Oxidants examples: hypobromite

Gravimetric Methods.—The main difficulty is to obtain the cobalt in the form of one of its compounds entirely free from nickel or other metal. This may be accomplished by the cyanide method described under Wet Tests above. The solution, after separation of the nickel, is evaporated with dilute sulphuric acid until white fumes are evolved. On addition of water a solution of cobalt sulphate results, and the cobalt may be precipitated in a variety of ways, for example as oxide with hypobromites or persulphates,2 as sulphide, as cobalti-nitroso p-naphthol, or as basic carbonate.3 In each case the precipitate is ignited and reduced to metallic cobalt in a current of pure hydrogen. 

Good results are obtained by the oxidation of the commercially available cyclo-propyl methyl ketone with sodium hypobromite solution, and the preparation may be regarded as an excellent example of the oxidation of the —COCH, group to — OOH ... 

The vast majority of the preparative oxidations of methyl ketones are carried out with alkaline hypochlorites or hypobromites. The same effect can be achieved by alkaline hypoiodites, but examples are scarce. One example is the opening of the D ring of benzyl estrone to benzyl marrianolic... 

It is known from Houben-Weyl, Methoden der organischen Chemie, volume 8, pages 415-416, that carboxylic acids can be manufactured by oxidation of methyl ketones with hypohalites in an aqueous medium. The publication recommends dispersing the ketone by means of oxidation-resistant emulsifiers or carrying out the reaction in the presence of dioxane all the examples were carried out in this way. In most cases the reaction only takes place satisfactorily with hypobromite solutions, which are more expensive and less stable than hypochlorite solutions. For this reason alone, industrial utilization of the reaction is confined to special reactions with aromatic ketones. 

Alkyl hypochlorites and hypobromites are relatively stable molecules alkyl hypoiodites can only be prepared in situ, usually by the reaction of alcohols with metal acetates or oxides and iodine or by the reaction of alcohols with a hypervalent iodine compound and iodine.1319 Alkyl hypochlorites and hypoiodites can be utilized in reactions that parallel those of the organic nitrites (Barton reaction Section 6.4.2). For example, the photochemistry of the steroidal hypoiodite 497, prepared by the reaction of the corresponding alcohol with iodine oxide (I2O) generated from mercury(II) oxide and molecular iodine in situ, affords a new five-membered ring via an O I bond fission, 1,5-hydrogen abstraction and substitution (Scheme 6.244).1353... 

Jackson and Hudson obtained a dicarboxylic acid (104), isolated as its crystalline strontium salt, in a yield of 20% by oxidizing methyl a-n-mannopyranoside in an aqueous solution of barium hypobromite. This acid, which is normally obtained by oxidation of the dialdehyde obtained by periodate oxidation of the n-glucoside, is most probably another example of a product arising from the cleavage of a bond between adjacent keto groups. Heyns found that changing the pH, in the catalytic oxidation of benzyl S-n-arabinop3Tanoside, to pH 7.3 resulted in the formation of a dicarboxylic acid (105) (isolated as its crystalline barium salt) in 42% yield. He considered this to be a further oxidation product of the 4-keto compound normally formed. 

For a long time before the ring structure of pterins was known, compounds containing the pteridine ring were being prepared. In 1895, 2,4-dihydroxy-pteridine was prepared by oxidation of tolualloxazine and decarboxylation of the resulting 2,4-dihydroxypteridine-6,7-dicarboxylic acid, and the same compound was prepared in 1907 by the action of hypobromite on pyrazine-2,3-dicarboxamide. The condensation of 4,5-diaminopyrimidine and benziF to form 6,7-diphenylpteridine reported in 1906 was the first example of the most versatile general method of pteridine synthesis. 

---