Oxidation of Primary Alcohols to Aldehydes using PCC

by James

Description: Treatment of alcohols with PCC leads to formation of the aldehyde.
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{ 14 comments… read them below or add one }

Nikunj patel February 17, 2012 at 5:07 am

how to decompose the tar obtained after using the PCC as an oxidising agent in the reaction

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james February 17, 2012 at 5:20 am

Best approach is to prevent tar formation by adding molecular sieves or Celite to the reaction; the tar will stick to that instead of the flask.

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mat March 27, 2012 at 4:57 pm

Thanks for the tip. Would you happen to know the best way to get the chromium out of the sample afterwards? I was going to filter it through Celite, but if that’s already in the reaction vessel, would it even be necessary?

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james March 27, 2012 at 5:11 pm

Generally I’d suggest filtering through a pad of fresh Celite to get rid of the chromate ester byproducts and other crap; typically rinse with CH2Cl2. You’ll find that the brown color will be very difficult to remove, however, without purification through a plug of silica or by distillation.

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james June 21, 2012 at 11:00 pm

Also, recently found this tip:
” Quench with 1M citric acid: it complexes all the brown Chromium junk. Much better than the usual “Celite filtration” work up.
God bless E J Corey :-)

John May 1, 2013 at 5:35 am

Nice tip james, but normally DMC is used as the solvent for PCC oxidation, how did you use mix 1M citric acid water solution with it to complex the brown junk and how to get rid of residual citric acid? Looking forward to your answer. Thank you.

Ghazaleh May 27, 2012 at 8:15 am

Hi there,
Why is it that oxidation of ALDEHYDE will not happen under PCC? What is exactly the reason for that? We have a hydrogen in aldehyde, how come that does not get oxidized?

and why is that you say “as long as” Water is excluded? does that imply we can deliberately introduce water do the system to further oxidize the aldehyde if we want to?

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james May 27, 2012 at 11:25 am

Good question!

Water is key.

If water is not added, the aldehyde will not oxidize.
However, if water is added, it will add to the aldehyde to form a hydrate (carbon with two OH groups attached). And this will undergo oxidation, (through a mechanism similar to that of a primary alcohol) to give a carboxylic acid.

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kiran January 23, 2013 at 2:38 am

if we add water then how we stop reaction at aldehyde stage while converting primary alcohol to aldehyde

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james January 24, 2013 at 4:07 pm

Generally you don’t want to add water in this reaction, except in the workup stage when trying to isolate the product.

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Rajarshi Banerjee November 2, 2012 at 8:42 am

check the last step of the mechanism, you accidentally made the hexane ring into a benzene ring

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Rajarshi Banerjee November 3, 2012 at 5:16 am

and what might be a solvent then

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james November 5, 2012 at 7:32 pm

Solvent for this reaction is usually CH2Cl2 or DMF.

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james May 2, 2013 at 1:48 pm

DMC? Do you mean DMF?

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