Monosaccharides oxidation reactions

Oxidizing the aldehyde group present in aldoses is easy oxidizing the carbonyl group in a ketose is far more difficult. The susceptibility (or lack thereof) to simple oxidation is a useful method of distinguishing between aldoses and ketoses. The next sections explore the various types of monosaccharide oxidation reactions that can occur. 

The presence of alcohol and, in some cases, an aldehyde group makes monosaccharides susceptible to oxidation, whereas the presence of a carbonyl group makes monosaccharides susceptible to reduction. Because monosaccharides are the fundamental carbohydrate, you need to know what happens in the many reactions in which they re involved. The following sections are here to help you out with that. Welcome to the nitty-gritty of monosaccharide oxidation and reduction ... 

A. G. Fadnis, Metal-ion oxidation reactions of monosaccharides a kinetic study, Carbohydr. Res., 146 (1986) 97-105. 

Preliminary examinations of dextran structures were conducted by optical rotation, infrared spectroscopy and periodate-oxidation reactions. More detailed results can be achieved by methylation analysis [19]. The hydroxyl groups are methylated with methyl iodide after activation with sodium methylsulfinyl carbanion (Fig. 2). The methyl dextran is hydrolysed to the corresponding different methylated monosaccharides, which are furthermore reduced and peracetylated. The resulting alditol acetates of methylated sugars are separated by gas chromatography and identified by their retention times. In particular, a combined capillary gas-liquid chromatography/mass... 

Because the products of oxidation reactions are osones, they can tautomerise again to new ene-diolates, which can then in their turn be oxidised. This means that the exact titre depends on the sugar effective extinction coefficients for monosaccharides assayed by the 2,2 -bicinchoninate assay range over a factor of 3 for common sugars." Similar differences between sugars are found with PAHBAH. 

Aldoses can be distinguished from ketoses by observing what happens to the color of an aqueous solution of bromine when it is added to the sugar. Br2 is a mild oxidizing agent and easily oxidizes the aldehyde group, but it cannot oxidize ketones or alcohols. Consequently, if a small amount of an aqueous solution of Br2 is added to an unknown monosaccharide, the reddish-brown color of Br2 will disappear if the monosaccharide is an aldose, but will persist if the monosaccharide is a ketose. The product of the oxidation reaction is an aldonic acid. 

What are some oxidation-reduction reactions of sugars Monosaccharides can undergo various reactions. Oxidation reactions make up one important group. 

Write reactions for monosaccharide oxidation and glycoside formation. (Section 7.5)... 

Write reactions for monosaccharide oxidation and glycoside formation. 

Although five- and six-carbon monosaccharides exist predominately as hemiacetals and hemiketals, they undergo the characteristic reduction and oxidation reactions of simple aldehydes and ketones. The reduction or oxidation reaction occurs by way of the carbonyl group in the small amount of the open-chain form of the monosaccharide in equilibrium with its cyclic hemiacetal or hemiketal. As the reduction or oxidation occurs, the equilibrium shifts to produce more of the carbonyl form until eventually all the monosaccharide reacts. 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

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