DDTea - 28-7-2006 at 08:51
To start, I have done plenty of reading on this and have finished a full year of organic chemistry. One of our labs even had us separating
Acetaminophen/Caffeine/Aspirin from an OTC analgesic, so I'm fine with the theory and the general procedure.
But pills are nice and clean, and now I'm trying to move into the world of natural product extracts and alkaloid chemistry, so there are a few
differences.
The general procedure, as I recall is something like this:
-Grind up plant matter and soak in hot, acidic water
-Add non-polar solvent, mix, let the layers separate, and discard non-polar layer.
-Basify aqueous mixture, then extract alkaloids with non-polar solvent.
-Evaporate non-polar solvent to leave your final product.
My first question is once the mixture is defatted (while the alkaloids are still in water soluble form), couldn't one just put the whole mess in an
ice bath, basify it, and collect the crystals which (in theory) should precipitate? That is to say, why do we have to basify and *re-extract* with a
non-polar solvent and then collect our crystals by evaporating the said solvent--it seems like extra, needless work. The only reason I can see this
*not* happening is that one would be working with say, 50 grams plant matter and trying to collect 50 mg of alkaloids; thus it might not be feasible
to collect crystals in this manner.
Secondly, when is it appropriate to use activated/decolorizing charcoal? My chemistry books never really explained quite how it works, and I haven't
been able to find an explanation online...
Say, for example, we want to extract alkaloids from a cup of tea...lemon tea, let's say, so that we can assume the alkaloids are in water soluble form
If we add activated charcoal, mix it a bit, and then filter it out, we should
be left with a colorless, acidic liquid containing our alkaloids, right? But would we lose some of our alkaloids in this process??
Here is where I'm confused. If the alkaloid crystals are say, bright red, but are dissolved in water, would charcoal remove them, whereas if the
crystals were white/colorless, would charcoal ignore them?
solo - 28-7-2006 at 09:20
Nothing like trying out the theories to varify for one self...I used to clean up extracted alkoloids dissolved in a solvent thrugh activated charcoal
and did get some cleaning of the color and also removes some impurities.........solo
DDTea - 30-7-2006 at 18:02
Solo--do you mean that you followed the normal alkaloid extraction procedures, then did a recrystallization of your products in which you used the
charcoal to purify them further??
My point of confusion is at what stage it's used; and if one has only a limited supply of materials, waste and lost products becomes a concern
(otherwise I would be experimenting away 
)
solo - 30-7-2006 at 18:08
Prior to recrystallizing I would do the norite(activated charcoal ) soak and filter the do the regular recrystallizing ................solo
Vitus_Verdegast - 31-7-2006 at 06:01
After basifying your "defatted" acidic aqueous plant extract, when the mixture is shaken with a non-polar solvent, you will very likely encounter the
most frustrating emulsion a man can ever encounter during his life.
You can wait a day or three for the mousse to settle...
Or there is a very neat trick, just vacuum filtrate the mess once or twice through a layer of Celite or a similar filter-aid. It's a god's gift to
clear up an evil emulsion.
It took me years until I've learned this trick, luckily I still have most of my hair left.