Oxidation by bromine water

Oxidation with Bromine Water.—With 2- or 3-desoxy-hexoses or -pentoses, oxidation by bromine water follows the usual course and converts them into the corresponding 2- or 3-desoxy-hexonic or -pentonic acids. The oxidation is more rapid if the hydrobromic acid that is produced in the reaction is removed as it is formed, by barium or calcium carbonate227 or barium benzoate.228 In view of the sensitivity of 2-desoxysugars to prolonged contact with mineral acids, it is advantageous to adopt this latter procedure for their oxidation.112 Sometimes for the preparation of desoxy -pentonic and -hexonic acids the method of oxidation (or slight modifications thereof) introduced by Goebel229 is employed. 

The well-known conversion of certain furans into lactones has been further studied recently. 2-Furoic acid, which was labeled in the carboxyl group, gave radioactive C02 when oxidized by bromine water to mucobromic acid.341... 

One very interesting case is that of L-rhamnose. Hart and Everett obtained not only the expected 5-keto-L-rhamnonic acid but also 5-keto-L-mannonic acid (5-keto-D-gulonic acid) this was the first reported instance in which a — CH3 group had been oxidized by bromine water to a — CHaOH group. The yields of the brucine salts of the two acids were... 

Oxidation of an aldose with bromine water at neutral pH converts the aldehyde group to a carboxyl group. Hydrobromous acid formed by the reaction of water with bromine acts as an oxidizing agent. Ketoses are not readily oxidized by bromine water. Aldoses are not only oxidized by bromine water but also by the alkaline iodine solution. 

There are a number of ways in which an aldose can be converted into another aldose of one less carbon atom. One of these methods for shortening the carbon chain is the Ruff degradation. An aldose is oxidized by bromine water to the aldonic acid oxidation of the calcium salt of this acid by hydrogen peroxide in the presence of ferric salts yields carbonate ion and an aldose of one less carbon atom (see Fig. 34.3). 

In the presence of a tertiary amine, in particular pyridine (Sec. 31.6), an equilibrium is established between an aldonic acid and its epimer. This reaction is the basis of the best method for converting an aldose into its epimer, since the only configuration affected is that at C-2. The aldose is oxidized by bromine water to the aldonic acid, which is then treated with pyridine. From the equilibrium mixture thus formed, the epimeric aldonic acid is separated, and reduced (in the form of its lactone) to the epimeric aldose. See, for example, Fig. 34.4. 

When borneol (ROH) is fed to a dog, this toxic substance is excreted as compound P, QHgOe—OR, where R stands for the bornyl group. Compound P does not reduce Benedict s solution. It reacts with aqueous NaHC03 with the liberation of a gas. Treatment of P with aqueous acid yields borneol (ROH) and D-glucuronic acid (Table 34.1), which is oxidized by bromine water to D-glucaric acid. 

The sugar T is levorotatory and has the formula C HjoOj it reduces Tolicns reagent and Benedict s solution. T is oxidized by bromine water to optically active CsHioO, and by nitric acid to optically inactive C5HHO7. T forms an osa/one that is identical with the osazone obtained from another pentose, (- )-U. Degradation of (- )-U, followed by oxidation by nitric acid, yields optically inactive C4Ht,Oft. 

Oxidation by bromine water converts (+)-maltose into ihe monocarboxylic acid D-maltobionic acid. Treatment of this acid with methyl sulfate and sodium hydroxide yields (octa-O-methyl-D-maltobionic acid. Upon hydrolysis in acidic solution, the methylated acid yields two products, 2,3,5,6-tetra-O-methyl-o-gluconic acid and 2,3,4,6-tetra-O-methyl-D-glucose. 

Oxidation by bromine water of (-) erythrose and (-) threose will give the same carboxylic acids formed from R-glyceraldehyde ... 

Isomaltose is oxidized by bromine water to isomaltonic acid. Methylation of isomaltonic acid and subsequent hydrolysis yields... 

Isomaltose is oxidized by bromine water to isomaltonic acid. Methylation of isomaltonic acid and subsequent hydrolysis yields 2,3,4,6-telra-O-methyl-D-glucose and 2,3,4,5-tetra-O-methyl-D-gluconic acid. 

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