Sugar peroxide, oxidation

Isbell and co-workers (51) have tried to minimize the oxygen reaction and to maximize the peroxide reaction. When a large excess of peroxide and a low temperature were maintained, they found that the monosaccharides are converted almost quantitatively to formic and two-carbon acids. Table II presents results for the peroxide oxidation of 14 sugars. The total acid produced from aldo-hexoses under favorable conditions is about six moles, consisting almost entirely of formic acid. Aldopentoses react more rapidly than aldo-hexoses and yield about five moles of formic acid per mole of pentose. Fructose and sorbose yield approximately five moles of total acid of which four moles are formic acid. Glycolic acid was identified qualitatively but not determined quantitatively. L-Rham-nose and L-fucose yield about five moles of acid, including four moles of formic acid. Acetic acid was identified only qualitatively. 

One of the most useful methods for shortening the carbon chain of a sugar involves oxidation of a soluble salt of the aldonic acid with hydrogen peroxide in the presence of ferric acetate 184), Prior to the development of this method by Ruff, H. J. H. Fenton had shown that tartaric acid is oxidized by hydrogen peroxide in the presence of ferrous salts, but apparently no oxidative cleavage of carbon-carbon bonds was noted. The ferrous ion-catalyzed oxidation was extended to many carbohydrates by associates of Fenton (Chapter VI) and by other workers 185), The ferric ions used as the catalyst in the Ruff method permit the oxidation of aldonic acids but are inactive with respect to sugars. Ferrous ions are much less selective. 

Catalytic oxidation of sugars and alcohols is a more direct method. Hydrogen peroxide and iron salts were used originally (see under Hydrogen peroxide oxidations). However, much better yields have been obtained by the direct oxidation with cupric salts 159). The action of a limited excess of cupric acetate for a short time on methanol solutions of L-sorbose or l-xylose has given a 60 % yield of the osone. 

Ghromium(III) Compounds. Chromium (ITT) is the most stable and most important oxidation state of the element. The E° values (Table 2) show that both the oxidation of Cr(II) to Cr(III) and the reduction of Cr(VI) to Cr(III) are favored in acidic aqueous solutions. The preparation of trivalent chromium compounds from either state presents few difficulties and does not require special conditions. In basic solutions, the oxidation of Cr(II) to Cr(III) is still favored. However, the oxidation of Cr(III) to Cr(VI) by oxidants such as peroxides and hypohaUtes occurs with ease. The preparation of Cr(III) from Cr(VI) ia basic solutions requires the use of powerful reducing agents such as hydra2ine, hydrosulfite, and borohydrides, but Fe(II), thiosulfate, and sugars can be employed in acid solution. Cr(III) compounds having identical counterions but very different chemical and physical properties can be produced by controlling the conditions of synthesis. 

Exhaustive oxidation of sulphones to sulphate using a mixture of potassium chlorate, sodium peroxide and sugar in a bomb has also been recommended220. This procedure is known as the Parr method and produces a mixture of soluble alkali sulphates. 

A micro-bomb calorimeter exploded when the wrong proportions of sample and oxidants were used. Instead of 4 g of peroxide and 0.2 g of nitrate for 0.2 g of the sugar sample, 0.35 g of peroxide and 2.6 g of dextrose were used. The deficiency of peroxide to absorb the decomposition gases and excess of organic matter led to a rapid rise in temperature and pressure, which burst the bomb calorimeter. 

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