Vibrating_Lights (Hive Addict)
06-18-03 16:37
No 440822
      ROmoval of halogens from Rings  Bookmark   

Is It possible to remove a p-halogen from a phenylacetone Bisulfite adduct.  By reacting the comound in anhydrous THF With ButLi.  The add H2O to leave an unsubstituted ring. Recoverng the desired ketone by liberation with a base?

Start thinking more like a chemist and less like a criminal
(Chief Bee)
06-19-03 01:55
No 440912
      Bisulfite adducts doesn't like n-BuLi  Bookmark   

Bisulfite adducts are not compatible with n-BuLi, the Li will add sequentially to the three oxygens on the SO3 group, wasting the precious reagent.

A better suggestion might be to dehalogenate using Superhydride (LiEt3BH) or maybe BER - see Post 241350 (foxy2: "Aromatic Dehalogenation [ BER - Ni(OAc)2 ]", Chemistry Discourse)?
06-19-03 12:26
No 440995
      Wouldn't that also hydrogenate the keto group?  Bookmark   

Wouldn't that also hydrogenate the keto group? The ketone could be protected as an acetal...
(Chief Bee)
06-19-03 16:05
No 441017
      protecting group  Bookmark   

If the bisulfite stayed on the entire time, the ketone could survive - but I do not know if that is possible though. Using an acetal as protection group is of course infinitely better, if making that is an option.
(Active Asperger Archivist)
06-19-03 20:33
No 441089
      Option?  Bookmark   

Why wouldn't that be an option?  Acid sensitivity?  Polymerization?

Act quickly or not at all.
(Chief Bee)
06-19-03 20:51
No 441095
      Why I was unsure the advice would help  Bookmark   

The original poster wanted to dehalogenate the bisulfite adduct of a p-Halophenylacetone, and I have cotten used to that many people here just say "aw, fuck it" when my advice involves adding another step to their original route... I cannot help becoming a little cynical. The problem is definitely not with the actual acetal protection, but if the poster would bother to do it or not...

In this case the acetalization of the ketone would be effected by refluxing the phenylacetone in toluene with excess ethyleneglycol and 1% of a suitable acid catalyst (tosic acid) while separating the formed water using a dean-stark apparatus (the water removal drives the rxn forward). Workup involves washing twice with 5% bicarbonate, once with brine, dry the solution over MgSO4 (or even better Na2SO4, as it is less acidic) and evaporating the toluene in vacuo. Ideally this Phenyl-2-propanone ethylidene acetal should now be vacuum distilled before the next step.

Deprotection is a breeze - heating the acetal in 5% H2SO4, or by any other well-known method, UTFSE.
(Active Asperger Archivist)
06-19-03 20:57
No 441096
      Rhodium  Bookmark   

I know the pro/depro techniques, I just thought maybe there was an exception for this compound that you knew about.  Thanks for the information though.  And it's nice to know at least somebody's willing to do some work.  (no offense to bees like Barium, et. al.)

Act quickly or not at all.