[Babcock_Hall]

We are alkylating cysteine with propylene oxide and using triethylamine as the base.  We used free cysteine, as opposed to cysteine hydrochloride, but otherwise our procedures were similar.  "The residue was extracted by boiling absolute ethanol to remove triethylammonium hydrochloride, and the insoluble substance was filtered and washed with ethanol."  Zilka, A. and Weinstein, M., Bulletin of the Research Council of Israel, Section A Chemistry (1961), 146-148.

I am not sure how to do this.  I could picture taking a test tube or a small flask and heating.  Using X amount of ethanol, I would mash the solid around a bit with a stir rod, but I am not sure that this is what they had in mind.  Any thoughts.

[curiouscat]

Yes, I'd say something like that.

[Dan]

Me too, sounds like a standard trituration.

[curiouscat]

Another thought: Could you keep solids on a filter paper in a fritted funnel and pour over them some hot EtOH?

[Dan]

You can do that, but it tends to be less efficient. I often suspend solids in an Erlenmeyer, mash them up with a glass rod and stir with a magnetic stirrer (heating if required) for about 30 min to give the impurities some time to dissolve. Then let the solids settle, carefully decant the solvent, and then repeat the process a couple of times. If the solid is very fine and does not settle easily (causing significant loss during decanting), I decant the solvent through filter paper and return any collected solids to the flask for the next repeat.

For each repeat I usually check the composition of the solution by TLC - once I can see that no more of the impurity is present in the solution, I collect the remaining solid by filtration. I'm not sure if monitoring is feasible for NEt₃.HCl though.

We are alkylating cysteine with propylene oxide and using triethylamine as the base.  We used free cysteine, as opposed to cysteine hydrochloride

Hang on a minute - so where does the NEt₃.HCl come from in your reaction?

[Babcock_Hall]

That's a good question.  The original protocol used cysteine•HCl and 2 equivalents of triethylamine as the base.  I think that my student used two equivalents of triethylamine, even though we used the neutral form of csyteine as our nucleophile.  He did not attempt any purification before running an NMR, and so the spectrum was a bit ugly.  However, it occurs to me that at least some of the TEA should still be neutral and should come off with rotary evaporation.