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One would expect the reaction of ethylene glycol with acidified potassium permangnate to result in oxidation of ethylene glycol to oxalic acid. But a Q&A guide book tells me it is oxidized to formic acid. Which is wrong: the book or my reasoning?

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I think the final oxidation product should be carbon dioxide ($\ce{CO_2)}$ if acidified potassium permanganate is present in excess amount.

Firstly, ethylene glycol will be oxidised to oxalic acid. But oxalic acid can still be oxidised. In fact, it is the concept of titration of oxalates with potassium permanganate ($\ce{KMnO_4}$). Under acidic conditions, oxalic acid ($\ce{H_2C_2O_4}$) will be oxidised to $\ce{CO_2}$ by $\ce{KMnO_4}$ as:

$$\ce{2MnO_4^- + 5C_2O_4^{2-} + 16H^+-> 2Mn^2+ + 10CO_2(aq) + 8H_2O}$$

Thus the final product should be $\ce{CO_2}$

Also, note that, formic acid is an oxidisable acid because it gives silver mirror in reaction with Tollen's reagent $(\ce{[Ag(NH_3)_2]OH})$, and thus, formic acid can not be the end product, as it is still oxidisable and hence it will definitely react with acidfied $\ce{KMnO_4}$ if both are present in the reaction medium.

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  • $\begingroup$ according to this en.wikipedia.org/wiki/Alcohol_oxidation#Diol_oxidation oxalic acid is not fromed but formic acid is ? $\endgroup$ – WARhead Apr 24 '18 at 15:59
  • $\begingroup$ I Know that. But you should carefully look into the reagents. Periodates and Lead tetra acetates can cleave diols. Only $\ce{KMnO_4}$ can not cleave bonds between diols under Normal conditions. See, Lemieux Reagent for this concern. $\endgroup$ – Soumik Das Apr 24 '18 at 17:31

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