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Felab
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[*] posted on 14-11-2018 at 01:53
Extraction of gallic acid


I want to make some calotype negatives and I have all the components I need except for gallic acid. Researching in the internet I found that chestnuts are the food with the highest content in gallic acid, with a content of aprox 0,5 g/100g of chesnuts. that means that with one or two kilos of chestnuts I can have all the galic acid I need. I want to extract it by the folowing procedure:
1. First, crush the chesnuts into a powder or a paste.
2. Add water with low calcium and iron content (I think 3l is enough) and boil in a galvanized steel bucket for a few minutes.
3. Decant of the gallic acid contanining water and repeat two or three times for maximum yield.
4. Add acetic acid to hydrolise the gallotanins to gallic acid and sugar.
5. Precipitate gallic acid by the adition of calcium carbonate, and then boil the solution for a few minutes, generating insoluble calcium gallate.
6. Decant the solution and add sulfuric acid to the precipitate until the ph is around 4.
7. Add water and remove calcium sulphate by filtration, geting gallic acid in solution.
8. Dry, and store properly to prevent oxygen from degrading my gallic acid.
Is there someone who has tried something similar? Is the gallic acid in free state in the chesnuts, or is it trapped in the form of gallotanins? Is there a more straight foward method of extracting gallic acid? Can tannic acid be hydrolised to gallic acid? How can I remove off the egallic acid contaminant that is going to be present in the final product? Should I develop my calotypes with tea instead of doing such a procedure?
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[*] posted on 14-11-2018 at 02:13


I've thought about doing that. My plan was to extract tannins from maple leaves.

I am not sure that boiling is a good idea. Gallic acid is easily oxidized or decarboxylated.

Is acetic acid strong enough to hydrolyze tannins? Chestnuts likely contain some free gallic acid, but a lot of it would be locked up in tannins. Acorns are high in tannins. The exact variety of chestnut matters quite a bit too... sweet chestnuts would not contain as much gallic acid as horse chestnuts.

Gallic acid and tannins are easy to purchase. There are several papers on extracting/purifying gallic acid. These papers contain clear and detailed procedures.




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Felab
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[*] posted on 14-11-2018 at 02:49


Quote:


I've thought about doing that. My plan was to extract tannins from maple leaves.

I am not sure that boiling is a good idea. Gallic acid is easily oxidized or decarboxylated.

Is acetic acid strong enough to hydrolyze tannins? Chestnuts likely contain some free gallic acid, but a lot of it would be locked up in tannins. Acorns are high in tannins. The exact variety of chestnut matters quite a bit too... sweet chestnuts would not contain as much gallic acid as horse chestnuts.

Gallic acid and tannins are easy to purchase. There are several papers on extracting/purifying gallic acid. These papers contain clear and detailed procedures.

From the information I found, the classic procedure of extracting tannins involves boiling it. I think acetic acid is the perfect acid since it is relatively strong, non oxidising and easy to separate. Maybe hydrochloric bould be better though.
I live in the most arid region of Europe so to find acorns I need to travel several hundred kilometers. For the same reason I coudn´t dind gallic acid at a reasonable price. I can buy tannic acid very cheaply though so that could be an option. All the papers I found where not free acess so I need to develop my own procedure.
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[*] posted on 14-11-2018 at 16:50


Quote: Originally posted by Felab  


All the papers I found where not free acess so I need to develop my own procedure.


Did you check Sci Hub?
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[*] posted on 14-11-2018 at 17:36


If there is a particular paper you are looking for, someone can probably find a copy for you.



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[*] posted on 14-11-2018 at 19:12


I tried a few times to hydrolise tannic acid to gallic acid - I kept getting stuck with a tarry mass that would not filter. (looking for the procedure I tried to follow now - as far as I remember, it was a base hydrolysis using NaOH).

In the end I just used tannic acid. (I was tinting cyanotypes). It (tannic acid) didnt seem to do a better or worser job than green or black tea.

Ah - found the procedure here :-
(the one I tried to follow was garage chemists')
https://www.sciencemadness.org/whisper/viewthread.php?tid=20...

