AHHH…somebody has his thinking cap on…
Everything you say is “right on target”….but you are thinking
Crystallization from nonpolar solvent mode…not solubilization.
For a year or so I have been stressing the exact same thinking mode
In ‘Butane works but no theory”…
When you stress the weak acid nature of the R-COOH of THCA…
You are not stressing the salicylicate nature of the acid as well…
Which complicates things further.
This is NOT a regular carboxylic acid anion.
In aqueous…the pKa of THCA is
3 . And Yes is does dissociate in aqueous. If you buffer it to pH 6.5 it is readily
Ion paired and bound to SAX resins…which is a standard preparation procedure
Published by Agilent. (BTW SAX are quaternary Ammonium…heresy?)
However, the pKa for Salicylic acid in non polar alkane
Is more like 11. so yes, when you are talking about precipitation (crystallization from Butane) your analysis is correct.
When we think about butane extraction to butane precipitation…we have vastly different solution matrices.
If you look in the list of total know extractables from the trichomes you will find
Palmitamide present in almost equimolar concentrations to cannabinoic acids…
And the amides can and do provide ion pairs as you suggest.
If it is not an amide or amine or a Hydrogen ion ….the ion pair has to come from somewhere….in order for BUTANE TO WORK AS A SOLVENT in the first place.
THCA is not crystalline in the trichome…how can it be highly concentrated in the
Trichome…and then Extractable into alkane…only to crystallize spontaneously from butane?
Clearly the problem you delineate is thinking non-polar solvent…chemistry.
And you are on tract…aprotic-nonpolar.
How did the THCA get into that environment in first place?
What does it mean to have CANNABINOIC ACID IN BUTANE?
Below contains a 30 page introduction/guide to how a Ph.D.
Chemist might begin thinking about the subject.
The original thought …of extracting from semi-aqueous (terpene as detergent) soup
In trichomes…where the pH is about 5…then we would think
The RCOOH salicylic acid moiety should be half ionized in the terp-soup trichome storage…and maybe we are extracting BOTH FORMS as a ternary Ionized pair with some bound water. [Trying to think in the simplest terms and explain all observations)
It is possible your RCOOH is actually binding the anion RCOO- (as a substitute for weak base amine non protonated) and carries a water molecule or two in a complex extractable (from terpene detergent soup) by the Butane at -40C.
This falls apart in dilute alkane where the pKa is now 11 forming two RCOOH molecules and robbing a H+ from the water.
{{ [HA]—h—{A-}—H— OH}}. Ternary, non polar h-bonded solubility complex…at -40 (FROM terpene soup).
Technically speaking , a heterologous DIMER MONOHYDRATE.
So precipitates out as homologous-dimer crystals after robbing water of H+ ion.
To me this is most simple explanation of butane solubility.
The second would be an amide playing the role of the amine you suggest but in extraction side, but not necessarily in the precipitation side (crystallization of dimers).
Third may be the Plant pumps Hydrogen ions into the trichome storage area sufficient to Pair each Cannabinoate with and hydrogen ion…and form a butane-extractable R-COOH.
Now in technical terms, it would be the direct extraction of
Homologous-Dimer hydrate. Remember this is aprotic Butane;
But when shifted to protic formic-water-methanol solvent
For RP-HPLC with MS analysis…returns the “happy-form”
That everyone wants to think about: monomer, unionized THCA.
The non polar alkane solution your are thinking about is far more complicated to begin with…and you are thinking about amines from Gas tanks complicating an already complicated solution which for some reasons wants to precipitate THCA
With or without the gas tank contaminates.
A while back I posted a thread: https://future4200.com/t/re-cocrystals-and-salts-cannabinoates-in-never-never-land/174502/10
This provides a modern interpretation of your carboxylate salt chemistry review.
I hope everyone appreciates the deep thought you have put into this subject.
Above I am just “throwing out’ some additional ideas that might stimulate more thought. None of which negate your proposed schema.
Finally it seems we have a discussion of the cannabinoate acidity-ionpair-salt concept. …in PROTIC, in APROTIC and NONPOLAR solvent environments……
With cannabinoates morphing into different forms depending on the environment.
and yes…it has something to do with Pka’s …and “over-thinking”…and sarcasm. ( The latter having nothing to do with your post).