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(-). (Th=
is
is quite likely as the transition state for this reaction is relatively stab=
le,
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 accoun=
t
for the other products not being identifiable.
As for stopping this unwanted reaction, the best option would be to deactiva=
te
the carboxylic group in some way, so it becomes a worse nucleophile. Runnin=
g
the reaction in a non-nucleophilic organic base (eg. DBU) would deprotonate =
the
carboxylic group without the solvent reacting with the BzCl. (Out of intere=
st,
which solvent are you using for this reaction?)
Alternatively, using a metal salt of the acid or complexing the acid anion w=
ith
a transition metal (and displacing it with EDTA afterwards) would effectivel=
y
deactivate the carboxylic group too. (It is less likely to coordinate throu=
gh
the amino group because rearranging the geometry of the bonds at the N is le=
ss
thermodynamically favourable; also, steric hindrance would be quite a proble=
m.)
However, complexing the acid and isolating the desired product afterwards
would make the whole reaction a good deal more complicated, so if this react=
ion
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 coupl=
ed
> product.
>
> A Saini
>
_______________________________________________
ORGLIST - Organic Chemistry Mailing List
Website / Archive / FAQ: http://www.orglist.net
To post a message (TO EVERYBODY) send to everybody$##$orglist.net
To unsubscribe, send to everybody-request$##$orglist.net the message: unsubscribe your_orglist_password your_address
List coordinator: Joao Aires de Sousa (coordinator$##$orglist.net)
This archive was generated by hypermail 2.1.4 : Thu Feb 18 2010 - 16:58:09 EST