Forgotten tools of separation

First of all, you might say: “Forgotten by whom? Not by me!”… You might be right, I admit that it is rather presumptuous of me to come up with post titles boasting the words “forgotten”, “neglected”, etc. But I would still venture to say that, given the wealth of high tech machines a synthesis laboratory might have these days, the majority of us do not resort to the older, more obscure purification methods. Today I want to bring to life silver nitrate (SN) impregnated chromatography as a method par excellence in really tricky separations. Below you can see two pinene isomers that are rather difficult to separate using conventional silica gel chromatography, yet are differentiated by the delta Rf of 0.2 using SN chromatography. I am including an excellent review by Mander that goes into the details of this great method. Some of you wonder if this would work best on alkene-containing molecules and you are right (due to silver-alkene coordination), but the method is not limited to separating on this basis alone. In Mander’s review, you will notice some intriguing examples of heterocycles that have been successfully separated using SN chromatography. So let’s keep these old methods in our lore of separation tricks, ladies and gentlemen.


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