shrent
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Triphosgene Removal
I performed a reaction making a cycloaliphatic isocyanate using ORGSYN process of aq. bicarbonate & dichloromethane in biphasic media. The
reaction goes nicely using 1/3 eq. of triphosgene giving 85-90% final yield.
However, I'm facing severe problem of the remaining excess triphosgene in the reaction media after the completion. It is not being removed at all with
any sort.......
I tried it giving multiple washes of aq. bicarbonate, caustic, but still it remains ! Even if I take some lower % of triphosgene in the reaction, then
also it consequently gives lower yield with some excess remaining ! 
I even tried distilling my isocyanate with high vacuum & low vacuum but at this stage also triphosgene comes alongwith the isocyanate in the
receiving flask.....!!!!! 
I just fed-up with this situation............Pls try to suggest me some solution for this.
[Edited on 18-6-2006 by shrent]
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vulture
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This is strange, as the MSDS says it produces toxic gasses with water, so you shouldn't have any left at all once you get water in there.
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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shrent
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Triphosgene Removal
Technically you may be right. But when I distill the isocyanate even at high vacuum (<1mm @ 25-30degC), the material in the flask is showing acidic
pH.
Actually at that time, the pH paper not suddenly shows acidic pH, but once I kept the piece of pH paper in to the flask of distilled material, after
1-2 hours, it started showing pinkish tint & then after some hours, became completely pink !
It means (as per my view), the triphosgene remined in the flask releases its acidity slowly......
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frogfot
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I find it funny that an isocyanate would survive aqueous basic reaction/workup conditions.. So, I guess your compound is too sensitive to say boil
with water to decompose triphosgene or do silica chromatography..
How does that compound look? Maby we'll get any idea on it's stability/other properties.
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shrent
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I know its quite funny that I'm producing this isocyanate with aq. bicarbonate process. But it is true that it is being made by this process by me
with quite good quality without any more impurities as per the GC of my final material.
Here, my one more view is that, the final residual TPG is remaining in the mixture due to this large volume of solvent which also protects it.
Pls revert with your comments........
regards,
shrent
[Edited on 18-6-2006 by shrent]
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frogfot
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Could there be incompleate conversion? Cause something isn't right... you said that minimal yield is 85%, and you're using 1/3 eq of the TPG.
So, assuming that each TPG molecule reacts with 1 amine, releasing 2 phosgene molecules, if at least 85% of starting material reacts you shouldn't
have any triphosgene left. That is if TPG is less active than evolved phosgene.. maby it is..
Checked some refs, seems like people always use theoretical amount of TPG to amine.
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