Question

Which of the following reagents can be used to oxidise primary alcohols to aldehydes?
(a) $Cr{O}_3$ in anhydrous medium
(b) $KMn{O}_4$ in acidic medium
(c) Pyridinium chlorochromate
(d) Heat in the presence of Cu at 573K

Answer 1

$Cr{O}_3$ in anhydrous medium is used to oxidise primary alcohols to aldehydes.
$RC{H}_{2}OH\stackrel{Cr{O}_3\left(anhydrous\right)}{\to }RCHO$
Acidic $KMn{O}_4$ is a very strong oxidising agent. It oxidises primary alcohols into carboxylic acid.
$RC{H}_{2}OH\stackrel{KMn{O}_4}{\to }RCOOH$
Pyridinium chlorochromate $\left(C_6{H}_5\stackrel{+}{N}HClCr{O}_3^{-}\right)$ is a very good reagent for the oxidation of primary alcohols to aldehydes.
$RC{H}_{2}OH\stackrel{PCC}{\to }RCHO$
When the vapours of primary alcohols are passed over heated copper at 573 K, dehydrogenation takes place and an aldehyde is formed.
$RC{H}_{2}OH\underset{573K}{\overset{Cu}{\to }}RCHO$