From: Sandra Bartoli (sandy13_1$##$hotmail.com)
Date: Tue Aug 29 2006 - 10:04:22 EDT
Yes,
you are quite right, you should really use an excess of triphosgene to avoid
the formation of the symmetrical thiourea (note that 0.3 times ratio of
triphosgene means nearly 1 eq.). The problem is that you can't remove the
excess of triphosgene after the reaction with the first aniline, so you
probably will have to use an excess of the second aniline (same as for the
triphosgene or more).
Consider also that anilines are a lot less reactive than usual aliphatic
amines so give them time to react. If the reaction is not too slow you could
consider the possibility of dropping down slowly a dilute solution of the
first amine into a concentrated solution of the triphosgene, which would
minimise the formation of the urea. The rate of the reaction depends upon
the aniline used.
Hope it helps.
Sandra
>From: "Ohad Ilovich" <ilovich$##$pob.huji.ac.il>
>To: <everybody$##$orglist.net>
>Subject: ORGLIST: triphosgene and urea formation
>Date: Tue, 29 Aug 2006 15:56:20 +0200
>
>Dear all
>I wish to use triphosgene to create an isocyanate from an aniline and then
>react this isocyanate with a different aniline to form an urea.
>I saw in a few article varying milimolar ratios of phosgene. from 0.3 to 3
>times ratio of the first aniline.
>Won't using an excess of the first aniline enable the creation of an
>isocyanate and continue to create the urea with the same starting aniline?
>If anyone has had any expirience with this reaction i would appriciate any
>comments.
>
>Ohad Ilovich, M.Sc, B.Pharm
>
>
>
>
>
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