..and now I read thru it - I remember that I thought oxygen was my problem - I remember stuffing around with plastic wrap ! I've got a good source of argon now - perhaps I should revisit it.
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[*] posted on 14-11-2018 at 22:25


Acetic acid will not hydrolyse complex tannins, you need a mineral acid, dilute hydrochloric or sulphuric acid but acid hydrolysis also cause much formation of insoluble (presumably polymerised) tannins. My experience is that caustic alkalis give better, faster yields and I have reported on this procedure in several previous threads. Depending where you live in Europe, oak tree galls are amongst the best source of soluble tannins, particularly the large Mediterranean galls that grow on cork oaks. I collected a bag full in central Italy two years ago.

As you can buy tannic acid I would go down this route as its often the cheapest but be aware that there are several types of tannin and purchased tannic acids can be either catchetutannin or gallotannins, only the latter yield gallic acid. Check out the last post on this thread:

http://www.sciencemadness.org/talk/viewthread.php?tid=20487#...

I explain how to type test bought tannins.

I recently purchased some tannic acid from a Chinese ebay seller and the quality was excellent.
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Felab
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[*] posted on 15-11-2018 at 01:15


Quote: Originally posted by ahill  
I tried a few times to hydrolise tannic acid to gallic acid - I kept getting stuck with a tarry mass that would not filter. (looking for the procedure I tried to follow now - as far as I remember, it was a base hydrolysis using NaOH).

In the end I just used tannic acid. (I was tinting cyanotypes). It (tannic acid) didnt seem to do a better or worser job than green or black tea.

Ah - found the procedure here :-
(the one I tried to follow was garage chemists')
https://www.sciencemadness.org/whisper/viewthread.php?tid=20...

..and now I read thru it - I remember that I thought oxygen was my problem - I remember stuffing around with plastic wrap ! I've got a good source of argon now - perhaps I should revisit it.


I´ve looked up this procedure and I will try it out in the future.

For tonning cyanotypes, you can even use coffe. The type of tannin you have doesn´t matter very much.

But for making calotypes, gallic acid is desired since it doesn´t stain the negative like tannic acid would, and it doesn´t react immediatly with silver nitrate, wich is very important to get a good density.

The only argon I can easily get is the one present in lightbulbs so I will just asume that the reacction will give a lower yield.
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[*] posted on 15-11-2018 at 20:24


Quote: Originally posted by Boffis  
dilute hydrochloric or sulphuric acid but acid hydrolysis also cause much formation of insoluble (presumably polymerised) tannins.


If dark precipitate comes out of a clear tannic solution, it's not the gallotannin, unless maybe you poured in 96% acid...the acid solutions are much less sensitive to air than alkaline, so that's not it. Addition to strong tannic acid solution does precipitate the gallotannin but this is good...decant, wash...heat w/dil. acid for a bit and cool for...a few days maybe. Sulfuric acid in water or methanol (methyl gallate) is used analytically on gallotannins, so one might think it's not such a bad method.

PS Before this came up I already planned to extract sumac over the holiday, if the experiment goes well it will be posted in the relevant thread. Sumac is the only reliable local plant source of pure gallotannin here.

[Edited on 16-11-2018 by S.C. Wack]




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Felab
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[*] posted on 18-11-2018 at 08:51


I want to buy some tannic acid to do experiments, but the page that sells it offers two types: water and alcohol soluble and water soluble. Wich one sould I choose to get gallic acid? I coudn´t find if gallotanic acid is soluble in alcohol.
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[*] posted on 18-11-2018 at 11:36


It's impossible to say without knowing the source or how it was extracted. Transesterification is even a possibility. I note ebay is full of Majuphal whole, powdered, or extracted with ???. This traditional source does not have as much free or easily lost gallic acid compared to a sumac gall or leaf source. Stahl and Schild (Isolierung und Charakterisierung von Naturstoffen) extract it with methanol in a Soxhlet and end up with 35-45% yield of tannin. In the old days they used ether with a little ethanol in it, so strong polarity is not required for this source. Other sources can be more stubborn and of course tannin can be lost just by bad treatment of the material.

I've bought beige "USP tannic acid" that most definitely did not conform to USP spec.




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[*] posted on 18-11-2018 at 13:17


I´ve seen that the shiping is 4 times more expensive than the tannin itself so I have changed plans. I will try several possible sources in a small scale such as chesnuts, pomegranate, wood, oak bark and whatever I find that can contain tannins. I will see which plant gives the best result and yields the most gallic acid.

