Chemistry Forums for Students > Organic Chemistry Forum for Graduate Students and Professionals

copper sulfate washes, lutidine, and DCM

(1/4) > >>

Babcock_Hall:
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?

Babcock_Hall:
The paper that we followed with the copper sulfate washes was Barrett Anthony, J Organic Chemistry 2000 65(20) 6508-6514.  10.1021/jo000690p.

We patterned an earlier synthesis, the one with a 1 M HCl wash, after the supporting information in Lindner J-P 2011 Chemistry a European Journal 17(15):4090-95. DOI: 10.1002/chem.201003163.

Both papers produced tetra-TBDMS ethers of glycosides from TBDMSOTf and lutidine.  Lindner's paper had more washes, including a brine wash.  Barrett used DCM as the solvent whereas Lindner used diethyl ether.

rolnor:
I think 1M HCl is a bit acidic for TBDMS-ethers. You can shake with copper sulfate then add Celite and filter through a pad of Celite, then separate. Also if you use chromatography lutidine will be removed I think.

Babcock_Hall:
Thank you; your replies are always helpful.  Chromatography is the next step, but I was trying to get ride of as much stuff as I could before then.  We will try celite next time, but I think that some DCM will evaporate if we do it under vacuum.

rolnor:
You will probably wash the Celite so there will be plenty DCM? Dont use full-vacuum when you filter, it just cloggs the filter.

Navigation

[0] Message Index

[#] Next page