Chromium dichloride reductions

Chromium (II) salts reduce water into hydrogen. This gradual transformation at ambient temperature has been responsible for accidents of the same nature. A glass bottle, in which chromium dichloride was stored for several years, detonated spontaneously. A sealed tube, in which there was chromium (II) sulphate heptahydrate and water in excess, detonated after being stored in darkness for a year. In both cases the accidents were interpreted as the result of water reduction, forming hydrogen whose pressure eventually caused the explosion of the containers. 

Chemical deoxygenation of sulfoxides to sulfides was carried out by refluxing in aqueous-alcoholic solutions with stannous chloride (yields 62-93%) [186 Procedure 36, p. 214), with titanium trichloride (yields 68-91%) [203], by treatment at room temperature with molybdenum trichloride (prepared by reduction of molybdenyl chloride M0OCI3 with zinc dust in tetrahydrofuran) (yields 78-91%) [216], by heating with vanadium dichloride in aqueous tetrahydrofuran at 100° (yields 74-88%) [216], and by refluxing in aqueous methanol with chromium dichloride (yield 24%) [190], A very impressive method is the conversion of dialkyl and diaryl sulfoxides to sulfides by treatment in acetone solutions for a few minutes with 2.4 equivalents of sodium iodide and 1.2-2.6 equivalents of trifluoroacetic anhydride (isolated yields 90-98%) [655]. 

Aldehydes, RCHO, have been reductively olefinated (to /ran -RCH=CHR) using chromium dichloride and trichlorosilane, apparently via a novel chromium Brook rearrangement.189 In one case, a trans- 1,2-diol (a putative intermediate in such a mechanism) was isolated. 

These are listed in Table 17-C-2. The anhydrous Cr11 halides are obtained by action of HF, HC1, HBr, or I2 on the metal at 600 to 700°C or by reduction of the trihalides with H2 at 500 to 600°C. Chromium dichloride is the most common and most important of these halides, dissolving in oxygen-free water to give a blue solution of Cr2+ ion. 

For the synthesis of (69), the enol ether (71) from the indanone (70) was carboxylated with COa-n-butyl-Iithium in THF at —70 C to yield (72). The methyl ester (73) was converted into (75) via the maleic anhydride adduct (74), essentially as described in earlier work. Lithium aluminium hydride reduction followed by oxidation with dicyclohexylcarbodi-imide afforded the aldehyde (76). This was condensed with excess (77) to yield a mixture of the diastereomers (78). Oxidation with chromium trioxide-pyridine in methylene dichloride gave (79), which could be converted into the diketone (80) by treatment with excess benzenesulphonylazide. The diketo-lactam (81) was prepared from (80) as described for the synthesis of the analogous intermediate used in the synthesis of napelline. Reduction of (81) with lithium tri-t butoxyaluminohydride gave the desired dihydroxy-lactam (82). Methylation of (82) with methyl iodide-sodium hydride gave (83). Reduction of this lactam to the amine (84) with lithium aluminium hydride, followed by oxidation with potassium permanganate in acetic acid, gave (69). 

Reductive dechlorination of 1,3-dichlorides requires modified conditions. Zinc dust in ethanol/water containing sodium iodide as mediator has been used. Chromium(II) perchlorate in the presence of 1,2-diaminoethane in dimethylformamide/water has been used, for example to prepare methylcyclopropane from 1,3-dichlorobutane in 94% yield. ... 

TiCU is produced by the reduction of the tetrachloride with hydrogen or a metal like silver or mercury. When heated in the air it breaks up, giving the volatile tetrachloride and the solid dichloride. TiCl is deli quescent, forms a reddish violet solution with water, and violet crystals, TiCU 6 H20, from a hydrochloric acid solution. An unstable green hydrate of the same composition is formed when an aqueous solution of the trichloride is covered with ether and saturated at 0° with HC1. From the violet form all the chlorine may be removed by AgNO , but this is probably not true of the green modification. The trichlorides of chromium and vanadium likewise are known in two forms. TiCla forms double salts with the chlorides of rubidium and caesium. It is a more powerful reducing agent than stannous chloride and on this account finds extensive application in both qualitative and quantitative analysis. 

Chromium, pentaamminethiocyano-base hydrolysis, 504 Chromium, pentaaquachloro-dichloride hydrate hydrate isomerism, 183 Chromium, pentaaquahydroxy-electron transfer with hexaaquachromium, 370 Chromium, pentaaquamaleato-electron transfer, 374 Chromium, g-sulfatodi-reduction... 

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