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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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Tuesday, January 01, 2013

Oxidation of Salycylic Acid


Salicylic acid is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plane hormone. It is derived from the metabolism of salicin. In addition to being an important active metabolism of aspirin (acetylsalicylic acid), which acts in part as a prodrug to salicylic acid, it is probably best known for its use in anti-acne treatments.

I have a question: Can Salycylic Acid be oxidized by Potassium Permanganate in a Neutral Solution?
The answer is yes. It gives brownish black precipitate and brown solution as the result.

Now the problem is, how it can be?
How the mechanism reaction of this oxidation?

From internet, I found that only very strong oxidizing reagents, such as permanganate, dichromate or Fremy's salt (KSO3)2NO, oxidize simple phenols to 2,5-cyclohexadien-1,4-ones (benzoquinones).

From the reaction above, I propose a mechanism of the oxidation of phenol as follows:
First, hydroxy group will resonance to form a carbonyl.
In carbonyl form, the aromatic property will be lost so that the benzene ring will act as an alkane. This compound will be attacked by permanganate ion to form an inorganic ester (syn-addition reaction).


hypomanate ion (in the form of dihydrohypomanganic acid) is an unstable acid which will be disproportionated to mangan dioxide and permanganate ion (concluded from the result given by the reaction).

For the last, the compound will release water molecule to form a derivate of quinone.


The weaknesses of my proposed mechanism are: 
1. Can we break the aromatic property in benzene easily like that?
2. Why water molecule released in this reaction?

If you have another proposed mechanism, please share with me. 

Thank You


Bibliography:
http://www.chem.ucalgary.ca/courses/351/Carey5th/Ch24/ch24-3-5.html

http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/2/vlu/oxidation_reduktion/oxi_phenol.vlu/Page/vsc/en/ch/2/oc/reaktionen/formale_systematik/oxidation_reduktion/oxidation/entfernen_wasserstoff/oxidation_phenole.vscml.html

http://users.humboldt.edu/rpaselk/C328.Su04/C328Notes/C328nLec15.htm

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