Aldoses Ruff degradation

The Kiliani-Fischer synthesis accomplishes the opposite of the Ruff degradation. Ruff degradation of either of two C2 epimers gives the same shortened aldose, and the... 

Kiliani-Fischer synthesis converts this shortened aldose back into a mixture of the same two C2 epimers. For example, glucose and mannose both undergo Ruff degradation to give arabinose. Conversely, the Kiliani-Fischer synthesis converts arabinose into a mixture of glucose and mannose. 

The well-known Ruff degradation of aldonic acids to aldoses with one less carbon was first applied with bromine as the oxidant. Calcium D-gluconate was treated with an excess of bromine at 20° for ten hours the acidity of the solution was kept low with lead carbonate. The filtrate was processed and D-arabinose was obtained in small yield as the oxime. However, Ruff found that the effect of hydrogen peroxide was much better and abandoned the use of bromine. Fenton noted the same effect in the oxidation of tartaric acid to dihydroxymaleic acid the action of oxygen was more effective than that of the halogens. It was assumed that a keto aldonic acid was the intermediate in the degradation of the aldonic acid to the new aldose, and the apparent stability of the keto acids to further oxidation by bromine may be the reason for the low yields with this oxidant. 

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]. 

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). 

Thus in the Ruff degradation, for example of o-glucose to o-arabinose, the aldose is oxidized electrolytically to the aldonic acid and this on treatment with hydrogen peroxide and ferric acetate affords the 2-ketoaldonic acid (aldosulose), which yields D-arabinose by loss of carbon dioxide. The yield of aldopentose from the aldonic acid... 

The Ruff degradation, in its classical version, conversion of the calcium salt of an aldonic acid to the aldose of one fewer carbon atoms by treatment with Fe and hydrogen peroxide, was one of the reactions used by Emil Fischer in his determination of the structure of the aldoses. Its success with Fe is mysterious, as one would expect Fenton chemistry involving HO to give molecular rubble, rather than good yields of a single product. However, the reaction is catalysed by transition metals in general (even with... 

The Ruff degradation is the opposite of the Kiliani-Fischer synthesis. Thus, the Ruff degradation shortens an aldose chain by one carbon Hexoses are converted into pentoses, and pentoses are converted into tetroses. In the Ruff degradation, the calcium salt of an aldonic acid is oxidized with hydrogen peroxide. Ferric ion catalyzes the oxidation reaction, which cleaves the bond between C-1 and C-2, forming CO2 and an aldehyde. It is known that the reaction involves the formation of radicals, but the precise mechanism is not well understood. 

The calcium salt of the aldonic acid necessary for the Ruff degradation is easily obtained by oxidizing an aldose with an aqueous solution of bromine and then adding calcium hydroxide to the reaction mixture. 

Reduction of an aldose forms one alditol reduction of a ketose forms two alditols. Br2 oxidizes aldoses, but not ketoses ToUens reagent oxidizes both. Aldoses are oxidized to aldonic acids or aldaric acids. Aldoses and ketoses react with three equivalents of phenyUiydrazine, forming osazones. C-2 epimers form identical osazones. The Kiliani-Fischer synthesis increases the carbon chain of an aldose by one carbon— it forms C-2 epimers. The Ruff degradation decreases the carbon chain by one carbon. The OH groups of monosaccharides react with acetyl chloride to form esters and with methyl iodide/silver oxide to form ethers. 

Treatment with sodium borohydride converts aldose A into an optically inactive alditol. Ruff degradation of A forms B, whose alditol is optically inactive. Ruff degradation of B forms D-glyceraldehyde. Identify A andB. 

The hydroxyamine (f) readily loses NH3 on the heating to give the aldehyde. This sequence achieves the removal of Cl from an aldose to form a new aldose with one less carbon, just like the Wohl and Ruff degradations. 

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 ... 

The Ruff degradation and the Kiliani—Fischer synthesis allow us to place all of the aldoses into families or family trees based on their relation to D- or L-glyceraldehyde. Such a tree is constructed in Fig. 22.7 and includes the structures of the D-aldohexoses, 1-8. 

In Chapter 19 (Section 19.2.4), a carboxylic acid was reduced to an aldehyde. When the salt of an aldonic acid such as the calcium salt of d-gluconic acid (87) is treated with hydrogen peroxide and iron(III), the product is an aldose of one fewer carbon atom—in this case, 14 (d-ribose). This reaction, which oxidatively cleaves one carbon (lost as CO2), is called the Ruff degradation, after Otto Ruff (Germany ... 

The Ruff degradation is an oxidative decarboxylation. The sugar is first oxidized to the aldonic acid by aqueous bromine. Exposure to hydrogen peroxide in the presence of ferric ion then leads to the loss of the carboxy group and oxidation of the new terminus to the aldehyde function of the lower aldose. During this process, the stereochemistry of the hydroxy carbon next to the carbonyl is lost. Consequently, two epimeric aldoses at that center will give the same new sugar. 

RUFF - FENTON Degradation Oxidative degradation of aldoses via a-hydroxy acids to lower chain aldoses. 

Ferric ion catalyzes the formation of the hydroperoxyl radical, according to Eq. (35) such a radical appears to constitute the oxidant in the Ruff method of degrading aldonic acids to the next lower aldoses. A number of examples of the use of this reagent in the laboratory are given in a review article by Moody.108 The hydroperoxyl radical, which is not so effective an oxidant as the hydroxyl radical, does not attack aliphatic alcohols accordingly, a substantial yield (about 50%) of the aldose is obtained from the higher aldonic acid. In the presence of an excess of hydrogen peroxide, however, the accumulation of ferrous ions in solution catalyzes the production of hydroxyl radicals and lowers the yield of aldose [see Eq. (36)]. 

Starting from a salt of an aldonic acid, the Ruff oxidative degradation reaction1 leads to an aldose with loss of one carbon atom. Known since 1898, the original process used aqueous hydrogen peroxide as oxidant, in the presence of catalytic amounts of ferric salts. 

RUFF - FEMTOH Degradation Oxidalive degradation [Pg.397]

The Wohl deffvdation, an alternative to the Ruff d radation, is nearly the reverse of the Kiliani-Fischer synthesis. The aldose carbonyl group is converted to the oxime, which is dehydrated by acetic anhydride to the nitrile (a cyanohydrin). Cyanohydrin formation is reversible, and a basic hydrolysis allows the cyanohydrin to lose HCN. Using the following sequence of reagents, give equations for the individual reactions in the Wohl degradation of D-arabiiK>se to D-erythrose. Mechanisms are not required. 

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