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Magpie
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[*] posted on 13-9-2007 at 15:36
KOCN


I have made several attempts to make KOCN from urea and KOH based on the guidance of US patent 3935300 (Feb 20, 1974), and encouragement from Hilski. My urea is PTS brand fertilizer. KOH is technical.

I mixed finely ground urea and KOH at a 2:1 mole ratio of urea:KOH. This was placed in an assay crucible and heated gently but steadily (at ~130C) until foaming stopped. This product was then placed in a muffle furnace preheated to 240C. Heating at this temperature was continued for 6 hours.

What resulted was a soft, light brown clinker. This was ground up, mixed with water, and filtered. Suspended mud was discarded. The filtrate was mixed with 95% ethanol and the resulting ppt caught on a Buchner funnel. This was dried and weighed. Assuming it was KOCN the yield was 12%. Placing some in water the pH was 9. Melting point is >280C (limit of my silicone mp oil).

I'm very skeptical that I actually made any KOCN (mp 315C). However, I don't know of any way of proving, or disproving, this.

Nicodem, in a recent post on the MSG thread says:

Quote:

(NaOCN or KOCN can easily be prepared in a home lab).


If he, or anyone else, can tell me what I'm doing wrong, or provide a better procedure I will be grateful.




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[*] posted on 13-9-2007 at 16:15


I, like Magpie have no real way of determining what I actually made using the procedure in the patent he referenced. But I did try a few things which varied from the patent, so I will describe the basic procedure I used.
For one, I didn't bring the temperature to 130C and leave it there for any real length of time. I added the KOH and urea to the vessel I was using, and turned up the heat as high as it would go. The urea melted at 130 like it was supposed to and everything kept bubbling reacting and emitting ammonia fumes for some time. Right around 180C, everything went solid, pretty much like the patent said it would.
Also, I didn't use an oven the keep the temperature at 240C after the initial reaction. I basically just left the mixture on the electric hotplate turned up on high for about 5 hours. I used a Fluke infrared thermometer to measure the temperature on the surface of the mixture from time to time, and it remained a solid at or about 240C the whole time.
I dissolved everything in water, and filtered out the brown stuff as Magpie mentioned. Then, I boiled off a lot of the water and poured what was left into a beaker of cold denatured alcohol to precipitate the alleged KOCN, which was then vacuum filtered.
I used 21g urea and 10.3g KOH for the reaction. This is close to a 1.9:1 molar ratio, which the patent claims is ideal for best yields. I don't remember what the actual yields were, but I do remember that they were a good bit lower than I expected.
Like I said, I really don't know a way to test the result to see what % KOCN was actually made, so they yields may have even been lower than I think they were.




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[*] posted on 13-9-2007 at 16:32


The usual industrial method is to use an alkali metal carbonate as the base instead of the hydroxide:

Manufacture of alkali-metal cyanates. (du Pont de Nemours, E. I., and Co.). Brit. (1969), 5 pp. CODEN: BRXXAA GB 1145777 19690319 Patent written in English. Application: GB Priority: US 19660801 - 19670710. CAN 70:116709 AN 1969:116709 CAPLUS

Abstract
Na cyanate (I) or K cyanate (II) of 98% or higher purity, free of cyanide is obtained by the low temp. reaction of stoichiometric amts. of tech. grade alkali metal carbonate and shotted urea in the presence of a suitable quantity of a heel of 98% purity (45 and 55 wt. % of the heel for manuf. of I and II is of the reaction mixt., resp.) in muller-type mixers or screw conveyors having provision for intensive mixing and rubbing and a suitably efficient heat transfer arrangement. A small excess of urea (.apprx.2%) is desirable to eliminate contamination from unreacted alkali metal carbonate. The low operating temps. employed in the process (95-150° and 95-225° being the optimum ranges for I and II, resp.) do not cause severe corrosive conditions and permit the use of cast iron, wrought iron, or stainless steel reaction vessels and batch or continuous operations are practicable. Heating times of 4-7 hrs., depending on mixing and heat transfer characteristics are required for completion of the reaction. Cyanide impurity detected in the end product is <1 ppm. Thus, charge a jacketed, stainless steel, double-arm mixer, heated with steam at 110 psig. (173°) with 5.20 parts of heel of I of 98% purity. Engage the blades turning at 50 rpm. and heat for 1.8 hrs. to 164°. Add 2.25 parts soda ash and 8 min. later 2.25 parts of shotted urea. Heat the slightly wet and lumpy charge for 6 hrs. After 2 hrs., the batch becomes free-flowing and dusty. Vent off the discharge gases throughout the heating period. The yield obtained of 7.8 parts I from the mixer is 99.5% based on the starting amt. of urea, with a purity of 98% and shows <1 ppm. cyanide. About 86% I is formed during the 1st hr. while the temp. of the mix reaches 140° and 94.9% of the total product synthesized is formed in 2 hrs.


