# Oxidation of conjugated dienes into carboxylic acids by potassium permanganate

In the book - MS Chouhan; Advanced Problems In Organic Chemistry; 11th ed, Chapter Alkenes Q32 - the following reaction is given:

The given solution says that:

Conjugated dienes on oxidation by $\ce{KMnO4/\Delta}$ give oxalic acid

However, the mechanism for this reaction is not given. Also, the formation of a dicarboxylic acid on the parent ring is not explained. I am also unsure what would the products be in a simpler case like buta-1,3-diene. What products will it give?

I checked the internet but could not find a mechanism for the same. The related question of oxidation of arene subsituents by $\ce{KMnO4}$ is not a duplicate.

What is the mechanism for this oxidation?

• – Mithoron Mar 12 '18 at 18:22

Here is a relevant extract from a PDF (Dr. P.G. Hultin, 28 July 2016) depicting oxidative cleavage. For the compound in hand (your question) the process will be done twice. $\ce{H2O2}$ will serve as the source of $\ce{H3O+}$.
When alkenes are treated with $\ce{KMnO4}$ in acidic solutions, the diol is not formed. Instead, the alkene is cleaved. The reaction proceeds by the same mechanism at the start, forming a cyclic manganate ester (although since the reaction is under acidic conditions the structure is protonated). In the schemes below, the alkene carbons are highlighted throughout, so you can see where they end up in the product.