Sciencemadness Discussion Board

HCN by chloroform and ammonia in base

guy - 25-10-2006 at 00:00

Carbylamine reaction is reaction of chloroform with an amine and alcoholic KOH to produce an isonitrile. If you can do this with ammonia instead, it should be able to make hydrocyanic acid. Is this plausible?

Polverone - 25-10-2006 at 00:14

It is plausible and I have done it, confirmed by the prussian blue test. It is not a terribly efficient method, of course. I was unable to get it to work with household aqueous ammonia (5%? 10%? something like that) but there was a vigorous reaction when I used 28% concentration. I seem to remember that I was able to get it to work in water, without ethanol, if I added a bit of winter pool algaecide (mixed quaternary ammonium salts).

not_important - 25-10-2006 at 01:04

With the KOH there, I asume that you would get KCN rather than HCN. I fthat is the caserunning in alcoholic KOH would make isolation of the KCN easier than from water, unless you really wanted to acidify it and distill the HCN from it.

When you say it is not terribly efficient, how do you mean this? Low conversion, with lose of chloroform as formate?

Polverone - 25-10-2006 at 10:12

I mean that you end up with a lot more chloride than cyanide (of course), and that the use of chloroform, strong aqueous ammonia, and alcoholic KOH seems like a rather expensive way to make impure KCN.

guy - 25-10-2006 at 11:29

I was thinking about bubbling gaseous ammonia into the solution. Actually the cyanide salt is what I want not HCN. So if I use KOH I would get a mixture of KCl and KCN, and the best way to separate this would be to add Pb2+ precipitate to Cl-. Then filter that off and leaves you with fairly pure KCN. Unless lead cyanide is also insoluble...

Dr. Beaker - 25-10-2006 at 17:07

I used a very efficient way to make nitriles from aldehydes using iodine and aquaos amonia. look for Fang and nitrile in scifinder.
the mechanism involves oxidation of the imine and elimination of HI, so if u keep the right stoichiometry there shouldn't be oxidation of the exta alpha H.

btw - the notorious NI3*NH3 forms, but it's not dangerous when wet, and the black ppt. of that sensetive exposive dissapears with the advance of the reaction.

advantages:

1. cheap reagents (methanol or formaldehyde), I2, amonium hydroxide
2. very quick (mostly minutes) rxn. time and easy to follow (wait until the black ppt. dissolves)
3. easy to seperat the product - kill excess I2 with Na2S2O3 and add KOH in same amount of HCN, then evap. the solution (u can recycle excess of NH3) and seperat NH4I and KCN by fraction crystelazation or by sublim. NH4I. (maybe even NH4+ and CN-react to give NH3 and HCN which u can remove and condense.
u can then easily get back the I2 by oxidation with, say bleech+HCl (also good way to eliminate any traces of cyanides)

[Edited on 26-10-2006 by Dr. Beaker]

not_important - 25-10-2006 at 17:50

Quote:
Originally posted by Polverone
I mean that you end up with a lot more chloride than cyanide (of course), and that the use of chloroform, strong aqueous ammonia, and alcoholic KOH seems like a rather expensive way to make impure KCN.


Very true, but easier for many than the high temperature routes. I find I find blowing air through steel pipe filled with charcoal and soda ash fun, but some people might not have the room to do it.



Fang :

http://www.sciencemadness.org/talk/viewthread.php?tid=5864

Updates

http://pubs3.acs.org/acs/journals/doilookup?in_doi=10.1021/j...

http://www.chemistrymag.org/cji/2005/071004ne.htm

guy - 25-10-2006 at 21:13

Quote:
Originally posted by Polverone
It is plausible and I have done it, confirmed by the prussian blue test. It is not a terribly efficient method, of course. I was unable to get it to work with household aqueous ammonia (5%? 10%? something like that) but there was a vigorous reaction when I used 28% concentration. I seem to remember that I was able to get it to work in water, without ethanol, if I added a bit of winter pool algaecide (mixed quaternary ammonium salts).


