Re: ORGLIST: coupling

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From: chm4sdw$##$
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 =
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(-). (Th=
is quite likely as the transition state for this reaction is relatively stab=
due to extensive delocalisation over the Bz-OH(+)-C=O system.) The Cl(-) =
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 accoun=
for the other products not being identifiable.

As for stopping this unwanted reaction, the best option would be to deactiva=
the carboxylic group in some way, so it becomes a worse nucleophile. Runnin=
the reaction in a non-nucleophilic organic base (eg. DBU) would deprotonate =
carboxylic group without the solvent reacting with the BzCl. (Out of intere=
which solvent are you using for this reaction?)

Alternatively, using a metal salt of the acid or complexing the acid anion w=
a transition metal (and displacing it with EDTA afterwards) would effectivel=
deactivate the carboxylic group too. (It is less likely to coordinate throu=
the amino group because rearranging the geometry of the bonds at the N is le=
thermodynamically favourable; also, steric hindrance would be quite a proble=
 However, complexing the acid and isolating the desired product afterwards
would make the whole reaction a good deal more complicated, so if this react=
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$##$> on Wed 01 Jun 2005 12:00:10 =

>  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 coupl=
> product.
> A Saini

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