Identify the industrial/laboratory preparation route of potassium permanganate

Potassium permanganate, $\mathrm{KMnO_4}$, is prepared from pyrolusite, $\mathrm{MnO_2}$, in two steps:

• Step 1: Oxidation of $\mathrm{MnO_2}$ with fused $\mathrm{KOH}$ in presence of an oxidizing agent such as $\mathrm{KNO_3}$ or air/oxygen to form potassium manganate.
• Step 2: Conversion of manganate, $\mathrm{K_2MnO_4}$, into permanganate, $\mathrm{KMnO_4}$.

Write the first-step reaction

In the first step, manganese in $\mathrm{MnO_2}$ has oxidation state: $x + 2(-2) = 0 \Rightarrow x=+4$

In manganate ion, $\mathrm{MnO_4^{2-}}$, oxidation state of Mn is: $x + 4(-2) = -2 \Rightarrow x=+6$

So Mn is oxidized from $+4$ to $+6$, giving manganate.

The product formed is therefore: $\mathrm{K_2MnO_4}$

A representative reaction is: $2\mathrm{MnO_2} + 4\mathrm{KOH} + \mathrm{O_2} \rightarrow 2\mathrm{K_2MnO_4} + 2\mathrm{H_2O}$

When $\mathrm{KNO_3}$ is used, it acts as the oxidizing agent in place of oxygen.

Check options

• A: $\mathrm{K_3MnO_4}$ — not the product formed in this process.
• B: $\mathrm{K_4[Mn(OH)_6]}$ — not involved here.
• C: $\mathrm{K_2MnO_4}$ — correct, this is potassium manganate formed in step 1.
• D: $\mathrm{KMnO_4}$ — this is the final product after step 2, not the first-step product.

Final answer

The first step produces: $\boxed{\mathrm{K_2MnO_4}}$

Comparison with stored correct answer

Stored correct answer: C

Derived answer: C

Hence, they agree.