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lysander
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Quote: Originally posted by fluorescence  |
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.
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Yeah, that sounds like a good safety measure. I've never had HCN outside of a strong vapor hood while wearing a face mask, so I don't know if I can
smell it. I do note a pungent, almost nauseating odor from wet cyan salts. Do those smell the same as HCN?
[Edited on 16-8-2015 by lysander]
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fluorescence
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We had that discussion on Versuchschemie some time ago. Back then when I worked with Cyanides for the first time
at the university. I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of
air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.
The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's
like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.
So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.
For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The
smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a
second.
But be careful !
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lysander
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| Quote: Originally posted by Dan Vizine | 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.
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I think I have failed to find that thread, even after attempting to review all posts with your username! Could you provide a link?
FYI, here is one possible explanation for your HCN turning black:
| Quote: |
A polymer of hydrogen cyanide is slowly produced when an aqueous solution of the latter is kept in presence of alkali carbonate or cyanide. Under
these conditions the liquid turns brown, and a black mass separates after some days.... [P]robably the dinitrile of aminomalonic acid, NH2CH(CN)2.
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fluorescence
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I just tried that Ferricyanide method on a very small scale.
I've added a bit of conc. sulphuric acid in a test tube to
the red ferricyanide and left it over night. As you can see nothing
changed, so those two don't react if they aren't heated.
I then placed the test tube for about 5 minutes into a beaker
with about 85°C hot water. As you can see the color changed
from orange-brown to a pink-purple.
I then took it out and heated it very gently and carefully with
a heat gun that was set to be somewhere between 200 and 300°C
The mixture became nearly colorless so the ferricyanide must have
reacted. As I heated the test tube filled with a gas, you can see that
marked with a red arrow.
Since sulphuric acid and water form an azeotrope and I wasn't heating it for the boiling point of the Acid it should be HCN gas, I guess.
At least this method seems to work and does not produce toxic gases
the second you add the acid. So the destillation setup can be prepared with all the time it needd and you don't have to rush there.
Note: The gas can be some water, too. I'm not sure about that.
[Edited on 17-8-2015 by fluorescence]
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nux vomica
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| Quote: Originally posted by fluorescence | We had that discussion on Versuchschemie some time ago. Back then when I worked with Cyanides for the first time
at the university. I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of
air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.
The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's
like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.
So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.
For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The
smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a
second.
But be careful ! |
You could just stand outside a electroplating shop they always smell strongly of the zinc cyanide solutions they use.
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careysub
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| Quote: Originally posted by fluorescence | I just tried that Ferricyanide method on a very small scale.
...
I then took it out and heated it very gently and carefully with
a heat gun that was set to be somewhere between 200 and 300°C
The mixture became nearly colorless so the ferricyanide must have
reacted. As I heated the test tube filled with a gas, you can see that
marked with a red arrow.
Since sulphuric acid and water form an azeotrope and I wasn't heating it for the boiling point of the Acid it should be HCN gas, I guess.
At least this method seems to work and does not produce toxic gases
the second you add the acid. So the destillation setup can be prepared with all the time it needd and you don't have to rush there.
Note: The gas can be some water, too. I'm not sure about that. |
How much is a "very small scale"? The lethal dose of HCN, inhaled all at once, is 25 mg and will kill you immediately. If you can see the HCN as a gas
you are making too much.
HCN is detectable at about 1 mg/M^3 (but individuals vary, the minimum level is usually given as 0.7 mg/M^3).
It takes 10 minutes of breathing for 200 mg/M^3 to become deadly. Even at 1000 mg/M^3 exactly one normal resting breath (~0.5 L) is harmless (actually
ten times this concentration is still harmless for one single breath, but I would rather have a safety factor of 50 than 5). So you have a large
safety margin to see what it smells like if you approach cautiously from below.
If you can't place a firm upper bound on how much HCN you have, you shouldn't be trying this.
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careysub
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| Quote: Originally posted by fluorescence | ...I asked whether there was a safe way to test if you can smell it and we came up with the idea
to smell on an open bottle of KCN or NaCN. So don't put your nose on the bottle but rather fan a bit with your hand.
