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Question
What will happen when D−(+)− glucose is treated with methanolic −HCl followed by Tollens' reagent?
What will happen when D−(+)− glucose is treated with methanolic −HCl followed by Tollens' reagent?
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Solution
The correct option is C No characteristic colour or ppt. will be formed
When D−(+)− glucose is treated with methanolic −HCl followed by Tollens' reagent, no characteristic colour or ppt. will be formed.
Reaction of D−(+) glucose with methanolic −HCl leads to formation of methyl glucoside
(−OH group at C1 of hemiacetal is methylated to form acetal). Acetal, is not hydrolysable by base, so it will not respond Tollen's reagent.
Note: Tollen's reagent oxidises aldehyde to carboxylate group. Tollen's reagent itself is reduced to black silver mirror. If aldehdye group is not free (such as converted to acetal), this reaction will not occur.
When D−(+)− glucose is treated with methanolic −HCl followed by Tollens' reagent, no characteristic colour or ppt. will be formed.
Reaction of D−(+) glucose with methanolic −HCl leads to formation of methyl glucoside
(−OH group at C1 of hemiacetal is methylated to form acetal). Acetal, is not hydrolysable by base, so it will not respond Tollen's reagent.
Note: Tollen's reagent oxidises aldehyde to carboxylate group. Tollen's reagent itself is reduced to black silver mirror. If aldehdye group is not free (such as converted to acetal), this reaction will not occur.
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