Question

Name the reagents used in the following reactions : (i) Oxidation of a primary alcohol to aldehyde (ii) Oxidation of a primary alcohol to carboxylic acid

Hint:

Remember: PCC is a mild oxidizing agent that stops oxidation at the aldehyde stage, whereas acidified potassium dichromate and potassium permanganate are strong oxidizing agents that convert primary alcohols into carboxylic acids.

Answer 1

Step 1: The key principle is selectivity of oxidation.
Primary alcohols can be partially oxidized to aldehydes or completely oxidized to carboxylic acids. The reagent strength determines which product forms.
Step 2: Reagent for oxidation to aldehyde.
Pyridinium Chlorochromate (PCC) in $CH_2Cl_2$ is a mild, selective oxidizing agent. It converts primary alcohols to aldehydes and stops: $RCH_2OH \xrightarrow{\text{PCC}} RCHO$. Stronger agents would over-oxidize to carboxylic acid. \[ \boxed{(i)\ \text{PCC (Pyridinium Chlorochromate)}} \]
Step 3: Reagent for oxidation to carboxylic acid.
Acidified potassium dichromate ($K_2Cr_2O_7/H_2SO_4$) or acidified $KMnO_4$ is a strong oxidizing agent that converts the primary alcohol completely to carboxylic acid: $RCH_2OH \xrightarrow{K_2Cr_2O_7/H^+} RCOOH$. \[ \boxed{(ii)\ \text{Acidified } K_2Cr_2O_7 \text{ (or acidified } KMnO_4)} \]