Organic 2 Review Problem 161

Organic 2 Review Problem 161 - PREPARATIONS '45...

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PREPARATIONS '45 a-methylglucoside, together with the more soluble (3-methyl- glucoside: the amount of the latter is too small, however, to warrant attempted isolation. If difficulty is experienced in inducing the first crude crop of the a-glucoside to ciystallise, place a few drops of the solution on a watch-glass and expose freely to the air, with occasional scratching: meanwhile keep the main volume of the solution securely corked in the conical flask. After an interval of varying length (possibly several days), partial crystallisation occurs in the material on the watch-glass. Then seed the solution with this material: crystallisation of the first main crop will rapidly follow. a-Methylglucoside responds to General Tests i and 2 for carbo- hydrates given on p. 366 (blackening with sulphuric acid, and Molisch's test). Since, however, the glucoside does not contain a free aldehydic hydroxyl group, it does not possess the reducing properties of glucose itself. Confirm this by applying to pure a-methylglucoside Tests i and
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