chemrox
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frustrations
I have been trying to form the carbmoyl product from KOCN and an aryl alkanolamine. It's an aquaeoue medium at a pH of around 5. After 2.5 hours of
reflux there should be formation of the carbmoyl intermediate. After three attempts, the third refluxing for over four hours, no evidence of any
reaction having taken place.
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roamingnome
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im not the practicum guru on this, but i feel the pain...
the ph should rise to 10-11 as a reaction indicator
theres good refs lurking on this site regarding carbamylation, which suggest buffering at ph 7-8 is the best for the process....
if your not certain of the ppa it could have a methyl group preventing carbamylation
reacting with 1 gram size reactions has failed thrice for moi, thats why im hard knocks and swinging bitch
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jon
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What "signs" are you supposed to look for? are you expecting an oil to seperate, color change? etc.
here's a thought carbamoylations don't work so well at lower Ph's maybe your amine was too protonated to add an isocyanic acid moiety to it? what
you'll see then is decomposition of cyanic acid to CO2 and NH4OH, notice any bubbles?
how did you do this? did you titurate your solution down to PH5 or was that the PH when your added your alkanolamine salt to nuetral water?
[Edited on 25-1-2007 by jon]
[Edited on 25-1-2007 by jon]
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chemoleo
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Chemrox, please, turn your title to something meaningful. Why? Because people search for it, and more importantly, the title is supposed to suggest
what the thread is about!
That way, you'll undoubtedly have more page views, and potentially more responses.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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chemrox
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MAR-frustrations overcome
The pH started neutral and rose to around 9-10 during the process. An intermediate was formed on cooling the mixture, weighed, collected and was
dissolved with 3x HCl. The solution thus obtained was clear and remained so with an almost invisible pinkish tinge that was dismissed as imaginary
until more data accumulated. On adding base a precipitate immediately formed. It was refrigerated and the crystals collected the following day.
The succes was confirmed by treating the resultant base with HCl and obtaining a pink solution. This is an expected color devlopment on cyclization
in this reaction.
The process for making the HCl salt is involved and the steps are adding the acid in about equimolar amount followed by adding xylene and using
azeotropic distillation to remove water. Then acetone crystallizes the salt from xylene solution. The product was flushed rather than made into the
salt. The anticpated trimethoxy version will be made into HCl, first by the usual method and then as above if the usual way is unsatisfactory.
It was learned that temperature is critical in this process. Slow boiling doesn't do it. The solution must reflux! Not merely bubble. pH seems to
take care of itself though a critical matter. A good paper was offered by one of our friends which I pass along:
www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.c...
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