orgchem712 - 24-4-2023 at 00:59
Hi, I'm having trouble disolving potassium carbonate in DMF.
Literature says solubility is 7.5g of K2CO3 per 1000ml of DMF at 25c. Yet it won't seem to dissolve even at boiling point...
I'm worried about DMF degrading into dimethylamine if left at boiling point for a prolonged period of time in the presence of K2CO3.
Would it be possible to reflux under reduced pressure in order to keep temperature down and avoid degradation of DMF into dimethylamine?
Any suggestions?
Osmiridium - 24-4-2023 at 02:56
Well, at higher temperatures the dissolution should be significantly faster. And usually, with few exceptions, the solubility will be higher the
higher the temperature is.
I see no point in refluxing it at reduced pressure. You could just let it stand at any desired temperature under atmospheric pressure without boiling.
Where have you found this solubility in literature? Have you tried with a much smaller amount if it dissolves at all? Seems it's not really that
soluble if it doesn't dissolve after longer reflux. Depending on your use it might not be necessary to dissolve it entirely.
orgchem712 - 24-4-2023 at 05:41
Its for cyclization of a benzophenone via microwave radiation.
The syntheses seems to work without K2CO3 been completely dissolved.
I just thought yeild could be improved if K2CO3 was fully dissolved in the solution but perhaps it's not necessary as you say and would not improve
the yield either.
So K2CO3 works as a scavenger?
The literature I was referring to was from a solubility chart I found online for K2CO3 different solvents.
[Edited on 24-4-2023 by orgchem712]
Osmiridium - 26-4-2023 at 15:16
I assume it's supposed to to scavenge a hydrogen halogenide?
But yes, it shouldn't be a problem if it doesn't dissolve entirely. But it's important that it's powdered very finely.
clearly_not_atara - 27-4-2023 at 04:58
If your DMF is even a little wet it's possible that some of the K2CO3 was converted to KCO3H by rxn with water and absorbed CO2 from the atmosphere.
You're talking about 0.7% w/w solubility, so even a very small amount of water would produce this effect -- likewise if the K2CO3 itself is wet.
But some of it probably dissolves and works as the base that you wanted. Except for a few rare cases where the base is truly catalytic, you usually
need stoichiometric base or more, which means that you will have much more than 0.7% K2CO3 and it will be heterogeneous (so it must be finely
powdered, etc).