Question

Write a reaction to distinguish acetaldehyde from acetone.

Write a chemical test to distinguish between the following pair of compounds:

Acetaldehyde and acetone

Answer 1

1. Tollens’ reagent test: Acetaldehyde being an aldehyde reduces Tollens’ reagent to shining silver mirror, whereas propanone being acetone does not.

\[\ce{\underset{\text{Acetaldehyde}}{CH3CHO} + \underset{\text{Tollens’ reagent}}{2[Ag(NH3)2]+} + 3OH- -> \underset{\text{Acetate ion}}{CH3COO-} + \underset{\text{Silver metal}}{2Ag ↓} + 4NH3 + 2H2O}\]

\[\ce{\underset{\text{Acetone}}{CH3COCH3} ->[Tollens{'}reagent] No silver mirror}\]

2. Fehling’s solution test: Acetaldehyde reduces Fehling’s solution to red precipitate of Cu₂O, whereas acetone does not react.

\[\ce{\underset{Acetaldehyde}{CH3CHO} + \underset{{From Fehling’s solution}}{2Cu^2+ + 5OH^-} → \underset{Acetate ion}{CH3COO^-} + \underset{Cuprous oxide (Red ppt{.})}{Cu2O↓} + 3H2O}\]