Organic 2 Review Problem 473

Organic 2 Review Problem 473 - Q UANTITATIVE A NALYSIS 19-2...

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QUANTITATIVE ANALYSIS 457 19-2 390 ."• 39° g- C 1 G. MoI.) pcntacetylglucose contain X Acetyl group iooo 1-500 = 4 99 Acetyl groups NOTE, (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 number lof acetyl groups present (and therefore the number of hydroxyl groups iri the -original alcohol) is then estimated by the above method. The advantage of this 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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