Copper cyanurate (and other cyanurates}

** There are many threads on copper cyanurate on Sciencemadness, for example:

http://www.sciencemadness.org/talk/viewthread.php?tid=155534...
http://www.sciencemadness.org/talk/viewthread.php?tid=29474#...
http://www.sciencemadness.org/talk/viewthread.php?tid=73900#...

But as far as I could see all involve the chlorinated compound while I wanted to try and make the 'basic' (for lack of a better word) cyanuric acid salt. Thus I started a new thread.

I previously made the well known purple compound copper-sodium-dichloroisocyanurate but I was keen to try and make copper cyanurate. Wikipedia says copper cyanurate forms in swimming pools when cyanuric acid reacts with high levels of copper, and shows a purple product.

I wanted to make copper cyanurate using only OTC materials. I had cyanuric acid and copper sulphate (from pool or hardware shops), sodium hydroxide (from a local department store), and copper carbonate that I made a long time ago from copper sulphate and sodium hydroxide. See photo.

A few months ago I tried to react a cyanuric acid solution with both copper sulphate and copper nitrate and that did not seem to do anything. So this time I decided to react copper carbonate with cyanuric acid:

CuCO3 + C3N3H3O3 = C3HCuN3O3 + H2O + CO2

- 11g cyanuric acid was added to 300ml water, stirred and heated. It seems quite insoluble until the solubility suddenly seems to increase at the water boiling point and the solution then clears up.
- Slowly add 10g of copper carbonate, stirring all the time (to crudely check if my old carbonate still behaves as a carbonate i earlier added some to a bit of concentrated HCl - it bubbled vigorously and all quickly dissolved into a green solution so seemed more or less good).
- A sea green suspension resulted with some foamy bubbles, which I presume was CO2. See photo.
- After 4 hours of stirring and keeping it warm the solution was grey, with a hint of purple which is hard to see on a photo. There was no more bubbles, and no smell. I stopped the stirring and grey ppt settled out. See photo. I started the stirring again and left it going overnight, but it looked the same the next morning.
- The solution was filtered. The filtrate was clear. The grey remainder was washed a few times with water in the filter.
- The clear filtrate was tested with sodium hydroxide, there was no ppt or cloudiness but just a very slight gold tinge; as I saw later this is often observed when NaOH is added to cyanuric acid so my filtrate probably had a slight excess of cyanuric acid dissolved and no copper salts. Which was good.
- The grey remainder was dried on a steam bath. The predominantly grey color became slightly lighter towards very pale purple. See photo.
- Final recovery of dry powder was 18g. The target from the above formula was 16g, so it is either not 100% dry (although it appears very dry and free flowing) or it is a hydrate.

So, if this is copper cyanurate, why is it not a more pronounced purple color? I could not find another description of copper cyanurate anywhere. I saw link to reports on studies of cyanuric acid reactions with metals, but they are not freely accessible. In swimming pools, when "copper cyanurate" is said to form, there is of course always also sodium and chlorine present and I wondered if the presence of these are needed to get the purple compound. This then lead to the next experiment which I will detail in the next post.

Comments from anyone with knowledge about copper cyanurate will be greatly appreciated.





[Edit: title changed at request of OP.]

[Edited on 10-7-2020 by j_sum1]

Part 2.
The next step following from the above was to add sodium to the reaction to see if I get a purple compound. I did quite a few trial runs with various results. Eventually the below ratios and method gave consistantly a similarly looking product.

