We are adding tert-butyldimethylsilyl groups to an aromatic glycoside, following a publshed procedure. We used 4% (w/v of solution) copper sulfate to try to remove excess lutidine from our synthesis (which also involved an excess of TBDMSOTf and the solvent, which was DCM). We obtained an emulsion, which broke over a long time as we filtered through Whatman #1. A milk chocolate colored solid remained on the paper. On the one hand, I am tempted to increase the copper sulfate concentration to about 25% or so in the future (which we also did in our second wash), in the belief that higher ionic strength disfavors emulsions. On the other hand after our second copper sulfate wash, we tried a brine wash, and some of the extraction became an emulsion also, which we also broke by filtration. The procedure did not specify two copper sulfate washes, only one, and it did not suggest a brine step.
We attempted a similar reaction a few months ago, which used an HCl wash, not a copper sulfate wash. Based on crude mass, I don't believe that we removed all of the by-products. That is one reason we tried a different literature protocol for this reaction.
Does anyone have any suggestions for ways to avoid the emulsions or any other things we should change?