and

US4000249
Sochol, et al. December 28, 1976

Preparation of alkali metal cyanates

Abstract
Process for the preparation of alkali metal cyanate by the reaction of urea and alkali metal carbonate. The addition of water to the reaction in an intermediate step activates partially blocked alkali metal carbonate and provides an alkali metal cyanate product of high purity.


:cool:




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[*] posted on 13-9-2007 at 16:52


Calcium cyanurate decomposes to HOCN gas and solid calcium cyanamide under mild orange heat. The HOCN could be bubbled through NaOH or KOH leaving the cyanate.



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[*] posted on 13-9-2007 at 17:21


YEe Ha indeed :D.


Just to save the search:

http://www.sciencemadness.org/talk/viewthread.php?tid=8594&a...

Cheers,

O3




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[*] posted on 13-9-2007 at 18:46


Quote:
Abstract
Process for the preparation of alkali metal cyanate by the reaction of urea and alkali metal carbonate. The addition of water to the reaction in an intermediate step activates partially blocked alkali metal carbonate and provides an alkali metal cyanate product of high purity.

I tried that procedure also. I didn't see any difference in yield, but the product possibly could have been more pure. I have no way of knowing.




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[*] posted on 14-9-2007 at 14:14


The_Davster says:

Quote:

Calcium cyanurate decomposes to HOCN gas and solid calcium cyanamide under mild orange heat. The HOCN could be bubbled through NaOH or KOH leaving the cyanate.


That's an interesting approach. I wonder what the relative poisonous level is of HOCN vs HCN? :o




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[*] posted on 14-9-2007 at 14:54


I would use the procedure found in Inorganic Syntheses vol. 2. They've already done the heavy lifting of adapting and validating the patent literature for lab scale preparations.



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[*] posted on 14-9-2007 at 15:27


Thank you, Polverone. I'll check out that reference.

I just dissolved some of my preliminary KOCN in water and then added some AgNO3. I did get a white precipitate. So it likely is at least partially composed of KOCN. Could be some cyanide in there too I suppose. But I don't think it was ever hot enough to form that.




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[*] posted on 14-9-2007 at 18:21


What about decomposition of potassium cyanurate directly into potassium cyanate? I have a couple of sources that say that cyanurates decompose into cyanates. I suppose a potential problem would be that the cyanatewould further decompose into cyanide.

Is this at all a practical method?
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[*] posted on 15-9-2007 at 17:55


From the depths: https://sciencemadness.org/talk/viewthread.php?fid=2&tid...

Cyanuric acid can be fused with alkali carbonate.




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[*] posted on 15-9-2007 at 22:36


Thanks I was actually looking for that patent but I lost it in my files. It states that significant decomposition of cyanate to cyanide takes place at temperatures lower than 500C when operated in air so that's why a CO2 atmosphere is employed.

From what I can tell, it doesn't matter whether the free acid is fused with carbonate or if a salt of cyanuric acid is heated- both will result in cyanate, and in an oxygen environment, a good deal of cyanide.
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[*] posted on 15-9-2007 at 23:06


Heating plain cyanuric acid to around 300 - 380 C gives cyanic acid and other products. You could condense it at 5 C or so to separate it from some of the less condensible products, and continuously & immediately react it with a base to get the cyanate salt.
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[*] posted on 16-9-2007 at 10:05


Quote:
Originally posted by Cesium Fluoride
Thanks I was actually looking for that patent but I lost it in my files. It states that significant decomposition of cyanate to cyanide takes place at temperatures lower than 500C when operated in air so that's why a CO2 atmosphere is employed.

From what I can tell, it doesn't matter whether the free acid is fused with carbonate or if a salt of cyanuric acid is heated- both will result in cyanate, and in an oxygen environment, a good deal of cyanide.

That does not make any sense. How can HOCN be reduced to HCN (or cyanates to cyanides) in the absence of a reducent? And why would an oxidative atmosphere help the reduction and absence of O2 prevent it?

In my experience the trisodium or tripotassium salt of cyanuric acid easily decomposes to NaOCN or KOCN if heated already on a hotplate (I would say that is about 300°C or less). Of course, no cyanide formed even though the heating was done on air.