The first step was to make sodium cyanurate in solution:

NaOH + C3N3H3O3 = C3H2N3NaO3 + H2O

- 16.5g of cuanuric acid was added to 450ml water, stir and heat.
- At boiling the solution just about cleared up, still slightly cloudy.
- Add 4g solid sodium hydroxide while stirring and keeping hot.
** These quantities was to allow for the cyanuric acid possible being a hydrate - if dehydrated, the acid is in excess. Important not to have the sodium hydroxide in excess as this then yields unwanted copper hydroxide during the next part.
- As the NaOH is added the solution cleared up and again the very slight golden tinge was seen.
- After 20 minutes of stirring the solution turns white due to a suspension. I assume this is sodium cyanurate, whith low solubility in hot (bit not near boiling) water?
- Stirring was continued for a total of one hour. pH was checked with my swimming pool test kit and found to be 8.
* This should have given some 15g of sodium cyanurate in solution (or rather suspension)

Next step was to add copper sulphate. But, I could not find a formula for copper-sodium-cyanurate (without the chloride) anywhere. The below equation was one of a few that my app would allow, but the one which seems to best fit the amounts of reactants used and product yield:

2C3H2N3NaO3 + CuSO4 = Cu(C3N3NaO3)2 + H2SO4 + H2 ???

- 6g CuSO4.5H2O was added. The solution immediately turned purple. See photo. There seemed a bit of fizz for a few seconds but whether this was hydrogen as per the formula I do not know. After 15 minutes stirring was stopped. A purple ppt settled, and the supernatant solution was very pale blue. Another 2g of CuSO4.5H2O was added abd stirred for an hour, the supernatant solution was now more strongly blue indicating that copper sulphate was now in excess. See photo.
- Vacuum filter. The filtrate was slightly blue, and the remainder purple.
- Wash a few times in the filter with room temperature water, until run-through is clear.
** The first time I tried to wash with boiling water, as I knew sodium cyanurate and cyanuric acid is much more soluble in boiling water. But the very top layer of the purple compound turned green when in contact with the boiling water, plus the purple compound itself becomes soluble at boiling point! See photo. I will investigate the formation of this green compound further.
- Dry the remainder on the steam bath for hours until the weight stabilised. See photo. The color slightly lightened as it dried.
- Final recovery was 15.1g of the fine dry light-purple powder. The color is a bit lighter than the better known copper-sodium-dichloroisocyanurate. See photo of the 3 products together: the (suspected) copper cyanurate, the copper-sodium-cyanurate, and the copper-sodium-dichlorocyanurate.

So I got the purple color I was after, but a lot of assumptions and guessing what is actually going on. Please comment and correct as required! Links to relevant literature will also be appreciated as I found very little.

Quote: Originally posted by j_sum1

My understanding is that the purple is a complex involving the NaDCCA salt. This indeed does form in swimming pools and is probably what is being described. I don't know anything about the copper cyanurate product you are after. But with the inclusion of HCl in your first procedure it is easy to imagine you getting a mixture that includes a purple substance and appears grey as a consequence.

Hi J_sum1 I think I was not clear. In the first procedure there was only cyanuric acid and copper carbonate. HCl was only involved to crudely test the old copper carbonate and give me some assurance it is indeed a carbonate prior to using it

In my original posts up above I mentioned that at one point when I tried to wash the purple sodium copper complex with boiling water it formed a layer of green. I investigated this further and after trying various things I was able to get the purple to green change again:
- 4.5g of purple sodium copper complex was added to approximately 250ml water in a beaker and stirred and heated, giving a purple colored solution/suspension mix. See photo.
- As this was vigorously boiled the color changed to grey. See photo (interestingly, if boiling is continued it becomes purple again at a low water volume).
- The contents was transferred to a large beaker and water added to a total of approximately 500ml and boiled and the color changed to green! See photo.
- The solution was vacuum filtered while still hot. The filtrate was completely clear, and the remainder was green, see photo.
- The filtrate was later boiled down and then cooled, and gave white crystals. See photo.

So it seems the sodium copper complex breaks up when boiled in a large excess of water. I am not sure what the green copper remainder is; it is not copper carbonate as there is no bubbling with HCl. It dissolves into a yellowish solution with concentrated HCl which becomes green when the HCl is diluted.

Also to mention that on my stirring hotplate, which boils large volume solutions much less vigorously, I did not yet see this "break-up" happening. So far, only on my cooking hotplate which is much more powerful.

