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Author: Subject: Preparation of cyanides
SimpleChemist-238
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[*] posted on 19-7-2015 at 17:39


Quote: Originally posted by madscientist  
Alternative method of production, by madscientist PREPARATION OF HYDROGEN CYANIDE FROM POTASSIUM PERMANGANATE, METHANOL, SULFURIC ACID, AQUEOUS AMMONIA, AND POTASSIUM HYDROXIDE

Notes:
-all potassium chemicals can be substituted with their sodium parallel, if mass ratios have been properly adjusted
-it is highly recommended that nbk2000 dismiss all described and inferred safety precautions

PREPARATION OF POTASSIUM FORMATE (HCOOK) AND MANGANESE FORMATE (Mn(HCOO)2):
126.4 grams of potassium permanganate (KMnO4) is added to 32 grams (approximately 40.2mL) of concentrated methanol (CH3OH):

10(CH3OH) + 8(KMnO4) --} 10(HCOOH) + 10(H2O) + 8(MnO) + 4(K2O)
10(HCOOH) + 10(H2O) + 8(MnO) + 4(K2O) --} 10(HCOOH) + 8(KOH) + 8(MnO) + 6(H2O)
10(HCOOH) + 8(KOH) + 8(MnO) + 6(H2O) --} 8(HCOOK) + 2(HCOOH) + 8(MnO) + 14(H2O)
8(HCOOK) + 2(HCOOH) + 8(MnO) + 14(H2O) --} 8(HCOOK) + Mn(HCOO)2 + 7(MnO) + 15(H2O)

Mixture is then filtered to remove the manganese oxide (MnO), and the filtered solution is then allowed to evaporate. What is left is a ratio of eight : one of potassium formate : manganese formate. The remaining crystals should weight approximately 81.77 grams if you acheived a 100% yield.


PREPARATION OF FORMIC ACID (HCOOH):
The mixture of potassium formate and manganese formate is added to concentrated sulfuric acid. That is, all 81.77 grams of the potassium formate and manganese formate crystals are added to 49 grams (26.5mL) of concentrated sulfuric acid. The remaining mixture is heated, and the vapors, which are composed of formic acid, are condensed. WARNING! FORMIC ACID IS TOXIC. PURE FORMIC ACID IS A COLORLESS FUMING LIQUID WITH A PUNGENT ODOUR; IT IRRITATES THE MUCOUS MEMBRANES AND BLISTERS THE SKIN.

8(HCOOK) + Mn(HCOO)2 + 5(H2SO4) --} 10(HCOOH) + 4(K2SO4) + MnSO4]

I thought that this over oxidized the potassium formate to potassium carbonate and water?






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[*] posted on 7-8-2015 at 20:23


Quote: Originally posted by ChemPlayer_  

This also seems to be a much faster and cleaner process than heating ferrocyanide either on its own or by heating with an alkali carbonate, and doesn't require a very silly high temperature. There's no carbonate residue in the product.


I thought I'd try the potassium ferrocyanide : sodium carbonate mix (8:2). I had to get it above 450C to melt, and even then the iron didn't clump but pretty much stayed suspended so it required extra filtration after dissolving. What is the carbonate residue left in this reaction?

Also above 500C I was getting bubbling in the crucible's hot points. Does some gas need to be cooked off?
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[*] posted on 8-8-2015 at 07:04


@lysander; What did you heat together? Did you use hydrated K ferrocyanide (trihydrate) and anhydrous sodium carbonate?

Then consider the likely reactions:

K<sub>4</sub>(CN)<sub>6</sub>Fe + Na<sub>2</sub>CO<sub>3</sub> &rarr; 4KCN + NaCN + NaCNO + CO<sub>2</sub> + Fe

K<sub>4</sub>(CN)<sub>6</sub>Fe &rarr; 4KCN + 2C + Fe + 2N

so it seem likely that carbon dioxide will be evolved when sodium carbonate is used. These equations are modifications of the ones given by Williams in his book (from the forum library). All of these equations are rather theoretical since I can also tell you from my own experience that carbon monoxide is also produced and that the yield of cyanide is only about 70% of that present in the original ferrocyanide. Using less than the theoretical amount of sodium carbonate results in much, difficult to filter, carbon being formed.
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[*] posted on 8-8-2015 at 07:30


Was using anhydrous K-ferrocyanide. Just realized I didn't dehydrate the Na-carbonate, so indeed it must be the carbon that was suspended!

