From: chm4sdw$##$leeds.ac.uk
Date: Wed Jun 01 2005 - 17:23:42 EDT
Hi Anil,
I take it you're trying to produce the amide product (I'm not familiar with the
Vogel book.) It looks as if the carboxylic group on the p-aminophenylacetic
acid is reacting instead of the amino group; the -OH may be acting as a
nucleophile, attacking the carbonyl group on BzCl and displacing Cl(-). (This
is quite likely as the transition state for this reaction is relatively stable,
due to extensive delocalisation over the Bz-OH(+)-C=O system.) The Cl(-) would
then attack the other carbonyl group (from the p-aminophenylacetic acid) and
displace BzOH. The other products in this case would be a mixture of
p-aminophenylacetyl chloride and whatever it reacts with, which would account
for the other products not being identifiable.
As for stopping this unwanted reaction, the best option would be to deactivate
the carboxylic group in some way, so it becomes a worse nucleophile. Running
the reaction in a non-nucleophilic organic base (eg. DBU) would deprotonate the
carboxylic group without the solvent reacting with the BzCl. (Out of interest,
which solvent are you using for this reaction?)
Alternatively, using a metal salt of the acid or complexing the acid anion with
a transition metal (and displacing it with EDTA afterwards) would effectively
deactivate the carboxylic group too. (It is less likely to coordinate through
the amino group because rearranging the geometry of the bonds at the N is less
thermodynamically favourable; also, steric hindrance would be quite a problem.)
However, complexing the acid and isolating the desired product afterwards
would make the whole reaction a good deal more complicated, so if this reaction
is part of a multi-step synthesis, I wouldn't go down that road.
Hope all this is some help to you.
Sam Woodman (2nd year Chemistry student)
University of Leeds
Quoting Anil Saini <sainianil3$##$rediffmail.com> on Wed 01 Jun 2005 12:00:10 BST:
> Hi everbody
> i want to couple p-aminophenylacetic acid with benzoyl chloride by method
> reported in vogel book but i am getting benzoic acid and unidentified
> product.Would any body suggest better reaction condition to get only coupled
> product.
>
> A Saini
>
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