What are the products of the reaction of 1,3-butadiene with hot $\ce{KMnO4}$ (excess)?
I know that $\ce{KMnO4}$ will first cleave the double bonds and we should get $$\ce{CH2=CH-CH=CH2 ->[KMnO4] 2CH2=O + O=CH-CH=O}$$ Now the aldehydes will further oxidise to $$\ce{H2C=O <<=> H2C(OH)2 ->[KMnO4] O=C=O}$$ $$\ce{O=CH-CH=O ->[KMnO4] HOOC-COOH}$$
I don't understand how and why $\ce{HO2C-CO2H}$ would further oxidise to $2 \ \ce{CO2}$?