Cyanide Salts react with moisture in the air to form HCN. If you have a bottle where there isn't that much cyanide left there is quite an amount of
air and if you keep that bottle closed for some time and then open it up you can clearely smell
a strong odour of HCN. I've tested this with a small sample of very dry KCN and was able smell it.
The KCN that I have is quite wet since the bottle is very old. It's quite useful since the crystals are a bit bigger and you don't have any dusts it's
like handling any other hygroscopic potassium salt. But due to the water there is always a strong smell of HCN when you open that bottle.
So if you have any cyanide salt you could smell the air that comes from the bottle if you do this very carefully.
I think it's the safest way to really test it and better than just making HCN gas.
For people who say it smells like almonds I can't really relate that. What is ment by almonds is rather green almonds not the ones you can buy. The
smell is very characteristic and I don't remember anything that would smell like HCN.
But I've heard that you can even smell small quantities of cyanide in air. Like with H2S. So smelling it doesn't mean that you'll drop dead in like a
second.
But be careful ! |
Indeed, be careful!
The general procedure, slowly approaching a detectable concentration from a situation of high dilution, is sound - but I do not buy that the bottle of
cyanide salts is in any way safer than making a small, known amount of HCN. You have no idea how much HCN vapor might be in the bottle.
Right - no one knows what "bitter almonds" smells like, really. It is not a item most people ever come in contact with.
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lysander
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HCN via acidification & heating of aq. K3Fe(CN)6
Following Dan Vizine's notes, backed up by mentions I've since found in texts, I've tried this reaction twice, and it's not working:
1. Saturate 2 parts distilled water with K3Fe(CN)6, and leave stirrer running
2. Add 1 part H2SO4
3. Connect to condenser
At the instant of adding the H2SO4 some HCN vapor forms (detectable by smell before connecting to condensation apparatus).
However, after that it appears that nothing happens. Each run I increased heat slowly over half an hour until the mixture was just below 100C, but
all I have gotten is a tiny amount of water condensate with a hint of HCN.
Dan suggested including a gram of copper shavings as a catalyst. I tried that on the second attempt but they ultimately reacted (leaving me with
green acidic sludge instead of blue acidic sludge).
What could I be missing?
The only questionable part is the use of ferricyanide: more of the published mentions of this reaction cite ferrocyanide. But Dan insists
ferricyanide is typically used, and the two are so easily confused/typo'd I'm inclined to believe him. Also since it's a dissolved salt I'm not
expecting it to make a big difference since the anion is the same. Balanced equations suggest one of the following:
2 K3Fe(CN)6 + 6 H2SO4 = 12 HCN + 3 K2SO4 + Fe2(SO4)3
or
3 K4Fe(CN)6 + 6 H2SO4 = 12 HCN + 6 K2SO4 + Fe2[Fe(CN)6]
4 K4Fe(CN)6 + 6 H2SO4 = 12 HCN + 6 K2SO4 + 2 K2Fe[Fe(CN)6]
[Edited on 29-8-2015 by lysander]
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cyanureeves
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i have used ferrocyanide and sulfuric acid but just bubbled the gas expelled straight into cold potassium hydroxide solution.not much condensate was
made but hydrogen cyanide sure as hell went into my solution.i used the solution to gold plate and it all turned into ammonia eventually.you are
producing HCN gas i'm sure but i'm guessing you want to liquify the gas?
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lysander
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Yes, I'm trying to condense (and store in freezer) as feedstock for later reactions.
What are the specifics of the reaction you used to generate the gas? Did you add heat? Did you add water, or just mix H2SO4 with K4Fe(CN)6
trihydrate?
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cyanureeves
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i did add heat and probably too much and also used water on both flasks except i had ice on the receiving flask and hydroxide.i used the yellow
crystal ferrocyanide not my ferricyanide because it cost more.i think you will produce HCN with or without heat. i think this method of making cyanide
is way more inferior to the method shown in that youtube video shared in the cyanide thread here.potassium/ sodium cyanide is made and can be turned
aqueous as needed just like you are trying to make.i think you have already succeeded in making something dangerous so be safer now and take advantage
of this wonderful video while it lasts.i did not use stoichiometric amounts as the folk here at first but did on all other runs.the cyanide thread
here has all that and is where i got it from.i will never ever do this method again.oh! i remember why i stopped using this method.it is so similar to
making ammonia gas and if you let up on the heat it can create suck back pressure.as i said,i bubbled the gas into a liquid but i know you are not.my
reaction flask exploded when i was making ammonium hydroxide.
