Reaction dichromate-bromide

The bromyl ion decomposes spontaneously. Chloryl and iodyl ions were studied through their attack on chloride and bromide ions respectively. By determining the rate of disappearance of dichromate and using an analysis similar to the pyrosulfate-nitrate case, the following equilibrium constants were found for the dichromate-halate reactions which produce halyl and chromate ions (not calculated as BaCrC>4, but as [Cr04 2] in solution) (2). 

Another highly versatile building block derived from diacetone-glucose 54 is the 1,2-acetonide of 3-C-methyl-a-D-allose in its furanoid form 57, which has been utilized as the key compound in a convergent total synthesis of ACRL Toxin I (63). Its elaboration from 54 starts with a pyridinium dichromate / acetic anhydride oxidation (64), is followed by carbonyl olefination of the respective 3-ulose with methyl (triphenyl)phosphonium bromide and hydrogenation (— 55 56), and is completed by acid cleavage of the 5,6-isopropylidene group. This four-step process 54 -> 57, upon optimization of reaction conditions and workup procedure, allows an overall yield of 58 % (63), as compared to the 22 % obtained previously (65). 

Amongst other inorganic catalysts are to be included the iodides 9 (also bromides and chlorides but less active) and chromates or dichromates. The agent in the former case appears to be the iodide ion, the mechanism of the reaction probably involving oxidation to hypo-iodite which then reacts with more hydrogen peroxide with formation... 

DICHROMIC ACID, DIPOTASSIUM SALT (7778-50-9) Noncombustible, but many chemical reactions can cause fire and explosions. A powerful oxidizer. Violent reaction with many substances, including combustible materials, reducing agents, organic materials, finely divided metals, ammonium nitrate, ammonium perchlorate, fluorine, hydrazine, hydrazinium nitrate, hydroxylamine, iron powder, nitric acid, potassium iodide, sodium borohydride, sodium bromide, sodium tetraborate and its decahydrate, tungsten, and zirconium dusts. 

The silylated methyl ester was then a-methylated with lithium diisopropylamide and methyl iodide in tetrahydrofuran. Reduction of methyl 10-( erl-butyldimethylsilyloxy)-2-methyldecanoate with DIBAL in ether at -78°C afforded the corresponding aldehyde. The 10- tert-butyldimethylsilyloxy)-2-methyldecanal was subsequently coupled in a Wittig reaction with 1-hexyltriphenylphosphonium bromide and n-butyllithium affording (Z)- and ( )-1 -(teri-butyldimethylsilyloxy)-9-methyl-10-hexadecene in a 9 1 ratio, respectively. Deprotection with tetrabutylammonium fluroride (TBAF) in tetrahydrofuran and final oxidation with pyridinium dichromate (PDC) in dimethylformamide resulted in a 9 1 mixture of (Z)- and ( )-9-methyl-10-hexadecenoic acid as shown in Fig. (7). As was also the case with acid 6, the stereochemistry at C-9 in 7 is not known. The key step in the synthesis of the allylic methyl group was a-methylation of a methyl ester, followed by reduction to the corresponding aldehyde, which was used in the subsequent Wittig reaction. 

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