Oxidation of secondary alcohols to ketones using PCC

by James

Description: Treatment of secondary alcohols with pyridinium chlorochromate (PCC) leads to ketones.
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Notes: The same transformation can also be carried out by H2CrO4 or KMnO4.

Examples:

Notes: The byproducts of this reaction are H2CrO3 and pyridinium chloride.

Mechanism: Note that the mechanism is generally not considered important for the purposes of Org 1 / Org 2.

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 ketone.

Notes: There are many other reasonable mechanisms for the proton transfer step. Also there are several species present which could alternatively be used as the base.

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{ 3 comments… read them below or add one }

Rajarshi Banerjee

If the byproducts are H2CrO3 and pyridinium chloride then bond G should never be formed and the bond J should be a bond formed with O-H

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Richard Zipper

How about the selective oxidation of benzylic alcohol via MnO2 ? We use that in class in synthesis problems.

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James Ashenhurst

Good suggestion!

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