Glucose on prolonged heating with HI gives:

A) hexanoic acid

B) iodohexanal

C) n-hexane

D) 1-hexene

When glucose is subjected to prolonged heating with hydrogen iodide (HI), the primary product formed is iodohexanal (option B). This reaction involves the conversion of glucose, a six-carbon sugar, into a more stable compound through a series of steps that include the cleavage of the sugar's ring structure and subsequent reactions with HI.

The Reaction Process

To understand why iodohexanal is the product, let’s break down the process:

• Initial Breakdown: Glucose, which is a hexose (six-carbon sugar), can undergo a process called hydrolysis when heated with HI. This involves breaking the glycosidic bonds and converting the cyclic form of glucose into its open-chain form.
• Formation of Iodo Compounds: The open-chain form of glucose contains an aldehyde group (-CHO) at one end. When HI is present, it can react with this aldehyde group, leading to the formation of iodohexanal. This reaction replaces the hydrogen atom of the aldehyde with an iodine atom.
• Further Reactions: Depending on the conditions, further reactions can occur, but the primary product remains iodohexanal.

Why Not the Other Options?

Let’s briefly consider why the other options are not the correct answers:

• Hexanoic Acid (A): This is a carboxylic acid with a six-carbon chain. While glucose can be oxidized to form acids, the reaction with HI does not lead to this product.
• n-Hexane (C): This is an alkane and would require a reduction process rather than the reaction with HI, which does not favor the formation of alkanes from sugars.
• 1-Hexene (D): This is an alkene and would require elimination reactions, which are not the primary pathway when glucose is heated with HI.

Conclusion

In summary, the prolonged heating of glucose with hydrogen iodide primarily yields iodohexanal due to the reaction of the aldehyde group with iodine. This process highlights the unique reactivity of sugars under specific conditions and the transformation of functional groups in organic chemistry.