I couldn't find equations for this reaction; thanks for the reference!

I assume the excess O will almost always bind to create cyanates before it binds to the Fe?

I was trying this because I recall this being a preferred industrial method of producing cyan-salt. It's supposed to produce iron carbide as the precipitate, but now I'm wondering how this could possibly work with all that excess oxygen creating cyanates.
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[*] posted on 8-8-2015 at 15:10


Well I ran it twice more today with anhydrous reagents. The second time I added a slight excess of Na-carbonate. Both times it came out with a lot of suspended carbon. I'm suspecting that temperature has to be more tightly controlled, perhaps along with heating and mixing rates. Also I'm probably not cooking it long enough: Half an hour after melting it still bubbles, but I ended it both times at that point.

Even so it appears reasonably practical: One pass of the solution through a cellulose filter removes the carbon. The solution also passes the acid test.

What other assays are easy to run to determine proportion of cyanides to cyanates, and K to Na, in the product?

[Edited on 8-8-2015 by lysander]
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[*] posted on 9-8-2015 at 22:21
Stoichiometry


Quote: Originally posted by Boffis  
These equations are modifications of the ones given by Williams in his book (from the forum library). All of these equations are rather theoretical since I can also tell you from my own experience that carbon monoxide is also produced and that the yield of cyanide is only about 70% of that present in the original ferrocyanide. Using less than the theoretical amount of sodium carbonate results in much, difficult to filter, carbon being formed.


I still haven't been given access to the library. What's the Williams book that details these?

And now I'm second-guessing the stoichiometry: is it supposed to be equal mols K-ferrocyanide and Na-carbonate, or 4:1 mass? Because I was using the mass ratio, but that gives 15% more mols of the K-ferrocyanide. To get equal mols the mass ratio should be 7:2 not 8:2! Unless there reaction is more complicated?
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[*] posted on 9-8-2015 at 23:09


lysander the library can be accessed at http://library.sciencemadness.org/library/index.html. It is available to everybody. The references section of the forum where articles are requested and shared is restricted access, however.
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[*] posted on 11-8-2015 at 08:30


IMHO, You are making this unnecessarily complicated. Add H2SO4 to a concentrated soln of potassium ferricayanide containing a few grams of copper shavings*. Stir mechanically with heat in a larger than usual flask. At times the suspension foams badly. A few drops of silicone anti-foaming reagent helps. Circulate 0 C degree H20 through condenser. Put a few drops of H2SO4 in the receiver flask to lessen the explosive decomposition potential of the endothermic HCN product. Can be stored weeks in a flask with greased stopper in freezer (probably much longer). All ingredients are strictly OTC.

*Supposed to catalytically release more of the HCN according to an old patent that I have.

Exact experimental details are found in the much longer HCN thread located elsewhere in this forum under my user name.





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[*] posted on 11-8-2015 at 11:43


Dan: I assume you mean this thread. (Which, BTW, contains this helpful link to assays I had been looking for.)

I'm trying to create cyan-salts, not HCN.

[Edited on 11-8-2015 by lysander]
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[*] posted on 11-8-2015 at 14:24


Greetings, mad scientists!
I want to share with you my experience with the preparation of KCN. First of all, I have visited this forum for some time(a couple of years maybe), but never actually posted anything. It's a very good place for sharing exotic information which a fellow home or even professional chemist sometime needs to fulfil his needs. Thank you all for keeping the forum alive.
So, let's begin with some background first. I'm last year bachelor student, currently working in a copper metal refining company. I've been using cyanides(esp KCN) in my home lab for refining gold metal from computer chips' pins, so I am aware of the potential uses and hazards of the chemical. I usually get KCN from trusted chemical companies, but if you’re not certified chemist, you can try make it yourself. The driven force of my synthesis was just pure interest and exploring the science of it. I suggest anyone who tries to synthesize any sort of cyanide to be thorough careful and to understand what is needed, why is needed, how it has to be done and what are the precautions to be taken in advance.

