Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: shalikadm on July 29, 2012, 11:15:28 AM
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I know that alkylbenzene compounds can be converted into benzoic acid using acidic strong oxidizers like MnO4-,Cr2O72-,..etc.And also we must have directly bound H atom to the carbon which is attached to the aromatic ring...That's why we can not get benzoic acid from butylbenzene...
But that rule does not apply to non-alkylbenzene compounds.My book shows that we can oxidize following non-alkylbenzene compounds to benzoic acid.
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Can you tell me the theory that lay behind in selecting non-alkylbenzene compounds which can be oxidized to benzoic acid ? Can we just oxidize any non-alkylbenzene compound which has a carbon atom attached to the aromatic ring just like benzyl alcohol,benzyl chloride,benzal chloride,nitrile benzene,..etc using acidic strong oxidizers?
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Oxidation of alkylbenzenes is different than oxidation of an alcohol or double bond, or at least in part. The oxidation of an alkylbenzene is a radical reaction and is often (generally) done with heat. The product of that reaction is an alcohol or something that is oxidizable.
Oxidation of an alkenylbenzene or alkynylbenzene is like an electrocyclic reaction. You can draw a cyclic intermediate for the reaction of ozone, MnO4(-), or OsO4. If the manganate cyclic ester is not hydrolyzed, it can decompose with cleavage of the C-C bond. If styrene were being oxidized, the intermediate would be benzaldehyde. If water is present, it will form a hydrate which is a geminal dialcohol. Oxidation of it gives a carboxylic acid.
If you were doing an oxidation under mild conditions, ketones are not oxidized further as a methyl group will not give up electrons as easily as loss of a proton.
PhCH(OH)O-X ---> PhC(OH)=O + X- + H+
PhCCH3(OH)O-X -X-> PhC(OH)=O + X- + CH3+
This requires more vigorous oxidation conditions to form an enol or peroxide (Baeyer-Villiger type) for further oxidation.
This is a little sketchy and brief, but if you understood the how alkylbenzenes oxidize and know how the other groups can oxidize, this should explain the difference.
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Don't focus on the "rule" stated in your book. Focus on the mechanism of the reactions. Oxidizing toluene to benzoic acid proceeds through a different mechanism than the conversion of the substrates you showed. Remember, the key to understanding reactions such as these is to understand the mechanism of the transformation and not memorizing the "rule".
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Yes, all these 4 compounds using these two oxidizers will form the benzoic acid as the final product. Benzyl alcohol, benzyl chloride,benzal chloride - also. Benzonitrile (C6H5CN) is a derivative of benzoic acid and need no oxidation - hydrolysis instead of.