$\mathrm{CH}_3 \mathrm{CHO}$ and $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}$ can be distinguished…

$\mathrm{CH}_3 \mathrm{CHO}$ and $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}$ can be distinguished chemically by
  1. Benedict test
  2. Iodoform test
  3. Tollen's reagent test
  4. Fehling solution test

Solution

$\mathrm{CH}_3 \mathrm{CHO}$ and $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}$ both being aliphatic aldehydes react with Tollen's reagent, Fehling solution and Benedict solution. So, these reagents cannot be used to distinguish them. $\mathrm{CH}_3 \mathrm{CHO}$ reacts with $\mathrm{NaOH}$ and $\mathrm{I}_2$ to give yellow crystals of iodoform while $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}$ does not react with it.
$\begin{aligned}
\mathrm{CH}_3 \mathrm{CHO}+3 \mathrm{I}_2+ & 4 \mathrm{NaOH} \longrightarrow \mathrm{CHI}_3 +\mathrm{HCOONa}+3 \mathrm{NaI}+3 \mathrm{H}_2 \mathrm{O} \\
\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}+\mathrm{I}_2 & +\mathrm{NaOH} \longrightarrow \text {No reaction }
\end{aligned}$
Thus, $\mathrm{CH}_3 \mathrm{CHO}$ and $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{CHO}$ can be distinguished by iodoform test.

Asked in: NEET 2012 (Screening)

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