My experiment is done under custom made fume hood. If you are unsure of yours, do the experiment outside.
Used chemicals:
K4[Fe(CN)6].3H2O - technical grade
85% H3PO4 - technical grade
KOH - technical grade
Absolute ethanol(99.8%) - analytical grade
Bidistilled water(custom distilled)
Used apparatus:
Distillation flask with a thermometer
Non-mechanical magnetic stirrer with a teflon stir bar
Liebig's condenser
Wash bottle with a cut tail to collect the distillate

15 g of K4[Fe(CN)6].3H2O is partly dissolved in 30 ml of bistilled water. I'm using the water to cut away potential foaming during distillation(a part of the salt remains undissolved, don't mind it). A teflon magnetic stir bar and 3-4 crystals of pumice are added and the solution is heated up to 60 C. Then 28 ml of 85% H3PO4 is added and the distillation flask is connected to a Liebig's condenser and a wash bottle with a cut tail to collect the distillate(I'll talk about the tail later). The wash bottle contains 100 ml saturated solution of KOH in absolute methanol. To do this you just simply crush KOH in a pestle and mortar, add it to the ethanol, stir, add more KOH until undissolved KOH appears on the bottom(I added around 25-30 g of KOH). Then you filter the solution. The filtrate is the saturated solution which is then added to the wash bottle.
When the apparatus is all properly assembled, a green to blue change to the color(from yellowish) is almost instantly visible. That's due to the formation of Fe3(PO4)2 and K2Fe(CN)6. K3PO4 is also a product but it's dissolved in the water, so it's not visible. When the temperature of the gas phase reach 78-85 C, first drops of distillate is obtained. When they get in contact with the alcoholic solution of the KOH, the distilled HCN react with the KOH and KCN is instantly crystalized. The instant crystallisation is possible because KCN has very low solubility in ethanol. So you get a product with lowest possible losses. When the temperature of the gas phase in the distillation flask start to go up, you are finished. It took 35-40 mins in my experiment. Mind that my stirrer is somewhat powerful, it can take more.
The slurry in the wash bottle is then filtered through a Buhner and the product is collected in petri. The product is transferred to a vacuum exicator with KOH used for a drying agent. Yield is weighted after a couple of days. In my case I got 10.48 g KCN. After calculation that means that 77.39% of the CN- ions are obtained as KCN. Possible losses are from evaporated HCN through the distillation of by polymerization and what not.
The product is tested qualitative with AgNO3 solution.Wwhite sediment appears. The sediment is compared with the sediment from KCN(that I got from Aldrich) solution. It is the same. I tested the pH from the exact amouth of salts and got similar results(difference only in 0.0x). I am not insisting on the purity of the product, titration was not made, that was not my goal. This is just raw data.
I promised that I'll talk about the wash bottle. I have one with a cut tail and I prefer using it when I make distillations. With a tail that is immersed in the solution reflux can occur and some of the solution used as a receiver can be sucked in the condencer. And you DO NOT want that to happen. The increased internal pressure can damage your apparatus, break it and cause leaks. So I recommend receiving the distillate through freely falling drops. Bubbling can be dangerous and since the nature of the HCN(even if you distillate other gases it's the same) you don't want anything bad to happen. So better safety than higher yield. Trust me on this one.
You’ll get residuum after the whole process. The distillation flask’s residuum can be neutralized with H2O2 or NaClO(preferred and easily to get). The alcoholic solution can contain HCN/KCN too so it’s better to neutralize it too. Flushing after that is possible. Read your country’s procedures for disposing chemical waste. Still if you don’t care about this stuff, please at least burry the residuum in a glass jar with a good cap.
Please, read some information about the used chemicals in advance before jumping to the synthesis. HCN is highly toxic. Take all the precautions needed. Use the above synthesis method at your own risk.

