Preparation of Hydrogen Cyanide

Hydrogen cyanide is extremely toxic. Breathing even small amounts can kill you. The preparation of HCN must be done in a good fume hood or in a very well ventilated area outside. Make sure that the wind never blows any vapours into your face. Prussic acid is not suitable as a homicidal poison. It's super easy to detect and you're immediately convicted as the killer. Please don't poison yourself with it either. Death can be very painful. Nobody wants to die like that. Please: search for professional help, if you think about killing yourself.


Procedure: I added 300 grams of 50 % sulfuric acid into a 1 liter erlenmeyer flask with stir bar. A Liebig condenser and a receiving flask (ice cooled) were attached. Under fast stirring, I added 250 grams of powdered potassium ferrocyanide trihydrate.



A bluish white slurry formed.



I switched on the heating and after some minutes of stirring the first liquid condensed, but it wasn't very warm. The liquid is a mixture of hydrogen cyanide with a bit of water. When less hydrogen cyanide condensed, the temperature was raised from time to time in small steps. When the drops didn't wet the glass anymore, the majority of the hydrogen cyanide is driven off and the condensing liquid consists mainly of water.



At this point, stirring and heating were switched off. I received about 80 milliliters of HCN, contaminated with traces of sulfuric acid and some water.



The residue in the erlenmeyer flask is a yellowish slurry with a blue surface, containing half of the cyanide.



This can be recycled (explained further below). The impure hydrogen cyanide had to be dried. I combined two batches of HCN (from this 250 g ferrocyanide + from another 80 g). I used anhydrous calcium chloride, made by heating CaCl₂ dihydrate. CaCl₂ was added in small portions and the flask was swirled around. At the bottom, a layer of aqueous saturated CaCl₂ solution formed and the supernant became cloudy.



I added more CaCl₂ until the supernant was clear again, and sucked up the CaCl₂ solution with a pipette. This was discarded. To stabilize the anhydrous HCN, one can use a tiny amount of 85 % phosphoric acid. I added a small drop (~30 mg) into a washing bottle.



The HCN was again distilled directly from the flask, still containing the calcium chloride, into the ice-cooled receiving flask (washing bottle). I also added some peaces of anhydrous calcium chloride into the condenser. The HCN boiled at about 25 °C (in a water bath).



The temperature was rised slowly. When no more liquid condensed, the operation was done (at about 40-50 °C of the water bath). The residue was still wet and contained some hydrogen cyanide.



Weight of the anhydrous HCN from 330 grams of ferrocyanide: 58 grams.
Yield: 92 % (based on the reaction scheme)

The density was measured with a volumetrical flask and an electronic scale.
Measured density: 0.6924 g/ml
Theoretical density: 0.6876 g/ml

I filled all of the hydrogen cyanide in ampoules and sealed them with a bunsen burner.



After more than one year, the HCN in all of them is still crystal clear. I also made some unstabilised HCN (without phosphoric acid). After one day, they looked yellowish (left ampoule):



After one year, the unstabilised HCN formed a brown solid (left ampoule).





So even 0.05 % of phosphoric acid prevents this polymerisation reaction for more than one year (according to the literature: even much longer).

Recycling of the side product: The residue from the preparation is so called Everitt's Salt. To convert this back to ferrocyanide, the erlenmeyer flask was left open, so that the salt could be oxidised by air. I occasionally swirled the flask. When the whole mixture was dark blue, the oxidation was complete.



I filtered and dried the blue compound.



The filtrate was neutralised with some soda and flushed down the drain. The blue compound was added to a soda solution, containing about 45 grams of soda in 600 ml water.



Under stirring, the whole mixture was heated and more soda added in small portions until the colour changed to brown.



While still warm, I filtered it.



The filtrate was evaporated somewhat, cooled, and the yellow crystals of ferrocyanide collected.



The rest of the filtrate was evaporated to dryness and the residue was combined with the crystals. The stuff in the filter is iron oxide. I dried, weighted and discarded it.



Yield: 121 grams of Na/K ferrocyanide hydrate (less than expected, I don't know why)
Weight of the iron oxide: 40 grams (more than expected, I don't know why)

I successfully used the recycled salt in another batch.


