kenofken
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Heat concerns with molecular sieve in reaction
I'm doing some work with porphyrazines and my first step is a one-pot synthesis that forms imine links and also a Fisher esterification (from
methanol). My yields are stuck around 26%, and I suspect its because of all the water generated in those steps tends to push the reaction backward as
it accumulates. I plan to try adding 3A sieve to the pot. My concern is heat. Too much heat (and too long a run time) turns this reaction into tar. My
hope is that because water generation happens somewhat gradually over two days that it won't get super hot at any one point. Should I perhaps add the
sieve in portions over that time or try to set up the flask in a cooling bath of some sort?
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Magpie
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I've used 3A mol sieves to dewater ethanol and ether, and 5A to dewater toluene. Never saw any significant heat generation. Then again I only use
the sieves for solvents that are very low in water to start with, ie, a few 100 ppm at most I would guess.
Come to think of it I did try to dewater rectified spirits (95% ethanol) with 3A sieves - not really successful IIRC.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Nicodem
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Thread Moved
21-4-2012 at 01:35 |
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