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.

    21/132 (page 5)
    This action being reversible, it is to be supposed that when an agent such as phenylhydrazine,1 which will act upon aldehyde, is added to the aqueous solution, the small amount of aldehydrol present is attacked and removed; the equilibrium is thereby disturbed, but is rapidly restored by the formation of a fresh quantity of the aldehydrol, which in turn disappears but only to have its place taken by a further quantity. Ultimately the whole becomes converted into the aldehydic derivative. In considering the structure of glucose, the compounds which deserve attention in the first place are the two isomeric methyl-gluco- sides (a and /3), which are formed by the interaction of glucose and methylic alcohol under the influence of hydrogen chloride. These compounds are the prototypes of the natural glucosides. They were discovered by Emil Fischer in 1893. He prepared them by dis- solving glucose in cold methylic alcohol, saturated with dry hydrogen chloride gas. After several hours, when it had lost all cupric reducing power, the mixture was neutralised with lead carbonate. Crystals of the a-compound were obtained on concentrating the solution ; the /3-compound was isolated later from the mother liquor, and was first obtained crystalline by Van Ekenstein. The methyl-glucosides differ considerably from glucose, more par- ticularly in never behaving as aldehydes ; and their rotatory power in solution is the same in a freshly-prepared solution as it is in one which has been kept for some time, which is not the case with glucose. They are undoubtedly formed by the introduction of methyl, in place of an atom of hydrogen, in the hydroxyl group attached to the carbon atom which exercises aldehydic functions in the open-chain form of glucose (glucose-aldehydrol). It is to be noted that the introduction of methyl in this position has the effect of rendering the ring far more stable than it is in glucose, as it is to be supposed that compounds such as phenylhydrazine, and oxidising agents such as Fehling’s solution, are without action because the glucosides do not undergo hydrolysis in solution in the way that glucose does. On reference to the closed-chain formula of glucose, it will be seen that the potentially aldehydic carbon atom (printed in clarendon type), as well as the three other carbon atoms in the ring, and also the atom which is immediately contiguous to the ring on the right-hand side of the formula (page 4), are all asymmetric, in the sense that each of them is associated with four different radicles. Consequently the 1 See Chapter II.