recently i noticed some posts from rhodium about tannins and i learned something i'd somehow managed to miss in previous searches of the subject - that tannins are esters of sugar and gallic acids etc etc... well, some of them anyway. And the other type, which are 'condensed', i don't think these can be hydrolysed back to sugar and gallic acids etc however.
In reports of the extraction from both acacia and mimosa there is some kind of change in consistency that occurs and undergoes three main states from pH 1 up to pH 14. Below 9 it is a brownish-red material, which thickens when dehydrated to a black brittle substance that seems to absorb moisture quite readily. Between 9 and about 12 it precipitates a pink/grey precipitate, and then at higher pH's it starts to turn into a black thick substance.
Is this a hydrolysable tannin or is it condensed? Do these solubility behaviours reveal anything about how they may be removed?
I can't quite work out what is the best way to remove this material. Some have suggested boiling off the water until it is significantly concentrated and then filtering it. It seems to help somewhat to do this, in terms of the final result, but this reddish brown gunk is nasty to filter, it clogs everything. Refrigeration and decanting is a method that is gaining some popularity amongst extractors recently.
An acacia was recently extracted from and boiled down to a small volume and the semi-solids were painstakingly filtered out. When basified the usual phenomenon of the grey precipitate and black result failed to appear. The solution clearly changed in consistency. Unfortunately the experimenter did not use pH measuring so the lack of result cannot be narrowed down further than a lot of washing of the freebase extract (including one pas bicarbonate solution) and (obviously) over-basification.
now, it seems to me that the use of sodium hydroxide might be strongly implicated in the failures to date for many of these alleged extractors. Could it be a base conjugate? Or is it something to do with those tannins?
Now, the lines of attack on this problem i see as being twofold - some of the solutions may attack both points of weakness in the process - removing the majority contaminant compounds in the solution (ie the tannins) and finding a way to ensure that neophytes can correctly basify without introducing solubility problems at the margins of the pH window that is optimal.
What about using calcium hydroxide to basify, which forms salts with the tannins that are insoluble in water? The other advantage is that one cannot raise the pH above 12 and CaOH precipitates tannins.
as to the preparation of the CaOH to be used for this, i figured the method would be to soak hydrated lime (garden quality, i assume to be high in calcium carbonate, certainly it's solutions are not easy to clarify) and then decant or pipette it and let it settle until it's adequately clear.
I considered the idea of denaturing tannins in the bark as a means to eliminating them, but i'm not sure the conditions are very friendly to tryptamines - from what i gather so far, tannins of all sorts decompose under strong alkaline conditions. When basifying the extract from these tannin rich plant sources, the black thick soupy consistency is very intense, and when the pH rises to the point it makes the black, the emulsion formation seems to cease too. Extracting from this black aqueous soup seems to work quite well, however two things are problematic. There is some suggestion that the main yellow contaminant material does not extract at lower pH's but... and here's the bind, at these lower pH's the emulsions are intense... and if basification is not done high enough the alkaloids are not effectively extracted.
I was thinking maybe if one basified with the CaOH, which should, theoretically make a nice resistant precipitate out of the tannins which will probably decant off quite easily. And the other advantage iswe don't raise the pH of the solution above 12, which means that higher pKa alkaloid/amine type materials are selectively retained in the aqueous phase.
Would cooling be helpful in this kind of operation as well? like in a refrigerator type cooling. The insolublity of the tannin's conjugates with calcium ions should mean pH would not change rapidly until the tannins which form these insolubles fell out completely, so it should be added slowly then i would think. Is there any reason why one shouldn't just use plain unpurified garden grade hydrated lime neat to basify, if one intends to decant the liquid off any precipitation anyway, is there any reason why calcium carbonate and calcium hydroxide excess (and possible likely contaminants) will cause any problems?
I considered the use of magnesium hydroxide however for the purpose of extracting a base with a pKa of 8.68 and almost full de-ionisation at pH 11. MgOH is inadequate for this purpose in a liquid liquid extraction. I have seen it work to a good degree as a dry acid/base extraction base however, but i cannot comment as to it's relative performance. The requirement of drying it was somewhat onerous however the experiment to which i refer a great excess of additional materials was added to it which made the process more difficult than it needed to be.
The dry acid base extraction using MgOH seemed to yield quite pure material, however it had a different character to the usual material, it was a very slighly pale yellow, but cleaner than seen prevously. a vaguely different smell too.
On a side topic, related to this because of it's presence associated with this high tannin content - cellulose. The plant material is difficult to work with because of the amount of very hard cellulose fibres it is made of. Is there some way to make the cellulose depolymerise without damaging the amines? Pressure cooking is one option considered, and seems to help somewhat increasing the extraction from less well shredded plant material. Is there an economic source of a cellulose decomposing enzyme, or an organism which could be used to encourage this to occur?
Any method used to render the acacia bark more readily extractible has to be mild in its effect on the alkaloids, so this narrows down methods quite a bit.