Ok so does a vigorous reaction means lots of heat? Should I cool the reaction to increase yields?

Polverone - 25-10-2006 at 22:04

Quote:
Originally posted by guy
Ok so does a vigorous reaction means lots of heat? Should I cool the reaction to increase yields?

It did noticeably generate heat. I don't know how bad it would be on a large scale, nor do I know if yields are affected (apart from the obvious problem of volatilizing reactants). I only tried this enough times to confirm that it works -- how to optimize it will be a project for you to have fun with ;).

not_important - 25-10-2006 at 23:03

Hmm... long stainless steel tube and packed with NaOH or KOH. Still pot with CHCl3 and alcohol. Feed ammonia gas into the still pot, heat the pot so the chloroform-ethanol boils. Take the ternary azotrope of chloroform-ethanol-water off the top, fairly dry product accumulates in the still pot. Any hydroxide carried done into the still pot should react there. Vent to a flame or outside, as some carbon monoxide will be formed. At the end wash the remaining hydroxide with alcohol, run the pot contents through a filter to remove the alkali chloride, evaporate to recover the cyanide. Might work.

guy - 26-10-2006 at 15:14

I have a question, for the reaction with the quaternary ammonium salts, will 10% ammonia solution work?

I didn't have too much luck when I bubbled ammonia gas in; I don't think it dissolved well enough. I used 10g NaOH in about 100mL ethanol with 5mL chloroform. I bubbled in ammonia gas. Then I tried adding the solution to iron(II) and iron(III) sulfate but did not get any blue color.

Edit:
For the Carbylamine reaction, refluxing is nessecary!

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv6...

[Edited on 10/26/2006 by guy]

Polverone - 26-10-2006 at 15:22

I don't know if 10% is enough. How did you generate the ammonia? I thought that NH3 should be readily absorbed in ethanol, but if not you might add a bit of water.

If you really don't care about purity initially, you might try mixing an ammonium salt with excess alkali hydroxide in alcohol and then add chloroform.

guy - 26-10-2006 at 15:29

I used NaOH and (NH4)2SO4 to generate the gas. I think when water is present a phase transfer catalyst in necessary to give satisfactory yields. So gots to get some of that pool algaecide.

28% ammonia is needed, so is that about 13M ammonia.

Theoretical procedure:

26 g NaOH is dissolved in 50mL water and reacted with 43g ammonium sulfate. This gives about 28% ammonia solution.

Then some quaternary ammonium salts are added as a phase transfer catalyst.

