Question

Give one chemical test to distinguish between the following pairs of compounds:
(i) Ethylamine and diethylamine
(ii) Acetaldehyde and benzaldehyde

Answer 1

(i) These can be distinguished by the carbylamine test. Ethylamine is primary $\left(1^o\right)$ amine therefore, it gives carbylamine test i.e., when heated with an alcoholic solution of $KOH$ and $CH{Cl}_3$, it givers an unpleasant foul smell of isocyanide which is easily detectable.
$C_2{H}_5{NH}_2+CH{Cl}_3+alc.KOH⟶\underset{Ethylisocyanide}{C_2{H}_{5}NC}+3KCl+3H_{2}O$
On the other hand, diethylamine is a secondary $\left(2^o\right)$ amine and hence does not give this test.
(ii) When acetaldehyde is heated with Fehling's solution, red precipitate of cuprous oxide is formed
$\underset{Acetaldehyde}{{CH}_{3}CHO}+\underset{\downarrow Fehlin{g}^{\prime }ssolution}{2CuO}⟶\underset{(Redppt.)}{{Cu}_{2}O\left(s\right)\downarrow }+{CH}_{3}COOH$
On th eother hand, benzaldehyde does not give red precipitate with Fehling's solution.