Explanation:

Potassium ferrocyanide reacts with sulfuric acid to form hydrogen cyanide, potassium hydrogen sulfate and a complex salt, called Everitt's Salt.

2 K₄[Fe(CN)₆] + 6 H₂SO₄ → 6 HCN + 6 KHSO₄ + K₂Fe[Fe(CN)₆]

As you can see, only half of the cyanide is converted to hydrogen cyanide. With this method, that's the maximum yield. A patent claimes that you can get 100 % yield by using copper chloride as a catalyst.

The Everitt's Salt can be recycled in two steps. First the oxidation by air:

4 K₂Fe[Fe(CN)₆] + 4 KHSO₄ + O₂ → 4 K[Fe₂(CN)₆] + 4 K₂SO₄ + 2 H₂O

The product is called Prussian Blue. This is a pigment, from which HCN was first made in early days. That's why HCN is also called "Prussic Acid".

To convert Prussian Blue to Ferrocyanide, it can be reacted with soda:

4 K[Fe₂(CN)₆] + 6 Na₂CO₃ → K₄(Fe(CN)₆) + 3 Na₄(Fe(CN)₆) + 6 CO₂ + 2 Fe₂O₃

The product is K/Na ferrocyanide in the molar ration 1:3. If you use potash instead of soda, you will get pure potassium ferrocyanide.


Sources:

Preparation of anhydrous HCN:

Trautwein: Darstellung der trocknen Blausäure (a). In: Gmelin, L. (1848) Handbuch der organischen Chemie: Organische Chemie im Allgemeinen. - Organische Verbindungen mit 2 und 4 Atomen Kohlenstoff. 4. Auflage, Heidelberg, Winter, p. 314.

Stabilisation of HCN with H₃PO₄:

Walker (1938) Stabilization of liquid hydrocyanic acid. Patent US2194370A.

Reaction schemes:

Kraft (2014). On the History of Prussian Blue: Thomas Everitt (1805-1845) and Everitts Salt. Bulletin for the history of chemistry / Division of the History of Chemistry of the American Chemical Society. 39. p. 18-25.

Czelechowsky, J. R. (1841) Chemisches Wörterbuch zum Gebrauche Ärzte, Pharmaceuten, etc, Carl Gerold, p. 144.

Catalysed HCN production:

Dewrance & Williams (1909) Verfahren zur Darstellung von Alkalicyanid. Kaiserliche Patentschrift Nr. 224950.

This is just a q&d description. I'm also making a video about it with more details and better footage....



....and some experiments with HCN and so on. But I don't know, where to upload it.

That photo is beautiful and horrifying at the same time

It sounds very, very oddly

*E.Williams, J. of the Soc. of Chem. Ind., 1912, pages 468-471


[Edited on 23-1-2024 by kmno4]

Quote: Originally posted by unionised

Everyone knows that HCN is very toxic. Not many people realise it's explosive. https://www.icheme.org/media/8681/paper-52-hazards-25.pdf Sealing explosive, toxic chemicals in glass ampoules is... not recommended.

Quote: Originally posted by woelen

Do you have plans for further interesting experiments with HCN? It sounds like a really interesting, albeit it somewhat scary, chemical. Only something for people who really know what they are doing and know the risks of working with it.

Quote: Originally posted by woelen

Does it also stabilize aqueous solutions of HCN, prepared from NaCN or KCN and some acid?

Quote: Originally posted by kmno4

Much better solution is using small amount of CuCl "catalyst" (see 'cyanide thread'). It distroys all ferrocyanide, via CuCN formation and destruction*.

Quote: Originally posted by kmno4

Quote: Please: search for professional help, if you think about killing yourself It sounds very, very oddly

Very nice work! I love these ampuoles
It is interesting to see that adenine is formed after polymerazion of HCN

Quote: Originally posted by ItalianChemist

Very nice work! I love these ampuoles It is interesting to see that adenine is formed after polymerazion of HCN

Yeah, I found that interesting too! Good idea for some sci-fi or fantasy story on the planet with HCN oceans and HCN based life .

