Question

The most suitable reagent for the conversion of $RC{H}_{2}OH\to RCHO$ is

• A. $KMn{O}_4$
• B. $K_{2}C{r}_2{O}_7$
• C. $Cr{O}_3$
• D. $PCC$ (pyridine chloro chromate)

Answer 1

Answer: (D)

Pyridinium chlorochromate (PCC) $\left(C_5{H}_{5}NHCr{O}_{3}C{l}^{-}\right)$is a very good oxidising agent for converting $1^{\circ }$ alcohol to aldehydes and $2^{\circ }$ alcohols to ketone. It prevents further oxidation of aldehydes to carboxylic acid.
$\underset{\text{p-alcohol}}{RC{H}_{2}OH}\underset{C{H}_{2}C{l}_2\text{solvent}}{\overset{(C{H}_2{H}_{5}N{)}_{2}Cr{O}_3}{\to }}\underset{\text{Aldehyde}}{\mathrm{RCHO}}+H_{2}O$
[PCC is prepared by mixing pyridine $\left(C_5{H}_{5}N\right),Cr{O}_3$ and $HCl$.
$ROH\underset{\text{ acidified }{K}_{2}C{r}_2{O}_7}{\overset{\text{alkaline}KMn{O}_{4}or}{\to }}$ Carboxylic acid
$ROH\stackrel{Cr{O}_3/C{H}_{3}COOH}{\to }$ aldehyde