PS: Sorry for my bad Englando.

[Edited on 11-8-2015 by jokovi4]
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[*] posted on 11-8-2015 at 17:50


Interesting: There are plenty of ways to generate HCN. You get KCN by condensing it into a solution of KOH and ethanol. But isn't water the other product of that reaction, so don't you end up with water hydrating the KCN as it's formed? Or does deliquescent KCN still precipitate out of the saturated ethanol?
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[*] posted on 11-8-2015 at 19:18


Yes, freshly precipitated alkali salts contain water and alcohol. Careful drying procedures are very important to avoid hydrolysis. And, yes, I don't belong in this thread....

Sorry.





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[*] posted on 11-8-2015 at 20:23


Yeah, I've learned the hard way a lot of methods to not use in drying cyan-salts:

  1. Heating above 100C. Not only do they splatter, but I also imagine they oxidize if the atmosphere is not kept inert.
  2. Heating at less than 100C. Not sure what the reaction is, but I got tons of ammonia and the salts started turning yellow. (There was some aluminum involved though :o)
  3. Drying on pretty much any metal. (Why is it that we can cook them in steel but not glass, but we can store them on glass but not most metals?)
  4. Putting in an ambient dessicater (circulating dry air): This will remove excess moisture but can't seem to get them past deliquescense.

The old literature seems to suggest that one should first press out excess water using absorbent cellulose paper, and then vacuum dry them.

I'm also wondering if freeze-drying (i.e., freezing in combination with the vacuum) would be efficient, since AFAIK vacuum alone can supposedly take days.

It would be convenient to have a dry supply, which I assume in a sealed container has a good shelf-life, so one doesn't have to make the salts every time one needs them.

[Edited on 12-8-2015 by lysander]
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[*] posted on 11-8-2015 at 20:33


Freeze drying ought to be ideal if you have aqueous salts. I remember being dubious about the process at first, but if you have a really good vacuum at a high throughput, it amazes me. It's a viable process! It was very facile as long as you kept the LN2 traps topped off.

I would precede this by collecting the salt in a funnel with a good rubber dam or by the classical pressing method.





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[*] posted on 11-8-2015 at 23:36


lysander, yes it still precipites. Mind that the water is really in low quantity, so it does not dilute the alchoholic solution to the point that all the KCN get hydrolized. Yes, it still do it though. That's why I mentioned in the end that the alcholohic solution still can contain HCN exactly due to the hydrolisis. You get good yield and solid phase nonetheless.
And yes, as you all mentioned, drying is very crucial. It seems that my method is working. I didn't point out that I use cellulose paper at the bottom of the petri and then put it in the exicator. It is just a habit and I've been doing this since I started to do chemistry, so I forgot to mention it- I thought everyone is doing it the same way :D.
You could try good ol' fashioned furnace pressing drying at room temperature. But I don't feel the need to make my life hard and I just use vacuum drying in exicator instead.
The product is stored in custom designed dish with a very tiny whole in it, where I suck up all the air possible after closing it. Then I use parafilm to pack up the thing and store it somewhere where people doesn't get access to.

PS: One more thing: after drying the water with KOH, you can use CaO, anhydrous K2CO3 or anhydrous CaSO4 to dry the ethanol remained due to filtration. On a teoritical stand of view it is a good way to get really dry KCN.

[Edited on 12-8-2015 by jokovi4]
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[*] posted on 12-8-2015 at 05:31


Quote: Originally posted by Dan Vizine  
It was very facile as long as you kept the LN2 traps topped off.


You're freeze drying with LN2?! I assumed just putting the vacuum vessel in an ice bath, maybe -20C, would be adequate for deliquescent salts. Maybe stepping down to dry ice at the limit? (I don't have LN2 but I guess dousing the salts with that before closing and turning on the vacuum would be faster and easier!)
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[*] posted on 13-8-2015 at 18:15


Quote: Originally posted by Dan Vizine  
Add H2SO4 to a concentrated soln of potassium ferricayanide containing a few grams of copper shavings*. Stir mechanically with heat in a larger than usual flask. At times the suspension foams badly. A few drops of silicone anti-foaming reagent helps. Circulate 0 C degree H20 through condenser. Put a few drops of H2SO4 in the receiver flask to lessen the explosive decomposition potential of the endothermic HCN product.


