Oxidation of primary alcohols to aldehydes

by James

Description: Treatment of primary alcohols with PCC leads to formation of the aldehyde.

Notes: The same transformation can also be carried out by CrO3 and pyridine, a combination known as the Collins reagent.

Oxidation of the aldehyde to the carboxylic acid will not happen as long as water is excluded.



Mechanism:  Not generally considered important for the purposes of Org 1/ Org 2, but provided here for completeness.

Oxygen from the alcohol attacks chromium in a 1,2-addition (Step 1, arrows A and B) and then a proton is transferred to the oxygen on chromium (Step 2, arrows C and D). After 1,2-elimination of chloride ion (Step 3, arrows E and F), a proton is removed from C–2 in an elimination reaction (Step 4, arrows G, H, I and J) to give the aldehyde.

Notes: Note here that all we’re basically doing is putting a good leaving group on oxygen (the chromium) and then doing an elimination to form the C=O bond.

There are many other reasonable ways of depicting the proton transfer step. Furthermore there are several species present which could alternatively be used as the base in Step 4.


{ 2 comments… read them below or add one }

Alex Goodnough

The title of this page is “Oxidation of primary alcohols to aldehydes,” But every example shows primary alcohols being oxidised to carboxylic acids. What’s the deal?



Fixed. Thanks for catching that.


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