10 g of additonal NaOH and 5mL chloroform are added to the solution.

~~~~~~

also one experiment, I accidentally added CHCl3 to basic ethanol first and got a very violent exothermic reaction that produced some orange liquid...weird

[Edited on 10/26/2006 by guy]

Polverone - 26-10-2006 at 17:48

No, PTC isn't needed if the alcohol concentration is high enough, so there's no distinct phases. I used it only when I tried an alcohol-free reaction.

guy - 30-10-2006 at 18:34

So I tried it again today. I didnt get it to work the Prussian blue test (I mixed the solution with FeSO4 and put a drop of H2O2 and acetic acid in). But when I put CuSO4 and FeSO4 I got some brown precipitate.

Polverone - 30-10-2006 at 19:44

Did you make sure the solution was slightly acid before you added the H2O2? Depending on the size of your reaction, a single drop of acetic acid may not be sufficient. I tried it again recently to refresh my memory. Some water is useful because it increases NaOH solubility, and if you don't add too much, chloroform will still dissolve. It seems denatured alcohol (large percentage MeOH) works better than 95% ethanol, because two phases form in ethanol/water when NaOH is added. I used NaOH in denatured alcohol with finely ground ammonium sulfate or nitrate as the ammonia source; nitrate works better because of higher solubility. It was easy to get a boilover even with just a few grams of reactants in 20 mL or so of liquid, so you probably do need reflux apparatus, slow addition of chloroform, temperature control, or some combination of the above. And, of course, you would probably want to use ammonia gas or aqueous ammonia rather than just dumping a salt in if you hope to eventually produce somewhat pure cyanides.

I acidifed with citric acid, added a bit of iron oxalate, and was rewarded with the lovely prussian blue when H2O2 was introduced.

guy - 30-10-2006 at 20:19

Wow, it seems I just have bad luck. Ill follow you procedure exactly tommorow and hope to get some luck.

Do you remember how much of each reagent you used? Like how much NaOH? Your total volume was about 20mL, so how much water vs. denatured did you use?

And btw, I appreciate you trying it out again to check it.

[Edited on 10/31/2006 by guy]

Polverone - 30-10-2006 at 22:10

I'd try 6 equivalents NaOH, 2 NH4NO3, and 1 CHCl3 (hydroxide and ammonia in excess to favor cyanide over formate and to help make sure that chloroform doesn't react too slowly as hydroxide is used up). 15 mL denatured alcohol and 5 mL water dissolve 4.8 g NaOH, and then 3.2 g finely powdered NH4NO3 are added. It won't all dissolve. While the mixture is still warm, 2.4 g of chloroform are added and the mixture is swirled around.

After the reaction is over and the mixture has cooled to room temperature, try the prussian blue test.

guy - 31-10-2006 at 12:02

YEs! I finally did it. At first I was mixing only a little of the cyanide solution in so I didnt get any results (probably my big mistake from other runs). So I was dissapointed, so I was like "what the heck" and dumped all my iron sulfate into the cyanide solution and put a whole bunch of vinegar in. And then I put a few drops of H2O2 and got a beautiful prussian blue color!

ScienceHideout - 10-12-2012 at 08:01

Sorry to bring back an old topic- but the preparation of cyanides is really sparking my interest now, and I was thinking if there is any way to produce them without high heat or encounter with HCN gas... I started thinking about this and trying some stoiciometry.

If I simply bubble NH3 gas though some alcoholic NaOH and CHCl3, couldn't I get the cyanide, chloide, and water?

NH3 + CHCl3 + 4 NaOH ---> NaCN + 3 NaCl + 4 H2O

I should get 4.901 g NaCN if I use 11.938 g of chloroform and 15.999 g NaOH. I need a tenth of a mole of NH3, so that means what- 2.24 L? That can be prepared quite easily.

Anyways- I am just wondering a couple things:
Can I get a delta G value to see if this will work? Delta G's are telltale of if inorganic reactions will work, but because this is derived from the carbylamine reaction, I was not sure if I could get a delta G.
