I am working up a reaction which calls for the use of excess 3-chloroperoxybenzoic acid in methylene chloride. Any suggestions on how to quench the excess peroxy acid?
It slightly depends on your substrate. Listed below are some of my favorite salts for reducing O-O bonds. I recommend you do this in the stirring round bottom, not the separatory funnel.
Na2S2O3 (sodium thiosulfate) is the most aggressive in this list I believe, though is fairly nucleophilic (it can do SN2).
NaHSO3 (sodium bisulfite) less nucleophilic though forms adducts with aldehydes.
Na2SO3 (sodium sulfite) more basic version of above. Good for quenching mCPBA IMHO.
Na2S2O5 (sodium metabisulfite) is the most selective for reducing peroxides. It does not have any nucleophilic behavior.
Prepare a chosen salt above in water (anywhere from 5% to saturated), test your peroxide content with starch paper.
Brennan has it right, the easiest method is the addition of aqueous Na2SO3. Avoid Na2S2O3 as under acidic conditions it can precipitate elemental sulfur. Acetone also works but can be somewhat reactive depending on the functional groups of your molecule.
Add KI aqueous solution and extract with ethyl acetate, the solution will turn into dark red. Then put Na2SO3 saturated aqueous solution to the organic phase to quench free iodine. The solution will turn into light yellow . Continue extraction as usual.
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