Bandil (The Archetypical "Good Guy") 05-29-04 10:56 No 510159				Purification of P2P's by oxidation?
						Hi! When using this (../rhodium /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 Nuke the whales!
		Barium (Heavyweight Chempion(eer)) 05-29-04 18:40 No 510175				Easier
						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. Severe Aztecoholic and President of Sooty's fanclub - Sooty for President!!
		Megatherium (Hive Bee) 05-29-04 19:41 No 510184				Oxidation of ketone = possible with KMnO4
						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. Aztec fanclub member
		hest (Hive Adickt) 05-31-04 11:26 No 510508				The Bisulfit solution proposed by barium works
						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 (Hive Bee) 07-17-04 02:13 No 519805				MnO2 removal
						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 "..ein Trank von unterschiedlicher Farbe, in ihm ist Heilung für die Menschen."
		hest (Hive Adickt) 07-17-04 13:18 No 519884				how to remove MnO2
						Post 296793 (hest: "The H donor is the alcohol.", Newbee Forum)
		wolff_kishner (Stranger) 07-28-04 21:04 No 522267				How about Fehling's solution?
						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.