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[*] posted on 16-9-2007 at 10:25


Quote:
That does not make any sense. How can HOCN be reduced to HCN (or cyanates to cyanides) in the absence of a reducent? And why would an oxidative atmosphere help the reduction and absence of O2 prevent it?


I understand what you mean, but I was simply summarizing patent GB710143. Here is direction citation:

Quote:
Alkali metal cyanates have been found, however, to decompose in air at 500-900C to give a variety of products including cyanide. We have indeed found that such decomposition occurs even below 500C in air. Even in an atmosphere nitrogen free from oxygen, decomposition of cyanate to cyanide has been found to occur, although no sources of ammonia or hydrogen were present. Even at 500C, 7% decomposition occurs on heating sodium cyanate in nitrogen for one hour, and sodium cyanide is prominent amongst the decomposition products. Such formation of cyanide is obviated at temperatures up to 550C by operating in an atmosphere of carbon dioxide, whether in reactions with calcium cyanamide as described in USP 2,208,033, or in reactions in absence of calcium salts according to the process of the present invention.


You tell me...completely bogus?

Quote:
In my experience the trisodium or tripotassium salt of cyanuric acid easily decomposes to NaOCN or KOCN if heated already on a hotplate (I would say that is about 300°C or less). Of course, no cyanide formed even though the heating was done on air.


Great! That's probably exactly what I'll end up doing. A bit of cyanide doesn't even really bother me, but according to the above info, you produced at least some CN-.
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[*] posted on 22-9-2007 at 14:15


I was able to find a copy of the potassium cyanate procedure in Inorganic Syntheses, vol II.

It calls for the mixing of 70 g of K2CO3 with 80 g of urea in a porcelain evaporting dish and heating until a melt results.

My first attempt was with a 1/3 scale batch in a 6" porcelain evaporating dish. Because of too rapid and/or uneven heating the dish cracked. :( I didn't use a wire gauze either.

Today I heated a 1/10 scale batch in an aluminum drinking cup placed on a wire gauze. At first there is some melting (urea I suppose) and off-gassing. Then some more off-gassing. Eventually this stops. Then gradually turning up the heat it begins to char and at full heat it melts with some foaming. I then placed the mostly solidified melt into a mortar and ground it to a powder.

The procedure claims a clear melt and says nothing about charing. I didn't see this. It claims a 94% yield. Mine was 77%, but I did have a much smaller batch.

The powder dissolves very quickly in water and gives a strong test for cyanate. (The cyanate test is given in the procedure and merely consists in adding a few drops of a solution of a cobalt salt to a small sample. A blue color is positive for cyanate.) It also tested positive for carbonate. (This test calls for Ba(NO3)2 and is also in the procedure. The procedure also provides tests for ammonium ion, urea, and cyanide.)

The picture below shows the KOCN in the weighing pan. The two test tubes with blue solution are the results of the cyanate test.

This procedure was written by Allen Scattergood and checked by Don R. McAdams and James P. McReynolds and I would think it should be pretty solid. What puzzles me most is that they make no mention of charing and refer to a clear melt that I never saw. One possibility is my materials. They call out USP grade K2CO3. Mine is pottery grade. My urea is fertilizer grade. They likely used a lab grade.

If others have tried this procedure I would be very interested in hearing of their results. I would also be interested in any ideas as to why I'm getting this charing.

Edit: Later testing (titrating wth dilute HCl) showed the product is at least 50% K2CO3.

[Edited on by Magpie]

KOCN.jpg - 54kB




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[*] posted on 12-10-2007 at 12:06


just a doubt..

If the trisodium or tripotassium salt of cyanuric can form cyanates, will worth a try mixing powdered stoichiometric amounts of trichloroisocyanuric acid and KCl , moist and heat very mild to give chlorine and then washing with alcohol ,dring a bit and heat with care (or not) depending if you want make KOCN or KCN (?) I think that this can be made, although Polverone related in other thread which cyanates undergo hydrolisis,decomposing, and also some of the reactants would probably contaminate the formed salts..

But maybe the main advantage can be the fact that making KCN is easily than NaCN (also explained by Polverone) by pyrolising KOCN and also KOH (watched chemical in many places) isnt needed,since we would be using OTC KCl.. and as side benefit you can get chlorine...

I'm remembering also which this is a subject in a thread on E&W, but cann't remember..

so, what about?




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[*] posted on 12-10-2007 at 13:57


Aqua_Fortis, I don't see what the driving force for your proposed reaction would be.