The purple compound, the "copper-sodium-cyanurate", in the second post is something I have prepared as well, the literature says it is a complex salt of four monodeprotonated cyanurates, one central copper and two sodium ions as counter ions: Na₂[Cu(C₃H₂N₃O₃)₄] This matches 1:1 the complex with NaDCCA by the way, which has the formula Na₂[Cu(C₃N₃O₃Cl₂)₄]

The write-up (in German) can be found here, you can also prepare three ammonia derivatives of copper cyanurate, a di-, tri- and tetraammine compound: https://illumina-chemie.de/viewtopic.php?p=76471

Werner says in his paper that the coordination happens over the deprotonated nitrogens to the copper center.


Here is the tetrakiscyanurate (left) and tetrakisdichloroisocyanurate (right) next to each other:

@Boffis - I managed to download the book but unfortunately only the first edition - still looking for a place to download the second edition that does not want my credit card details.

Over the last week or so I reacted cyanuric acid with fine copper powder and finally got a lovely deep purple compound:
- 5.1g copper powder, 6g cyanuric acid, and 70ml water added to a small beaker (cyanuric acid in excess).
- Stirred with magnetic stirrer. Heated to near boiling once to dissolve the cyanuric acid and heat then switched off.
- Solution was initially copper colored due to the suspended copper powder
- After 24 hours still the same and I was just about to stop but then saw it was slightly less copper colored. Started to heat the beaker to around 50 degrees. Still some copper visible when stirring stopped.
- After 48 hours the copper color was much faded and it appeared to be heading to white-grey. Still copper present.
- After 72 hours it was starting to look purple. Mo more copper to be seen.
- Once it started to become purple the change was faster and after some 84 hours it was deep purple.
- After 96 hours the color was still the same deep purple and the stirring was stopped (4 days!)
- The solution was vacuum filtered. The filtrate was clear and the remainder a dark purple. The remainder was washed in the filter with excess water.
- A few gram of the remainder was dried on a steam bath to see if the color changed - it did not, and all was then dried on the steam bath.
- Final product was 10.6g of dark purple color.

The document I referenced and linked higher up "Cyanuric Acid and Cyanurates by GB Seifer" mentions only 2 salts for copper reacting on its own with cyanuric acid: a trisubstituted salt Cu3C3N3O3.xH2O or a basic salt (CuOH)H2C3N3O3.2H2O; I do not know which one I ended up with but I am happy I managed to get a purple copper cyanurate without any other metals included), which was the original target.

Below photos shows the color change from copper to dark purple and the final dried product.

Manganese:
I had a go at reacting manganese powder with cyanuric acid. According to "Cyanuric Acid and Cyanurates by GB Seifer" linked in an post higher up, manganese on its own forms either the disubstituted salt Mn2HC3N3O3 · xH2O or a basic salt (MnOH)H2C3N3O3 · 2H2O. I mixed 5.4g manganese powder and 8.6g cyanuric acid which puts the acid in slight excess assuming 1) the acid is the dihidrate and 2) the disubstituted salt will form. 90g water was added and the lot was stirred with moderate heat.
There seem to be an immediate reaction with small bubbles, and after some 12 hours no more manganese powder could be seen and the solution was a pale peach color. Stirring was continued for another 30 hours or so but there was no further color change. To note though was that the mixture became a bit like a slurry, quite thick.
The solution was filtered; the remainder was very fine and a light tan color. It was dried on the steam bath until the weight was stable; this took quite a while.

Final product was 13.5g of a white powder with a hint of pink. I've labelled the bottle "manganese cyanurate?" with no formula as I do not know exactly what it is.

Woelen - it certainly looks darker on the previous photo (of the dried product) than with the eye. I’ll take another photo in natural light. The deep purple color of the copper compound got me keen to see which colors other metals may give

Edit: Attached photo of the product of the cyanuric acid and manganese powder stirring plus, for interest, some manganese carbonate I made long go. Photo taken outside on a cloudy day.



[Edited on 11-7-2020 by Lion850]

I tried a small test at making your copper cyanurate. I only had sodium dichlor isocyanuric acid. (DCA) I put some copper wire in a test tube containing DCA and water. I then gentle heated the test tube in boiling water bath briefly.

