Is there a way to figure out what pH an alkiloids will become freebase when extracting?

And at what pH it then will percipitate out?

For an example, extracting harmine and harmaline they percipitate out at different pH.


Also, I was reading about pKa and I wanted to make sure I grasp it's relivance. And acid with a higher number pKa would convert to another acid with a lower pKa was introduced. Like an acetate would convert to a fumarate if exposed to fumaric acid. Is that correct?

No thats not correct, pka is the -log of the equilibrium constant for a weak acid.

To try to simplify: strong acids such as hcl (hydrochloric acid) completely dissociate into h+ and cl- so the more hcl you add to a solution the more acidic it becomes -the pka is basically infinite. Weak acids are not like that, COOH which is the acid in vinegar dissociates to COO- and H+ but it wont dissociate 100%: so if you have 1 mole of a strong acid (hcl) in 1 litre of water you have a PH of 0 by definition. But If you have 1 mole of acetic acid in 1 litre of water you will have a PH of more than zero (i dono, 2ish) and you can calculate this using the pka.

Alright so what this means for you. At a PH under the pka value the weak acid will be protonated (meaning there is a H molecule on it, COOH rather than COO- & H+) so if you mix acetic acid into somthing with a PH of 0 nothing will happen. The acetic acid will remain as COOH and will not add any acidity to the solution. If you take this PH 0 solution with acetic acid and use base on it the PH will rise until the COOH dissociates into COO- & H+ then it will stay at that PH (the pka) until all of the acetic acid has been neutralized, then as you add more base the PH will begint to rise again: COOH acts as a buffer arounds its pka range.

So for alkaloids they are basic: under there pka range they form NH3+ and above there pka range they form NH2 with no charge. Since charged molecules are soluble in water NH3+ will dissolve in water but since most organic molecules are greasey or non-polar when you convert it back into freebase form (N2) then it wont dissolve in water. NH3+ will form a salt with somthing like acetic acid COO- and if all of the water is removed you will be left with (Molecule of alkyloid)-NH3+ bound to -OOC-(Molecule of acetic acid) because opposite charges attract. That would be your alkaloid acetate salt.

Ok so if your alkaloid has a pka of 9.5 you want to get the PH above 12.5 to make sure you convert it all into free base form, note that the free base will be a base in your body so you might not want to ingest it this way. If you want it as a salt you need to get the PH down past 6.5 to make sure its all in its NH3+ salt form.

To answer your questions more specifically: salts are generally very soluble in water so that they will not precipitate out until water is removed by evaporation. You need to get at least 3 PH units above/below a pka to totally change your substance from salt to free base and vice versa. Adding two different acids does not change there character. If you add acetic acid and then citric acid they both remain as they are but the one with the lowest pka is going to deprotonate and acidify the solution -the rest will remained protonated as they have a higher pka, so they wont matter if you trying to lower the PH but will matter when you try to raise the PH as they will have to be neutralized (they will act as a buffer around there pka range).

I hope this helps clarify things, if not please feel free to ask more questions! One thing i am fairly good at is chemistry.