Palladium abundance

Cheng, H.X., Xie, X.J., Yan, G.S. 1998. Platinum and palladium abundances in floodplain sediments and their geochemical provinces. Chinese journal of Geochemistry, 27, 101-106. 

The reaction is used for the chain extension of aldoses in the synthesis of new or unusual sugars In this case the starting material l arabinose is an abundant natural product and possesses the correct configurations at its three chirality centers for elaboration to the relatively rare l enantiomers of glucose and mannose After cyanohydrin formation the cyano groups are converted to aldehyde functions by hydrogenation m aqueous solution Under these conditions —C=N is reduced to —CH=NH and hydrolyzes rapidly to —CH=0 Use of a poisoned palladium on barium sulfate catalyst prevents further reduction to the alditols... 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

Palladium and platinum are the longest known and most studied of the six platinum metals [1-11], a reflection of their abundance and consequent availability. Platinum occurs naturally as the element, generally with small amounts of the other platinum metals. It was used as a silver substitute by Colombian Indians and first observed there by Ulloa (1736), who called it platina del Pinto ( little silver of the Pinto river ) but the first sample was actually brought to Europe in 1741 by Charles Wood, Assay Master of Jamaica. Palladium was isolated in 1803 by W.H. Wollaston, who was studying the aqua regia-soluble portion of platinum ores (he announced his discovery by an anonymous leaflet advertising its sale through a shop in Soho) and named it after the newly discovered asteroid Pallas [12],... 

For metals, the close-packed surfaces have, in general, the smallest surface free energy and therefore these surfaces dominate on small particles, e.g. the (111) surfaces for the fee and hep metals, and the (110) surface for the bcc metals, although on iron particles the (100) surface is abundantly present. Surface free energies have been tabulated [L. Vitos, A. Ruban, H. Shriver and J. Kollar, Surf. Sci. 411 (1998) 186], To give an idea of how the values depend on crystal face we list some values for palladium ... 

Table I. Evolved Gases From 2 MeV He+ Irradiation of 0.9 nm Palladium Acetate Film. Molecules arranged in order of decreasing abundance within each group...

In conclusion, the already rich chemistry of pyrroles is greatly expanded by the palladium reactions presented in this chapter. The abundance of both 2- and 3-pyrrolyl halides and triflates has led to many examples of high-yielding Negishi, Suzuki, Stille, Sonogashira, and Heck reactions. Noteworthy are the excellent approaches to alkynyl pyrroles and porphyrins using Sonogashira, Stille, and Suzuki reactions. 

Palladium is considered a rare metal, making up only about 1 part per 100 million parts of the Earth s crust. It is considered the 77th most abundant element on Earth, although it is... 

Metal chemical shifts have not found extensive use in relation to structural problems in catalysis. This is partially due to the relatively poor sensitivity of many (but not all) spin 1=1/2 metals. The most interesting exception concerns Pt, which is 33.7% abundant and possesses a relatively large magnetic moment. Platinum chemistry often serves as a model for the catalytically more useful palladium. Additionally, Pt NMR, has been used in connection with the hydrosilyla-tion and hydroformylation reactions. In the former area, Roy and Taylor [82] have prepared the catalysts Pt(SiCl2Me)2(l,5-COD) and [Pt()i-Cl)(SiCl2Me)(q -l,5-COD)]2 and used Pt methods (plus Si and NMR) to characterize these and related compounds. These represent the first stable alkene platinum silyl complexes and their reactions are thought to support the often-cited Chalk-Harrod hydrosilylation mechanism. 

One of the most frequently studied transition metal catalyzed transformations of azoles and indole is their participation in cross-coupling reactions. Due to the abundance of examples in this field we only present some representative examples of the different reaction classes. In this chapter reactions where a halogenated azole is used to introduce the five membered ring onto the palladium in the oxidative addition and processes,... 

Palladium occurs in combination with platinum and is the second most abundant platinum group metal (pgm), accounting for 38% of pgm reserves. The USSR produces over 50% of the world s palladium, which is more than double that produced in South Africa. Two major sources of the metal are braggite, a mixed sulfide of platinum, palladium and nickel, which contains 16-20% palladium, and michenerite (PdBi3). 

Nickel, palladium and platinum - The low natural abundance of the 61Ni isotope means that there is a paucity of data on NMR spectroscopy of this element, although much useful information can be derived from spectra of ligand nuclei (e.g. Zschunke et al., 1992 Oik et al., 1992). In the case of 105Pd, the large value of the quadrupole moment presents additional difficulties for direct spectroscopic measurements and, as with nickel, NMR studies have concentrated on the characterisation of ligand nuclei. An example here is the application of two-dimensional NMR to investigate the structure of a nucleic acid palladium complex (Bichenkova et al., 1992). 

Starch is an abundant, inexpensive polysaccharide that is readily available from staple crops such as com or maize and is thus is mostly important as food. Industrially, starch is also widely used in papermaking, the production of adhesives or as additives in plastics. For a number of these applications, it is desirable to chemically modify the starch to increase its hydrophobicity. Starch modification can thus prevent retrodegradation improve gel texture, clarity and sheen improve film formation and stabilize emulsions [108], This may, for example, be achieved by partial acetylation, alkyl siliconation or esterification however, these methods typically require environmentally unfriendly stoichiometric reagents and produce waste. Catalytic modification, such as the palladium-catalyzed telomerization (Scheme 18), of starch may provide a green atom-efficient way for creating chemically modified starches. The physicochemical properties of thus modified starches are discussed by Bouquillon et al. [22]. 

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