Dan: I was thinking of giving this a try, but there's confusion from both this and the other mention of this recipe. Here you say ferricyanide, there you say ferrocyanide. What molarity sulfuric acid (on both ends)? What temperature does the reaction run at? Some reaction equations would be a nice bonus! Thanks!
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[*] posted on 14-8-2015 at 11:00


<iframe sandbox width="560" height="315" src="https://www.youtube.com/embed/VUeooyhD5Xk" frameborder="0" allowfullscreen></iframe>



Kept you waiting, huh?

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[*] posted on 14-8-2015 at 12:10


Quote: Originally posted by lysander  
Quote: Originally posted by Dan Vizine  
It was very facile as long as you kept the LN2 traps topped off.


You're freeze drying with LN2?! I assumed just putting the vacuum vessel in an ice bath, maybe -20C, would be adequate for deliquescent salts. Maybe stepping down to dry ice at the limit? (I don't have LN2 but I guess dousing the salts with that before closing and turning on the vacuum would be faster and easier!)

I wasn't freeze-drying a sample at LN2 temps. LN2 trapped the water vapor.
This was a simple setup. A flask with a frozen aqueous solution was connected to a trap cooled in LN2 which led to the vacuum pump. Dry ice and acetone would also be fine. As I recall, the ice stayed frozen at room temp or just slightly below because of the evaporative cooling.

[Edited on 15-8-2015 by Dan Vizine]





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[*] posted on 14-8-2015 at 13:37


I see there is quite much discussion on that topic. I don't want to read through all 27 pages,
at least not tonight.

So I need quite a bit of cyanide for my research. Too much I guess to really make it. At least
I don't want to destill that amounts of gaseous HCN. So for my work on d-metal cyanides I
simply purchased a bottle so I never really made it myself.

However a close friend of mine who works in a small laboratory once needed some KCN for
an experiment. And they didn't have any in the lab. So he and his team decided to test
a simple method and made some. He once told me but I'm not really sure if I remember that
correctely. I could ask him however.

So they set up a simple destillation setup and filled their flask with some Ferricyanide.
They then added sulphuric acid which does not automatically start the reaction as he says.
But if you start to heat it you can controll the amount of HCN coming off quite well.
The destilled it into a beaker with KOH solution, quite saturated I guess. You have to calculate how
much you need so there is as little KOH left as possible in the end. And then they simply added
a large amount of Ethanol. Cyanides are really poorely soluble in Ethanol. Methanol works quite
good, I use that to stabilize stuff like Cu(II)Cyanide at low temperatures but Ethanol just works
perfectely. He said the second they added Ethanol it was all full with white precipitate.
And then they filtered it and washed it with ethanol. It was pure enough to work with it.

So I guess this method is the esiest and you can do this with OTC chemicals.
I really don't recommend that. And just warn you to not do it.
That is just what I have been told. I never tried it. It should work quite well
but it's still extremely dangerous to destill large amounts of Cyanides.
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[*] posted on 14-8-2015 at 15:12


Quote: Originally posted by fluorescence  
So I need quite a bit of cyanide for my research. Too much I guess to really make it. At least
I don't want to destill that amounts of gaseous HCN. So for my work on d-metal cyanides I
simply purchased a bottle so I never really made it myself.


You can buy HCN? Where? I can't imagine any common carrier, or anybody sane, would transport that!
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[*] posted on 14-8-2015 at 16:41


Quote: Originally posted by lysander  
Quote: Originally posted by Dan Vizine  
Add H2SO4 to a concentrated soln of potassium ferricayanide containing a few grams of copper shavings*. Stir mechanically with heat in a larger than usual flask. At times the suspension foams badly. A few drops of silicone anti-foaming reagent helps. Circulate 0 C degree H20 through condenser. Put a few drops of H2SO4 in the receiver flask to lessen the explosive decomposition potential of the endothermic HCN product.


