RE: ORGLIST: Isocyanate purification

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From: Bert Kruiswijk (e.kruiswijk$##$
Date: Tue Mar 29 2005 - 07:43:46 EST

Dear Kamal,
I have worked with isocyanates through out my PhD and I think that your
impurity is the formation of corresponding urea. We always had trouble
removing the last bits of urea.

From: everybody-bounces$##$ [mailto:everybody-bounces$##$]
On Behalf Of mailbox
Sent: 29 March 2005 06:25
To: everybody$##$
Subject: ORGLIST: Isocyanate purification

Hello Friends !
I had got good advices from some friends thro' this site regarding to my
reaction of producing Isocyanate from an Amine HCl. But I'm finally getting
difficulties in purifying this Isocyanate. As per the final GC, Isocyanate
comes as 94-95% maximum alongwith 4-5% peak of some impurity before the main
peak (comes as lower boiler). This impurity comes as cloudy solid & extends
more slowly making the isocyanate more & more turbid on standing.
Can anyone pls suggest me how I can remove this impurity & purify my
isocyanate ?? However, I had got one reference according to which, "Do the
distillation with column (fractional) distillation with shorter time".
(Actually, how it can be performed practically ? Because if the column is
there, then travelling time for vapor would be obviously longer !! )
By the way, I had performed this reaction in MDC & aq. bicarbonate media in
biphasic mode with triphosgene.
I will be anxiously awaiting your kind advices.
Pls help me.
Thanking you in advance,

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