Strong And Weak Oxidants

by James

There are generally two classes of oxidants you’ll meet in Org 2. Strong oxidants and weak oxidants.

Look at the table below. See how these molecules are arranged, with carbons of higher oxidation state at the top, and lower oxidation state at the bottom? This is called an “oxidation ladder”. Each “rung” in the ladder represents a change in oxidation state. As we “climb” the ladder we go to higher oxidation states.

“Weak” oxidants [common example: pyridinium chlorochromate (PCC)] can oxidize primary alcohols to aldehydes and secondary alcohols to ketones. The maximum they’ll go is up one rung.

“Strong” oxidants (common example: CrO3 and other sources of chromium in the +6 oxidation state (VI)  in acid such as K2Cr2O7) can go up two rungs (from primary alcohol to carboxylic acid). However it will still just oxidize secondary alcohols to ketones.

Note that for our purposes neither of these will oxidize ketones or tertiary alcohols. Why not?
Because there’s no C–H bond on the carbon attached to O. And the easiest types of oxidations involve breaking a C–H and forming C–O.

Thanks for reading! James

P.S.  From the Reaction Guide – oxidation of primary alcohols to aldehydes.
Reagent Friday: Chromic acid, H2CrO4
Reagent Friday: Pyridinium chlorochromate, PCC