I have also found an old 19th century book wich gives another pathway on the syntesis of gallic acid:http://albumen.conservation-us.org/library/monographs/sunbeam/chap14.html#heading51

If you have some idea of what plant I could use please tell me.
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[*] posted on 18-11-2018 at 14:37


Chestnuts have a high enough starch content that step 2 will make porridge.
I doubt decantation will be an option.
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[*] posted on 20-11-2018 at 11:28


Quote: Originally posted by unionised  
Chestnuts have a high enough starch content that step 2 will make porridge.
I doubt decantation will be an option.

I have tried pomegranates and they seem very promising. I am yet purifying the tannic acid but it definitely makes some ferric sulphate turn blue and it tastes very astringent.
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[*] posted on 25-12-2018 at 19:43


70% acetone (or MIBK) has been recommended for a long time for leaf material, and crushed air-dried sumac leaves were 57% soluble in it. After removing the acetone, a single wash with DCM (or chloroform) removes all the green acetone-solubles. What was really surprising was powdered nutgalls were 80% soluble, and the wash is unnecessary. BTW there is lit showing great variation in extractable tannin depending on how the material was treated before extraction.



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[*] posted on 5-1-2019 at 17:54


One may question involving organic solvent at all, but concentration of the extraction solution is generally desirable and acetone is much easier to remove with a minimum of heat. My sumac extract is still in the desiccator but some experiments have been done on the ease of acid hydrolysis of extract of alleged Q. infectoria galls.

Sulfuric acid hydrolysis is in the old books as the method of Liebig. One recipe calls for boiling 10% tannin in 2.5M acid for 20 min. and setting aside for a week. At the other end is the HPLC method calling for boiling M acid for 24 hrs. At 80-85C a 10% solution still forms a precipitate with aq. gelatin. At 105-110C with no air there is no precipitate. The color is the same tea-coffee. On cooling, there is a light brown fine but filterable mud of gallic acid, and a smaller amount of black glassy thin flakes on the walls of the digester. The flakes may contain condensed gallic acid but my guess is no. Gallic acid that escapes purification can be extracted out with ethyl acetate (substantial neutralization may be wise with ester solvent)

NaOH hydrolysis may be preferable industrially but I wonder if that involves considerations such as acid resistant construction, since one wouldn't want dissolved iron.




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[*] posted on 3-5-2021 at 18:48


Maybe I should mention how this turned out...not well obviously...the sumac solution was evaporated because I wanted to know how much there was, but once evaporated to a gum it really did not want to dissolve in hot sulfuric acid. Lots of gallic acid there, good luck getting to it...It's not impossible, but one will have to deal with a sticky black tar residue, almost half the part insoluble in DCM...The funny thing was the DCM wash. Probably half the weight of the extract. The DCM was partially distilled off and in the end there were what can only be described as rock hard, giant rat turds that precipitated out. It looked very unpromising but I wondered if it might in fact be an ester...dissolved in hot dilute sulfuric acid and after an hour it was cooled...ended up with easily recrystallizable gallic acid! No idea WTF.

Found some galls on this species (R. glabra) too. It looks as if they fruit thin mint cookies. When broken open (very thin shell) it's completely filled with pure white cotton, no insects to be found. Not a lot to work with though, would investigate if more were found.

[Edited on 4-5-2021 by S.C. Wack]




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[*] posted on 9-5-2021 at 23:23


From our library....

170 INTERMEDIA TES
12. Gallamide and Gallic Acid from T annin
The most important starting materials for the preparation of galla- mide and gallic acid are gallnuts and sumac (Rhus coriaria). The tan- nins from these are split either into sugar and gallic acid by the action of sodium hydroxide, or into sugar, gallamide, and gallic acid by the action of ammonium sulfite. In the latter case, about equal parts of the amide and the acid are obtained.

