Sciencemadness Discussion Board - Report on making Copper iodide

Report on making Copper iodide

Lion850 - 15-12-2019 at 03:07

After the struggles with hygroscopic iodides I decided to try one that should be easier. And it was. I almost did not post this report as this syntheses is straightforward but maybe some beginner (like me) wants to make it and find this useful.
1) 30g potassium iodide dissolved in 75ml water
2) 22g copper sulfate dissolved in 75ml water. This was the familiar blue hydrate but purchased at a garden center thus without any details of the composition.
3) Pour together in a 500ml beaker. The solution became brown and then black because of free iodine.
4) Pour in 300ml ethanol. This was "Diggers Methylated Spirit" from the local hardware which says minimum 95% ethanol.
5) Stir for a few minutes. Wait for the brown ppt to settle with the black layer on top.
6) Decant off the black layer, as much as can be without losing the precipitate. Both by pouring and use of a pipette.
7) Repeat 4, 5, and 6 another 2 or 2 times, until most of the black color has faded.
8) Pour the white-brown ppt into a funnel with filter paper and flush a few times with ethanol until the funnel run-out is just about clear (I split this between 2 funnels to speed things up).
9) Remove the filter paper (with the ppt) and place it on top of a stack of paper towel to help suck out the water.
10) Place the filer paper on a 200mm watch glass. Place the watch glass on top of a boiling beaker. This should dry the copper iodide to a soft powder in 30 minutes.
11) Scratch off from the filter paper and bottle.
I recovered 16.5g of CuI. The color agrees quite well with online pictures, which tells me I managed to remove most of the iodine.

** As per the app I use for stoichiometry this is a yield of more than 90% which is a surprise - if I used the app correct!

Pumukli - 15-12-2019 at 07:49

Great!
The colour looks good, yes.
I thought these Cu+ compounds are more sensitive to oxidation in the air and they require careful preparation to prevent this.
Now it seems that at least the iodide can be prepared and dried without much deterioration. Thanks for the synthesis report!

woelen - 15-12-2019 at 09:41

Your product looks good, but you could double the yield (in terms of iodine) by using a suitable reductor.

Now you lose half the iodine as the element, only half of it ends up in CuI.
When you use a suitable mild reductor under mildly acidic conditions, then you can use all iodide for making CuI.
I made CuI with Na2S2O5, KI and CuSO4. I obtained an off-white product with nearly 100% yield. Most losses were mechanical losses.

DraconicAcid - 15-12-2019 at 10:47

You can also take CuI and dissolve it in concentrated KI(aq). Keep it in a sealed vial with a small amount of acid and some metallic copper to prevent oxidation/decomposition.

beta4 - 26-5-2020 at 14:50

I tried making copper iodide using the method described in this topic and using it to make a fluorescent copper complex

https://woelen.homescience.net/science/chem/exps/fluorescent...

but it the resulting compound did not fluoresce at all. Trying another synthesis of copper iodide using copper sulfate, potassium iodide, sodium sulfite and sulfuric acid (described in the link) followed by the complex synthesis did result in a product that fluoresced.

So it looks like the synthesis of copper iodide described here either results in a product too contaminated with iodine to work, or it does not produce copper iodide at all.

Lion850 - 28-5-2020 at 18:33

Hi Beta4 I do remember that I used a lot of ethanol to get it the color shown, basically I washed and washed until the ethanol stayed clear indicating the bulk of the free iodine was washed out.

If you look at my report in this post on separating coper and nickel

https://www.sciencemadness.org/whisper/viewthread.php?tid=15...

then you will see that I did some tests comparing the copper iodide from last December (at the top of this post) with another batch of copper iodide I made slightly differently as described in the above link, and while it seems certain they are the same basic compound there are subtle differences: signs that the original copper iodide does contain more free iodine. Whether this was the case from when it was made or whether it slowly deteriorated being stored in a clear vial I do not know. Although the color did not change much, and I know from recent experience that iodides often degrade quickly.

woelen - 28-5-2020 at 23:00

I myself once made copper(I) iodide (with bisulfite as an added reductor, or with sulfite plus some additional acid) and I kept that copper(I) iodide around for many years (I still have some of it). I store it in a well sealed container and it still is OK. It also works with the experiment with the fluorescent pyridine complex.

Maybe your copper(I) iodide contains a lot of ethanol? Sometimes, this can be incorporated in the crystal lattice, just like water. It might negatively affect its purity.

Chemi Pharma - 28-5-2020 at 23:50

Quote: Originally posted by beta4

I tried making copper iodide using the method described in this topic and using it to make a fluorescent copper complex

https://woelen.homescience.net/science/chem/exps/fluorescent...

but it the resulting compound did not fluoresce at all. Trying another synthesis of copper iodide using copper sulfate, potassium iodide, sodium sulfite and sulfuric acid (described in the link) followed by the complex synthesis did result in a product that fluoresced.

So it looks like the synthesis of copper iodide described here either results in a product too contaminated with iodine to work, or it does not produce copper iodide at all.

I think when @Lion850 added ethyl alcohol to the solution he also precipitate potassium sulfate that's insoluble in ethanol. So, his CuI probably was contaminated with it. It's the same principle used in ammonium iodide synthesis. See PrepChem:

"Preparation of ammonium iodide

254 g of potassium iodide dissolved in 125 ml of water are mixed with 100 g of ammonium sulfate dissolved in 125 ml of boiling water. After cooling, 40 ml of alcohol are added and the mixture is kept 12 hours. The obtained precipitate of potassium sulfate is filtered and the filtrate is evaporated occasionally adding ammonia water containing some alcohol, until crystallization begins. The crystals of potassium sulfate are additionally washed with dilute alcohol (20%), and after combining the filtrates and evaporation the ammonium iodide is obtained. Ammonium iodide crystallizes in cubes and deliquesces in the air. It should be preserved in a dark place, as light decomposes the salt, causing it to turn brown. This coloration may be removed by dissolving in distilled water, treating the solution with ammonium sulfide, filtering, and evaporating the filtrate on the steam bath, to crystallize. It is readily soluble in alcohol. The aqueous solution becomes yellow on standing, owing to decomposition and separation of iodine. One part of the salt dissolves in 0.60 part of water.

Inorganic chemical preparations, by Thorp, Frank Hall, 60, 1896"

Lion850 - 29-5-2020 at 01:41

For interest, I think this is where I got the idea from:

https://thosci.com/synthesis-of-copperi-iodide/

And this site in turn mentions "http://illumina-chemie.de/kupfer%28i%29-iodid-t2107.html" but it seems this link does not work anymore.

mayko - 29-5-2020 at 13:47

WayBack's got it:
https://web.archive.org/web/20100627023436/http://illumina-chemie.de/kupfer(i)-iodid-t2107.html

Quote: Originally posted by Pumukli

Great!
I thought these Cu+ compounds are more sensitive to oxidation in the air and they require careful preparation to prevent this.
Now it seems that at least the iodide can be prepared and dried without much deterioration. Thanks for the synthesis report!

I had also encountered claims that cuprous halides were photosensitive, but I was never able to observe this, even with sunlight and a magnifying glass!

[Edited on 29-5-2020 by mayko]