Cloner
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extraction of salicin from willow bark
I have a few students who are trying to extract salicin (a compound resembling aspirin and with similar effects) from willow bark.
The compound is used in a 'tea' of willow bark, but this tea is bitter due to tannins. I assume it can be liquid-liquid extracted, but the question
remains which solvent to use.
Does anyone have prior experience with salicin?
PS: the following article from Annals is likely to contain more information. If someone has free access to it, would you please be so kind as to share
the article?
http://onlinelibrary.wiley.com/doi/10.1002/jlac.18450560104/...
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Neil
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http://www.freepatentsonline.com/EP1901698.html
The above patent suggests alcohols and water.
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bbartlog
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I tried to do a related extraction (salicyl alcohol), but largely failed. The old school method for salicin appears to be
- aqueous extraction from willow bark (I assume cold water to avoid hydrolysis)
- addition of lead hydroxide to precipitate tannic acid and other impurities
- filtering and evaporation
(summarizing from Elements of Organic Chemistry, part II, 1857 ... it's on Google Books).
I didn't want to use lead hydroxide due to toxicity, so I ended up hydrolyzing the salicin with HCl and then trying to do a solvent extraction on the
salicyl alcohol; anyway so far things look pearshaped as I had no ether and tried to improvise. I'm not sure what solvent to use for salicin, though.
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ScienceSquirrel
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Pure salicin could be produced by solvent extraction and precipitation of the tannins as above followed by concentration and chromatography,
preferably preparative HPLC.
If you have access to the right facilities and kilos of willow bark to hand, piece of piss really! 
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Cloner
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Cool, thanks for these links. Both look like useful resources.
The kilo of bark we've got. Let's see about the rest. I think ether is pretty bad for extracting salicin but it will do salicylic acid.
One thing I notice from the patent is their low temperatures of extraction. It cant be because of instability of salicin, they rotavap the solvent off
at 60 degrees.
The book describes the use of lead compounds. Once the hydrated oxide is used to remove tannins, the next lead acetate is used to precipitate the
salicin. Anyone knows what lead does in this situation?
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bbartlog
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If the low temperatures aren't to avoid hydrolysis, they're probably to avoid picking up too much other junk. Presumably salicin is soluble enough in
cold water while various impurities (like tannins) are far more soluble in hot.
I have no idea why lead acetate would precipitate salicin. Some sort of complex or adduct?
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