Felab
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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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JJay
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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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| 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.
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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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monolithic
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Did you check Sci Hub?
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JJay
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If there is a particular paper you are looking for, someone can probably find a copy for you.
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ahill
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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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Boffis
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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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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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S.C. Wack
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| Quote: Originally posted by Boffis | | dilute hydrochloric or sulphuric acid but acid hydrolysis also cause much formation of insoluble (presumably polymerised) tannins.
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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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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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S.C. Wack
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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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Felab
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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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unionised
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Chestnuts have a high enough starch content that step 2 will make porridge.
I doubt decantation will be an option.
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Felab
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| 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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S.C. Wack
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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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S.C. Wack
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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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S.C. Wack
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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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zed
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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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S.C. Wack
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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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unionised
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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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S.C. Wack
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...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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