You can try ion exchange resins

Hi Piet,

Perhaps one possibility would be to use preparative chromatography.

Hi Piet,

Perhaps one possibility would be to use preparative chromatography.

Hello Piet,

many thanks for sharing this very interesting chemical problem with the RG community. There are different possibilities you can try. One would involve heating of your ester product under high vacuum to ca. 60-80 °C (estimated) in order to get rid of the residual methanesulfonic acid (MSA). However, this method is often insufficient because small amounts of catalyst will be retained in the oily material.

Depending on whether your ester is a solid or not, you can also try recrystallization e.g. from acetonitrile or diethyl ether / pentane mixtures.

I think the safest way to remove residual catalyst would be a washing procedure. You can dissolve your ester in an excess of diethyl ether and wash the solution 2-3 times with water. For an even more effective acid removal you can use a solution of sodium bicarbonate (NaHCO3) for the washing procedure. This will neutralize and remove the acid without hydrolyzing the ester. Then separate the ether phase, dry over anhydrous Na2SO4 or MgSO4, filter and evaporate the diethyl ether solvent using a rotary evaporator. This will give you the pure ester product. I'm pretty sure that this will work.

Good luck with your research and best wishes, Frank Edelmann