Chemistry 2008 JAMB Past Questions - Question 42: If glucose is heated with concentrated tetraoxosulphate(VI) acid, it will be dehydrated to

Correct Answer

A

Explanation

When glucose is heated with concentrated tetraoxosulphate(VI) acid (H2SO4), it will be dehydrated to **levoglucosan**.

Here's the explanation:

**Reaction:**

C6H12O6 (glucose) -> C6H10O5 (levoglucosan) + H2O

**Mechanism:**

1. Concentrated H2SO4 acts as a **dehydrating agent**, meaning it removes water molecules from the reactant molecule.
2. In this case, H2SO4 abstracts a hydroxyl group (-OH) from two adjacent carbon atoms in the glucose molecule, forming a double bond between the carbons and releasing a water molecule.
3. This process continues throughout the glucose molecule, resulting in the formation of a six-membered ring with a double bond (levoglucosan).

**Key points:**

* Levoglucosan is a six-carbon sugar with a similar structure to glucose but with one less water molecule.
* The dehydration reaction occurs due to the strong acidic properties of concentrated H2SO4, which readily accepts protons from hydroxyl groups.

**Additional notes:**

* The specific position of the double bond in levoglucosan can vary depending on the reaction conditions.
* This dehydration reaction is an example of a more general class of reactions called **acid-catalyzed dehydration**.