[Edited on 8-29-2015 by cyanureeves]
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lysander
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I don't want this for cyan salts, although I agree that for that purpose heating sodium with ferrocyanide as shown in that video is tough to beat! I
can certainly go that route, and then hit the cyan salts with H2SO4 to get (bonus!) anhydrous HCN.
But given the apparent popularity of the approach I'm attempting here I'm intent on figuring out what's going wrong, because half of this is about
proving/verifying/maintaining my proficiency.
The addition of H2SO4 to the solution in this reaction generates plenty of heat -- I measured the mix hitting 70C. And right there is a reasonable
amount of HCN. But something is stopping HCN production pretty quickly thereafter. I'm wondering if I have some polymerization going on, perhaps due
to contaminants. Certainly by the time I let the mix cool it has a sludge-like consistency. (Fingers crossed than an orgo expert will weigh in!)
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Nicodem
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Threads Merged
29-8-2015 at 01:56 |
lysander
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Recap on HCN from ferrocyanide
I found this old thread: Distilling HCN from potassium ferrocyanide... which contains a copy of Potassium Ferrocyanide Decomposition Using Sulfuric Acid - HCN generation.pdf, which gives some great reaction equations and empirical analysis
for ferrocyanide:
H4Fe(CN)6 = Fe(CN)2 + 4HCN and
Fe(CN)2 +H2SO4 = FeSO4 + 2HCN
It specifies the sulfuric acid be diluted with water to at least a 10:1 molar ratio. It is unclear about the reaction temperature (boiling?) but
suggests full evolution of HCN takes about 2 hours, and gives the final equation:
K4Fe(CN)6 + 5(H2SO4,10H2O) = 4KHSO4 + FeSO4 + 6HCN + 50H20
... so there's a lot of work left to get the water out! For dehydration this patent provides useful information on distillation. (The alternative method of producing anhydrous HCN from cyan salts is covered in this patent.)
Brauer's Handbook of Preparative Inorganic Chemistry (p.659) prescribes the following preparation:
200g potassium ferrocyanide trihydrate
Cold mixture of 160g sulfuric acid and 250g water
"Gentle" heat applied
Gas passed through three CaCl2 drying tubes immersed in 40C water bath before hitting Liebig condenser
Buffer condensate with two drops of hydrochloric acid for storage
In both these cases ferrocyanide is the prescribed reagent, and sensitivity to the dilution of the sulfuric acid is noted.
And in both cases required heat is unclear. (And presumably one would want to keep it as low as possible to minimize water evaporation.)
[Edited on 29-8-2015 by lysander]
[Edited on 30-8-2015 by lysander]
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papaya
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I'm sorry if this was asked before, what will happen if you drop a nitrile glove into a molten sodium hydroxide(or even boiling water solution), what
will happen with -CN groups? Is there any chance that some way NaCN forms ?
[Edited on 29-8-2015 by papaya]
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Hawkguy
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| Quote: Originally posted by papaya | I'm sorry if this was asked before, what will happen if you drop a nitrile glove into a molten sodium hydroxide(or even boiling water solution), what
will happen with -CN groups? Is there any chance that some way NaCN forms ?
[Edited on 29-8-2015 by papaya] |
Tried it today smelled like shit. I tried adding Ferrous Sulfate to the
dissolved product, and got a blue precipitate. Likely Ferrous Carbonate, and not the Ferrocyanide.
Also tried heating Potassium Nitrate/ Charcoal at about 900 degrees C and got the same result. Hmm.
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papaya
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You should have added gold into it. But seriously, anyone tried what I asked above? I mean to analyze the products..
[Edited on 29-8-2015 by papaya]
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Hawkguy
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Like add Acid and distil? I'll try that once the power comes back on. Once the distillate is collected, the Prussian blue test will be 100% accurate.
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lysander
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Not going to let this practical beat me!
My previous two attempts at evolving HCN from ferricyanide failed, I have concluded, because I diluted the cyanide in the full amount of water first
and then (while that was mixing) added the full dose of concentrated H2SO4 all at once. That produced a puff of HCN, but, I surmise, then polymerized
enough in the solution that most further evolved HCN bonded to the polymers instead of evaporating, so I only got a few mL of HCN out of the process..
