Thermochromic Tetrachlorocuprate

For quite a while now I've been wanting to try making the compound smaerd shared in the Pretty Pictures (1) thread, and I finally have the reagents necessary. Here's progress so far.

Summary: Synthesis of lime green crystals resembling the desired product was successful, but they are highly unstable (tend to melt, the copper in the compound is easily reduced to the metal) and I have not gotten them to change colors yet. They simply melt into a brown oil, which returns to green but stays liquid upon cooling.

Procedure
Synthesis of thermochromic bis(diethylammonium) tetrachlorocuprate(II), ((CH₃ CH₂) CH₂NH₂)₂CuCl₄ was attempted primarily following "Thermochromic Tetrachlorocuprate(II), An Advanced Integrated Laboratory Experiment" by Choi & Larrabee (as well as smaerd's information). This is a bright lime green at room temperature, and exhibits discontinuous thermochromism at 50C, changing to bright yellow.

Solution A: 2.20g diethylamine hydrochloride was dissolved in 15.1mL anhydrous ethanol with gentle heating and magnetic stirring. Procedure uses isopropanol, but none was available and ethanol is listed as a substitute. This resulted in a clear solution.
Solution B: 1.70g anhydrous copper(II) chloride was dissolved in 3.2mL anhydrous ethanol with gentle heating and magnetic stirring. I had quite some trouble getting this to dissolve completely, and after decanting from the solids only 1.60g had gone into solution. This was a very dark olive green liquid.

Solution B was added to solution A, mixed completely, and transferred to a beaker while both were warm. The mixture was placed in the fridge to cool. After cooling and waiting 1 day, the color had lightened to a "forest green" but no crystals were observed. Placed the flask on low heat to attempt to reduce volume. Briefly accidentally heated to boiling before lowering the heat. Volume was reduced from ~22mL to ~15mL. Decanted this liquid into another flask, and after cooling a bright green residue was left on the walls of the beaker. This exhibited the thermochromism on heating! Unfortunately, though, nothing had crystallized in the rest of the solution even after cooling. Transferred 4mL of this liquid onto a watch glass to try slow evaporation. This crystallized somewhat, but into dark olive green crusts instead of the lime green needles predicted by the procedure. I left this out over the weekend.

Upon returning, all traces of the solids in both the beaker and watch glass had disappeared and I was left with a dark "oil." This oil was transferred to a beaker and placed back in the fridge, after consulting with smaerd. After about a week, I returned to find the "oil" had completely solidified into dark green crystals! Strangely, these liquefy rapidly upon removal from the fridge and warming up a bit.
I took a sample of these crystals and put them on a watch glass, placed under vacuum for ~40 minutes, to attempt to remove any remaining solvent. The crystals remained solid while under vacuum at room temperature, but immediately upon releasing the vacuum most of them slumped back down to a puddle. What I was left with, interestingly enough, was a small puddle of olive green liquid and lots of tiny lime green crystals. This liquid was drained off as best as possible and returned to the cold beaker. Immediately, this froze back into the dark green crystals. The lime green crystals remaining on the watch glass were transferred to a filter paper circle to absorb adhering liquid. The first photo is the crystals on the filter paper, and the second is the remaining liquid on the watch glass.



These crystals appear to be stable, in that they do not melt back into a liquid at room temperature. (Why would these particular crystals be any different?)

I took the very small amount of lime green crystals I recovered and placed them in a tiny vial, after adhering liquid had been absorbed by the paper.


I then took this vial and placed it on a pre-heated hot plate. Almost instantly, the crystals melted into a brown liquid drop. Removing from heat and cooling back down, the drop changed to yellow-green, then back to a green color but still remained as a liquid. Severe overheating, perhaps?


IMPORTANT OBSERVATION: Apparently the crystals, especially when wet with the liquid, are highly sensitive to metal implements. Scraping and transferring them with a metal spatula caused the oil to go almost totally black, which when wiped on a paper towel left rusty red stains. This is almost certainly copper metal.


Finally, I have no information on how to dispose of this stuff. Since it looks like it's quite a fragile compound, I may be able to precipitate all the copper by adding a suitable oxidant, say, hydrogen peroxide? But then what of the diethylamine hydrochloride leftovers?

This is apparently a difficult synthesis; more difficult than the publications would have you believe. I thought it would be a simple matter of combining solutions and collecting crystals. All of my reagents are high quality, from Alfa Aesar, so the problems lie elsewhere. Interesting process, though, that I'm enjoying exploring. I'll report back if I make any more progress.

I might if I ever get it to work!

Quote: Originally posted by DraconicAcid

The reaction of sodium hydroxide with the diethylammonium cation will be diethylamine, which you could probably distill fairly readily, or react with hydrochloric acid to get the diethylammonium chloride back. http://en.wikipedia.org/wiki/Diethylamine

I finally got a chance to distill my isopropanol, which was dried by shaking with 10% of its weight of NaOH then decanting from the saturated water layer. I took the clear alcohol and distilled under reduced pressure in a rotovap. I had assumed that there would only be very little hydroxide dissolved, and I'd only be removing traces of it. Turns out I was very wrong - and when about 80% had distilled over a crapload of NaOH dropped out!



I guess NaOH has decent solubility in isopropanol. This has got to be what fouled my second experiment using undistilled isopropanol. The distilled product is crystal clear, and I'll give this experiment another go next week (hopefully).

Quote: Originally posted by MrHomeScientist

Right, from what I read on the forum here saturating with salt is the first step to remove a good bit of water if you can only get the 80% variety of alcohol.

Quote: Originally posted by MrHomeScientist

The paper I'm using specifies anhydrous solvents and reagents, but it looks like smaerd was able to make it with hydrated copper chloride so this might be forgiving of some moisture. I can't think of a way to test the water content of my IPA, so I'll just try it as is and see how it goes. By the way, here's the thread I referenced above. The drying method was posted by entropy51, in the green text.