Sciencemadness Discussion Board

Synthesis of sodium thiocyanate.

White Yeti - 15-1-2012 at 10:29

Note: I know I can just buy the stuff, but I want to try to synthesise it myself, just for the hell of it.

I will attempt to synthesise sodium thiocyanate very soon, as soon as the urea I extracted from fertiliser comes out of solution.

In the meantime, I wanted to make sure the way I'm going about this synthesis is correct.

I worked out the heat of reaction involving the conversion of sodium carbonate and urea to sodium cyanate, water, ammonia and carbon dioxide ( endothermic +210KJ/mol).
The reduction of cyanate to cyanide with carbon powder was also endothermic (about 420KJ/mol, a little less if carbon is converted to dioxide instead of monoxide).

But the conversion of cyanide to thiocyanate is exothermic (-680KJ/mol), so much so, that the heat released in this step would cancel out the heat requirement of the other two initial steps, increasing the chances of success for this reaction.

But I'm afraid that dumping all these reactants into one big reaction vessel (made of steel, this may be a problem) would suffer from many side reactions that would severely lower yield. I fear that the sulfur may boil off, as its boiling point is quite low.

I have limited equipment, a charcoal furnace, and it's much more convenient for me to perform this synthesis in one step rather than 3. But, I'm not going to do it if the yields will be extremely low.

Which is better, mixing everything in one big step, or performing every step separately?

kmno4 - 15-1-2012 at 23:30

Your methode will not work.
"conversion of cyanide to thiocyanate is exothermic (-680KJ/mol)"
- very improbable and surely wrong value. How did you calculate it ?

plante1999 - 16-1-2012 at 15:00

Quote: Originally posted by White Yeti  

Which is better, mixing everything in one big step, or performing every step separately?

If you do every step separately, it will give better yield , sulfur adition to cyanide is endothermic.

kmno4 - 16-1-2012 at 15:34

Quote: Originally posted by plante1999  
, sulfur adition to cyanide is endothermic.

No, it is not.

plante1999 - 16-1-2012 at 15:39

Mayby I made a mistake but in solution, from wath I remenber, the cyanide sol. need to be heated to disolve the sulphur.

[Edited on 16-1-2012 by plante1999]

plante1999 - 17-1-2012 at 16:44

Maybe sulphur reduction of cyanates is possible? If C can reduce cyante I suppose S8 could to....
More research is needed here.

White Yeti - 17-1-2012 at 17:30

Quote: Originally posted by plante1999  
Maybe sulphur reduction of cyanates is possible? If C can reduce cyante I suppose S8 could to....
More research is needed here.

That's not a bad point, but I'm afraid that the sulfur could potentially boil off before reducing the cyanate. This is definitely not an issue with carbon, which is both more accessible and better at removing oxygen than sulfur.

I was thinking about reducing cyanate with carbon and having sulfur in the same vessel to react with the subsequent cyanide salt. I'm wondering if this method would also generate carbonyl sulfide, as carbon is oxidised to CO and then to COS as sulfur is in close proximity.

blogfast25 - 19-1-2012 at 12:07


I'd definitely research your subject a helluvalot more, if I were you!

Random - 17-1-2014 at 19:21

Anyone has some new information on this subject? Would cyanate react with sulphur while heating it to form thiocyanate?

AJKOER - 18-1-2014 at 08:14

Per (see ) to quote:

"The salts of thiocyanic acid are generally obtained by the direct action of sulphur or a polysulphide on the cyanide, by the action of hydrogen cyanide or cyanogen on a polysulphide,

(NH4)2S2 + HCN = NH4CNS + NH4HS,
Na2S2 + (CN)2 = 2NaCNS,

or by the decomposition of a complex cyanide by fusion with an alkali carbonate and sulphur.
The thiocyanates are generally soluble in water, the exceptions being those of lead, silver, mercury and copper. Most of them dissolve also in alcohol and ether. Aqueous solutions of the alkali thiocyanates undergo atmospheric oxidation under the influence of sunlight; with solutions of medium concentration this change takes place rapidly, with separation of a yellow, amorphous precipitate consisting of pseudo-cyanogen sulphide, (CNS)3. The concentration of thiocyanate most favourable to the separation of this sulphide is about 50 per cent, in summer and 10 per cent, in winter. In addition to this substance the products of the photochemical oxidation of potassium thiocyanate include hydrocyanic acid, sulphate, carbon dioxide, ammonia and ammonium salts:

12KCNS + 12O2 + 6H2O = 6K2SO4 + 3HCN + 3CO2 + 3NH3 + 2(CNS)3.

