Sciencemadness Discussion Board

Attempt at cyanide via crucible heating.

PirateDocBrown - 5-1-2017 at 02:58

So, I ran a simple experiment.

I mixed .2 mol urea (local garden store), and .1 mol KOH (Duda Energy), in a porcelain crucible from a local surplus store.

I bent a clothes hanger into a bipod to support a Bernzomatic propane torch into an upright position, and heated the crucible while it was held on a ring stand.

The melt bubbled quite a lot, with a gas that was obviously ammonia.

When that stopped, I let it cool, and banged the mass out of the crucible.

I boiled this in a small amount of distilled water, but some parts would not dissolve, and remained in suspension. I neutralized to about pH 7-8, using "cleaning vinegar" (Walmart).

I don't have a working vacuum pump, so I reheated to about 60C, and gravity filtered, washing with a small amount of boiling water from a dropper.

I used 100% isopropanol (Duda) to crash out the product from the filtrate, and cooled to below 5C, then filtered again, washing with ice cold iPrOH.

I put this in a small beaker, which was in a larger one, the larger had a layer of Damprid (Walmart), covered with Saran wrap, and left it for the last week.

Today, it was dry, and I put it back into the crucible, and added .4 moles powdered charcoal (PyroChemSource), and heated to red hot, until the reaction (gas evolution) ended.

A small amount of DW to dissolve, and filter again to remove unreacted carbon.

My hope was to create KCN, so I tested the filtrate with Fe(II) sulfate (local pottery supply), mixed with Fe(III) chloride (Professor Fullwood, via Amazon).

SUCCESS! Prussian blue color strongly indicated.

I'm loving this OTC chemistry! I like that I can do this with almost nothing, at a very low cost. After working for years in professional laboratories, using expensive equipment, to be able to do this sort of stuff on my own is truly liberating!


[Edited on 1/5/17 by PirateDocBrown]

[Edited on 1/5/17 by PirateDocBrown]

[Edited on 1/5/17 by PirateDocBrown]

[Edited on 1/5/17 by PirateDocBrown]

[Edited on 1/5/17 by PirateDocBrown]

Tsjerk - 5-1-2017 at 03:47

Nice, do you have any idea about the purity? I guess it should form quite pure crystals when aloud to crystalize slowly.

Jon snow - 5-1-2017 at 07:16

Sorry but i can't understand how the reaction would work because the urea decomposed to ammonium cyanate which reacted with the potassium hydroxide yielding potassium cyanate but at this point i can't understand how the cyanate would be converted to cyanide whitout a reducing agent

Geocachmaster - 5-1-2017 at 07:20

Quote: Originally posted by Jon snow  
Sorry but i can't understand how the reaction would work because the urea decomposed to ammonium cyanate which reacted with the potassium hydroxide yielding potassium cyanate but at this point i can't understand how the cyanate would be converted to cyanide whitout a reducing agent


The powdered charcoal was the reducing agent

Jon snow - 5-1-2017 at 07:33

Quote: Originally posted by Geocachmaster  

The powdered charcoal was the reducing agent

Thank you very much
Can i ask why did you do the reaction in two part instead of mixing the three reagent and heating only once ?

WGTR - 5-1-2017 at 08:05

1. It's not necessary to have it there until the second part.
2. Adding charcoal increases the viscosity of the mix, making the first gas evolution messier.

[Edited on 1-5-2017 by WGTR]

Jon snow - 5-1-2017 at 09:57

I'll try in a few weeks and of i remember i'll post the yields

JJay - 6-1-2017 at 06:39

Nurdrage recently discussed his frustrations with using a similar procedure to produce pure sodium cyanide. He ended up purifying it by making Prussian blue and converting it back to cyanide.

PirateDocBrown - 6-1-2017 at 06:45

Yes, I can believe separation could be a bear, if you wanted a pure product. I have no analytical means of determining the fraction of conversion from cyanate to cyanide, yet.

JJay - 6-1-2017 at 07:52

I've been a little reluctant to play around with alkali cyanides. I had thought there there was a huge difference in the solubilities of cyanide and cyanate in ethanol, but I can see how it might be hard to achieve higher than 95% purity with a simple alcohol extraction / vacuum evaporation, and even that may be overly optimistic if you have to guess at the yield.

Edit: I just ran across this procedure for titrating cyanide while I was researching something else: http://www.kyoto-kem.com/en/pdf/industry/IronandSteel/ETIN-0...



[Edited on 6-1-2017 by JJay]

Dan Vizine - 6-1-2017 at 18:25

Quote: Originally posted by JJay  
Nurdrage recently discussed his frustrations with using a similar procedure to produce pure sodium cyanide. He ended up purifying it by making Prussian blue and converting it back to cyanide.


What's the motivation? Just to know you can do it or to obtain cyanides for preparative uses? If your answer is the latter, I highly suggest you look over the ferricyanide and acid route. It beats this route by every conceivable metric. It's a lab method, this is an industrial method. But, if you're just drawn to this route for interest, then, best of luck. I'm convinced that getting all of the variables just right is harder than it seems.

JJay - 6-1-2017 at 19:19

I agree that ferricyanides provide convenient routes for producing cyanides. I think that Prussian blue is somewhat easier to purify, especially if extremely high purity is required.

Nurdrage's motivation was to prepare para-chlorophenyl acetonitrile as part of his quest to make pyrimethamine from OTC compounds. I am personally not equipped at this time to prepare any toxic cyanides, but they do have many uses if you are prepared to handle them.

gdflp - 6-1-2017 at 19:44

Quote: Originally posted by Dan Vizine  

What's the motivation? Just to know you can do it or to obtain cyanides for preparative uses? If your answer is the latter, I highly suggest you look over the ferricyanide and acid route. It beats this route by every conceivable metric. It's a lab method, this is an industrial method. But, if you're just drawn to this route for interest, then, best of luck. I'm convinced that getting all of the variables just right is harder than it seems.

I think that one of the main draws of the cyanate reduction methods is the avoidance of working with HCN. Though the acid method is undoubtedly superior, HCN is something that many would not be comfortable working with without a fume hood or at the very least ideal environmental conditions(aka wind), so I can see the motivation.

At the same time, if the workup of the product from the cyanate reduction is a substantially longer process, one could argue that the greater handling time increases the likelihood of an accidental exposure occurring.

[Edited on 1-7-2017 by gdflp]

Dan Vizine - 7-1-2017 at 15:41

Actually, I've seen that the longer isolation period frequently causes the procedure to become safer. For many home labs, this affords time for hydrolysis and the longer it takes, the less cyanide remains.

Point taken on the safety aspects. And HCN is an endothermic compound, something that often gets ignored.

The acid method, followed by subsequent addition to base and dilution with alcohol, is a perfect way to make a medium to effect SN2 displacements with cyanide ions. The "dry" method is safer, I'll agree there. But a certain proportion of attempts by members will fail to yield much, because our understanding of the proper process parameters, and those of our attempts, are poorly understood.

[Edited on 7-1-2017 by Dan Vizine]

Magpie - 7-1-2017 at 16:58

I agree that the carbothermic method can be finicky, and gives an impure product (cyanate). I did not attempt to purify mine when I used it but just compensated by using sufficient moles of the CN. This may not be possible for all reactions, however.