My question stands:

Is it possible to oxidize toluene to benzoic acid using PCC?


1 Answer 1


PCC is generally regarded as a milder oxidizing agent, used to effect selective oxidation of alcohols to aldehydes (from $1^{\circ}$ alcohols) or ketones (from $2^{\circ}$ alcohols). While over-oxidation to a carboxylic acid from a primary alcohol is definitely possible, PCC should not react with a simple unfunctionalized benzylic carbon.

However, oxidation at the benzylic position is easily achieved with more aggressive oxidizing agents. In particular, chromic acid (generated in situ from chromium salts in aqueous sulfuric acid, as in the Jones oxidation) as well as aqueous potassium permanganate will fully oxidize virtually any benzylic carbon all the way to the carboxylic acid, providing the benzylic carbon has at least one hydrogen. Of course, the rest of the chain is completely cleaved in the process.

Edit: Out of curiosity, I consulted my copy of March's Advanced Organic Chemistry to determine if any other common reagents were able to effect the same benzylic oxidation. Nitric acid is listed along with the two methods I described above. Naturally, a survey of various more exotic methods is also given. Intriguing was the use of sodium hypochlorite in acetonitrile, or NBS in aqueous sodium hydroxide under photochemical conditions, for the specific complete oxidation of aryl methyl groups.


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