An unstable intermediate peroxygenated compound is also always formed. This gives a blue coloration to fresh guaiacum tincture and is possibly analogous to Caro's acid.
Any pink colour that may develop in solutions of alkali thiocyanates on exposure to light is due to oxidation of traces of ferrous salts usually present by dissolved oxygen."

I would add CuCl2 or CuCO3 to form the insoluble Copper salt.

Another possible path (probably need more info on any catalyst, reaction temperatures,..., which was discussed previously on Sciencemadness no less, see ) per Wkipedia ( ):

"Ammonium thiocyanate is made in the United States by the reaction of carbon disulfide with aqueous ammonia. Ammonium dithiocarbamate is formed as an intermediate in this reaction, which upon heating, decomposes to ammonium thiocyanate and hydrogen sulfide:

CS2 + 2 NH3(aq) → NH2C(=S)SNH4 → NH4SCN + H2S"

Interestingly, the patent cited in the prior SM thread ( ult&ct=result&resnum=7&ved=0CEAQ6AEwBjgK#v=onepage&q=manufacture%20carbon%20disulfide&f=false ) notes on the 1st page 2nd paragraph, the need for diluents for the reaction to occur, and the use of water, alcohol,... may actually result in Ammonium thiocyanate (our goal).

If created, I would add CuCO3 to form a precipitate, or just add NaHCO3 and heat to isolate the NaCNS.

On how to prepare CS2, per ( ) to quote:

"Carbon disulphide is prepared by passing sulphur vapour over red hot charcoal. The preparation may be carried out on a small scale by heating pieces of charcoal in a combustion tube placed in a furnace slightly tilted, a Liebig potash bulb, immersed in ice, being attached to the lower end of the tube, and small pieces of sulphur introduced into the upper end of the tube which is then closed with a cork. Sulphur vapour passes over the red-hot charcoal and impure carbon disulphide containing sulphur in solution is gradually formed and collects in the cooled receiver. The reversible reaction

C + 2S ⇔ CS2 "

I would find the formation of Ammonium thiocyanate interesting as per, for example, "Synthesis of aryl thiocyanates using Al2O3/MeSO3 H (AMA) as a novel heterogeneous system " link: to quote:

"Indoles and various aromatic and heteroaromatic compounds undergo smooth thiocyanation with ammonium thiocyanate in the presence of a mixture of Al2O3/MeSO3H (AMA) under mild conditions without use of any organic solvents to afford the corresponding aryl thiocyanates in excellent yields and with high selectivity."

and then, using chlorobenzene, as an example of an aryl (C6H5) chloro derivative, a possible reduction of C6H5SCN to the cyanide as cited in this reference "Electrochemical Reduction of Aryl thiocyanates: A Unique Autocatalytic Process and Evidence for a Concerted-Stepwise Mechanism Transition", link: where the author lists the reactions:

ArSCN + 2e ---> ArS- + ArSCN-
ArS- + ArSCN ---> ArSSAr + CN-
ArSSAr + 2e ---> 2 ArS-

although the absence of more specifics is disappointing.

Here is a reference on the preparation of methane sulfonic acid (or, MeSO3H per US patent 6207025) by irradiating a mixture comprising acetic acid, sulfur dioxide and oxygen with light, link: .

[Edited on 19-1-2014 by AJKOER]

Antiswat - 19-1-2014 at 06:45

if sulfur doesnt work out you could try polysuphides as stated above

of what i recall about golden powder, an interesting mixture, supposedly polysulphides are formed aswell as nitrogen sulfides

3:2:1 KNO3 K2CO3 S
if the 2 parts K2CO3 and 1 part S is mixed and heated beforehand it should form polysulphides which will when mixed with the 3 parts KNO3 all finely powdered burn violently, as the polysulphides acts as a fuel, reaching 8 times the burn speed of blackpowder

~~you can make polysulphides by melting K2CO3 with S~~

Random - 19-1-2014 at 19:09

But I asked for cyanate not cyanide

Fulmen - 26-4-2018 at 00:08

Random: Did you solve this? I too am looking for a non-cyanide route to thiocyanates, preferably from sodium cyanate.

