Question

What is oxidative cleavage?

Answer 1

Oxidative cleavage is the cleavage of carbon-carbon bonds to generate carbon-oxygen bonds. Sometimes `"C"-"C"` bonds are oxidized, and sometimes `"C"-"C"` and `"C"-"H"` are oxidized.

OXIDATIVE CLEAVAGE: PERIODIC ACID

In general, an oxidative cleavage of a vicinal diol (commonly with periodic acid---pronounced "per-iodic") looks like this:

Notice how the `"C"-"C"` bond is cleaved, and the resultant alcohol is oxidized one step forward (e.g. primary alcohol `->` aldehyde `cancel(->)` carboxylic acid, using periodic acid).

PERIODIC ACID OXIDATIVE CLEAVAGE MECHANISM

The mechanism goes as follows (ignore the red iodine; the valency ought to be fine):

You don't have to know the mechanism, but I think it helps to have some idea on what happens "behind the scenes".

OXIDATIVE CLEAVAGE: OZONE (ALKENE)

On the other hand, an oxidative cleavage of an alkene using ozone looks like this:

For the first step, notice how in essence, the `"C"="C"` bond was "transformed" into a `"C"="O"` bond, and split into two carbonyl compounds. What follows depends on the type of workup reaction you perform on step 2.

REDUCTIVE WORKUP

For the second step, adding `"Zn"`, or adding `("CH"_3)_2"S"`, performs a "reductive workup", which ultimately gives you a "transformed" `"C"="C"` bond and stops at the aldehyde or ketone.

OXIDATIVE WORKUP

For the second step, adding `"H"_2"O"_2`, a strong oxidizing agent for an "oxidative workup", ultimately gives you a "transformed" `"C"="C"` bond as well as an oxidized `"C"-"H"` bond.

Instead of stopping at the aldehyde or ketone, you go all the way to a carboxylic acid or ketone.

OZONE OXIDATIVE CLEAVAGE MECHANISM (ALKENE)

The general mechanism for oxidative cleavage of an alkene using ozone is:

OXIDATIVE CLEAVAGE: OZONE (ALKYNE)

For an alkyne:

OZONE OXIDATIVE CLEAVAGE MECHANISM (ALKYNE)

You don't have to know either mechanism, but I think it helps to have some idea on what happens "behind the scenes".