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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    As already stated, the two methyl glucosides are regarded as stereo- isomeric 7-oxides,1 and have the following structural formulae:— CH30—CH HC OCH3 ' / HCOH HOCH \ HC HCOH HCOH CH2OH a-Methyl glucoside. CH2OH /3-Methyl glucoside. Glucose Pentacetates.—Under proper experimental conditions, all five hydroxyl groups in glucose become acetylated, the a- or 0- pentacetate predominating in the product according to the method adopted. As these compounds form the starting-point for a number of syntheses, it is important to understand fully the methods of pre- paring them. They have the following formulae :— HC . OAc CH2 . OAc a-Glucose pentacetate. [Ac = C2H30] HC—OAc 0 HC . OAc i H2. OAc /3-Glucose pentacetate. To obtain the a-pentacetate it is necessary to acetylate glucose instantly before isomeric change can take place, since the presence of acid greatly accelerates the isomeric change from a- to /3-glucose. This is done by adding anhydrous a-glucose to boiling acetic anhydride con- taining a small quantity of zinc chloride as catalyst. A violent action ensues, and the sugar passes into solution. The product is poured into water, which is changed from time to time to remove the acetic 1 It (is a characteristic property of ■y-hydroxyacids to lose water very readily, forming ring compounds containing four atoms of carbon and one of oxygen : these are termed 7-lactones. Thus— CH2(OH) . CHa. CH2. C02H = HoO + CH2. CH2. CH2. CO 7-Hydroxybutyric acid. 7-Butyrolactone. Similar four carbon-oxygen ring compounds when derived from 7-hydroxy compounds other than acids are named 7-oxides. The ring is termed a pentaphane ring.
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