Precursors metal salts

Both its solubility and any potential side reaction with reductant dictate the choice of precursor metal salt or complex. In many cases the reductant is an aluminium alkyl or electropositive metal (Goups 1,2, 12 or 13, possibly amalgamated with mercury), requiring the use of anhydrous metal salts or complexes. Carbonyls of higher nuclearity are... 

Catalysts All catalysts prepared contained 0.3% Pt, 0.6% Re and 1.0% Cl. The precursor metallic salts used were H2PtCl6 and NH4Re04. A y-Al203 (180 mVg) was used as support. Monometallic catalysts with the same composition were prepared as reference materials. Bimetallic catalysts were prepared according to the following methods ... 

The inclusion of metallic particles can be done in two different ways. The first one consists in carrying out the metal deposition during the electropolymerization process in a solution containing both the monomer and the precursor metallic salt. This leads to a dispersion of the metallic particles inside the polymer layer, but, all these particles are not accessible for the electrocatalytic reaction. The second way is to electro-deposit the metal after the electropolymerization process. This electrodeposition can be carried out at a fixed potential, at a constant current or during continuous potential cycling. 

Inorganic precursors Metal salts Metal alkoxides... 

Instead of precursor metal salts, metal oxides could also be used. Silver-PS coreshell particles were thus recently synthesized using a two-step procedure [346]. First, hydrogen reduction of a saturated silver(I) oxide solution at elevated temperature was carried out in the presence of commercial sulfate-functionalized PS particles (200 nm) used as support for the reduction of Ag salt into silver. The formed Ag nanoparticles were attached to the PS particles (Fig. 42a). Subsequent acetone treatment led to the encapsulation of the silver nanoparticles inside the PS spheres (Fig. 42b), accompanied by a red-shift of the characteristic plasmon resonance frequency of the particles (Fig. 42c). 

There are two types of precursors inorganic precursors (metal salts) or metal-organic (alkoxide) precursors. It is not the aim of this chapter to give an overview on all materials made by sol-gel processing, but instead to discuss the chemistry of the precursors, including ways to influence their reactivity, and the basic chemistry of sol-gel processes. 

Another preparation method for gradient array is gel-transfer eleetrodeposition, whieh was developed by Hiller and coworkers. This method involves the controlled diffusion of precursor metal salts into a hydrated gel from spatially distinct locations, followed by an eleetrodeposition to create a surface composition gradient. As illustrated in Figure 12.2(a), a ternary catalyst gradient was created by diffusing precursor metal salts, from three different locations, into a... 

The first step in designing a precursor synthesis is to pick precursor molecules that, when combined in organic solvents, yield the bulk crystalline solid. For metals, a usual approach is to react metal salts with reducing agents to produce bulk metals. The main challenge is to find appropriate metal salts that are soluble in an organic phase. 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Overview. Three approaches are used to make most sol—gel products method 1 involves gelation of a dispersion of colloidal particles method 2 employs hydrolysis and polycondensation of alkoxide or metal salts precursors followed by supercritical drying of gels and method 3 involves hydrolysis and polycondensation of alkoxide precursors followed by aging and drying under ambient atmospheres. 

These complexes can be isolated in some cases in others they are generated in situ from appropriate precursors, of which diazo compounds are among the most important. These compounds, including CH2N2 and other diazoalkanes, react with metals or metal salts (copper, palladium, and rhodium are most commonly used) to give the carbene complexes that add CRR to double bonds. Ethyl a-diazoacetate reacts with styrene in the presence of bis(ferrocenyl) bis(imine), for example, to give ethyl 2-phenylcyclopropane-l-carboxylate. Optically active complexes have... 

The field of surface-mediated synthesis of metal carbonyl clusters has developed briskly in recent years [4-6], although many organometallic chemists still seem to be unfamiliar with the methods or consider themselves ill-equipped to carry them out. In a typical synthesis, a metal salt or an organometallic precursor is brought from solution or the gas phase onto a high-area porous metal oxide, and then gas-phase reactants are brought in contact with the sample to cause conversion of the surface species into the desired products. In these syntheses, characteristics such as the acid-base properties of the support influence fhe chemisfry, much as a solvenf or coreactant influences fhe chemisfry in a convenfional synfhesis. An advanfage of... 

Addition of such a-lithiosulfinyl carbanions to aldehydes could proceed with asymmetric induction at the newly formed carbinol functionality. One study of this process, including variation of solvent, reaction temperature, base used for deprotonation, structure of aldehyde, and various metal salts additives (e.g., MgBrj, AlMej, ZnClj, Cul), has shown only about 20-25% asymmetric induction (equation 22) . Another study, however, has been much more successful Solladie and Moine obtain the highly diastereocontrolled aldol-type condensation as shown in equation 23, in which dias-tereomer 24 is the only observed product, isolated in 75% yield This intermediate is then transformed stereospecifically via a sulfoxide-assisted intramolecular 8, 2 process into formylchromene 25, which is a valuable chiron precursor to enantiomerically pure a-Tocopherol (Vitamin E, 26). 

Polycondensation pol5mers, like polyesters or polyamides, are obtained by condensation reactions of monomers, which entail elimination of small molecules (e.g. water or a hydrogen halide), usually under acid/ base catalysis conditions. Polyolefins and polyacrylates are typical polyaddition products, which can be obtained by radical, ionic and transition metal catalyzed polymerization. The process usually requires an initiator (a radical precursor, a salt, electromagnetic radiation) or a catalyst (a transition metal). Cross-linked polyaddition pol5mers have been almost exclusively used so far as catalytic supports, in academic research, with few exceptions (for examples of metal catalysts on polyamides see Ref. [95-98]). 

---