XeonTheMGPony - 21-9-2019 at 07:47

Older thread but been researching this as of late.

May be helpful.

Sodium thiosulfate by sodium bisulfite route.

(And this kids is why you shouldn't do any thing when tired! wrong substance entirely far as thread topic goes!)

[Edited on 22-9-2019 by XeonTheMGPony]

Bedlasky - 21-9-2019 at 12:33

If I know thiocyanates are produce in laboratory by heating potassium ferrocyanide with sulfur.

rockyit98 - 22-9-2019 at 02:12

Quote: Originally posted by Bedlasky  
If I know thiocyanates are produce in laboratory by heating potassium ferrocyanide with sulfur.

better yet you could heat Prussian blue with thiosulfate or sulfur .
if you want sodium salt you can melt the mixture with NaOH.

[Edited on 22-9-2019 by rockyit98]

rockyit98 - 22-9-2019 at 08:37

thio.PNG - 49kB

[Edited on 22-9-2019 by rockyit98]

XeonTheMGPony - 23-9-2019 at 18:44

found this source, yet to order so can't say of quality, but I can say last several chemical orders from said country been exceptional quality

Thiocyanate from NaCN and sulfur

BAV Chem - 30-4-2022 at 13:41

I'm currently trying to make thiocyanate by refluxing a solution of NaCN over sulfur. My cyanide is far from pure as I made it by heating a mix of Na2CO3, urea and carbon.

At the start the reaction worked well but then after I added the second half of my sulfur it started forming polysulfides in solution and stopped producing more thiocyanate. To make a long story short I then did some research and found that I have an ammonium contamination in there which will do anything to inhibit thiocyanate formation.

Where's that ammonia from? Some urea pyrolysis product maybe?
Any suggestions how to mitigate that apart from purifying the cyanide (which I want to avoid)?

Bedlasky - 2-5-2022 at 13:17

I doubt that you have ammonia in your solution. Your impure NaCN contain some sodium carbonate. Sodium carbonate will react with excess of sulfur to form polysulfide.

Boffis - 3-5-2022 at 23:20

Hi BAV Chem, I used to prepare my own thiocyanates until I discovered I could buy them so cheaply and easily. It is best to isolate the cyanide as a ferrocyanide salt first and then fuse this with sulphur. The easiest way to isolate the cyanide ions is to add a mixture of ferric and ferrous salts to the weakly alkaline mixture of and filter off the crude prussian blue, suspend it in clean water and then treat this with a strong (10-12% solution sodium or potassium hydroxide solution) until the suspended solid has turned a plain-chocolate-brown colour and filter. It is best to let the suspension settle overnight and decant as much clear liquid first as the ppt is a bitch to filter although kieselguhr addition helps a lot. The pale yellow solution is the simply evaporated down until a small sample crystallises on cooling. By this point the solution will have turned cloudy and brown and require treatment with charcoal and kieselguhr mixture and filtering hot to obtain a clear solution. The crystals of ferrocyanide are usually very pure. The conversion of ferrocyanide into thiocyanate or back into purer cyanide is widely reported.

BAV Chem - 6-5-2022 at 16:00

Hello Boffis, I know I can actually order some thiocyanate on amazon rather easily but I'm still trying to make some for fun. Also who knows maybe in a while even thiocyanate will be hard to come by. Very nice ferrocyanide preparation btw ;)

Also Bedlasky, I do actually know for a fact that there's an ammonia contamination as it fumes when I bring some HCl close. You're right about there being carbonate as a major impurity but weirdly enough there's still cyanide in solution which should react with the polysulfides but it doesn't... even after boiling out any ammonia it somehow doesn't react fully. Perhaps there's some thiocyanate <--> cyanide+sulfur equilibrium going on there.