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Author: Subject: Copper (II) Trifluoroacetate
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mad.gif posted on 5-6-2011 at 20:45
Copper (II) Trifluoroacetate


I just made copper (II) Trifluoroacetate from 25mL of 98% trifluoroacetic acid and copper oxide. I got a blue solution and boiled it down in order to crystalize it. It won't crystalize. I have dark cobalt blue viscous syrupy liquid that can be drawn into threads. WTF? Is there any way to crystalize this stuff? I have a funny feeling that if I attempt to keep heating it it will decompose. Would vacuum distillation of the remaining water work?
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[*] posted on 5-6-2011 at 20:53


Okay it seems to be hardening and crystalizing. This still quite strange though. Upon super saturating the solution and heating it becomes viscous, syrup, and has a molasses like consitancy. It can bee drawn into threads at this stage. Crystalization does appear to happen upon standing. No nice crystals form though.
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#maverick#
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[*] posted on 5-6-2011 at 20:56


Try a desiccator bag
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[*] posted on 5-6-2011 at 21:09


Quote: Originally posted by #maverick#  
Try a desiccator bag
I will try that. This stuff is now hard and glassy. Impossible to get out of the jar it set up in.
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[*] posted on 6-6-2011 at 07:59


In the case of many compounds crystallising stuff from very concentrated solutions may be difficult and can take a long time. Without a seed crystal your solution may become super saturated and eventually ‘freeze’ to a super cooled liquid. That is essentially the structure of glass: an amorphous state of matter, cooled below its glass transition temperature, so that it appears solid (infinite viscosity).

Try dissolving some of it in pure water, then add a few crystals of any copper salt to try and get crystallisation to start.

A dessicator bag is unlikely to change anything, IMHO.
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[*] posted on 6-6-2011 at 10:32


I had a similar experience while making cobalt nitrate from cobalt carbonate and nitric acid. When the solution becomes more and more saturated, it becomes viscous and on cooling down it solidifies. The solid, however, was by no means a pure product. It emitted fumes of acid and when stored in a glass container, a kind of acid 'frost' appeared on and near the container. There is a big chance that your copper trifluoroacetate also still has quite some free acid in it.



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[*] posted on 6-6-2011 at 11:30


Have you tried scratching the beaker with a glass stir rod?



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[*] posted on 6-6-2011 at 17:55


Your best bet might be to redissolve it in a minimal amount of water then precipitate it with a solvent in which it isn't soluble (I'm just guessing, but perhaps acetone?). Or, if it is soluble in an organic solvent such as acetone or ethanol (which many TFA salts are), then dissolve in that and precipitate with something even less polar, such as ethyl acetate, ether or even (as probably a last resort) hexane.

Whichever way you go, add the less polar solvent slowly. And it's unlikely you'll get nice big crystals - either small ones or an amorphous-looking powder are probable (if it works at all). The suitability of this method depends on what you need the material for.
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[*] posted on 7-6-2011 at 04:34


That reminds me of when I boiled down the solution found in a cold pack. (It could have been ammonium nitrate but it was more likely a mixture of NH4Cl and NH4NO3.) It became very viscous when cooled, almost like cake frosting, and eventually solidified as a large hard cake in the bottom of the beaker.

[Edited on 7-6-2011 by LanthanumK]
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