If this reaction will work at all, do I need a catalyst?

ScienceSquirrel - 10-12-2012 at 09:35

You have to remember that the reaction is not remotely stochiometric.
The first step in the reaction is deprotonation of the chloroform and the loss of chloride to form dichlorocarbene, this then reacts with ammonia to form an addition product that loses hydrogen chloride to form the cyanide.
I would guess a twenty per cent yield would be good with the rest turning in to other possible products.

S.C. Wack - 10-12-2012 at 16:20

People go (went) about extracting amines via A/B (NaOH) and chloroform all the time.

http://books.google.com/books?id=uelSAAAAcAAJ&pg=PA114
http://books.google.com/books?id=A49KAAAAYAAJ&pg=RA1-PA3...

ScienceHideout - 10-12-2012 at 17:23

Ooh! Time to test my German skills! "Ueber eine neue Reihe von Homologen der Cyanwasserstoffsaeure"

No expert- but cyanwasserstoffsaeure is cyanide hydrogen acid- hydrocyanic acid HCN- YIKES! It also seems to discuss much about amines. In this post we discuss a reaction where we replace an amine with ammonia.

"On the behavior of chloroform to other bodies, especially for ammonia, with higher temperature" seems more relevent, but it doesn't seem to talk much about cyanide. Hmm....

DoctorZET - 13-4-2014 at 11:44

I tryed 3 different series of reactions:

1)
4NH3(gas) + 3Cl2(gas) (excess) -( INTENSE BLUE LIGHT )-> NCl3(liquid) + 3NH4Cl(fine divided solid)
NCl3 (excess)(gas) + CH4(gas) -( AlCl3 cristals deposited in a glass tube, 80-100*C )-> NCH + 3HCl
___now you have HCN ...or, try the next method (is also a very well process)

2)
BLEACH (with little excess)(aq) + PROPANONE(acetone) (aq) -(some time)-> HCCl3 (insoluble layer under water) + CO2 + Others_compounds
HCCl3 (excess)(gas) + NH3 (gas) --(traces of H2O + AlCl3 cristals deposited in a glass tube, 90-150*C)--> HCN + 3HCl
___now you can have HCN in big amounts ... but if you have acces to some laboratory chemicals try next reaction:

3)
2 K Fe (CN)6 (potassium hexacyanoferrate) + 3 H2SO4 -(instant)-> K2SO4 + 2 FeSO4 + 12 HCN
___where 12 HCN means you can make a HUGE amount of hydrogen cyanide in no time ... but only if you have access to the hexacyanoferrate ion

[Edited on 13-4-2014 by DoctorZET]

Pickardjr - 13-4-2014 at 14:29

Dont know about you guys but the ferrocyanide and sulfuric works everytime, all you have to do is add KOH or NaOH to the distillate in stiochemetric amount and you have an aqueous cyanide salt. done it a gazillion times. cake walk

Metacelsus - 13-4-2014 at 16:59

The first reaction is a good way to get killed. Nitrogen trichloride AND hydrogen cyanide?!? :o

WGTR - 13-4-2014 at 17:24

I tried the "HCN by chloroform and ammonia in base" reaction a few years back, and it worked the first time (Thanks,
Polverone). An excess of concentrated ammonia was used, and alcohol was the main solvent. I noticed that no reaction
occurred if the solution was stirred at room temperature, but somewhere close to 40°C the reaction kicked off, and a sharp
exotherm was noted. At the same time, the KCl and KCN precipitated out quickly (when an excess of KOH was used).

Dan Vizine - 15-4-2014 at 16:07

Quote: Originally posted by S.C. Wack  
People go (went) about extracting amines via A/B (NaOH) and chloroform all the time.

http://books.google.com/books?id=uelSAAAAcAAJ&pg=PA114
http://books.google.com/books?id=A49KAAAAYAAJ&pg=RA1-PA3...


Have done it numerous times. Although, for obvious reasons, CH2Cl2 was far more preferable. No reaction occurs in a few minutes or longer at room temp. Considering the emulsions such mixtures form, that's a good thing. Aq. NaOH/chlorinated solvent emulsions are among the most troublesome for your typical synthetic chemist.



[Edited on 16-4-2014 by Dan Vizine]

DoctorZET - 16-4-2014 at 14:49

I think the best way to get HCN in a home-lab is the proces involving chloroform and ammonia... ;)
As Cheddite Cheese says, hydrogen cyanide is toxic enough ... and if you're doing the first process (involving nitrogen trichloride & methane) in a closed environment ... you will certainly have some very bad health issues after this.
