Chromium compounds chemistry

Chromium(III) Chemistry. The most characteristic reactions of Cr(III) in aqueous solution at >4 pH, eg, in the intestine and blood, and hydrolysis and olation (147). As a consequence, inorganic polymeric molecules form that probably are not able to diffuse through membranes. This may be prevented by ligands capable of competing for coordination sites on Cr(III) (see Coordination compounds) (147). Thus any large fraction of ingested Cr(III) should be absorbed. Chromium (ITT) in the form of GTF may be more efficiendy absorbed. 

Preparation and chemistry of chromium compounds can be found ia several standard reference books and advanced texts (7,11,12,14). Standard reduction potentials for select chromium species are given ia Table 2 whereas Table 3 is a summary of hydrolysis, complex formation, or other equilibrium constants for oxidation states II, III, and VI. 

A78. M. J. Udy, ed., Chromium, ACS Monograph No. 132. Reinhold, New York, 1956. Volume 1 Chemistry of chromium and its compounds. Chapter 6, M. C. Udy The physical and chemical properties of compounds of chromium. The last section, pp. 240-246, organometallic chromium compounds, is almost entirely concerned with a discussion of polyphenylchromium compounds, at the time of writing not recognized as bis-7r-arenechromium derivatives. 

The chemistry shown in Scheme 1 represents a novel route to Cr(V) complexes. Such a mechanism may be important in biological environments and potentially involved in complex processes responsible for carcinogenicity of chromium compounds (112). 

Chromium(V) chemistry is not extensive. Species of this oxidation state are frequently postulated as reactive intermediates during the reduction of chromium(VI). However, compounds of this oxidation state with reasonable stability are being discovered there are... 

Beyersmann D, Koster A, Buttner B. 1985. Model reactions of chromium compounds with mammalian and bacterial cells. In MerianE, Fre RW, Hardi W, et al., eds. Carcinogenic and mutagenic metal compounds Environmental and analytical chemistry and biological effects. London, UK Gordon and Breach Science Publishers, 303-310. 

Chromium complexes exist in a very wide range of formal oxidation states (-IV to +VI). The extremely low ones are stabilized by jr-acid ligands, notably carbon monoxide these are described in the article on organometallic compounds (see Chromium Organometallic Chemistry). The extensive coordination chemistry of Cr spans coordination numbers 3-7, but is dominated by octahedral complexes. Complexes of... 

The chemistry of Phillips catalysts is intimately linked to interactions between inorganic chromium compounds and silica. Basic steps are summarized below ... 

One of the main interests in chromium(VI) chemistry is the synthesis of new chromium(VI) compounds suitable for the effective and selective oxidation of organic substrates, especially alcohols, under mild conditions. Pyridinium... 

J. Halstenberg, H. Knopf, P. Schmidt, Chromium compounds in Ullmann s encyclopedia of industrial chemistry, Electronic Release, 6th ed., (Eds. B. Elvers, S. Hawkins), Wiley-VCH, Weinheim, 1999, pp. 485-520. Vol. 8. 

An example, developed by our group, has been presented 3-chloro-propenyl pivalate, the new synthon we propose as a formal a-hydroxy allyl anion, and chromium(II) chemistry allow to achieve the formal diastereo- and enantio-selective a-hydroxyallylation of carbonyl compounds by applying a catalytic cycle based on an in situ produced Salen-chromium complex (Table 8.3). 

Yamamoto, K., Ishihama, Y., Isobe, E., and Sugano, T. 2009. Ethylene polymerization behavior of Cr(in)-containing montmorillonite Influence of chromium compounds. Journal of Polymer Science, Part A Polymer Chemistry 47 2272-2280. 

A comprehensive commentary of the speciation of chromium compounds and methods of analysis is published by Kotas and Stasicka (2000). Radovic et al. (2000) present a historical review of the literature of the characteristics of chromium as an adsorbate. A reading of such literature is not that rewarding because of the way much of the research is faceted and uncoordinated. As indicated above, the need today is to consider, in the one study, the speciation of the adsorbate, the characterization of several carbon adsorbents (varying porosity and surface chemistry, including its amphoteric nature) and pH, and the effects of temperature. 

The Nobel Prize in Chemistry was awarded to Karl Ziegler and Giulio Natta in 1963 for their research in developing olefin polymerization catalysts primarily based on titanium compounds and aluminum alkyl compounds required for the catalyst initiation process. However, by 1963 the details on the discovery of the Cr-based catalyst system in which the chromium compound was supported on amorphous silica were widely published and commercially important for the manufacture of HDPE. In the view of this author, the 1963 Nobel Prize awarded in chemistry should also have included two additional scientists, John P. Hogan and Robert L. Banks from Phillips Petroleum. 

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