Properties of Hydrogen Cyanide

HCN has a low viscosity. When you shake it, small "waves" can be seen:


When frozen in a fridge, it solidifies to an ice-like solid:


During melting, the solid sinks to the buttom (unlike ice in water):


It's very volatile. Boiling point: ~ 26 °C. When some of it is poured on a warm surface, it vaporises rapidly:

Note: this should not be repeated. My hand was warm and dry. I blew hard to let the HCN evaporate within 3-5 seconds. Under other circumstances, this could be dangerous.

Some old textbooks say, that hydrogen cyanide can partially freeze during evaporation due to the cooling effect. I slowly let flow some of it out of a pipette on a cold day (+ 10 °C) with high air humidity. An "icicle" formed. I doubt that this is solid HCN. I rather think it's frozen water vapour. On the other hand, the water should dissolve in the liquid HCN, so this is a bit strange:




HCN is said to burn with a bluish flame. Unfortunately, this wasn't the case in my experiment. It looked like burning ethanol:


HCN is a very weak acid. It doesn't react with soda:

From left to right: dilute H₂SO₄ (reaction already complete), dilute acetic acid, pure HCN

The anhydrous liquid doesn't even react with magnesium powder:

From left to right: dilute H₂SO₄ (reaction already complete), dilute acetic acid, pure HCN

But if some water is added, it reacts violently with it (right test tube):


A pH test paper confirms that HCN is a weak acid. The paper doesn't change its colour:

left: H₂SO₄ (10 %), middle: acetic acid (10 %), right: HCN (~ 50 %)

Nevertheless, HCN is of course dangerous due to it's toxicity. I caught a mosquito* and tested this. After 10 seconds, it was dead:






*I love animals, but I would have killed this mosquito anyway. So I find it ethically legitimate so sacrifice it for this experiment.

Further experiments (in planning):
- qualitative HCN test (paper)
- pur HCN into ethanolic KOH solution to show the formation of a salt

When this is done, I can finish the video and upload it somewhere.

That demo with your finger, , I love it.

Quote: Originally posted by Pok

Under other circumstances, this could be dangerous.

Quote: Originally posted by Bedlasky

Very interesting! I am looking forward to that video. I found years ago very interesting document about chemistry of liquid HCN and saved it. Look at it, maybe you find some inspiration for interesting experiments with HCN. [Edited on 23-1-2024 by Bedlasky]

Sorry, I noticed that I didn't post link to that paper . Here it is:

https://sci-hub.se/https://www.sciencedirect.com/science/art...

There are mentioned some colorful transition metal complexes of HCN in table 5 and 6.

@Fery: You did some rough experiments when you were in high school! I remember one of our Forum members, he was a tenager, he was not even 15 years old, died trying to make HCN! I think his nickname was Myfanvy2013, or something like that...Glad you're alive

Beautiful and very interesting set of experiments with the HCN. The experiment with the liquid evaporating on your finger must be quite thrilling . I would be quite nervous about this. A dose of 50 mg can kill an adult healthy person!

Quote: Originally posted by Admagistr

@Fery: You did some rough experiments when you were in high school! I remember one of our Forum members, he was a tenager, he was not even 15 years old, died trying to make HCN! I think his nickname was Myfanvy2013, or something like that...Glad you're alive

Quote: Originally posted by Fery

Quote: Originally posted by Admagistr   @Fery: You did some rough experiments when you were in high school! I remember one of our Forum members, he was a tenager, he was not even 15 years old, died trying to make HCN! I think his nickname was Myfanvy2013, or something like that...Glad you're alive The young last classes of elementary school aged guy who died used the nick Virius, he made a lot of acetone peroxide and we knew only thanks to his friend with the nick mistr.vodic who wrote us what happened (mistr.vodic was only the tester of the product and the poor Virius only the producer). It happened in February 2006. [Edited on 25-1-2024 by Fery]

Quote: Originally posted by Admagistr

I found it: https://www.sciencemadness.org/whisper/viewthread.php?tid=13... In another thread, which I can't find right now, he is listed in our list of members who died in their experiments. It said he was doing experiments with HCN. His nickname was myfanwy94 and he was about 15 years old.

Quote: Originally posted by Bedlasky

There are mentioned some colorful transition metal complexes of HCN in table 5 and 6.

Quote: Originally posted by Fery

Antidotes are inhaling amyl nitrite + O2, intravenous infusion of NaNO2 and Na2S2O3, vitamin B12 and many more.

