Does heating of potassium ferrocyanide with carbonate and carbon yield potassium cyanide?

Does the following reaction occur? If so, at what temperature? Would $\pu{640 °C}$ be enough?


$$\ce{2 K4[Fe(CN)6] + 2 K2CO3 + C -> 12 KCN + 2 Fe + 3 CO2}$$




**Disclaimer**: This answer is just for education purpose only. DON'T TRY TO MAKE POTASSIUM CYANIDE ON YOUR OWN if you don't have profound laboratory experience. Potassium cyanide is **extremely toxic** and would even cost your life.




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Yes, your reaction of producing potassium cyanide has been discussed in a [forum](http://www.sciencemadness.org/talk/viewthread.php?tid=23&page=19):



> 
> ...Dry fusion of pure $\ce{K4Fe(CN)6}$ is a bit tricky, if you will
>  try to do this on air contact you will end with with cyanate and
>  cyanogen beeing evolved. To prevent (this) oxidation process,
>  $\ce{K2CO3}$ and carbon works the best - you don't need protecting
>  atmosphere you just must cover reaction vessel with lid to reduce free
>  air flow, reaction products CO and CO2 will form protecting buffer of
>  gas under the cover and prevent oxidation of product to cyanate,
>  remember you don't need completely airtight vessel (reaction gases
>  must evolve freely) just cover crucible with ceramic lid and heat it
>  up in electric furnace. **I made $\ce{K4Fe(CN)6 + K2CO3 + C}$ process
>  for many times now and produced a lots of cyanide using this method,
>  temperature program i've used ~30 min to 600C, then 1 hour at this
>  temp, rise to 650 in 30 minutes, and one more hour at 650. If your
>  crucible is high and you sit it long enough cyanide separates from Fe
>  and carbon particles and solidifies as shiny snow white layer at the
>  top layer,** however if this has't happened and resulting mass is
>  black and feromagnetic this is fine too, you can separate cyanide by
>  dissolving and filtering.
> 
> 
> 


Other methods are also possible like [simply decomposing potassium hexcyanoferrate](https://chemistry.stackexchange.com/questions/32189/how-to-prepare-potassium-cyanide-from-potassium-ferrocyanide/83702#83702) or [with any combination of potassium hexacyanoferrate/ potassium carbonate/carbon reaction.](https://books.google.co.in/books?id=PpTi_JAx7PgC&pg=PA351&lpg=PA351&dq=K4FeCN6%20%2B%20K2CO3%20%2B%20C&source=bl&ots=mr_SG1Ovnp&sig=eGkMeJXwlSLEgvOwZO_i7G-lEZ4&hl=en&sa=X&ved=2ahUKEwjtm8ntoKLaAhVIQo8KHbOQD9EQ6AEwAnoECAYQAQ#v=onepage&q=K4FeCN6%20%2B%20K2CO3%20%2B%20C&f=false)


$$\ce{K4Fe(CN)6 + K2CO3 -> 5KCN + KCNO + CO2 ^ + Fe}$$
$$\ce{K2CO3 + C + NH3 -> 3KCN + H2O}$$


 4

Best is the following reaction since there is no fire because there is no fuel to burn!


$$\ce{K4[Fe(CN)6] + K2CO3 + C -> 5KCN + KOCN + FeC + O2}\tag{R1}$$


The black solid is $\ce{FeC},$ which is slightly magnetic. Since $\ce{K4[Fe(CN)6]}$ melts at $\pu{300 °C}$ and decomposes at $\pu{400 °C},$ best is to heat at $\ce{390 °C}$ for 1 hour, then ramp up the temperature to $\pu{700 °C}$ to force the transition of cyanate to cyanide:


$$\ce{KOCN + C -> CO + KCN}\tag{R2}$$


Heat at $\pu{700 °C}$ about 20 minutes and then shut off the oven. With thermal gloves, take stainless steel crucibles out of oven to cool quickly. When about $\pu{120 °C},$ add $\pu{100 ml}$ water and let sit for 20 minutes.


Then use screwdriver to crack the solids off the crucible bottom and walls. Let the liquid settle and decant most of it. Filter the black iron carbide. pH of the liquid is about 12 and the test with iron(II) sulfate and iron(III) chloride forms beautiful Prussian blue!


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