stoichiometric_steve - 7-5-2009 at 13:45
I'm looking for a way of removing residual peroxides (H2O2, in this case) from a post reaction mixture which consists of a ketone dissolved in ethyl
acetate. It is not possible to use acidic Fe(2+) as the generated hydroxyl radicals completely kill the product in a matter of minutes.
Would NaHSO3/Na2S2O5 do the job? The ketone is rather reactive towards bisulfite but the reaction mixture is apparently pretty acidic due to residual
H2O2 and would thus quickly liberate any bisulfite adduct.
Any comments and suggestions are welcome!
EDIT: The original paper suggests passing the reaction mix through a column of alumina (activated alumina? this is a standard procedure of removing
peroxides from solvents). This is not really feasible in my case due to the large volume of solvent used. If everything else fails, though, would
using a Buchner funnel with a big alumina pad be likely to do the job? Do i have to use special "activated" alumina or can ordinary Al2O3 be used?
[Edited on 7-5-2009 by stoichiometric_steve]
chemoleo - 7-5-2009 at 17:36
Does MnO2 produce the same problem of generating OH(.) ?
PbO also catalyses decomposition upon boiling iirc- I think I mentioned that somewhere here in one of the lead oxide threads.
Catalase would be a good option if the solvent system was aqueous.
starman - 8-5-2009 at 03:57
Ther is a fair body of information on Fenton type chemistry on generatiing and scaveging the OH radical from H202.A few scavengers off the top of my
head,formates,salyicate,thiourea ,mannitol etc.
The thinking being go ahead with the Fe driven decomp and mop up with the scavenger(provided suitable in your solvent system) before it reacts with
your ketone.
stoichiometric_steve - 8-5-2009 at 12:49
i'm not trying to scavenge the OH radical but to avoid its generation altogether. the iron also has a deleterious effect in my application.
Panache - 12-5-2009 at 16:35
Would it be plausible to approach the problem differently and begin the workup by attempting to isolate the bisulfite adduct? if you have large
solvent volumes this could save tedious solvent stripping and solve your H202 problem. In my experience bisulfite adducts form best with excesss
solvent anyways (from the vast library of three ketone/bisulfite adducts i have formed, ha!). It would require neutralising to something approaching
neutral ph, say pH~6-7.
If you explore this approach i predict your greatest problem will be (assuming the adduct forms reliably) filtering the adduct quickly and completely.
I don't think you'll find a ready way to filter the entire shebang easily. A flocculant could be necessary to allow decantation of most of the
supernatant. A pool store will have a flocculant that works well around neutral pH and it may be an easy fix.
I understand much of this may be irrelevant or know to you, but hopefully there is something in this of use to you.
The filtered adduct would then be decomposed with HCl of course, given your molecules sensitivity to base.
Klute - 13-5-2009 at 00:52
I would use thiosulfate, no risk of it reacting with the ketone, and quick reduction of the peroxide.
Did you oxidize a secindary alcohol to the ketone? Did you use a catalyst for this? I'd love to hear more..