Chromatography Forum

Dear all,

What solvents is formic acid soluble in?

I am after an aprotic solvent that is less dense than water.

Thanks

Google the terms "formic acid solubility" and see what shows up. You have a wide selection. (I just checked.)

mmm...I am afraid it is not that simple.

Only very polar protic solvents show up, i.e. water and alcohols.

I discovered by testing that it is also soluble in CH2Cl2, but it denser than water.

I need a safe (reasonably high boiling point) aprotic solvent less dense than water...and immiscible with water. (too many things to ask for I think...)

Any ideas?

Ether(s)?

I think it is soluble in diethyl ether...but aren't they dangerous?
They form explosives peroxides as far as I know...

About any polar organic solvent should dissolve formic acid. Depending on the concentration you need, there is some degree of solubility in hydrocarbon solvents. (per Wikipedia)

I see a reference to a 50:50 mixture of formic acid and toluene being used for a reaction. (http://www.jbc.org/content/86/2/695.full.pdf) and other solvents are mentioned.


Diethyl ether can be used with proper precautions for storage - but it is not particularly high boiling.

what about acetonitrile?

Indeed, ACN comes to mind as well, but "immiscible with water" is the one criterion by which it would fail.

May I ask why you need to locate such a solvent? Intuitively it would seem to me that any solvent non-polar enough to be immiscible with water will be a poorer solvent for formic acid than water. So if you take a solution of FA in that hypothetical solvent and add an aqueous phase, the FA would in all likelihood partition to the water.

I missed the "immiscible with water" part.

However, if the object is to extract formic acid from water, what about simply acidifying the water to a pH well below the pKa of formic acid (sulfuric acid should do the trick) and then extracting with methylene chloride?

He also wants a density which is lower than that of water.

My brain is apparently on summer vacation. But the principle still stands: drop the pH below 2 to make sure the formic acid is in the free acid form and extract into an organic solvent of choice.