Chromium chloride, anhydrous solution

Chromium (II) chloride (anhydrous) [10049-05-5] M 122.9, m 824 , d]" 2.75, Obtained from the dihydrate by heating in vacuo at 180°. It is a very hygroscopic white powder which dissolves in H2O to give a sky blue solution. Stable in dry air but oxidises rapidly in moist air and should be stored in air tight containers. It sublimes at 800° in a current of HCl gas and cooled in the presence of HCl gas. Alternatively it can be washed with air-free Et20 and dried at 110-120°. [Inorg Synth 3 150 1950.]... 

When the apparatus has been flushed, a boiling solution of 16 g. (0.20 mol) of anhydrous sodium acetate dissolved in 35 ml. of water is added through E A slow nitrogen flow is maintained, and a solution of 9 g. (0.034 mol) of chromium(III) chloride 6-hydrate in 15 ml. of 0.4 N sulfuric acid is poured into the top of the redactor. The rate of flow of the chromium solution can be controlled by stopcock B. If too fast a rate is used, there is a possibility of incomplete reduction. Distilled water is poured after the chromium chloride until the effluent is only slightly colored by chromium. This requires approximately 125 ml. 

Grignard synthesis is the method that Hein [9] used first to synthesize organochromium compounds in 1919. Anhydrous chromium chloride reacts with PhMgBr in an ether solution, forming an inflammable, paramagnetic black solid. Phenyl-chromium compound is obtained by hydrolysis of the black solid. 

The condensation is usually carried out by adding a solution containing equimolar amounts of the allyl halide and the aldehyde or ketone to a solution of at least two equivalents of chromium-(II) chloride in THF at 0 5°C. Frequently, the less precious component is used in 50-100% excess. Although commercially available anhydrous chromium(II) chloride can be utilized (Method B), its in situ preparation from chromium(III) chloride and lithium aluminum hydride (Method A) is often preferred. The removal of chromium and aluminum hydroxide, which are formed on aqueous workup, can be accomplished by filtration in the presence of a filtration aid. 

This is prepared by passing dry hydrogen chloride over chromium, or hydrogen over anhydrous chromium(III) chloride. It is a white solid. If pure chromium is dissolved in dilute hydrochloric acid in the absence of air, a blue solution of the hydrated chloride, containing the hexaaquo-ion [Cr(H20)6]2+. is obtained. The same solution is also obtained by reduction of the + 6 oxidation state (through the + 3) using a solution of a dichromate(VI) and reducing with zinc and hydrochloric acid ... 

B. General Oxidation Procedure for Alcohols. A sufficient quantity of a 5% solution of dipyridine chromium (VI) oxide (Note 1) in anhydrous dichloromethane (Note 7) is prepared to provide a sixfold molar ratio of complex to alcohol. This excess is usually required for complete oxidation to the aldehyde. The freshly prepared, pure complex dissolves completely in dichloromethane at 25° at 5% concentration to give a deep red solution, but solutions usually contain small amounts of brown, insoluble material when prepared from crude complex (Note 8). The alcohol, either pure or as a solution in anhydrous methylene chloride, is added to the red solution in one portion with stirring at room temperature or lower. The oxidation of unhindered primary (and secondary) alcohols proceeds to completion within 5 minutes to 15 minutes at 25° with deposition of brownish-black, polymeric, reduced chromium-pyridine products (Note 9). When deposition of reduced chromium compounds is complete (monitoring the reaction by gas chromatography or thin-layer chromatography analysis is helpful), the supernatant liquid is decanted from the (usually tarry) precipitate and the precipitate is rinsed thoroughly with dichloromethane (Note 10). 

Elemental composition Cr 32.84%, Cl 67.16%. Chromium(HI) chloride may be solubilized in water by a reducing agent and the aqueous solution may be analyzed for chromium by AA, ICP, or other instrumental techniques. Alternatively, the compound may be digested with nitric acid, brought into aqueous phase, diluted appropriately, and analyzed for the metal as above. The aqueous solution (when a nonchloride reducing agent is used for dissolution of the anhydrous compound in water) may be analyzed for chloride ion by ion chromatography or chloride-selective electrode. The water-soluble hexahydrate may be measured in its aqueous solution as described above. 

Potassium Tetrathiocyanato-dipyridino-chromium, [Cr py2 (SCN)4]K.2H,0, is prepared by heating potassium ehromithiocyanate with anhydrous pyridine. The melt is reerystallised from a little wTater, and on cooling a stable red powder separates. The thiocyanato-groups are all within the complex, and the salt in solution therefore gives no coloration with ferric chloride. It is decomposed by chlorine in presence of cold water with formation of tetraquo-dipyridino-chromic chloride. If crystallised in the dry state from pyridine it forms transparent red crystals of the addition compound, [Cr py2(SCN)JK.4py, which quickly effloresce in air. 

Preparation of Anhydrous Chromium(III) Chloride. Perform the experiment in a fume cupboard Grind 5 g of charcoal into a fine powder in a mortar, mix it with 12.5 g of chromium(III) oxide, add a thick starch size or a dextrin solution in cold water, and make beads about 5 mm in diameter from the mixture. Put the beads onto a clay dish and dry them in a drying cabinet at 110-120 °C. Next put them into an iron crucible, cover them with the charcoal powder and a lid, and roast them. 

Any anhydrous chromium solution will work. Cr03 in acetonitrile or chromate esters in hexane are good candidates. Lower valent compounds, like diarenechromium in hexane, can also be used because they are oxidized to the same Cr(VI) surface species during the second calcining in air. Even chromyl chloride vapor can be used if enough surface hydroxyls are left to... 

I>ipyridine chromium(VI) oxide is available from Eastman Organic Chemicals. To be an effective reagent, it must be anhydrous. It should form a red solution on dissolution in anhydrous methylene chloride. 

A solution of chromic chloride is readily obtained by the action of dilute hydrochloric acid on chromic hydroxide, or on chromium sesquioxide which has not been ignited this solution on evaporation yields an amorphous, deliquescent, green mass, soluble in water and in alcohol. The product on heating in hydrogen chloride or chlorine at temperatures above 250° C. becomes anhydrous, at the same time assuming the usual colour of the anhydrous salt. Basic chlorides are formed by... 

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