After my third attempt today I think that for the first time in a decade I'm going to have nightmares about failing Orgo Lab:
This time I followed Ledgard's instructions precisely, with the sole exception of using a hotplate and Florence flask instead of a mantel. (However,
given that I was running a strong stirrer the whole time I don't believe that difference was material. Just to be sure, I regularly measured and
noted the exterior temperature of the lower half of the flask was always higher than that shown by the thermometer in the flask.)
54g K4Fe(CN)6 trihydrate (=47g anhydrous) put in flask
Added 50mL distilled water and began stirrer
Added 75g (41mL) H2SO4 to 100mL distilled water. Temperature measured 60C.
Slowly added dilute to flask. Solution gradually turned light blue
Added heat. Reaction is supposed to start and run at 60C. Somewhat <i>beyond</i> that temperature the solution gradually turned
darker, but absolutely no gas evolved.
Allowed to run for 2 hours at up to 80C but no vapor made it through the Kjeldahl bulb.
Exasperated, allowed solution to run up past 90C at which point condensate formed at the mouth of the Liebig condenser.
1 hour later shut down.
The collection flask, sitting in the ice bath that's also feeding the condenser, and which I had prepped with a few mL of H2SO4, yielded a grand total
of 15mL of two immiscible fluids in roughly equal portions. There was only a vague odor of HCN, and it was overpowered by a far more pungent
rubber-like odor that almost induced gagging. The lighter fluid was mostly water, I assume, because it mostly froze at 0F. I have no idea what was
mixed into it, or what the denser immiscible fluid is. Instead of a dark prussian blue the reagents had turned a more turquoise color you can see in
the following photo. Any guesses as to what chemicals were actually produced? When I cut the mix with sodium hypochlorite it reacted vigorously, and
when I dumped it from the flask the fumes almost knocked me over.
Could anyone <i>please</i> tell me what I might be missing here? Everything I've read suggests the majority of HCN should evolve out over
a few hours at 60C.
This time I used almost all different glass from the first two attempts, and I switched from ferri to ferrocyanide. Given the heat generated by
mixing the H2SO4 with the water I don't doubt its adequacy. I don't know what I could be doing to kill this reaction!
[Edited on 14-9-2015 by lysander]
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lysander
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HCN failure #4
For my fourth attempt I tried the Brauer/Vizine formula, which essentially doubles the amount of ferrocyanide but still uses a 25% dilution of H2SO4.
Combine 100mL distilled water with 100mL H2SO4. This reaction heats the dilute to 100C. Therefore wait for it to cool back to room temperature
Add 211g K4FE(CN)6 trihydrate to 1 liter boiling flask.
Add 200mL water and begin stirring. (This requires a more powerful stirrer).
Add the cooled 200mL H2SO4 dilute to boiling flask.
Heat solution to 60C.
Run for <i>four hours</i>. <B><I>Nothing</B></I> evolved!
Raised heat to 80C. Managed to get 15mL of condensate in cooled collection flask that smells of HCN, but also of something more strong and
pungent.
Hang head in disappointment.
Here's a photo of the apparatus running after about an hour:
The color gets perhaps a <i>little</i> darker by the end, as seen in this video taken right before shutdown:
http://youtu.be/dTFK_o-D_JI
(Compare that color to the two runs where I dropped the concentrated H2SO4 into the ferricyanide solution:
http://youtu.be/SqLJU862yMQ
Questions:
A. Does the color indicate any failure? What is the expected progression of color over the course of the reaction?
B. Is HCN miscible with H2SO4? (If not that would explain the two layers I'm getting in what little I collect.)
[Edited on 15-9-2015 by lysander]
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kmno4
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The mixture should be heated untill it starts boiling.
The temperature is then increasing from ~60 C to ~100 C as reaction goes on.
At relatively high concentrations (total), reaction ends at FeK2[Fe(CN)6] step (larger amount of H2SO4 will not help). Further conversion (to FeSO4)
is terribly slow. Great dilution and boiling expels all HCN but with large amounts of water. You can add some CuCl (or even CuSO4) to the reaction
mixure: it is converted to CuCN.
It has so small solubility that FeK2[Fe(CN)6] is (slowly, on boiling) converted to CuCN (-> HCN). In this way all CN can be removed as HCN.