Making KOCN in decent purity has become an obsession for me. I don't have any great purpose for it. It's just pissing me off that I can't prepare it.

I have tried numerous patents that claim it can be made with urea + K2CO3, or KOH. None have been satisfactory in my opinion. The prep from Inorganic Synthesis did produce some poor quality KOCN, however.

Right now I have two slow preps going simultaneously in my lab. The first is KOH refluxing with urea in denatured ethyl alcohol. I found a reference to this in a book on nitrogen chemistry. It refered to a paper in Ber,1887, a very old German paper I imagine. (I don't have the paper per se.) Some wispy white ppt is forming but only very slowly. NH3 is drifting out of the top of the reflux condenser equally slowly.

The second is an isocyanuric acid + KOH solution being evaporated down to, hopefully, potassium cyanurate. Then I'll heat that to form KOCN.

If these two methods also fail I will be left with decomposing isocyanuric acid to HOCN and piping this into a KOH solution. This is understandably the last on my list.

I have no intention of trying to make it by oxidizing KCN. Not that that wouldn't work, it just seems like cheating,




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[*] posted on 12-10-2007 at 15:23


Oh Magpie , sorry.. I really should have missed something..

Quote:
Originally posted by Magpie:
I don't see what the driving force for your proposed reaction would be


well if I understod correctly, if you react HCl with TCCA and some heat to complete the reaction, you will get Cl2 and cyanuric acid, right? So the same can probably apply to alcaline chlorides,etc..being 3 mols of xCl for each of TCCA..

Quote:
If these two methods also fail I will be left with decomposing isocyanuric acid to HOCN and piping this into a KOH solution. This is understandably the last on my list.


well, if you are obcessed with purity, this don't seem to be much reliable .. Since cyanuric acid decompose not only to HOCN, but a lot of more products, as said before..


Quote:
The second is an isocyanuric acid + KOH solution being evaporated down to, hopefully, potassium cyanurate. Then I'll heat that to form KOCN.


What the difference ,in your viewpoint , advantages and disadvantages between fusing cyanuric acid and a hidroxide without water and reacting both in an aqueous solution ? I'm little confused about that (side reactions,etc) , but still betting in aqueous solution + alcohol method..

I'm obsseced also in these chemicals..but more in KCN(for recovering gold from E-stuff and also from local ore) than KOCN, and the last seem to be great as start for me.

BTW , also planning in making my own TCCA , just for fun :D

[Edited on 12-10-2007 by Aqua_Fortis_100%]




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[*] posted on 12-10-2007 at 16:13


Aqua says


Quote:

well if I understod correctly, if you react HCl with TCCA and some heat to complete the reaction, you will get Cl2 and cyanuric acid, right? So the same can probably apply to alcaline chlorides,etc..being 3 mols of xCl for each of TCCA..


I suspect that part of the driving force for the HCl reaction is the formation of the weak acid: cyanuric acid. But by all means try the KCl. ;)

By Aqua:


Quote:

well, if you are obcessed with purity, this don't seem to be much reliable .. Since cyanuric acid decompose not only to HOCN, but a lot of more products, as said before..


I thought it just decomposed to HOCN.

Aqua:



Quote:

What the difference ,in your viewpoint , advantages and disadvantages between fusing cyanuric acid and a hidroxide without water and reacting both in an aqueous solution ? I'm little confused about that (side reactions,etc) , but still betting in aqueous solution + alcohol method..


Making the potassium cyanurate in aqueous solution avoids dealing with HOCN. This is then heated to form KOCN. It may or may not work - time will tell.

My attempts at fusing KOH and K2CO3 with urea or isocyanuric acid have not been satisfactory, despite all the patents.




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[*] posted on 13-10-2007 at 10:36


Magpie, I've seen the charring you refer to before, though I was always on the way to cyanides and didn't mind the addition of a little more carbon. I don't know if it's something expected but generally not mentioned, or if it's a consequence of using fertilizer grade urea. Personally, I would try the Inorganic Syntheses procedure again, this time using pure urea and K2CO3, before attempting obscure century-old procedures.

If you have any high-grade potassium hydroxide or bicarbonate on hand, I'd try using those to prepare the K2CO3 that you will use. If not, it might be worth ordering a bit of reagent K2CO3, KHCO3, or KOH to satisfy your burning curiosity. The same may be said of the urea, or you might want to just try purifying the fertilizer before using it.

