cant think of a username - 11-5-2017 at 18:13
hello, i was wondering how to decarboxylate heat sensitive carboxylic acid, since most decarboxylations use heat.
niacin --> pyridine + CO2
salycilic acid --> phenol + CO2
R-CO2Na + NaOH --> R-H + Na2CO3
so for a heat sensitive carboxylic acid like Sorbic acid that undergous a diels-alder reaction with it self at high temp how would you decarboxylate
it.
JJay - 11-5-2017 at 18:21
You might try heating it with an excess of lime. Then again, that might not work....
clearly_not_atara - 11-5-2017 at 21:08
I actually think that at a high temperature, the reverse reaction predominates... this is certainly true of dicyclopentadiene, so why not
1,3-pentadiene? You may want to quench the vapors into a cold solvent so the product doesn't dimerize, but I suspect most of it will be produced in
the trans- configuration anyway.
Melgar - 12-5-2017 at 18:22
That double bond adjacent to the carboxyl group is inevitably going to affect its reactivity, although I'm not sure exactly how. But you certainly
can't use the set of reactions that result in an alkane, because that isn't what you'd have. Also, decarboxylation reactions typically involve free
radicals, which tend to cause oligomerization in alkenes, so you'd probably have to look into catalytic reactions, but even then I'm not sure where
you might start. If there is a solution out there, I doubt it's straightforward.
Vinylogous - 15-5-2017 at 08:27
User Magpie was able to decarboxylate niacin to pyridine at approximately the boiling point of pyridine (115°C).
I don't know of any off the top of my head but you could try searching for some sort of Diels-Alder suppressor - an "anti-catalyst" if you will. Perhaps something like this article (paywall)
Pentadiene boils at 42 °C, so if you were to mess around with the pressure of the system, you might be able to get the decarboxylated diene to
evaporate out of the reaction solution and condense it before too much is consumed by DA.
[Edited on 15-5-2017 by Vinylogous]