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Topic: Alkaloid isolation help [a/b extraction]  (Read 7593 times)

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Abe

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Alkaloid isolation help [a/b extraction]
« on: October 20, 2005, 08:15:50 PM »
Im a noob to this chemistry stuff, so keep it simple please.

I have to an alkaloid in its HCl form in an acidic aqueous solution, just the alkaloid in acidic water, nothing else. I need to unhook its salt by adding a basic solution, in this case NaOH, which will cause the alkaloid to precipitate into its freebase form. However i do not want to use an non polar organic solvent at this point to extract the alkaloid, namely for personal reasons, as i detest handling that stuff.

1. Is the precipitation the alkaloid, or an alkaloid+NaOH compound?

2. Ive repeatedly pondered how to seperate the freebase alkaloid from the NaOH. If the precipitate is just the alkaloid, then i can simply filter it out and rinse. If its not, ive considered doing sublimation since the boiling/melting point of the alkoid is much lower than that of the NaOH. Given that the freebase alkaloid is soluble in NP solvents, but not that of water, and that NaOH is soluble in water but not NP solvents, what else can i do?

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Re:Alkaloid isolation help [a/b extraction]
« Reply #1 on: October 21, 2005, 12:26:11 AM »
I know you won't like this, but organic solvents are really the way to go.  I would recommend ethyl acetate for this particular purpose; it's not very toxic and is relatively polar and should be good at soaking up the alkaloid free base.  You would need to avoid prolonged exposure to NaOH though because you might begin to saponify the ester.

I think it is going to be difficult to get the alkaloid to come out of solution in just aqueous solution.  Alkaloids are made to function in biological systems, which is something that they generally can't do if they are insoluble in water (biological systems are mostly water, afterall).

Abe

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Re:Alkaloid isolation help [a/b extraction]
« Reply #2 on: October 21, 2005, 01:37:31 PM »
Isnt ethyl acetate miscible in water? i dont think that will work for this. The precipitate is NP, so adding polar solvents isnt really going to achieve anything. Thats why i said i didnt want to work with solvents, caused the only ones i can use are NP hydrocarbon based solvents, all of which are neurotoxic and carcineogenic.

Maybe the question i should be asking here is: During this basification step that produces a precipitate, what exactly is the precipitate? I was told by a friend that by basifing an alkaloid in its HCl form, im "unhooking its salt". What exactly is happening between the alkaloid and the NaOH, are they combining, or is the preseence of NaOH simply changing the chemical structure of the alkaloid?

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Re:Alkaloid isolation help [a/b extraction]
« Reply #3 on: October 21, 2005, 02:19:50 PM »
Alkaloids are called so because the basic character of much of them. Most of them have tertiary amonia structures which with acids form alkaloid salts. They all are well soluble in water. The free bases are less soluble at all and may form prcipitate in basic media.The best method for your case i think is filtration of the precipitate from NaOH solution, then washing and precrystalization maybe. What about if use amonia(NH4OH) insted NaOH because amonia could just evaporate and after that only drying the water from precipitate ;)
xpp

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Re:Alkaloid isolation help [a/b extraction]
« Reply #4 on: October 21, 2005, 03:29:49 PM »
Ethyl acetate is most certainly not miscible with water.

Abe

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Re:Alkaloid isolation help [a/b extraction]
« Reply #5 on: October 21, 2005, 07:51:48 PM »
Alkaloids are called so because the basic character of much of them. Most of them have tertiary amonia structures which with acids form alkaloid salts. They all are well soluble in water. The free bases are less soluble at all and may form prcipitate in basic media.The best method for your case i think is filtration of the precipitate from NaOH solution, then washing and precrystalization maybe. What about if use amonia(NH4OH) insted NaOH because amonia could just evaporate and after that only drying the water from precipitate ;)

So your telling me that the resulting precipitate is the pure alkaloid, and not an alkaloid/NaOH(or other base) compound? please i need a straight answer reguarding this it determines the next step in the process.

 Ive considered using ammonia, but have to do some tests reguarding the purity of my source.

Could you suggest some NP recrystallization solvents that arent hydrocarbon based?

btw, thanks for all the help.

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