaH2 treatment of oxide and metal mixtures we can say that long-term isothermic exposures and slow cooling process, in case of any deviation of chemical composition from stoichiometric one (La 32,13 %,wt), will result in appearances of second phases (La2Ni7 or Ni)... 

Another major drawback is that metals must be used in excess of the necessary stoichiometric amount because it is impossible to know how much of the metal sample is contaminated with metal oxide and metal hydroxide covering the surface after contact with air. Then excess metal must be destroyed very slowly by addition of absolute ethanol with the most extreme care, otherwise fire subsequent to reaction will occur almost systematically upon contact with air or water. Metals freshly cut into pieces are particularly reactive. Even more reactive are the metallic sands obtained by heating pieces of the metal above its melting point in a suitable solvent, e.g. dry toluene, and the metallic mirrors formed by subliming a piece of metal (Na or more often K) from the bottom of a Schlenk flask on to its walls imder vacuum. THE and DME are the solvents most often used for reductions with these metals, for example ... 

Fig. 7.7 The correlation between the dehydrogenation/dehydration ratio of ethanol on stoichiometric metal oxide single-crystal surfaces and the difference of Madelung potentials, which...

Non-stoichiometric oxides may contain either an excess of metal (e.g. zinc oxide, Zni+jO) or a deficiency of metal (e.g. nickel oxide, Ni,.jO). Some metal oxides (e.g. titanium oxide) may be prepared as either excess-metal or metal-deficit oxides. Excess metal is incorporated in the structure as interstitial cations together with the electrons removed through ionization. In metal-deficit or excess-oxygen oxides, excess oxygen is incorporated in the structure by formation of cation vacancies and positive holes, which may be achieved by oxidation of cations, e.g. 

Many studies have been intentionally concerned with relatively simple rate processes to minimize stoichiometric problems. However, even relatively simple reactions do not always give a single product, for example barium azide has been reported to give about 70% BajNj together with the metal [26]. The extensively studied decompositions of oxalates require that the identity of the residual solid be identified, for each constituent cation, as either carbonate, oxide or metal, together with any change of cation valency. The chemistry of oxalate breakdown can, however, be much more complicate as has been shown for the Y, Eu and Yb salts [27]. 

In this chapter, reagents are classihed mainly into three categories (1) for catalytic oxidation of phenols, (2) for phenolic oxidation with nonmetallic compounds and (3) for phenohc oxidation with metallic compounds. In the 21st century, regardless of metallic or nonmetallic compounds, catalytic oxidation systems with high efficiency must be constructed. K stoichiometric amounts of reagents are employed, efficient oxidation-reduction systems should be invented. 

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