locoghoul - 7-2-2006 at 18:54
So, i'm making 2'-hydroxy-5'methoxy bromoacetophenone from bromoacetyl bromide and p-methoxyphenol. According to Blatt (Organic Reactions), is better
to first form the phenyl esther and then get the alpha-bromoketone via a Fries rearrengement.
My problem is the workup from the first step. TLC monitoring and HBr decreasing flow shows that reaction is almost complete after 6 hours. I stop the
reaction after 6 hours even when some p-methoxyphenol is still in the mix because after 6 hours the acetophenone TLC spot starts to intensify
(possible rearrengement due to the reaction heat + the extra horus). I add water to the reaction mix after 6 hours and extract the organic layer with
hexane. Rotaevaporation and the follow recrystalization has given me 55% yields max of a white fine crystal powder (kinda pasty too), yet i think the
reaction should be quantitative. There isn't too much info available of the intermediate product so i guess it should have a low boiling point and
some product may be being sucked in rotaevaporation. Any advice on my workup?
Sandmeyer - 3-3-2006 at 17:19
Maybe you could have provided reaction details. I suppose that's why you didn't get any replies. 
regarding workup a steam-disillation will do.
Here are two high yielding rearrangement methods:
Garcia, Hermenegildo; Primo, Jaime; Miranda, Miguel Angel; Synthesis; 9; 1985; 901-902. They get 89% yield.
A Fries to corresponding propiophenone (74%):
Martin, Robert; Monatsh. Chem.; 112; 1981; 1155-1164.
Basicly, this sequence could be followed:
Step 1:
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0452
Step 2:
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0280
Step 3:
http://www.orgsyn.org/orgsyn/prep.asp?prep=CV4P0836
skip the step 3, of course, if p-methoxyphenol is already available.
[Edited on 4-3-2006 by Sandmeyer]