After cooling the was a very slight purple sediment on top of the undissolved DCA and some purple blue deposits on the lower part of the wire. Part of the deposit had apparently flaked off. Curiously the upper part of the wire remain bright copper coloured.

I suspect I need to add HCL.

Sorry about the almost useless pic. It was taken outside in the sun so that the colour was not distorted by my LED lighting. I could not see the phone display very well in sun light. Modern mobile phone technology can not compete with our sun. The pic is of the heated test tube to dissolve the DCA to reveal the wire and the precipitate.



[Edited on 7/11/2020 by wg48temp9]

[Below is a slightly better pic taken with LED lighting showing the colour distortion and the copper wire. The test tube has cooled down so part of the DCA is recrystallising.



PS: the test tube is now at room temperature. All the copper wire is now covered with a light blue/purple deposit.

[Edited on 7/11/2020 by wg48temp9]

Cobalt:
Cobalt carbonate (see photo) was reacted with cyanuric acid to see what will happen. Reagent ratios were what I thought was appropriate to arrive at a monosubstituted salt CoH2C3N3O3.xH2O, with the cyanuric acid in slight excess.
- 15g cyanuric acid was dissolved in 150g water, on stirring hot place. Solution was heated to near boiling to get the cyanuric acid to dissolve. pH was approximately 4.
- Cobalt carbonate was slowly added until a total of 10.5g was added. This resulted in a pink suspension swirling around. See photo.
- Temperature was kept at around 50C, After 17 hours the solution was still pink. Temperature was then increased to approx 60-70C.
- After another 2 hours (total 19) the solution was grey. See photo.
- After another 4 hours (total 23) the solution started showing blue-green shades, Temperature was increased to near boiling.
- At the 47 hour mark the solution was blue-green (see photo) but becoming very thick and difficult to stir. Water was added to increase the total volume from 300 to 400 to enable stirring.
- Color remained stable and at the 50 hour mark the heat was switched off but stirring maintained. As the solution cooled slowly the color changed back to more grey.
- At the 65 hour mark stirring was stopped and the grey ppt allowed to settle. The pH of the clear supernatant solution was approx 7.
- The solution was vacuum filtered and the grey remainder washed with excess water in the funnel before being recovered. See photo.
- The remainder was divided in two equal lots. One was taken outside to dry under a steel dish in the sun (still in progress).
- The second part was dried on a steam bath. It started to show hints of color but for most part still grey when fully dry. Dry weight was 11.5g
- It was then put in a crucible in a sand bath at around 220C. After a short time it turned blue. It was kept on the sand bath another 30 minutes and stirred every so often.
- After 30 min there was an occasional hint of an ammonia like smell and the crucible was cooled down. The color did not change during cooling.
- Final weight was 10g, so drying on the sand bath seemed to cause 1.5g weight reduction. The blue powder is very light and adheres to everything. See photo of the final product in the crucible.

I wish I knew what the final product is, I suspect it is some cobalt cyanurate salt but which I don't know. Any ideas from the color?

Cobalt continued:
The grey cobalt cyanurate salt was dried in the sun under a steel dish for 2 days. The final weight is 13g, but although it seems a free-flowing dry powder after grinding I think it probably still has some water. It did not change color, to my eyes it is grey. Which leads me to ask: how common are grey compounds? I have grey metal powders, but this is my most grey compound.....which turns purple on the sand bath, as per previous post.

Quote: Originally posted by Lion850

Cobalt continued: The grey cobalt cyanurate salt was dried in the sun under a steel dish for 2 days. The final weight is 13g, but although it seems a free-flowing dry powder after grinding I think it probably still has some water. It did not change color, to my eyes it is grey. Which leads me to ask: how common are grey compounds? I have grey metal powders, but this is my most grey compound.....which turns purple on the sand bath, as per previous post.

I noticed thermochromism in coppercyanurate earlier, see this thread. It seems like you found another example with cyanurate.

