Chromium, penta

Comparison of the electrical conductivities of chromium penta-phenyl hydroxide, sodium hydroxide and ammonia in absolute methyl alcohol and in methyl alcohol-water solution, shows that the former is a very strong base. In aqueous methyl alcohol solution the chromium compound does not appear to approach the limiting value with increasing dilution. The ultra-violet absorption spectrum examined in absolute ethyl alcohol solution resembles that of chromic acid and the dichromates, but the absorption is noticeably greater in the case of the organic compound. 

Chromium penta - p - tolyl bromide mercurichloride, (CyHyJgCrBr.HgClg, obtained from an alcohol solution of the crude bromides and mercuric chloride, is stable only for a few days, moisture and sunlight causing it to change from bright yellow to green. 

Chromium penta-p-tolyl carbonate, [(C7H7)5Cr]2C03.6H20.— When the crude bromides are treated with caustic alkali a solution of chromium penta-p-tolyl hydroxide is obtained, which passes into the carbonate. This salt forms orange crystals, M.pt. 139° to 140° C., soluble in alcohols, chloroform or nitrobenzene, sparingly soluble in water or cyclohexanol, insoluble in ether. 

Chromium penta-p-tolyl hydrogen anthranilate, 2(C7H7)5Cr. O2C.CgH4.NH2.NH2.CgH4.CO2H, occurs when a solution of the base is treated with an excess of anthranilic acid. It melts at 170° C. after previously sintering, dissolves in alcohols, is sparingly soluble in chloroform and insoluble in carbon disulphide. 

Although metal chains have identical ligands, similar crystallographic structures, and physical dimensions, the resistance varies with the identity of the metal. For example, the resistance values of penta-chromium, penta-cobalt, and penta-nickel strings are 3.2 MO, 10.0 MO, and 24.0 MO, respectively. The discrepancy is linked to the extent of coupling of tf-orbital electrons between... 

Trimethylene dibromide (Section 111,35) is easily prepared from commercial trimethj lene glycol, whilst hexamethylene dibromide (1 O dibromohexane) is obtained by the red P - Br reaction upon the glycol 1 6-hexanediol is prepared by the reduction of diethyl adipate (sodium and alcohol lithium aluminium hydride or copper-chromium oxide and hydrogen under pressure). Penta-methylene dibromide (1 5-dibromopentane) is readily produced by the red P-Brj method from the commercially available 1 5 pentanediol or tetra-hydropyran (Section 111,37). Pentamethylene dibromide is also formed by the action of phosphorus pentabromide upon benzoyl piperidine (I) (from benzoyl chloride and piperidine) ... 

Chemistry of tetra- and penta-valent chromium. K. Nag and S. N. Bose, Struct. Bonding (Berlin), 1985,63,153 (278). 

There are several examples of well-characterized tri- and tetranu-clear hydroxo-bridged complexes of chromium(III) and cobalt(III). Penta- and hexanuclear aqua chromium(III) complexes have been prepared in solution, but their structure and properties are unknown. Oligomers of nuclearity higher than four have not been reported for cobalt(IIl), with the exception of some hetero-bridged heteronuclear species (193, 194). There appear to be no reports of rhodium(III) or iridium(III) complexes of nuclearity higher than two. 

The earliest expectations of cupferron being a selective and specific reagent for copper and iron only were not justified as the reagent has been found to precipitate, with the exception of aluminum and chromium,83 almost all the tri- to penta-valent metals which form insoluble hydrous oxides. However, the reagent has acquired permanent value as an aid in separating certain metals, e.g. titanium from aluminum and chromium.84... 

Their strong reducing nature is a special characteristic of the penta-carbonyl metalates(-II) and decacaibonyl dimetalates(—I) of chromium, molybdenum, and tungsten that distinguishes them from the other carbonyl metalate anions of the 3d metals, e.g., [Co(CO)J. The oxidation of the mononuclear species with water... 

In organic chemistry one surely thinks at once of the construction of cyclopropane derivatives from olefins and carbenes. Indeed, it has been shown that this also is possible with our complexes and with C=C double bonds that are electron-poor and arc either polarized or easily polarizable (77-81). As an example of this, I would like to cite the reaction of penta-carbonyl[methoxy (phenyl) carbene]chromium (0), -molybdenum (0), or -tungsten(0) with ethyl vinyl ether (79). One obtains the corresponding cyclopropane derivatives in this case, however, only when one removes... 

As discussed above, the ligands that have been typically utilized for the preparation of chromium nitrides are multidentate. Consequently, ligand exchange reactions of such complexes are difficult and rare. Wieghardt and co-workers have reported such a process, however, for the synthesis of a nitrido chromium cyanide complex 43 (Eq. (13)) [18]. Thus, treatment of CrN(salen) 42 with excess sodium cyanide and tetramethyl ammonium chloride results in the formation of a six-coordinate penta-cyano chromium nitride [21]. 

Thermally induced cyclization of the l-methoxy-3-phenyl-[(2-methoxy)-alkenyljcarbene-chromium complex [= 2,4-dimethoxy-4-phenyl-l-(penta-... 

NIOSH REL (Chromium(VI)) TWA 0.025 mg(Cr(VI))/mh CL 0.05/15M SAFETY PROFILE Confirmed human carcinogen. Poison by subcutaneous route. Mutation data reported. A powerful oxidizer. A powerful irritant of skin, eyes, and mucous membranes. Can cause a dermatitis, bronchoasthma, chrome holes, damage to the eyes. Dangerously reactive. Incompatible with acetic acid, acetic anhydride, tetrahydronaphthalene, acetone, alcohols, alkali metals, ammonia, arsenic, bromine penta fluoride, butyric acid, n,n-dimethylformamide, hydrogen sulfide, peroxyformic acid, phosphorus, potassium hexacyanoferrate, pyridine, selenium. 

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. 

Vinyl halides represent yet another important class of intermediates in the conversion of ketones to alkenes. The most widely applied conditions for the conversion of ketones into vinyl halides are those developed by Barton et a/. ° for the conversion of 3p-acetoxyandrost-5-ene-17-one into 3P-hydroxyandrosta-5,16-diene (Scheme 44). These conditions of vinyl halide formation and subsequent reduction have been useful in a number of steroid systems for the introduction of a A -carbon-carbon double bond and have been shown to be compatible with such functional groups as alcohols, isolated double bonds and acetals. The scope of vinyl iodide formation from hydrazones has been studied by Pross and Stemhell, and recently the original reaction conditions were improved by using sterically hindered guanidine bases rather than triethylamine. Haloalkenes have also been prepared from the corresponding ketones by treatment with iodoform and chromium chloride or with phosphorous penta-halides. ... 

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