myristicinaldehyde
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"Indicator" solution of copper(ii) salicylate in dilute acetic acid
After playing around with the mystery green solution obtained with the end product of the hydrolysis of aspirin and a copper salt I mentioned a long
while back, I have arrived at a semi- reliable method for obtaining it- by combination of sodium salicylate with a dilute solution of copper ii
sulfate or copper ii chloride, then slowly acidifying with acetic acid until all precipitates dissolve (most likely due to excess base when preparing
the sodium salicylate) and a clear solution is formed- which takes very little acetic acid, so don't use glacial stock solution (I used about 20%). No
quantitative measurements were taken, but I repeated this a few times with repeatable results. Hopefully someone can repeat it.
The interesting thing about this is that adding excess acetic acid shifts the color to almost colorless, and adding sodium carbonate shifts the color
to a moderately intense blueish green. These colors are distinct from copper acetate, I think. Much less carbon dioxide was released by the addition
of carbonate/acetate than expected. This color shift is reveres able, by adding base or acid, but it "degrades" a bit, as well as becoming more dilute
(obviously)
Acetic acid was used because anything stronger seems to break the complex into salicylic acid and cucl2 or cuso4 depending on the acid, and I had
plenty of it on hand.
Gently heating the solution to dryness yields a green paste which does not easily dry out, which redissolves to form the green solution. Some copper
acetate is formed, based on the blue color in the process.
My theory on why this occurred is because in basic media, salicylate is bidentate (the phenol group and the carboxylic group are deprotonated)- one
salicylate per copper ion, but as the solution becomes more acidic, but not too acidic, the phenol but not the carboxylic group protonates and it
becomes monodentate(?) with 2 salicylates per copper, or a salicylate and an acetate, etc and that complex is more weakly colored. The color being due
to a complex forming would explain the blue black precipitate found with the addition of dilute hydrogen peroxide- some sort of ligand exchange.
That being said, I lack some of the knowledge expertise and equipment needed to absolutely prove that is the case. Can someone see if my results can
be replicated?
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DraconicAcid
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It's also possible that in basic solution, you have two salicylates coordinating the copper, and one or both of them have the phenolic proton removed
(so either [Cu(HSal)(Sal)]- or [Cu(Sal)2]=). I was trying to get copper(II) salicylate for the copper carnival last summer, and
ran into similar problems, trying to get one product that I could reproducibly make and declare its identity with confidence. Most of the literature
that I could find (as far as I recall) were low-quality pay-to-publish journals from African researchers which contained obvious errors.
I see that my google shows me *lots* of references to mixed salicylate complexes of copper, as well as articles about how healthy copper aspirinate
is, but also a mention of the simple salicylate here : Coordination Chemistry Reviews. 2002;232(1-2):95–126.
This paper: http://www.chempap.org/file_access.php?file=227a481.pdf
mentions bis(salicylato)diaquocopper(II) dihydrate, and refers to Chem Zvesti 19, 881 (1965).
This patent: https://data.epo.org/publication-server/rest/v1.0/publicatio...
Says that the Cu(HSal)2(H2O)2 dihydrate is pale blue, and that Na2Cu(Sal)2 is olive green.
[Edited on 3-10-2016 by DraconicAcid]
[Edited on 3-10-2016 by DraconicAcid]
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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myristicinaldehyde
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Olive green sounds right, and the most acidic solutions I got were a pale turquoise. Thanks for the references.
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justdusty
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I tried Copper nitrate and salicylic acid in water boiled till they dissolve beautiful emerald green and now cooling in to turquoise crystals. I want
to test it as an oxidizer
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