Question

What is the action of ethane-1, 2 - diol on acetone?

Hint:

Cyclic acetals/ketals are used in organic synthesis as "protecting groups" for the carbonyl group because they are stable to bases.

Answer 1

Step 1: Understanding the Concept:
Ketones react with 1,2-diols in the presence of an acid catalyst to form cyclic structures known as ketals.
Step 3: Detailed Explanation:
Acetone (\(CH_3COCH_3\)) reacts with ethane-1,2-diol (ethylene glycol) in the presence of dry \(HCl\) gas or \(p\)-toluenesulfonic acid.
One molecule of water is eliminated, and the two hydroxyl oxygens of the glycol bond to the carbonyl carbon of acetone.
The product is 2,2-dimethyl-1,3-dioxolane (ethylene glycol ketal).
Reaction:
\[ (CH_3)_2C=O + HO-CH_2-CH_2-OH \xrightarrow{H^+} \text{Cyclic Ketal} + H_2O \]
Step 4: Final Answer:
The action of ethane-1,2-diol on acetone produces a cyclic ketal.