200 grams of the tannin, 200 cc. water, 400 grams of 20 per cent ammonia, and 100 grams of sodium bisulfite solution (25 per cent S02 ) are heated for 12 hours at 50° (water bath) in a pressure bottle with a rubber stopper. The mixture must be shaken from time to time in order to get complete solution. The resulting solution is transferred to a large glass flask and concentrated to 400 cc. under reduced pressure.
After the residue has cooled, hydrochloric acid is added until the solution is just faintly acid to litmus. The gallamide separates completely in the course of 24 hours. (In laboratory preparations, it is often necessary to cool a small portion of the solution and scratch the container in order to start the crystallization.) The product is filtered off and washed well with water. To the mother liquor is added 100 grams of 30 per cent sodium hydroxide and ammonia is removed in vacuum. The solution is then concentrated to 300 cc. and enough con- centrated hydrochloric acid is added to make the solution just acid
to Congo red. The sodium salt of gallic acid separates, in the course of a few days, as a finely crystalline precipitate which is filtered off and pressed out without washing. The sodium salt is dissolved in 100 cc. water and gallic acid is precipitated from the solution by the addi- tion of hydrochloric acid. About 60 grams each of gallamide and gallic acid are obtained.
Technical Observations. Large scale preparations use tannin solutions which are obtained by countercurrent extraction of the tannin-containing material with hot water. The extracts are concentrated in vacuum to 30° Be. The hydrolysis of the tannin is carried out in huge concrete vats, adaptable to work under either reduced or increased pressure. Crystallization of the gallamide requires 10 to 14 days, that of the gallate even longer. Tannin solutions have a strong tendency to ferment, and must be worked up rapidly, especially during the summer. The purity of the gallamide is determined by distilling a weighed sample with sodium hydrox- ide, collecting the ammonia in 1 N hydrochloric acid, and back-titrating. A good grade of gallamide is 92 per cent pure. Gallamide and gallic acid are used in large quantities for the preparation of oxazines (see gallamine blue).
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[*] posted on 2-7-2021 at 14:15


FWIW I've been reading some old books on tanning...they say galls without a bug still in them are worthless; they're interested in gallotannin not gallic acid, maybe it's not a problem here...they don't like Soxhlets; they don't like organic solvents. Here's a quote that sums up the 1800's technique. It will make everyone happy, with imperial units. The acid hydrolysis is with battery acid, but not on the entire extract; just the part that's extracted by not-hot water and precipitated with acid. It's important not to get too crazy with the acid, or else rufigallol will be made. It's also important to reflux precipitated hopeless mud/gallic acid "enveloped in calico" with good decolorizing carbon for a while a couple times along with the recrystallization. Addition of antioxidants is unnecessary, but I wouldn't dry crude acid or expose solutions to air while waiting for precipitation. One may want to substitute a Buchner and vacuum for "powerful pressure".

The Dublin Pharmacopeia gives two methods of preparing gallic acid, one of which is based upon the process of Dumas, or Scheele, and the other on that of Graham or Liebig. 1. Galls, in coarse powder, 1 lb.; make into a stiff paste with water, and place in a porcelain dish, and expose in the moistened condition for six weeks. The solution of the first crop of crystals is made in 10 fluid ounces of boiling water, and then filtered. When the filtrate (the filtered liquor) has cooled down to 80° Fahr., it is to be poured off from the crystals which have formed, and the crystals are to be washed with ice-cold water, 3 fluid ounces, and then drained and dried—first on blotting paper, and finally by steam or water heat. By boiling the undissolved portion of the galls with 45 fluid ounces of fresh water, more crystals are obtained. 2. One pound of powdered nut-galls are steeped for 24 hours in 1 pint of water, and after being placed in a porcelain displacement apparatus, are treated with one and a half pint of water, added in successive portions; 5 fluid ounces of oil of vitriol, diluted with an equal bulk of water and allowed to cool, is then added to the percolated infusion, and when thoroughly mixed, the liquid is filtered from the precipitate which forms. Oil of vitriol 5 fluid ounces diluted with an equal bulk of water as before, is now added to the filtrate; the precipitates, enveloped in calico, are submitted to powerful pressure, and subsequently dissolved in a solution composed of oil of vitriol 16 fluid ounces, and water 56 fluid ounces. The solution is then boiled for 20 minutes, and set aside for a week, at the end of which time the deposit which forms is dissolved in three times its weight of boiling water, and the solution treated as before.




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[*] posted on 2-7-2021 at 15:55


Just a quick thought: does "expose in the moistened condition for six weeks." involve a fermentation (i.e microbiological) step?

Also, for the benefit of our American friends who think " A pint's a pound the world around"; no it's not.
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[*] posted on 2-7-2021 at 16:58


...a fluid ounce doesn't weigh an ounce in the US, like a gallon of water here doesn't weigh 10 pounds.

IDK whether these tannases are formed from fungi or are already there or both, but any obvious colonization is not to be considered detrimental.

Another USA note...R. copallina leaves gathered in the summer were preferred in the old days for gallotannin...though later study of R. glabra suggests that this genetic variation may be as much within species as without.




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