Author Topic: Purification of P2P's by oxidation?  (Read 2766 times)

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Bandil

  • Guest
Purification of P2P's by oxidation?
« on: May 29, 2004, 10:56:00 AM »
Hi!

When using

this

(https://www.thevespiary.org/rhodium/Rhodium/chemistry/p2p.sncl2.html) method for the reduction of nitopropenes to ketones, it seems that the major by-product is the benzaldehyde. It shouldn't be much (app. 5%) when using the ethylacetate method, but with IPA the contamination rises to about 40%. This can be removed by distillation, but it would nice to have a slick way of removing it.

I had thought about suspending the oil (ketone and benzaldehyde after steam distillation) in dilute cold aq. NaOH and titrating with 1M KMnO4, untill a purple color persists. In a perfect world the benzaldehyde would be oxidized to benzoic acid, and this should dissolve in the basic medium. The ketone could then be isolated directly by the extraction with a proper NP.

The only thing that worries me about this scheme is the possible oxidative cleavage of the benzyl CH2 group in the ketone. I have not found any conclusive answer to when permanganate will cause oxidative cleavage at the benzyl carbon.

Anyone have some neat suggestions or comments?

Kind regards
Bandil


Barium

  • Guest
Easier
« Reply #1 on: May 29, 2004, 06:40:00 PM »
If you know the ratio benzaldehyde/ketone formed you can simply add enough bisulfite to bound all benzaldehyde as the bisulfite adduct. The benzaldehydes will always form the adduct more easily than a phenylacetone because the aldehyde is less sterically hindered.


Megatherium

  • Guest
Oxidation of ketone = possible with KMnO4
« Reply #2 on: May 29, 2004, 07:41:00 PM »
Strong oxidizing agents (like KMnO4, CrO3) are able to oxidize ketones.  The reaction is only of synthetic use for cyclic ketones (to generate terminal aliphatic di-carboxylic acids), since oxidation of aliphatic ketones generates a hopeless mixture of compounds (destructive oxidation).

If one carefully titrates, I don't think there will be any problem, because benzaldehyde is a far better reductant than P2P.  If you want to play it safe, choose a milder oxidizing agent.

Probably the best idea is to form the bisulfite adduct, like Barium said.

I remember from developing a sprayed TLC in a chlorine atmosphere (KMnO4 / HCl) that it ruined the beaker pretty much ...  ::) , damned MnO2.



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hest

  • Guest
The Bisulfit solution proposed by barium works
« Reply #3 on: May 31, 2004, 11:26:00 AM »
The Bisulfit solution proposed by barium works lika a charm. I think it's the way to doo it. The is a short storie in Vogel abouth it (cant remmeber teh page).

armageddon

  • Guest
MnO2 removal
« Reply #4 on: July 17, 2004, 02:13:00 AM »
Hi!

Megatherium: cleaning your glassware from MnO2 isn't that hard: just use a few ml's of a strong aequ. SnCl2 solution and a squirt of conc. HCl - it reduces the manganese dioxide, I think. At least the brown remnants dissolve completely in water this way...

Greetz A


hest

  • Guest
how to remove MnO2
« Reply #5 on: July 17, 2004, 01:18:00 PM »

Post 296793 (missing)

(hest: "The H donor is the alcohol.", Newbee Forum)

wolff_kishner

  • Guest
How about Fehling's solution?
« Reply #6 on: July 28, 2004, 09:04:00 PM »
Fehling's solution (a solution of potassium bitartrate and copper sulfate) would oxidize the aldehyde, but leave the ketone unchanged. It is a much milder and more selective agent than permanganate.