Good thing I have do that outside :D

The Volatile Chemist - 16-4-2014 at 16:39

If I needed it, I always have extra Ferri- and Ferro-cyanides I could decompose by heat or acidification, but I'm a bit young to try it (14) and don't feel like I'm mature enough :) As well as being at a slight lack of glassware re-condensing stuff...

Dan Vizine - 17-4-2014 at 18:36

It isn't even debatable, HCN via acidification & heating of aq. K4Fe(CN)6 is unrivaled by any other method.

Always remember HCN is en endothermic compound, and explosive polymerization can be initiated by excess CN anions. Stabilize with 1% H2SO4.

It's beautiful and mesmerizing, looks very much like water. I love the smell in high dilutions. I'm one of the group that smells it, some people don't. It's a genetic thing.

DoctorZET - 18-4-2014 at 05:54

You should not smell it too much... it's highly toxic , remember O_o ?

Now I think about next process (starting from ammonium formate):

NH4OOC (ammonium formate)(solid) --(thermal decomposition)--> OCH-NH2 (formamide)(gas) + H2O (vapors) --(excess of powdered calcium oxide, 300-350*C)--> Ca(CN)2 (solid) + 2H2O(vapors)

I think is also a good process...

Mildronate - 18-4-2014 at 07:40

ScienceHideout asked dG for reaction:

NH3 + CHCl3 + 4 NaOH ---> NaCN + 3 NaCl + 4 H2O

, sorry i calculated for KCN

From my calculation dG must be -740.1 kJ/mol*K at 298K (see atachment)

[Edited on 18-4-2014 by Mildronate]

Attachment: dgkcn.xlsx (9kB)
This file has been downloaded 406 times

AJKOER - 20-4-2014 at 10:56

Here is a possibly small scale route based on photolysis that may be theoretically feasible. Comments invited as I suspect there are fine points of the procedure that may need refinement.

1. Gradually create some CHCl3 and other compounds including CH2Cl2, CCl4,.. by exposing a mixture of methane with an excess of chlorine to diffused daylight at 298 K. A finer point, direct sunlight as confirmed by Mellor (see "Modern Inorganic Chemistry" page 693 at http://books.google.com/books?id=1iQ7AQAAMAAJ&pg=PA694&a... ) with an excess of Cl2 should be avoid due to explosion hazard. The later can actually be expected based on the known explosive chain reaction of hydrogen and chlorine. Per this source (http://www.google.com/url?sa=t&rct=j&q=photolysis%20... ) some expected uv radical formation reactions:

Cl2 + uv = Cl + Cl
CH4 + uv = CH3 + H
H + Cl = HCl
CH3 + Cl = CH3Cl

For a net reaction:
Cl2 + CH4 + uv = HCl + CH3Cl

and similar progression of the chain for the creation of CH2Cl2, CHCl3 and CCl4. Note, per Wikipedia, there is a commercial production method for chloroform by directly heating CH4 and Cl2 between 400 C and 500 C (see
http://en.m.wikipedia.org/wiki/CHCl3). Also, given the associated poisoning of the H2/Cl2 chain reaction by O2 (see http://books.google.com/books?id=nirXFo1S9VkC&pg=PA120&a... ), I would similarly avoid the presence of any oxygen. Also, no CO2 as, per the prior cited source:

CO2 + uv = CO + O

or possibly water vapor, again liberating some oxygen in the presence of uv.

2. Lastly, the formation of some HCN with the introduction of NH3, again in the presence of uv light, most likely near 100 C.

[Edited on 20-4-2014 by AJKOER]

Mildronate - 23-4-2014 at 10:14

yeah CH4+Cl2 + UV= BANG!

DoctorZET - 23-4-2014 at 14:24

Well ... it's very possible to get a "bang" if you mix in a baloon Cl2 and CH4 (remember that H2+Cl2+UV=>2HCl+energy)
But think about mixing Cl2 and CH4 in a long and thin glass tube illuminated with UV and , as the input gases you have a continuos flux of Cl2 and methane. If you try this, is very probable to get a lot of heat instead of a "bang" (perhaps the tube must be submerged in water).

Mildronate - 24-4-2014 at 07:48

Anyway its much easier to make HCN from K3[Fe(CN)6 and sulfuric acid.

[Edited on 24-4-2014 by Mildronate]

DoctorZET - 25-4-2014 at 07:21

Agree, but only if you have access to a hexacyanoferrate salt (just like K3Fe(CN)6).
And, by the way, hexacyanoferrates it happens to be illegal substances in my country... so I need to produce HCN in my home lab from usual chemicals.
