Question

Write the reaction of glucose with: (a) HI

Hint:

Glucose reduces Br\(_2\) water → gluconic acid, and reacts with HI → straight chain alkane (n-hexane). Used for structural proof.

Answer 1

(a) When glucose is heated with excess HI, it is fully reduced to form n-hexane. This proves that glucose has a straight-chain structure. \[ \text{C}_6\text{H}_{12}\text{O}_6 + \text{HI} \xrightarrow{\Delta} \text{n-C}_6\text{H}_{14} \] \[ \boxed{\text{Glucose} + \text{HI} \rightarrow \text{n-hexane}} \] (b) Br\(_2\) water
Solution:
(b) Br\(_2\) water is a mild oxidising agent. It oxidizes the aldehyde group (–CHO) in glucose to carboxylic acid (–COOH), forming gluconic acid. \[ \text{C}_6\text{H}_{12}\text{O}_6 + \text{Br}_2 \rightarrow \text{C}_6\text{H}_{12}\text{O}_7 + 2\text{HBr} \] \[ \boxed{\text{Glucose} + \text{Br}_2 \rightarrow \text{Gluconic acid}} \]