According to at least some references, even dilute acids will cause cyanates to liberate cyanic acid with decomposition to ammonia and CO2. I'm not sure that hydrochloric acid titration is a reliable carbonate indicator.

You could also order a minimal quantity of reagent potassium cyanate so that you have a reliable standard to work against.




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[*] posted on 13-10-2007 at 12:37


After refluxing for 11 hours there was no significant production of insoluble KOCN in the alcoholic KOH/urea. It gave only a slight positive (blue) when tested with Co++.

I haven't tried heating my tripotassium cyanurate yet, if that is indeed what it is.

Polverone it seems like you have a good point about the reaction of HCl and KOCN. Using the brown powder previously made with the Inorganic Syntheses procedure, I get a strong blue test before the addition of HCl, and no blue once all fizzing stops after adding HCl. It would be better to test for CO3-- using Ba++ as the Inorganic Syntheses procedures recommends.

I will try the Inorganic Syntheses procedure again. I should be able to purify my urea and K2CO3 via recrystallization.

I may just have to accept some charring and/or remove this in a workup of some kind. I think this could be minimized if a hot bath was used to get the KOCN to a melt (320C) instead of my propane bunsen burner. I just don't happen to have any Wood's metal or such on hand.




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[*] posted on 14-10-2007 at 15:59


I've had some encouraging results today in my quest for KOCN:

Yesterday I had dissolved 4g of swimming pool grade isocyanuric acid in 400 mL of water. Then a stoichiometric amount of KOH was added to form the tribasic salt. (I later found out that isocyanuric acid is soluble in aqueous KOH, so it would have been wiser to do this in reverse order and cut way back on the water.) My salt solution was then reduced to dryness by evaporation on a hotplate, resulting in a slightly crumbly white powder.

Today I heated this powder to a liquid in a small aluminum cup using a bunsen burner w/gauze. Once the bubbling stopped I poured the melt into a mortar and ground it to a powder. There was very little charring and the final powder was white.

Now I carefully tested it with Co++ (for OCN-) and Ba++ (for CO3--) against the brownish KOCN I had made earlier using urea and K2CO3. For the Co++ test the blue was just slightly more intense for that made with the acid. For the Ba++ test first results were much more favorable for the KOCN made from acid, with no ppt. Further testing showed BaCO3 ppt was formed, but it still seemed to be an improvement.

I am now contemplating firing both of these products in my muffle furnace in an attempt to convert them to KCN. This could then be titrated with a standard AgNO3 solution to determine the %KOCN.




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[*] posted on 15-10-2007 at 20:49


Nice work Magpie.
Keep at it.

I've seen Cyanuric acid on the shelf while cruising the pool chemicals section in the local hardware store (as we all probably do!). It seems such an interesting chemical.
I've had a brief look around, but there does not seem to be much said about Cyanuric acid in the literature (reactions). Has anyone seen anything comprehensive? Everything I've seen is frustratingly brief.
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[*] posted on 15-10-2007 at 21:30


Thanks ciscodad. It seems my efforts are finally starting to pay some dividends.

This whole investigation of urea/cyanuric acid/KOCN/HOCN/biuret chemistry has been both interesting and perplexing. There is some information out there but as you say it can be hard to find. It seems most of the work was done back in Wohler and Lebig's time and has been forgotten since. What was most frustrating for me was trying a bunch of patents that didn't pan out.

Cyanate is pretty much insoluble in everything except water. Then in water it's subject to hydrolysis. KOCN also has a tendency to convert to K2CO3. So it's hard to work with.

Some results from recent tests on my product made from isocyanuric acid:

1. Placed ~30mg on a watchglass then added 3-4 drops of 10%HCl. Got a biting whiff of "acetic acid smell." This should be HOCN and is a good sign.

2. Realized that Co(OH)2 and CoCO3 are insoluble. So treated some KOCN solution with the BaNO3 first to take down the carbonate. Centrifuged. Added the Co(NO3)2 solution to the supernate for a strong blue color that persisted. Final pH was 8. It's too bad I don't have a spectrophotometer and some standard KOCN. With these I could likely determine the purity of my product.

3. Treated the centrifuged residue with 10%HCl. Surprisingly not much bubbling here. So not a carbonate. What it is I don't know.

4. Treated the supernate with some 10%HCl. Little stream of bubbles. When gently heated a great deal of bubbles. Assumed that the bubbles were HOCN.

I have hope that I can make some more product of even better quality. I'm trying to avoid use of K2CO3 as this is what I don't want in my product. My plan for tommorrow is to make a larger batch from the isocyanuric acid and do some more testing.




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