Re: ORGLIST - orglist Digest - V01 #169

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From: Jacob Zabicky (jzabicky$##$etseq.urv.es)
Date: Mon Aug 10 1998 - 10:28:23 EDT


>orglist Digest Sat, 08 Aug 1998 00:00:59 +0100 V01 #169
>
>Today's topics:
> 'acetylation of ...'
> 'Re: Oxidation state of cellulose'
> 'RE: ORGLIST: Re: Oxidation state of cellulose'
> 'FW: ORGLIST: Re: Oxidation state of cellulose'
>
>----------------------------------------------------------------------
>
>Date: Thu, 06 Aug 1998 17:43:44 PDT
>From: "barnabas liau" <barnabas_liau$##$hotmail.com>
>Subject: acetylation of ...
>
>
>Dear Colleagues,
>I met some problem recently when i tried to acetylate an amine compound
>namely, 2,5 Dimethoxyaniline.Below were some of the ways that i've
>attempted:
>1)Dissolved the amine( used as newly received-but there's lots of black
>stuff in there) in acetic anhydride and refluxed for 1-2 hrs (color of
>the solution turned brownish)and let cool before pouring into
>water.boiled to evaporate off the acetic acid.
>observn.: no precipitate.
>2)Dissolved the amine (purified by sublimation) in acetic
>anhydride,added two drops of conc sulphuric acid and refluxed for 1-2
>hrs and let cool before pouring into water.Boiled to evaporate off the
>acetic acid.
>observn:no precipitate, but the it couled be precipitated with acetone
>to give some brown solid.
>3)Dissolved the amine (not purified) in acetic anhydride,added two drops
>of conc sulphuric acid and left there for 1hr before pouring into warm
>water.Boiled to evaporate off the acetic acid.
>obsern: no precipitate
>Question:
>1)Can anyone please suggest to me the actual problem that's taking
>place?
>2)The aniline was suppose to be 98%+ pure but why is it giving me so
>much of black stuff?
>Thanks in advance.
>
>Regards,
>Barnabas

Hello Barnabas,

It occurs to me that your initial stuff may be impure to some extent; it
need not be very impure to start off a series of chain reactions promoted
by oxygen in the air, to end up with a mess. So, I would try one or two
alternative tactics:

1. In all cases work under a protective atmosphere of N2, Ar, or even CO2.
A small stream at the top part of your reflux setup should suffice. I
wouldn't bubble the gases though your boiling mixture, because this carries
away a lot of material that you wouldn't wish to throw out into the
atmosphere.

2. What about doing the acetylation in the cold or under the old
Schotten-Baumann conditions?

3. An alternative path would be using ketene (CH2=C=O). My personal
experience with this presumably "clean" reagent is nill, but probably
Organic Synthesis, or Fieser's Reagents for Organic Synthesis carry enough
info on the reagent and its applications to satisfy your needs.

All the best,

Jacob



*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Prof. Jacob Zabicky Fax. xx-34-977-559694
c/o Prof. Alberto Coronas Tel. xx-34-977-???
Department of Mechanical Engineering Private No.
Universitat Rovira i Virgili xx-34-930-119552
Cra. de Salou s/n
43006 Tarragona
Spain
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