Question

Differentiate between acetaldehyde and acetone with suitable reactions.

Answer 1

Acetaldehyde acts as reducing agent and reduce (i) Fehlings solution (ii) Tollen's regent, and (iii) Schiff reagent.
Acetaldehyde itself is oxidised to acetic acid.
Acetone is not oxidised with these reagents as Acetone has no H atom directly attached to carbonyl carbon atom.
(i) Fehlings solution
$C{H}_3-CHO+2C{u}^{2+}+5O{H}^{-}\stackrel{\Delta }{\to }C{H}_3-CO{O}^{-}+C{u}_{2}O\downarrow +3H_{2}O$
$C{H}_3-C\left(O\right)-C{H}_3+2C{u}^{2+}+5O{H}^{-}\stackrel{\Delta }{\to }$ no reaction
(ii) Tollen's regent
$C{H}_3-CHO+2\left[Ag\right(N{H}_3{)}_2{]}^{+}+3O{H}^{-}\stackrel{\Delta }{\to }C{H}_3-CO{O}^{-}+2Ag\downarrow +2H_{2}O+4N{H}_3$
$C{H}_3-C\left(O\right)-C{H}_3+2\left[Ag\right(N{H}_3{)}_2{]}^{+}+3O{H}^{-}\stackrel{\Delta }{\to }$ no reaction
(iii) Schiff reagent.
Acetaldehyde +schiff reagent $\to$ magenta colour is restored.
Acetone +schiff reagent $\to$ magenta colour is not restored.