The Volatile Chemist
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Tannic Acid Decomposition
I have some Tannic acid, and was just wondering if anyone knew of some synthesis or decomposition reactions I could do with it. I looked at it's
structure on Wikipedia and freaked out. It's a bit passed my level of synthesis. I can handle Haematoxylin, but that's about it. I read this on
Wikipedia:
| Quote: |
In 1880, Etti gave for it the molecular formula C17H16O9. He described it as an unstable substance, having a tendency to give off water to form
anhydrides (called phlobaphenes), one of which is called oak-red (C34H30O17). For him, it was not a glycoside. |
Obviously this person got a few things wrong, but I wondered if anyone knew how to make it change to an anhydride. (Or anything else really)
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DraconicAcid
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It gives a nice precipitate with ferric salts.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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The Volatile Chemist
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Great! I have some ferric sulfate lying around with no use. Thanks!
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Paddywhacker
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Tannin, or tannic acid can be hydrolysed to give gallic acid and other hydroxybenzoic acids that are sometimes difficult to otherwise obtain.
The following quote is from a text file that I no longer know the provenance of. If I was to follow it I would exclude air from the reaction mixture
by using deaired water (boiled and cooled) and by floating a barrier layer of parrafin oil on the surface.
| Quote: | I have actually tried the alkaline hydroylsis of tannin. I used wine-makers tannin from a home brew shop. I didn't have the benefit of
Garage_chemist's German preperation but I came up with a very similar "receipe".
Here is my method and results:
20g of wine-makers tannin powder was dispersed into 25ml of 40% (note 1) and 25ml of water in a 100ml beaker.
0.5g of sodium metabisulphite (note 2) were added as an antioxidant and heated to 60-70 C on a water bath for about 1.5 hours.
After cooling a little 14ml of 28% hydrochloric acid and a few drops of isopropanol were added (the latter to reduce the foaming).
The mixture was covered with a watch glass and left to cool overnight.
The brown mass was stirred to produce a thick slurry and filtered at the pump, washed with 2 x 15ml of ice cold water and dry dried over heating pipes
(about 35 C) for 24 hours.
The yield of crude brown crystalline gallic acid was 11.36g.
The crude product was recrystallised from 30ml of water, 2ml of 28% hydrochloric acid, a pinch (<0.1g) of ascorbic acid and 0.5g of decolourizing
carbon and boil for 5 minutes before being filtered hot through a preheated buchner funnel.
The pale brown solution was allowed to crystallize in a beaker for several hours until it had reached ambient temperature (about 8 C) and filtered at
the pump.
The filter cake was washed with 2 x 10ml of iced water and dried in a warm place as before; the yield was 6.09g of creamy buff coloured needles.
The initial filtrate was eveporated down in a shallow basin on the water bath after the addition of a future 0.1g of ascorbic acid to about 12-15ml
and allowed the crystallized, filtered and dried. The second crop of darker brown crystals of less pure gallic acid was 2.57g.
This will be recrystallized with the next batch prepared.
Note 1, I use and store sodium hydroxide as a 40% solution because in our damp climate attempt to measure out small weights of sodium hydroxide prills
tend to results in rapid caking, its much easier to weight out 400g and make up 1 L of solution. A 40% solution is approximately 10 Molar and the
sodium carbonate
produced by adsorption of atmospheric COText is almost insoluble in such concentrated sodium hydroxide and sinks to the bottom of the polythene
bottle.
Note 2, Since sodium metabisulphite reacts immediately with sodium hydroxide to form sodium sulphite, clearly the later compound may also be used. Its
just that sodium metabisulphite is also available from homebrew shops. During my small scale orientation experiments I tried ascorbic acid and this
also appears to work as an antioxidant but I wasn't sure it would survive the long in the sodium hydroxide digestion. In one of the books related to
dye chemistry in the SM library there is a detailed hydrolysis with ammonia to produce both gallic acid and gallamide (3,4,5 trihydroxybenzamide). I
haven't tried it but I will. |
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The Volatile Chemist
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Quote: Originally posted by Paddywhacker  | Tannin, or tannic acid can be hydrolysed to give gallic acid and other hydroxybenzoic acids that are sometimes difficult to otherwise obtain.
The following quote is from a text file that I no longer know the provenance of. If I was to follow it I would exclude air from the reaction mixture
by using deaired water (boiled and cooled) and by floating a barrier layer of parrafin oil on the surface.
| Quote: | I have actually tried the alkaline hydroylsis of tannin. I used wine-makers tannin from a home brew shop. I didn't have the benefit of
Garage_chemist's German preperation but I came up with a very similar "receipe".
Here is my method and results:
20g of wine-makers tannin powder was dispersed into 25ml of 40% (note 1) and 25ml of water in a 100ml beaker.
0.5g of sodium metabisulphite (note 2) were added as an antioxidant and heated to 60-70 C on a water bath for about 1.5 hours.
After cooling a little 14ml of 28% hydrochloric acid and a few drops of isopropanol were added (the latter to reduce the foaming).
The mixture was covered with a watch glass and left to cool overnight.
The brown mass was stirred to produce a thick slurry and filtered at the pump, washed with 2 x 15ml of ice cold water and dry dried over heating pipes
(about 35 C) for 24 hours.
The yield of crude brown crystalline gallic acid was 11.36g.
The crude product was recrystallised from 30ml of water, 2ml of 28% hydrochloric acid, a pinch (<0.1g) of ascorbic acid and 0.5g of decolourizing
carbon and boil for 5 minutes before being filtered hot through a preheated buchner funnel.
The pale brown solution was allowed to crystallize in a beaker for several hours until it had reached ambient temperature (about 8 C) and filtered at
the pump.
The filter cake was washed with 2 x 10ml of iced water and dried in a warm place as before; the yield was 6.09g of creamy buff coloured needles.
The initial filtrate was eveporated down in a shallow basin on the water bath after the addition of a future 0.1g of ascorbic acid to about 12-15ml
and allowed the crystallized, filtered and dried. The second crop of darker brown crystals of less pure gallic acid was 2.57g.
This will be recrystallized with the next batch prepared.
Note 1, I use and store sodium hydroxide as a 40% solution because in our damp climate attempt to measure out small weights of sodium hydroxide prills
tend to results in rapid caking, its much easier to weight out 400g and make up 1 L of solution. A 40% solution is approximately 10 Molar and the
sodium carbonate
produced by adsorption of atmospheric COText is almost insoluble in such concentrated sodium hydroxide and sinks to the bottom of the polythene
bottle.
Note 2, Since sodium metabisulphite reacts immediately with sodium hydroxide to form sodium sulphite, clearly the later compound may also be used. Its
just that sodium metabisulphite is also available from homebrew shops. During my small scale orientation experiments I tried ascorbic acid and this
also appears to work as an antioxidant but I wasn't sure it would survive the long in the sodium hydroxide digestion. In one of the books related to
dye chemistry in the SM library there is a detailed hydrolysis with ammonia to produce both gallic acid and gallamide (3,4,5 trihydroxybenzamide). I
haven't tried it but I will. |
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Thanks! I might try it.
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Boffis
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That text file is mine! It was attached to a post re the decomposition of kinotannins a year or so ago. I still haven't had time to try the ammonia
hydrolysis!
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Paddywhacker
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| Quote: Originally posted by Boffis | | That text file is mine! It was attached to a post re the decomposition of kinotannins a year or so ago. I still haven't had time to try the ammonia
hydrolysis! |
Sorry for not attributing it to you, Boffis. Your work lives on with a life of its own.
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