Hello, in my o-chem lab were doing an acid base extraction of a primary amine. The pKa is around 9.8.
We first take the solution with the amine salt and add NaOH to pH 13, and we calculated the ratio of base to salt from Henderson-Hasselbach. We mixed it up, let it sit, then added diethyl ether. We stirred it, then removed the ether layer and back extracted with more ether. The next step was to add a phosphoric acid solution (pH 2.0) mix, and remove the aqueous layer.
Here is my question: My TA said that after you extract the ether which contains your amine in base form, you can add distilled water, mix and keep the ether solution. He said this helps remove any left over NaOH that came along for the ride. After thinking about it, won't adding pure water (pH 7.0?) PROTONATE the amine in the ether and severly decrease your yield? The amine that gets protonated would end up in the aqueous wash and de discarded. Or does this not happen because theres no salt/counter-anion in solution? Why would you be so concerned about left over NaOH anyway couldn't you just add more acid or stronger acid?
Thanks for the replies