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

1 Answer
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^@#) alcohol and one proton on a secondary (#2^@#) alcohol that are attached to the same carbon as the one to which the #"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"#) and gain one #"C"-"O"# bond during the oxidation.

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

As far as I know, it's not possible to lose a #"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^@#) alcohol cannot be oxidized to anything.


Examples of oxidation of alcohols are:

  • #"H"_2"CrO"_4# (chromic acid) to get a carboxylic acid from a primary alcohol, or a ketone from a secondary alcohol.
  • #("CH"_3)_2"S"="O"# and #"Cl"-("C"="O")_2"Cl"# at #-60^@ "C"#, and then work up with #"Et"_3"NH"_2# (the Swern oxidation) to go from a primary alcohol to an aldehyde or a secondary alcohol to a ketone.
  • #"PCC"# in #"CH"_2"Cl"_2# to get an aldehyde from a primary alcohol, but not a carboxylic acid.