Sampsa Pellervoinen - 22-1-2011 at 09:47
I've been bothered by this question for a long time now and was hoping someone here might know the answer(s). Why are some alkaloids found as some
salts but not others?
For example: Dextromethorphan (the active ingredient of some cough medicine) is almost always found as the HBr salt. This seems bizarre to me since
the HCl salt would be cheaper to make, more soluble and avoid any bromine toxicity with extended use. What's the advantage of using the HBr salt over
HCl? For that matter why not use the Sulfate, Acetate, Phosphate... forms?!
I understand that organic bases react with acids to produce charged water soluble salts and organic acids react with bases to the same effect so this
is a broad distinction (between acid and base salts aka. Dextromethophan HCl vs. Levothyroxine Sodium) but what about within the subcategory of acidic
alkaloids?
There are many other examples of this seeming preference for one salt over another and I'm sure the underlying reasoning is complex and varied but I
don't even know where to start. Is there a chemical reason that I'm missing? Does it avoid drug patent laws? Etc.
[Edited on 22-1-2011 by Sampsa Pellervoinen]
[Edited on 22-1-2011 by Sampsa Pellervoinen]
Sedit - 22-1-2011 at 10:28
It more then likely boils down to physical properties of the various salts. In some cases the HCl salt is hygroscopic so some pharmacuticals opt for
the sulfate salt. Other times it boils down to absorbtion. Take for instance the illegal compound MDMA whos citrate salt manages to get degraded in a
different part of the gut then the HCl salt allowing for more complete absorbtion into the body before it is metabolised.
In the end there is no real clear cut answer to your question because it varies from compound to compound depending on its metabolism and physical
properties.
Sampsa Pellervoinen - 22-1-2011 at 10:40
Thanks for the quick reply Sedit! I figured that might be the case - that it is extremely compound specific and that there is no one answer. Could you
link me to an article about MDMA citrate vs. HCl metabolism? I tried googling it but couldn't find anything.
Sedit - 22-1-2011 at 10:46
I'll try to locate the source of the information and believe the artical is posted up somewhere over at Thevespiary.
jon - 22-1-2011 at 14:54
1 mole of mdma reacts with 1/2 mole of citric acid mdma(II)citrate.
mdma ethanol stoichiometric citric acid and diethyl ether work the best the problem with mdma citrate is it tends to suck up water and it's hard to
crystallize it turns gummy.
so mix the mdma with alcohol and citric acid then take the alcohol off under vacum and dry it under vacum/heat to a constant weight.
then, procedd to recrystallize.
azetropic distillation should also work .
petro ether works as a nonpolar recrystallization solvent also.
i don't know how i knew that, a little bird told me.
[Edited on 22-1-2011 by jon]