Stepan Bandera is a hero in Ukraine, it is true.
But in reality, he was ultra-nationalist collaborating with Nazi Germany and was responsible for ethnic cleansing. Ukrainians love him, but unfortunately, for me he is (more or less) a bandit. By the way of Germany in II WW.
They made large use of HCN for mass murderes in their Death Camps. Of cource, it was Zyklon B, produced escpecially for this purpose by German industry. Yes, genocide on industrial scale. It is very sad, especially when young Germans say that it was not Germans, it was some Nazists.....
It is called "relativization of history".
BTW.
Most of murderers from Death Camp were not Germans, but Austrians. Also Adolf H. was an Austrian.
Today, Austrians are very angry when somebody gives these facts and wish that all other people forget about it


[Edited on 27-1-2024 by kmno4]

Quote: Originally posted by kmno4

Stepan Bandera is a hero in Ukraine, it is true. But in reality, he was ultra-nationalist collaborating with Nazi Germany and was responsible for ethnic cleansing. Ukrainians love him, but unfortunately, for me he is (more or less) a bandit. By the way of Germany in II WW. They made large use of HCN for mass murderes in their Death Camps. Of cource, it was Zyklon B, produced escpecially for this purpose by German industry. Yes, genocide on industrial scale. It is very sad, especially when young Germans say that it was not Germans, it was some Nazists..... It is called "relativization of history". BTW. Most of murderers from Death Camp were not Germans, but Austrians. Also Adolf H. was an Austrian. Today, Austrians are very angry when somebody gives these facts and wish that all other people forget about it I read that during WWII the Ukrainians initially welcomed the Germans with the hope that they would liberate them from the Russians.Maybe the Bandera felt the same way, that the Germans would liberate them from the Russians? Yes the HCN was massively abused to murder defenceless and innocent people especially Jews, killing millions of them!!! [Edited on 27-1-2024 by Admagistr]

Quote: Originally posted by Admagistr

I read that during WWII the Ukrainians initially welcomed the Germans with the hope that they would liberate them from the Russians.Maybe the Bandera felt the same way, that the Germans would liberate them from the Russians?

Quote: Originally posted by Pok

As a German I have to say that it's absolutely true that Germans murdered millions of people, mostly Jews, with HCN. Sure, only a few murered with HCN, but practically all the others murdered by guns or making weapons, propaganda, etc. If we talk about history and politics, this must of course be said and not hidden. In the concentration camps they murdered in an "industrial" or "professional" way so that the murders didn't even had to fear poisoning themselves. As far as I know, they didn't use antidotes and not a single murderer was poisoned. I took the case of Bandera, because it's the only documentad case I know of in which antidotes have been used.

Quote: Originally posted by Fery

Great! Keep up good work. Also perfect experiment with the mosquito, so everyone could imagine how quickly the HCN causes its lethal effect. There was a forum in my country, but is already dead. 20 y ago a member with nick Cyano posted there his experiments with HCN distillation in his cellar and that all the rats there died (luckily he survived). Antidotes are inhaling amyl nitrite + O2, intravenous infusion of NaNO2 and Na2S2O3, vitamin B12 and many more. edit: I found his post in an archive in my harddisk, I like to save interesting things as they can disappear in the future, the forum had a name PXD: Quote: od: cyano 01.07.2003, 02:44:32 Též jsem dělal kapalný kyanovodík-- ale podcenil jsem délku chladiče a teplotu chladicí kapaliny-- byla 17 st, je zde nutná teplota kolem nuly. Došlo k explozi aparatury--nic se nestalo, pokus jsem dělěl ve sklepě rod. domku-- ale vše je k něčemu dobré-- pochcípali potkani--našl jsem jich další den asi 5-7 , nevím , bylo to před lety, když jsem chodil na gympl. here the translation into eng: I also did liquid hydrogen cyanide - but I underestimated the length of the condenser and the temperature of the cooling liquid - it was 17 C, the required temperature is around zero. There was an explosion of the apparatus - nothing happened, I was doing the experiment in the basement of the family house - but everything is good for something - the rats perished - I found about 5-7 of them the next day, I don't know, it was years ago when I studied Gymnasium (Gymnazium in my country is analogy of high school or grammar school). [Edited on 25-1-2024 by Fery]

Basement? without fume hood