Write a short note on oxidation of alcohols. What are the different reactions involved, with suitable examples?

1 Answer
Truong-Son N.
Mar 20, 2016

The oxidation of alcohols requires having a proton on the same carbon as the hydroxyl group.

Do you see how there are two protons on a primary (1^@1∘) alcohol and one proton on a secondary (2^@2∘) alcohol that are attached to the same carbon as the one to which the "OH"OH group is attached?

Also, notice that that proton is actually lost. You lose two hydrogens adjacent to each other (one of which is on the "OH"OH) and gain one "C"-"O"C−O bond during the oxidation.

In the case of an oxidation from the aldehyde to the carboxylic acid, you gain "H"_2"O"H2O and lose two hydrogens (one of which is on the same carbon as the "OH"OH as expected), overall giving you one more oxygen.

As far as I know, it's not possible to lose a "C"-"H"C−H bond for oxidation of an alcohol, if it is not attached to the same carbon as the hydroxyl group. That means a tertiary (3^@3∘) alcohol cannot be oxidized to anything.

Examples of oxidation of alcohols are:

  • "H"_2"CrO"_4H2CrO4 (chromic acid) to get a carboxylic acid from a primary alcohol, or a ketone from a secondary alcohol.
  • ("CH"_3)_2"S"="O"(CH3)2S=O and "Cl"-("C"="O")_2"Cl"Cl−(C=O)2Cl at -60^@ "C"−60∘C, and then work up with "Et"_3"NH"_2Et3NH2 (the Swern oxidation) to go from a primary alcohol to an aldehyde or a secondary alcohol to a ketone.
  • "PCC"PCC in "CH"_2"Cl"_2CH2Cl2 to get an aldehyde from a primary alcohol, but not a carboxylic acid.
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