(vii) Name the reagent which on reaction with glucose confirms
the presence of five hydroxyl groups in glucose :
Answers
The reagent, which on reaction with glucose, confirms the presence of five hydroxyl groups in glucose is acetic anhydride, represented by the chemical formula (CH₃CO)₂O.
• When glucose is reacted with acetic anhydride, it forms pentacetate, confirming the presence of five hydroxyl (OH) groups in it.
• It is a known property of an anhydride to form an ester and an acid on reacting with a compound containing the hydroxyl group.
• One OH group produces only one ester (acetate) group.
• Therefore, formation of five ester or acetate molecules on reaction of glucose with acetic anhydride confirms that five hyroxyl (OH) groups are present in one molecule of glucose.
• The above reaction can be represented as follows :
CHO(CHOH)₄CH₂OH (glucose) + 5(CH₃CO)₂O →CHO(CHOCOCH₃)₄CH₂OCH₃O (penta acetyl glucose / penta-acetate) + 5CH₃COOH