Question

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

Answer 1

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.

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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.