Aldonic acids hypoiodite

The fourth student in this group, Stanford Moore, began his doctoral thesis research with Link in 1935. His work involved the development of a new, and still useful, procedure for oxidizing aldoses to the aldonic acids by potassium hypoiodite in methanol solution the resulting aldonic acids were then converted into nicely crystalline benzimidazole derivatives that proved more suitable for the characterization of carbohydrates than the classical osazones. This method, developed by Moore and Link (1940), was extended to the characterization of hexuronic acids, as their bis(benzimidazole)s, after oxidation to the glycaric acid (R. Lohmar, Dimler, Moore, and Link, 1942), of lactic acid (Moore, Dimler, and Link, 1941 Dimler and Link, 1942), and of ribose, fucose, and digitoxose (Dimler and Link, 1943). During these... 

Bromine (hypobromite) and hypoiodite oxidations are particularly useful for the preparation of aldonic acids from aldoses and of aldaric acids from glycuronic acids. Primary alcohol groups also undergo oxidation by these reagents, although this conversion is of less value glycosides can thus be converted into glycosiduronic acids, and alditols into aldoses and aldonic acids. 

Alkaline hypoiodite oxidizes aldoses, under carefully controlled conditions, almost quantitatively to aldonic acids (see preceding chapter). Measurement of the iodine consumed permits quantitation of the amount of aldose originally present [Eq. (19)]. 

Ribose may be identified through the benzimidazole from ribonic acid, 2-(D-n6o-tetrahydroxybutyl)benzimidazole52 53 54 and its picrate and hydrochloride. However, caution must be used at two points in this procedure. In the first place, the customary oxidation of ribose with alkaline hypoiodite produces both ribonic and arabonic acids, the latter being formed by the alkali-induced epimerization of the former. While this epimerization may be avoided by using a buffered oxidizing mixture such as bromine-barium benzoate,65 there is, in the second place, further risk of epimerization during the condensation of the aldonic acid with o-phenylenediamine, particularly if there is insufficient acid present.9 10-11... 

The field of halogen oxidation has developed primarily in two directions. The first is the preparation of aldonic acids by oxidation with bromine in acid solution. The second is the use of alkaline hypoiodite as a quantitative oxidant. Little work has been done on the mechanism of these reactions. The conditions under which the reactions are carried out have usually been established empirically without extensive study. The further use of solutions of known concentration and the comparison of various oxidants under similar conditions are to be desired. Critical oxidation potentials of various sugars used in relation to possible oxidants and ranges of pH might yield promising results. 

Moore and Link developed a method for the oxidation of aldoses with hypoiodite in methanol to produce aldonic acids, which are isolated as the potassium or barium aldonates in 90% yield. The procedure was worked out for the purpose of preparing... 

Iodine is not reactive in an acidic medium. In a basic medium, it is converted into hypoiodite, a powerful oxidant, and quantitatively oxidizes aldoses into aldonic acids according to reaction (6.2), which is of analytical as well as preparative value. 

This method involves the oxidation of aldoses to aldonic acids by potassium hypoiodite in methanol and the condensation of the isolated potassium salt of the aldonic acid in hot acid with o-phenylenediamine (M3). The specific aldobenzimidazole can be identified by the solubility in water, optical rotation in acid, and melting point. This method is not as simple as chromatography. It requires dehydration of the sample and a relatively high concentration of the sugars to be identified. 

On oxidation (with hypoiodite) to the corresponding aldonic acid, of the disaccharide obtained by partial hydrolysis of chitin, and acetylation with sodium acetate in acetic anhydride, the product undergoes /3-elimination, to give the bionic acid derivative 2-acetamido-4-0-(2-acetamido-tri-0-acetyl-2-deoxy- -D-glucopyranosyl)-6-0-acetyl-2,3-dideoxy-D-erj/(firo-hex-2-enono-1,5-lactone (90). In the original work, the determination of the site... 

Bromine and hypoiodite oxidations are particularly suitable for the preparation of aldonic acids from aldoses. Similarly, uronic acids are converted to saccharic acids. Of less value is the oxidation of primary alcoholic to aldehydic groups. In this manner, glycosides can be converted to uronides and polyols to aldoses and aldonic acids. 

Oxidation of aldoses with alkaline hypoiodite under carefully controlled conditions can lead to a stoichiometric yield of aldonic acids. This reaction has been used both as a measure of the amount of aldose present in a solution and for the preparation of aldonic acids. Determination of the iodine con-... 

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