The purgent odour is possibly SO2 and/or HCOOH : it indicates too concentrated H2SO4. Better use 20-30 % solution (or H3PO4).
The paper you mentioned is disscused on previous pages - it turns out that it gives information that high concentration of H2SO4 is not good and
nothing more. From preparative point of view t is useless.
There are a lot of missinformation and lies in this topic, I understand that is may be hard to filter them off.
I conducted this reaction many times, you may read my posts (starting from page 4) if you wish.
I decided not to write any posts here: everything has been said and written. But sometimes it is worth to hepl someone who is really interested. I
think it is the case.
Слава Україні !
Героям слава !
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S.C. Wack
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There's something ugly about that phrase for some reason. Like this quote, considering that this member's last login came less than 2 weeks later:
BTW at the end of that article I posted an abstract of a while back, the 1912 Williams CuCl article, well there were comments from being a lecture I
guess, and there was some agreement on ferricyanide giving 85% with the standard treatment.
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lysander
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Indeed; I should have been more clear: The structure of the process is well-documented across many references. What varies are the concentration of
H2SO4 (from 20-26%, with theoretical maximum of 33%), the final dilution of ferrocyanide (from 25%-60%), rate of dilution (instantaneous to very
gradual), the temperatures indicated (from 50-100C), the process duration (from 2 to 4 hours), and the catalyst (if any). For #3 I was trying
Ledgard's exact values for each parameter, but they are within the ranges established by the other 5 references I made notes on.
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lysander
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| Quote: Originally posted by kmno4 |
The mixture should be heated untill it starts boiling.
The temperature is then increasing from ~60 C to ~100 C as reaction goes on.
I conducted this reaction many times, you may read my posts (starting from page 4) if you wish.
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Yes -- please! I just reviewed the entire thread again, focusing on your notes.
In general the temperature for the reaction is very poorly specified. Am I to understand that the evolution of HCN occurs gradually as temperature is
raised towards 100C? I don't think I have observed any boiling below 80C, even though a number of references suggest 60C should be adequate for the
reaction.
My objective was to run the reaction at as low a temperature as possible to minimize water evaporation as well as HCN decomposition. However if the
HCN does not evolve until closer to 100C I understand I'll just have to run a secondary distillation to get a decent HCN concentration since there is
so much water in the initial dilution (as well as evolved in the reaction).
I am trying it now without a catalyst to just get <i>some</i> significant output. At this point if I could get 50% yield without a copper
catalyst I would be ecstatic!
Can you offer any other sanity checks that might inform my progress? E.g., the boiling solution starts out "apple green." (But as noted on the first
two experiments, hitting a ferricyanide solution with 98% H2SO4 produced almost instantenous dark blue.) Should the color evolve? If I am not
observing significant boiling before 80C is something wrong? Do I actually need to run up to 100C to get maximum HCN output? How long should that
take for roughly half a liter? Is there anything I can/should watch for that could ruin the output or kill the process?
Thanks for the guidance!
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Hawkguy
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Sorry to disrupt flow of thread, but here's my current workings of making Cyanide from Hexamine. 30g Hexamine and 65ml 12M Hydrochloric Acid were
mixed and Formic Acid distilled at 105 degrees Celsius (approximately). Mix was refluxed to produce Methylamine Hydrochloride. I made Ammonium Formate
from the Formic Acid, and I'll heat it to 250 tomorrow and bubble the decomposition product HCN through alcoholic KOH. KCN should precipitate. The
Methylamine Hydrochloride will be mixed with Sodium Hydroxide, and the resulting MeN2 gas will be condensed in a flask in a liquid propane bath. An
Alkali metal will be added to the Methylamine, producing the corresponding Cyanide and Hydrogen gas. Read about this procedure in my ol' 1923 Bloxam's
Chemistry preparation textbook.
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lysander
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I ran decided to continue cooking the solution from test #4 today. Three hours at 80-85C produced another 40mL of a clear liquid. (I'm aggregating and waiting to resolve the
evolution issues before distilling the condensates to get a good idea of true HCN yield.) Solution also got darker during the process.
My current plan is to bring the CuCl catalyst into play and see if that results in greater evolution and/or evolution at lower temperature....
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