The simple carbohydrates and the glucosides / by E. Frankland Armstrong.

  • Edward Frankland Armstrong
Date:
1910
Catalogue details

Licence: In copyright

Credit: The simple carbohydrates and the glucosides / by E. Frankland Armstrong. Source: Wellcome Collection.

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    In practice it is preferable to heat the oxime with acetic anhydride and a grain of zinc chloride : a vigorous reaction ensues, and the pent- acetate of gluconic acid nitrile is formed from which hydrogen cyanide is eliminated by treatment with ammoniacal silver oxide. The alternative method due to Ruff makes use of Fenton s mode of oxidation with hydrogen peroxide and ferrous salts. The aldose is first converted into aldonic acid, the calcium salt of which is sub- jected to oxidation, with the result that the carboxyl group is eliminated and a pentose formed. CHO CO-H C02 + H20 CH(OH) I | CH(OH) 1 CHO CH(OH) CH(OH) CH(OH) I I —> CH(OH) —> CH(OH) 1 CH(OH) | | CH(OH) CH(OH) CH(OH) I CH3(OH) | CH2(OH) CH2(OH) Aldohexose. Aldonic acid. Aldopentose. Either of these methods is equally applicable to the conversion of a pentose into a tetrose, and by them it would be possible to pass from glucose to formaldehyde. Interconversion of Glucose, Fructose and Mannose.—Glucose, fructose and mannose pass over into one another in aqueous solution in presence of alkalis. This most important transformation was first observed by Lobry de Bruyn and Van Ekenstein ; it takes place slowly at ordinary temperatures, quickly and with much decomposition at higher temperatures. Starting from glucose, the optical rotation is observed to fall to about 0°; considerably more fructose than mannose is formed in the final product. The change was rightly explained by Wohl as due to conversion into the enolic (unsaturated) form common to all three carbohydrates :— CHO I HCOH I HOCH I HCOH I HCOH I CH2(OH) Glucose. CHO HOCH I HOCH I HCOH I HCOH I CH2(OH) Mannose. CH2(OH) I CO I HOCH I HCOH I HCOH I CHo(OH) Fructose. CH(OH) II C.OH I HOCH I HCOH HCOH I CH2(OH) Enolic form. The sugar originally present is slowly transformed into enol; this is reconverted into all three of the possible hexoses. It is to be sup- posed that the formation of enol from each one of the hexoses and the