Piperic acid oxidation

![Question 3b iii) ](https://i.stack.imgur.com/wsBvV.jpg)


There are 2 double bonds $\ce{C=C}$ present within each piperic acid molecule, thus when piperic acid reacts with hot excess $\ce{KMnO4}$, it oxidised into a carboxyllic acid. Why is $\ce{CO2}$ produced?


The carbon atom bonded directly to the benzene ring will get oxidised into a carboxylic acid and also that the carbon bonded to the $\ce{COOH}$ group will get oxidized also to a carboxylic acid to form a dicarboxylic acid. What changes will take place to the other 2 carbon atoms.





> 
> this paper stated that $\ce{CO2}$ could be formed as well, how?
> 
> 
> 


Usually when we consider permanganate oxidations we think of


* oxidation of alkyl benzenes to benzoic acid
* cleavage and oxidation of a double bond to an acid, through the aldehyde, if there is one hydrogen on the double bond
* cleavage and oxidation of a double bond to a ketone if there are no hydrogens on the double bond


However, there are a few **special cases** such as formic acid and oxalic acid, or their corresponding aldehydes. These compounds are oxidized by permanganate to $\ce{CO2}$ (for an idea as to why these compounds react differently than, say, acetic acid, see Scheme 1 [here](http://www.researchgate.net/profile/Laszlo_Kotai/publication/257955325_Kinetics_and_mechanism_of_oxidation_of_formic_and_oxalic_acids_by_bis(pyridine)silver_permanganate/links/0c96052c7cdb355b72000000.pdf)).


With this information in hand we can re-examine the permanganate oxidation of piperic acid.


![enter image description here](https://i.stack.imgur.com/9wyAd.jpg)


We see that oxalic acid is one of the primary products produced in this reaction. As discussed above, oxalic acid can then undergo further reaction to produce carbon dioxide.


 6