And that's our discussion about.

Mildronate - 25-4-2014 at 10:29

Why its illegal?

Pickardjr - 25-4-2014 at 17:07

potassium ferrocyanide is not a toxic cyanide metal salt. Its in table salt to keep it from clumping, and road salt for same reasons. Why would it be illegal?

Dan Vizine - 26-4-2014 at 07:07

It causes damage to aquatic ecosystems if I recall correctly.

Pickardjr - 26-4-2014 at 08:57

ah, yea I see that now. question retracted.

plastics - 26-4-2014 at 12:55

These posts on the original 'Preparation of cyanides' page (http://www.sciencemadness.org/talk/viewthread.php?tid=23&...) using only ferricyanide and KOH have always intrigued me

Densest:
One approach which I saw appeared to work:

To a cold saturated solution of KOH was added K4Fe(CN)6 crystals until no more would dissolve. The flask was sealed with plastic film to exclude CO2 and O2. Over a period of some days, Fe hydroxides and oxides precipitated, and the color of the solution changed from yellow-green to clear. The supernatant was decanted. On further chilling, transparent square plates and small cubes crystallized. Filtered quickly, washed with a minimum of very cold distilled water, a very small amount (milligrams) gave a very strong blue reaction with FeSO4 solution.

I believe it took several weeks overall, using an outdoor shed during autumn. It would seem to depend on KCN being somewhat less soluble than KOH or K2CO3 and very little O2 being available to destroy the KCN. Perhaps the air in the flask could be displaced with something else to improve the yield.

According to an old Chem Rubber handbook, the only likely substance in that solution which crystallizes to a square or cubic form would be KCN giving a second reason to believe the process worked.

len1:
Thanks for the info SC Wack. But none of the links work. The first two only give me the title pages the last hangs the computer.

ANYONE WHO WORKS WITH CYANIDES INCLUDING MYSELF MUST WEAR A GAS MASK, GLOVES and GLASSES!. Even in this case when theoretically no HCN is generated KCN spilled on a stray drop of HCl, can generate enough HCN to kill, especially if you are like myself and cant smell it. Grinding or picking KCN can stray particles into your face and mouth - also enough to kill. A mask will guard against all of this. Gloves give protection against KCN dissolving in skin moisture and penetrating though cuts etc. Glasses protect against KCN particles flicked into the eye dissolving in tears, being absorbed, and killing. Symptoms of mild CN poisoning resemble symptoms of fear of having been poisoned (anxiety).

Ive done the Ksp calculations, and the KOH method must work and it must work even better with K3FeCN6 since its last cyanide is weakly bound (making it poisnous) so that it can be substantially separated even in boiling water

[Fe(CN)6]3- + OH- -> [Fe(CN)5OH]3- + CN-; [Fe(CN)6]3- + H2O -> [Fe(CN)5H2O]2- + CN-


Removal of all the cyanides if you check the K's proceeds because of the low Ksp of iron hydroxide. BUT its all very slow and inefficient. In practice my method is better: simplest method imaginable - no mixing, weighing etc; takes a few hrs; directly gives pure KCN; is safe for non-specialist labs - no HCN at any stage

Yiled can be improved, but at the expense of a lot more dangerous work. At this level I think this method is perfect.

[Edited on 24-2-2009 by len1]


Anyone else tried this method?

lysander - 28-8-2015 at 17:07

Quote: Originally posted by Dan Vizine  
I love the smell in high dilutions. I'm one of the group that smells it, some people don't. It's a genetic thing.


I have a hard time believing you love the smell. I smell it but find it unquestionably unpleasant and somewhat nauseating. I wonder if maybe I got cyanide poisoning once and that gave me a bad association? I'm a supertaster who can also smell asparagus metabolites. Maybe there are genetic variations among HCN smellers?

Actually it would be neat to do a poll thread on cyanide, but I can't see that polls are possible with this forum:


  1. Can't smell it
  2. Don't like its smell
  3. Like the smell