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ORGLIST problems with Friedel Craft reaction

From: Alok Shaurya <alokv2.0>
Subject: ORGLIST problems with Friedel Craft reaction
Date: Wed, 22 Jun 2011 22:55:20 -0700 (PDT)
Dear all,

I have been doing Friedel Craft acylation of ferrocene for quite a
while now. At first the reaction went smoothly and gave good yields
(85-90%). But for last three times whenever I try to run the reaction
the solution first turns to purple (as expected), characteristic of
Friedel Craft, but after about 10 min it turns dark green as if the
AlCl3 has been destroyed and the yield comes to as low as 10% (that
too mono and di acylated products combined, I am trying di-acylation
here). I use dry conditions and all but I am not able to figure out
what could be the source of error here. I read somewhere in this forum
that AlCl3 bottle if fumes when opens is fir for FC rxn, I checked
mine and it fumes.
Please comment.

The protocol I use is as follows:
1. Dissolve 2 gm of ferrocene in 10mL dry DCM and 4mL Acetyl Chloride.
Purge it with N2 for a min.
2. Dissolve 4 gm of AlCl3 in 10 mL of dry DCM in a two necked RB flask
equipped with a reflux with a drying tube on top of it.
3. Using a dry syringe, transfer the first solution to RB Flask, while
stirring, dropwise.
4. Reflux overnight at RT while stirring.
5. At first the solution changes to purple (expected) but after about
10 min it turns dark green.

--
Alok Shaurya

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