QUANTITATIVE ANALYSIS 45719-2 390."• 39° g- C1G. MoI.) pcntacetylglucose contain X Acetyl groupiooo 1-500= 4 99 Acetyl groupsNOTE, (i) The above method (pp. 455~45?) is sometimes used in preference[,to that given on p. 450 in order to determine the number of hydroxyl groups.•.in an unidentified polyhydric alcohol. The alcohol is acetylated by any of the[ftandard methods, a marked excess of the acetylating reagent being used to!ensure complete acetylation of all hydroxyl groups present. The polyacetyl^compound is then purified and its molecular weight determined: the numberlof acetyl groups present (and therefore the number of hydroxyl groups iri the-original alcohol) is then estimated by the above method. The advantage ofthis longer method is chiefly that the estimation of the number of acetyl groups•by quantitative hydrolysis is more accurate (particularly for a substance of^unknown constitution) than that of the number of hydroxyl groups by quan-titative acetylation.
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