How far the use of diethylamine can be allowed or possible in purification of alkaloids by chromatography methods? Does diethylamine at any point of time react with alkaloids during purification steps?
Diethylamine is used to keep the alkaloid as the free base in my experience, so the peaks are sharper. It may also deactivate silica gel. It is typically used on silica at a level of about 0.1%, although I've seen concentrations of 10% used for TLC systems in the literature. The boiling point is 55° C.
Ack!! you're right, the BP is only 55° C (131° F)- I edited my original post to reflect the correct temperature. Thanks for the correction.
It may enhance the purification or it may have little effect. It really depends on the alkaloid. It probably won't react with anything, although, with the wide range of natural products, it's difficult to assert that no alkaloid will ever react with DEA.
There should be no problema. You may use Et3N; we have been employing it with flash silica with great success in the past. BP is similar to that of EtOAc (approx.)
@Teodoro Kaufman Thank you sir. I am trying to purify a compound of interest from methanol extract and it is detectable only by dragendorff reagent which made my compound of interest could be an alkaloid. In open column of silica it can be eluted with 4% DEA in chloroform. I wonder if I could use DEA along with hexane to get even more separation and doing that eventually involves more DEA in my column.
Hexane is less polar than chloroform, so the compound should remain for a longer period on the column, and _possibly_ not elute. To compensate, more DEA is likely required. I'm assuming you are using silica as the column packing as I write this. You _may_ also see a different elution order of your compounds as well due to a different selectivity of the solvents. If you can get a copy of Snyder & Kirkland, 2nd edition, the explain both polarity and selectivity of various solvents.
I use the solvent system CHCl3: MeOH: Et 3 N (13:5:2) and silica gel as a solid phase for separation of pyrrolizidine alkaloids and i have obtained excellent results in the purification of these compounds. Probably you can play with this system and achieve similar results. Molecules degradation does not occur in this model.
I would like to share my experience with DEA. I learned from my recent works which involved DEA in Column Chromatography is that the presence of trace DEA in my fractions lead to coloration and give additional spots on TLC. One reason could be that DEA is sensitive to light and air.
Diethylamine shouldn't decompose over the time required to run a TLC plate. There may be impurities in the DEA; old material often has a brown color (pure DEA should be clear). The extra spots may be from the DEA impurities or may be compounds that are better resolved as the free base than without the DEA.
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