Question

Which of the following methods can be used to synthesize potassium permanganate commercially?

• A. Fusing KOH with $Mn{O}_2$ and heating the mixture in air followed by electrolytic oxidation of the product in basic medium
• B. Heating a fused mixture of KOH, $Mn{O}_2$ and $KCl{O}_3$ followed by electrolytic oxidation of the product from in basic medium
• C. Heating a fused mixture of KOH, $Mn{O}_2$ and $KN{O}_3$ followed by electrolytic oxidation of the product from in basic medi
• D. Only b and c
• E. All three options – a, b and c are correct

Answer 1

The correct option is E

All three options – a, b and c are correct

Industrially, Potassium permanganate is produced in large quantities from manganese dioxide, which is obtained from the mineral pyrolusite. $Mn{O}_2$ is fused with potassium hydroxide and heated in air. Alternatively, we can fuse KOH, $Mn{O}_2$ and some other chemical compound that acts as a source of oxygen - like potassium nitrate or potassium chlorate.
In terms of a chemical reaction, we have:
$2Mn{O}_2+4KOH+O_2\to 2K_{2}Mn{O}_4+2H_{2}O$
When we use an oxygen source,
$3Mn{O}_2+6KOH+KCl{O}_3\stackrel{\Delta }{\to }3K_{2}Mn{O}_4+KCl+3H_{2}O$
Now Potassium Managanate $K_{2}Mn{O}_4$ solution (dark green) is electrolytically oxidized to Potassium permanganate.
$K_{2}Mn{O}_4+H_{2}O\to KMn{O}_4+KOH+\frac{1}{2}{H}_2$
Hence, option e is the appropriate choice.
Although not of any commercial value, these reactions are important in terms of understanding the chemistry of Permanganate anion.
$2K_{2}Mn{O}_4+C{l}_2\to 2KMn{O}_4+2KCl$
Acidifying the dark green solution of Potassium Manganate results in a disproportionation reaction:
$3K_{2}Mn{O}_4+2H_{2}S{O}_4\to 2KMn{O}_4+2K_{2}S{O}_4+Mn{O}_2+2H_{2}O$