Dan: I was thinking of giving this a try, but there's confusion from both this and the other mention of this recipe. Here you say ferricyanide, there you say ferrocyanide. What molarity sulfuric acid (on both ends)? What temperature does the reaction run at? Some reaction equations would be a nice bonus! Thanks!


The equations are more complicated than you might imagine.

Notice my earlier comment "Exact experimental details are found in the much longer HCN thread located elsewhere in this forum under my user name."

EVERY time I led gaseous or condensed HCN directly into base soln, it turned brown-black. Conversely, every time I collected the liquid and then dripped it into base solution, it only acquired a faint color.

I didn't isolate any KCN solid. The aqueous solution was used as is.

All H2SO4, unless otherwise noted, is always assumed to be conc. H2SO4.

Never underestimate the danger of strongly endothermic cmpds. Several drops of H2SO4 in the receiver is essential.

So are greased joints, Keck clamps and most importantly, substantial tubing connecting your reactor to the great outdoors.
If you aren't a professional chemist, I'd suggest doing it outside.

BTW, ferrocyanide, wherever I said it, is wrong. Ferricyanide is usually used.

[Edited on 15-8-2015 by Dan Vizine]





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[*] posted on 14-8-2015 at 23:34


Oh no I didn't buy HCN I bought KCN. I try to keep the amount of HCN liberated from experiments as low as possible. HCN is the last thing I want in the lab.

And for the ferro/ferricyanide thing, one person once told me "red = dead" so I guess that's easier to remember.
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[*] posted on 15-8-2015 at 18:58


Quote: Originally posted by Dan Vizine  
The equations are more complicated than you might imagine.


Here's a balanced equation with the ferricyanide:

2 K3Fe(CN)6 + 6 H2SO4 = 12 HCN + 3 K2SO4 + Fe2(SO4)3

However, researching this further it seems much more common to find the ferrocyanide mentioned in the H2SO4 distillation for HCN, in which case the primary reaction is one of the following:

  1. 3 K4[Fe(CN)6] + 6 H2SO4 = 12 HCN + Fe2[Fe(CN)6] + 6 K2SO4
  2. 2 K4[Fe(CN)6] + 3 H2SO4 = 6 HCN + K2Fe[Fe(CN)6] + 3 K2SO4


(The distinctions between the two make reference to iron ion characteristics with which I am not familiar.)

But like Dan said, it's probably not that simple. For one thing, there's a bunch of water (ideally, from what I've read, 2 parts water to 1 part sulfuric acid) on the left-hand side that I wouldn't expect to stay out of the reactions. Also note that this does not produce pure HCN, because of course some of the water ends up in the distillate. (For practically anhydrous HCN I saw one reference suggest dropping 50% H2SO4 onto KCN.)

Any more accurate descriptions of either reaction would be appreciated.

I'd like to try one of these since HCN is such a useful precursor, but not before I understand it!

[Edited on 16-8-2015 by lysander]
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[*] posted on 16-8-2015 at 03:00


I'm not sure, I've heard that you get less HCN gas than expected. Maybe it need further heating or there are
byproducts but they didn't really get that much out of quite some ferricyanide. That's something one has
to try under precise measurement and than calculate how much yield he got. But I think this is still the best way
to do it. It's safe to handle since the reaction only starts when it's heated and you can destill it directely into
the KOH with some washing bottles afterwards. So you won't get into contact with the HCN if you do everything
right. The other stuff I read here seems difficult like getting Permanganates and so on.
You need three easily accessable chemicals for that reaction.

The question is, can you smell cyanide ? I've tested it quite often and there is always a bit of cyanide smell in my lab
when I'm working on cyanides but if you don't have any KCN or NaCN laying around where you could smell that characteristic odour, I wouldn't start a destillation where I'm not sure if I could even sense any leaking gas.



[Edited on 16-8-2015 by fluorescence]
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