Nickel cyanurate

According to "Cyanuric Acid and Cyanurates by GB Seifer" nickel can form either a monosubstituted salt NiH2C3N3O3.xH2O or a disubstituted salt NiHC3N3O3.xH2O. I considered the following equation for the stoichiometry:

2NiCO3 + 2H3C3N3O3.2H2O + 4H2O = 2NiH2C3N3O3 + 2CO2 + H2O2

- 5g cyanuric acid (probably the dihydrate) was added to a beaker with 100ml water and heated to boiling to dissolve with continuous stirring. The water was increased in stages until around 170ml gave a clear solution.
- 3g nickel carbonate was added to the hot solution. Tiny bubbles were observed and the solution was left to stir overnight.
- The next morning there was still some of the larger bits of the carbonate seen swirling around. Another 2 gram of carbonate was added bringing the total to 5g and another 3g of cyanuric acid was added bringing the total to 8g. See photo of carbonate pieces swirling around.

** 8h cyanuric acid dihydate reacting with 5g nickel carbonate and expecting the monosubstituted salt should put the cyanuric acid in excess (and even more in excess if only the disubstituted salt formed). I wanted the cyanuric acid in excess, and not the carbonate, to get all the carbonate to react as I knew excess cyanuric acid could be washed out later with boiling water.

- The solution was left to stir hot for a total of around 50 hours. The level of the beaker was topped up to around the 150ml mark every morning and evening to make up for losses.
- After some 38hrs there was a thick lime green suspension with no more carbonate solid, but stirring was continued for another 12 hours (total around 50). See photo of the final solution.
- The solution was vacuum filtered, and the lime green remainder washed twice with excess boiling water in the filter. See photo.
- The filtrate was very pale green, so the final product is very slightly soluble in water. Once the filtrate cooled to room temperature the solution remained green, but some white ppt was seen, most likely the excess cyanuric acid.
- The lime green remainder was dried on a steam bath until the weight remained stable. Total drying time was around 5 hours.

The theoretical yield was around 8g, if the product was the anhydrous monosubstituted salt. The total recovery was 9.6g, probably due to it being a hydrate.

The only test I did on the product was to add some to concentrated hydrochloric acid. There was no immediate reaction. See photo of final product in bottle.

Neodymium carbonate and cyanuric acid is currrently stirring in the shed. Report to follow once completed.

Woelen - an update on nickel:
I dissolved 10g cyanuric acid in 300ml boiling water (all dissolved to clear solution) and then added 2.8g NaOH (forgot to take the pH). To this hot solution I then added a solution of 18g nickel nitrate hexahydrate. A lime green suspension formed. The solution was vacuum filtered, and the lime green remainder dried on a steam bath. The filtrate was still surprisingly green, although not as deep green as the original nickel nitrate solution.

The dry product looks exactly like the lime green powder I got before. See photo showing both. I did some tests on both the products:

When heated to 200+ degrees (in a small crucible with a lid on directly on my hotplate) the color turns from lime green to tan after some 10 minutes. See photo. What the crucible lid is removed (when still hot) there is no smell but only white fumes which looks like steam. The tan color remains the same when it is cooled to room temp, but when the tan powder is wetted with water it returns to lime-like color. See photo. So this change looks purely like a change in hydration.

I added small bits to each of sulphuric acid (>95%), nitric acid (70%), and hydrochloric acid (35%) and stirred with a stainless spatula for a few minutes (at room temp). There seems to be little if any reaction with the sulphuric or nitric acid, but with the hydrochloric acid it slowly forms a pale green solution which has a hint of blue if more water is added.

What surprised me is that the recovery of the lime green remainder once dried was only 6g. I expected more. I'm not sure if some disubstituted salt also formed and stayed in solution; which may also explain why the filtrate was still quite green.

I also wondered whether the nickel nitrate reacted with the NaOH and formed nickel hydroxide; but I would have expected the hydroxide to be easily soluble in all 3 the acids. And photos online shows nickel hydroxide to be more green; not lime green.

What I will try next is to stir nickel powder with hot cyanuric acid (for days) and see if I get something.