FireLion3 - 6-9-2016 at 07:49
Couldn't find any information on this but it seems like it would work in theory.
If there is a 50/50 split of two different amines, one of which has a single phenyl group, the other which has two, and 50% mol of an acid is added,
would only mostly the more polar amine be extracted, since the one with two phenyl rings would repel the water to a greater extent? The principle
being the additional phenyl group would result in lower water solubility. Perhaps if the effecting factor is not polarity, but rather sterics with the
second amine just being more bulky.
Example: diphenylmethylamine and benzylamine
I can think of several similar separation techniques for other types of compounds, but I've never seen this specific one used. If this doesn't work,
can anyone suggest another, other than distillation?
DraconicAcid - 6-9-2016 at 08:39
You'd have to check the pKb values of the amines, which are more likely due to the electron-withdrawing/donating nature of the substituents than their
size.
FireLion3 - 6-9-2016 at 08:59
I'm not talking about separating them based on differences in acidity, but rather sterics or hydrophobic interactions.
For instance, chiral acids can be used to selectively extract one amine enantiomer from a racemic mixture, by taking advantage of the steric
interaction between the acid and the amine. I've seen in literature these separations yield 97-99% the first time, with one specific enatiomer being
extracted almost exclusively.
What I was wondering is whether a similar principle can work for differences in steric bulkiness or differences in
polarity/hydrophobicity (to separate two different amines)
[Edited on 6-9-2016 by FireLion3]
DraconicAcid - 6-9-2016 at 09:37
Okay, I see what you mean. I'm not sure if that would work. But if you're looking specifically at diphenylamine and an aliphatic amine, you'll find
that the diphenylamine is a much weaker base. I don't have it's pKa at hand, but the pKa of anilinium ion (the conjugate acid of aniline, or
phenylamine) is 4.6, whereas that of benzylammonium is 9.35 (most other alkylammonium ions have a pKa of about 10). So if you use an aqueous solution
buffered around 6 or 7, the arylammonium ions will be deprotonated and stay in the organic solvent, and the alkylammonium ions will be protonated and
go into the aqueous layer.
You may be able to find anions that form insoluble salts (in whatever solvent) with the cation of one amine but not the other.