Chromium chloride, reduction

Vanadium chloride, 2 chromium chloride,33 and the combined use of tributylphosphine and diphenyldisulfide34 are also effective in promoting the reductive Nef reaction. 

Pinacol formation from ketones and aldehydes by cathodic reduction has been enhanced in the presence of Cr(II) complexes. Electrolysis of a mixture of ben-zophenone (364) and chromium chloride hexahydrate in a DMF-NaCl04 system... 

Other methods have appeared, but have been less frequently used, e.g. chromium chloride in acetone 140- 143 (y/yfe infra) and dissolving alkali-metal reductions.144,145 Hydrogenolysis with palladium/hydrogen has also given the monoreduced cyclobutanone.99,100... 

Liquid wastes containing hexavalent chromium require reduction of chromium to the trivalent state prior to metal removal. Commonly used reducing agents are sodium metabisulfite, sulfur dioxide, ferrous sulfide, and other ferrous ions (ferrous sulfate, ferrous chloride, or electrochemically generated ferrous ion). All of these reagents create some form of chromium sludge, which must be separated and dewatered before disposal. 

Reduction of Chromic Chloride, CrClj.—Wohler obtained metallic chromium by reduction of chromic chloride with potassium, while Fremy obtained the metal in a crystalline condition by passing sodium vapour over chromic chloride in an atmosphere of pure dry hydrogen. Wohler prepared similar crystals—minute octahedra— by fusion of chromic chloride with zinc under a layer of mixed sodium and potassium cHorides, and removal of the zinc from the alloy so formed by means of nitric acid. Metallic calcium reduces chromic chloride at a dull red heat without formation of an alloy. ... 

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. 

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. ... 

Chromium(II) chloride reduction of 9a-bromo-A -3-oxosteroids 19 leads to 5,9-cyclosteroids 20. The formation of these eyclosteroids is explained by assuming a one-electron transfer in the cleavage of the C-Hal bond with chromium(II) chloride to give a carbon radical, followed by a second one-electron transfer from Cr to give a carbanionic intermediate that intra-molecularly undergoes addition to the enone moiety and thus forms the cyclopropane ring. 

Fisher and Hafner [14] found the synthesis of Ti-aryl complexes with aromatic compounds, chromium chloride, aluminum chloride and aluminum metal in 1955 as shown in eq. (13.9). These mixture is heated to afford bisaryl cation, and bisaryl complexes are prepared by reduction with water soluble sodium dithionite (Na2S204). ( -(C6H6))2Cr is isolated as a dark brown material by sublimation by heating under a high vacuum [15]. 

For dichromate and I MS such a decrease can be attributed to breakages along the chain resulting in its fragmentation with reduction of molecular weight chromium chloride, instead, exerting its action on the nitrogen bases probably makes the molecule more flexible. 

In 2005, it was shown that the reduction of the aryl chromium(II) chloride species, Ar CrCl, with KCg afforded the Cr(I)-Cr(I) dimer Ar CrCrAr [19], in which the chromium atoms are linked by a fivefold metal-metal interaction. The effects of different terphenyl ligands on the quintuple Cr-Cr bonding in ArCrCrAr (Ar = 4-X-Ar, X = H, F, MeO or SiMeg) dimers were also studied (see Sect. 7.2), and these dimers were similarly prepared by reduction of the corresponding aryl chromium chlorides [20]. 

This scheme is consistent with the fact that one mole of [Cr(NH3)] + is produced per mole of Cr +, that small amounts of a dimeric species are formed, and with the observation that CrCP+ is produced in the presence of chloride ion even at fairly low concentrations. The mechanism of the vanadium(ii) reaction is not as readily described, the results being compatible with either an inner-sphere or an outer-sphere pathway. The spectrum of an intermediate complex formed in the chromium(n) reduction of isonicotinic acid has been described, the initial stage of the reaction involving partial... 

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) ... 

Titanium Sulfates. Solutions of titanous sulfate [10343-61-0] ate readily made by reduction of titanium(IV) sulfate ia sulfuric acid solutioa by electrolytic or chemical means, eg, by reduction with ziac, ziac amalgam, or chromium (IT) chloride. The reaction is the basis of the most used titrimetric procedure for the determination of titanium. Titanous sulfate solutions are violet and, unless protected, can slowly oxidize ia coatact with the atmosphere. If all the titanium has been reduced to the trivalent form and the solution is then evaporated, crystals of an acid sulfate 3 Ti2(S0 2 [10343-61-0] ate produced. This purple salt, stable ia air at aormal temperatures, dissolves ia water to give a stable violet solutioa. Whea heated ia air, it decomposes to Ti02, water, sulfuric acid, and sulfur dioxide. 

Ghromium(II) Compounds. The Cr(II) salts of nonoxidizing mineral acids are prepared by the dissolution of pure electrolytic chromium metal ia a deoxygenated solution of the acid. It is also possible to prepare the simple hydrated salts by reduction of oxygen-free, aqueous Cr(III) solutions using Zn or Zn amalgam, or electrolyticaHy (2,7,12). These methods yield a solution of the blue Cr(H2 0)g cation. The isolated salts are hydrates that are isomorphous with and compounds. Examples are chromous sulfate heptahydrate [7789-05-17, CrSO 7H20, chromous chloride hexahydrate... 

The anhydrous hahdes, chromium (II) fluoride [10049-10-2], chromium (II) bromide [10049-25-9], CrBr2, chromium (II) chloride [10049-05-5], CrCl2, and chromium (II) iodide [13478-28-9], 03x1, are prepared by reaction of the hydrohaUde and pure Cr metal at high temperatures, or anhydrous chromium (II) acetate [15020-15-2], Cr2(CH2COO)4, atlower temperatures, or by hydrogen reduction of the Cr(III) hahde at about 500—800°C (2,12). 

Steroidal 17-cyanohydrins are relatively stable towards chromium trioxide in acetic acid (thus permitting oxidation of a 3-hydroxyl group ) and towards ethyl orthoformate in ethanolic hydrogen chloride (thus permitting enol ether formation of a 3-keto-A system ). Sodium and K-propanol reduction produces the 17j -hydroxy steroid, presumably by formation of the 17-ketone prior to reduction. ... 

A 5% solution of chromium trioxide-pyridine complex in dry methylene chloride is prepared. The alcohol (0.01 mole) is dissolved in dry methylene chloride and is added in one portion to the magnetically stirred oxidizing solution (310 ml, a 6 1 mole ratio) at room temperature. The oxidation is complete in 5-15 minutes as indicated by the precipitation of the brownish black chromium reduction products. The mixture is filtered and the solvent is removed (rotary evaporator) leaving the crude product, which may be purified by distillation or recrystallization. Examples are given in Table 1.1. 

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