Bromine water, aldose oxidation

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. 

Oxidation of an aldose with bromine water at neutral pH converts the aldehyde group to a group and resulted to form. 

Bromine water oxidizes aldose to lactones which hydrolyze to alfonic acids. 

Aldoses can be degraded by the following two reactions. First the aldehyde is oxidized with bromine water to form a carboxylic acid. Next the carboxylic acid is decarboxy-lated with hydrogen peroxide and ferric sulfate leaving an aldehyde. The new aldose is one carbon shorter. When glucose is degraded in this manner, and the product is oxidized by dilute nitric acid, an optically active compound is formed. 

The oxidation of the aldehyde or hemiacetal group of an aldose sugar with bromine water leads to the formation of a strongly acid solution, regardless of whether the oxidant be considered as hypobromous acid or as free bromine hydrobromic acid is formed in either case. Since the... 

Isbell and Hudson identified lactones as the oxidation products of aldoses in buffered solution. The conditions were such that any free aldonic acid formed would be converted into the salt. Hence, lactones are the initial oxidation products and it was concluded that cyclic sugars give 5-lactones by oxidation with bromine water. The reactions were carried out in a solution buffered with barium carbonate and carbon dioxide. In the slightly acidic medium employed, the oxidation was rapid and interconversion between the anomeric forms of the sugars was relatively slow. In some cases the oxidation was 95% complete in five minutes. The extent of the reactions can be seen in Table X. 

In their speed of reaction with the halogens, in acid or in alkaline solutions, the simple sugars may be divided into two main classes, the aldoses and the ketoses. The oxidation of the former is very rapid compared with that of the latter. Kiliani showed that when D-glucose and D-fructose were each treated with an equal weight of bromine in water, the ketose required 350-500 hours for completion of the oxidation, in contrast to two to three hours for the aldose. The same difference exists in buffered solutions Honig and Ruzicka found that the rates were two hours and five minutes, respectively. In alkaline solution under controlled conditions, the aldoses can be quantitatively oxidized with sodium hypoiodite in the presence of D-fructose or L-sorbose without appreciable attack on the ketoses. Ochi reported a similar but less clear-cut difference with calcium hypochlorite as the oxidant. Chlorous acid attacks only the aldoses, leaving the ketoses unaltered. The same effect was noted with the keto acids Kiliani reported that 2-keto-L-rhamnonic acid was stable to the action of bromine water. A little preliminary work has been done with iodic acid by Williams and Woods who found that D-fructose was oxidized more rapidly than the aldoses. No confirmation of this work has appeared. 

The conversion of a-hydroxy acids into aldehydes with one less carbon has great importance in the chemistry of sugars. Oxidation with bromine water transforms aldoses into the corresponding aldonic acids, which, in the form of their calcium salts, are treated with aqueous hydrogen peroxide in the presence of ferrous or ferric sulfate (Fenton reagent) and are degraded to aldoses with one less carbon (Ruff degradation) (equation 479) [57]. 

Aldoses can be oxidized in four important ways (a) by Fehling s or Tollcns reagent (b) by bromine water (c) by nitric acid and (d) by periodic acid, HIO4. 

Bromine water oxidizes aldoses, but not ketoses as an acidic reagent it does not cause isomerization of the molecule. It can therefore be used to differentiate an aldose from a ketose, and is the reagent chosen to synthesize the aldonic acid (monocarboxylic acid) from an aldose. 

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. 

Aldoses oxidized with bromine. Aldaric acid obtained after nitric acid oxidation. Pyridine contained water. Reactions carried out in deuterium oxide. Am-berlite IRA-400 (OH). 

Bromine water is an oxidizing agent that oxidizes the aldehyde group to the carboxyl group and aldoses to aldonic acids. 

Isbell HS, Hudson CS. The course of the oxidation of the aldose sugars by bromine water. Bur Stand J Res 1932 8 327-338. 

Bromine water is a general reagent that selectively oxidizes the —CHO group to a — CO2H group, thus converting an aldose to an aldonic acid ... 

Just as the Kiliani—Fischer synthesis can be used to lengthen the chain of an aldose by one carbon atom, the Ruff degradation can be used to shorten the chain by a similar unit. The Ruff degradation involves (1) oxidation of the aldose to an aldonic acid using bromine water and (2) oxidative decarboxylation of the aldonic acid to the next lower aldose using hydrogen peroxide and ferric sulfate. d-(—)-Ribose, for example, can be degraded to D-(—)-erythrose ... 

With other oxidizing agents, it is possible to obtain reducing sugars. Bromine water produces a mixture of the corresponding aldoses and 2-ketoses. Before the bacterial process was perfected, oxidation of sorbitol by bromine to sorbose was widely used in the laboratory. (See 106).)... 

The mechanism of the oxidation of aldoses by bromine in the presence of barium carbonate and bromides (pH about 5.4) has been studied by Isbell and Pigman 187). Under these conditions the active oxidant is free bromine and not hypobromous acid. Molecular chlorine has been found to be the active oxidant in the oxidation of glucose by buffered chlorine water at pH 2.2 and 3.0 188). 

FIGURE 22.28 Oxidation of an aldose with bromine in water gives an aldonic acid. Note that the functional groups at the two ends of the molecule are stiU different from each other. 

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