Hexa chromium

Carboxylic acids, a-bromination of 55, 31 CARBOXYLIC ACID CHLORIDES, ketones from, 55, 122 CARBYLAMINE REACTION, 55, 96 Ceric ammonium nitrate [Ammonium hexa mtrocerate(IV)[, 55, 43 Chlorine, 55, 33, 35, 63 CHROMIUM TRIOXIDE-PYRIDINE COMPLEX, preparation in situ, 55, 84 Cinnamomtnle, a-phenyl- [2-Propeneni-tnle 2,3-diphenyl-], 55, 92 Copper(l) iodide, 55, 105, 123, 124 Copper thiophenoxide [Benzenethiol, copper(I) salt], 55, 123 CYCLIZATION, free radical, 55, 57 CYCLOBUTADIENE, 55, 43 Cyclobutadieneiron tricarbonyl [Iron, tn-carbonyl(r)4-l,3-cyclo-butadiene)-], 55,43... 

A method has been developed for differentiating hexavalent from trivalent chromium [33]. The metal is electrodeposited with mercury on pyrolytic graphite-coated tubular furnaces in the temperature range 1000-3000 °C, using a flow-through assembly. Both the hexa- and trivalent forms are deposited as the metal at pH 4.7 and a potential at -1.8 V against the standard calomel electrode, while at pH 4.7, but at -0.3 V, the hexavalent form is selectively reduced to the trivalent form and accumulated by adsorption. This method was applied to the analysis of chromium species in samples of different salinity, in conjunction with atomic absorption spectrophotometry. The limit of detection was 0.05 xg/l chromium and relative standard deviation from replicate measurements of 0.4 xg chromium (VI) was 13%. Matrix interference was largely overcome in this procedure. 

O32Cl8FeMn5N36Cii4Hi50 5H2O, Iron, hexa-kis cyano( 1,4-bis(2-pyridyImethyI)-1,4,7-triazacyclononane) manganese(II) -, octa-perchlorate, pentahydrate, 34 137 036Cl9CrCu6N3oC42Hio8-H20, Chromium, hexakis cyano(tris(2-aminoethyl)amine)-copper(II) -, nonaperchlorate, hydrate, 34 138... 

Chelating polyolefins displace carbon monoxide from chromium hexa-carhonyl to form stable olefin complexes. Thus cyclo-octa-1,5-diene gives the yellow complex [Cr(CO)4(C8H12)] for which the cfs-structure (VI M = Cr) is proposed (79). 

In their original investigations, Ayscough and Steacie42 stressed the simplicity of the reaction scheme and were unable to identify any product which could arise from the reactions of a trifluoroacetyl radical. Further, the ratio of quantum yields of carbon monoxide and hexa-fluoroethane was always close to unity, a fact which has been confirmed by later workers. Recently, Tucker and Whittle43 have shown that when hexafluoroacetone is photolyzed in the presence of excess bromine, trifluoroacetyl bromide is formed, suggesting that the trifluoroacetyl radical must intervene. The absence of hexafluorodiacetyl in the photolysis products of hexafluoroacetone is explained by the assumption that it is not stable. In fact, however, hexafluorodiacetyl may be prepared by the chromium trioxide oxidation of l,l,l,4,4,4-hexafluoro-2,3-di-... 

Cyclization of an allyl A-acyl-1 -phenylglycinate (398) with triphenylphosphine, hexa-chloroethane and triethylamine affords a 2-allyl-3-oxazolin-4-one (400) (81AG(E)395, 77AG(E)394). Reductive cleavage of the oxazolinone with chromium(II) acetate and aqueous hypophosphorous acid furnishes a j3,y-unsaturated ketone (Scheme 88). 

Local description of the arrangement around cations concludes unambiguously for [Cu-Cr-Cl] in a cationic ordering. The evidence of similar ordering for [Zn-Cr-Cl] was only obtained by a combined EXAFS and UV-Vis study of the formation of this LDH in solution [18], The structural pathway so-reported involves the heterocondensation between hexa-aquo zinc(II) complexes and deprotonated chromium monomers. 

Johansson A, Robertson B, Curstedt, et al. 1986a. Rabbit lung after inhalation of hexa- and trivalent chromium. Environ Res 41 110-119. 

The reaction, of metal carbonyls with 1,3-diketones generally results in a complete displacement of carbon monoxide accompanied by oxidation of the metal to yield 1,3-diketonato complexes. For example, iron pentacarbonyl, chromium hexa-carbonyl, and molybdenum hexacarbonyl afford FefCgHjOOs,1 Cr(CsHr02)8,2 and Mo(CgH702)s,2,s respectively, when allowed to react with 2,4-pentanedione. 

Infrared and electronic spectra confirm the nature of the hexa-N-thiocyanatometallate anions of chromium(III) (293, 639, 647, 656, 663, 665) and molybdenum(III) (293, 489, 647, 663, 664), and molyb-denum(II) (534) a variety of salts have been reported containing these anions (see the foregoing and also Refs. 30 and 528). Infrared spectra and magnetic measurements have been used to characterize [M(NCS)e] (M = Mo, W) and [W(NCS)g] (386). A large number of mixed-ligand thiocyanate complexes of chromium(III) have been reported, and many of these are of the type M[Cr(CNS)4L2], similar to the original Reinecke s salt where L = NH3. 

Atomic Weight.—From a consideration of the vapour densities of volatile compounds of chromium, and from the application of Dulong and Petit s Law, it is obvious that the atomic weight of chromium is about 52—that is, three times the chemical equivalent of chromium in chromic salts, or six times its combining weight in derivatives of chromium trioxide. Chromium thus exhibits di-, tri-, and hexa-valency in the chromous salts, chromic salts, and chromates and diehromates respectively. 

The chemistry of chromium is somewhat complicated owing to the varying degrees of valency exhibited by the element. In its tliree most important oxides, all of which give rise to corresponding series of salts, it functions respectively as a di-, tri-, and hexa-valent element, while in some of its compounds it behaves as a hepta-, penta-, or even tetra-valent element. 

The crystal structure has been investigated by the Hull powder method of obtaining X-ray diffraction patterns. The molecule is hexa-hedral, consisting of three atoms of oxygen at the corners of an equilateral triangle with two chromium atoms immediately above and below the centre of the triangle, three such molecules forming a unit prism. 

Atomic Weight.—For reasons similar to those applying in the case of chromium (p. 16), the atomic %veight of molybdenum is three times the equivalent of the metal in the molybdic salts, or six times that in the molybdates. Molybdenum may be di-, tri-, or hexa-valent. 

Atomic Weight.— Like chromium and molybdenum, tungsten may in its compounds be di-, tri-, or hexa-valent from a consideration of its specific heat, the isomorphism of its compounds, its position in the... 

The oxidation of secondary alcohols to ketones by compounds of hexa-valent chromium is not only the most common but also the best known reaction as far as the mechanism is concerned. The stoichiometry is the same as that of primary alcohols (equation 242). 

Lee, D. G. The Oxidation of Organic Compounds by Permanganate Ion and Hexa-valent Chromium Open Court Publishing LaSalle, IL, 1980. 

---