CyrusGrey
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Preparation of thiocyanates
Does anyone know a preparation for thiocyanates that is within the reach of the home chemist? I have searched the forums, then brauer, then googled
it. I only came up with a reaction between ammonia and carbon disulfide:
http://www.patentstorm.us/patents/5026534-claims.html
I would like to use it to prepare iron thiocyanate for April Fool's Day. 
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MagicJigPipe
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I know wikipedia is not the best source but it claims thiocyanates can be had from sulfur or thiosulfate and cyanide.
8 CN− + S8 → 8 SCN−
CN− + S2O32- → SCN− + SO32-
http://en.wikipedia.org/wiki/Thiocyanate
Also, here is a page that shows how to prepare a blood red solution of [Fe(SCN)(H2O)5]2+ ions.
http://www.chemguide.co.uk/inorganic/transition/iron.html
Is [Fe(SCN)(H2O)5]2+ your goal?
[Edited on 30-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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CyrusGrey
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I did not know the exact complex involved but yes, I was planning on trying to prepare some fake blood.
I looked on several MSDSs on thiocyanides and they look relatively tame, but I don't want to go smearing something made from cyanides on my skin!
Maybe it can be prepared by a sulfur and cyanate reaction? Though I would think that it would be a different compound, and reduction of that compound
might lead to traces of cyanide as well.
[Edited on 30-3-2008 by CyrusGrey]
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microcosmicus
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Fownes (Manual of Chemistry, p.545) has a nice procedure which
uses commonly available ingredients and does not involve cyanides.
Heat 46 parts dry potassium ferrocyanide, 32 parts of sulphur, and
17 parts of potassium carbonate in a closed vessel slowly to low red
heat (ca. 650C). Exhaust in water, evaporate to dryness, exhaust in
alcohol and crystallize.
[Edited on 30-3-2008 by microcosmicus]
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microcosmicus
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I just mixed up a batch of the stuff using a slightly different
procedure also from Fownes. Since I did not have the
potassium salt, I started with sodium ferrocyanide.
I dehyadrated the sodium ferrocyanide by heating it, then
added the sulphur, ground the two together to make a fine,
well-mixed powder, heated again to melt the sulphur and kept
the mixture at that temperature for a few minutes to react.
When it cooled down, I added water to the resulting blackish
mass and boiled to dissolve the thiocyanates. I then added
Na2CO3 to precipitate the iron and filtered.
Upon adding some FeCl3 to the filtrate, I got the deep red
complex. This stuff is a dead ringer for blood!
Later on, I may evaporate the filtrate and extract with alcohol
to purify the NaSCN and see how the crystals look. In addition
to its uses for the gag, this stuff is also useful as a test for
iron. Also, it can be used as a starting point for making thiourea
by a variation of Wohler's celebrated reaction --- prepare
NH4SCN, then heat it to 180C to turn it into NH2SCNH2.
Happy April Fool's Day 
[Edited on 31-3-2008 by microcosmicus]
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CyrusGrey
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Thanks for the great information Microcosmicus! Unfortunatly I don't have any cyanides or cyanide complexes.
I might try heating cyanuric acid and sodium bicarbonate together to form sodium cyanate. If I then add sulfur to the melt I think it would form
either sodium thiocyanate or maybe something like NaSOCN? I would think that the sulfur would reduce it as well though, minimising production of the
latter.
I'll post back with my results.
[Edited on 31-3-2008 by CyrusGrey]
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JohnWW
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Thiocyanates, especially the ammonium salt or amine salts, are used as a weedkiller. At least Dow sells the stuff for that purpose.
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CyrusGrey
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Never noticed thiocyanate weedkiller when I was looking for chlorate weedkiller. The stores here in the US might not sell it much.
I tried a test tube synthesis from cyanuric acid just now. I put in about 200-300mg cyanuric acid and then covered it in about 100mg of sodium
carbonate. I heated it until the cyanuric acid melted and started bubbling (Thick fumes). I then let took it off the heat and immediatly put a spatula
of sulfur in it which proceeded to melt together with the other reagents. I let it cool and then added about 3mL of distilled water. However, there
was no color change when I added 4 drops of iron chloride etching solution. I shook it, still no color change. I heated it up again until it almost
boiled out of the tube, this gave me a fuffy brown solid which settled in the bottom 2/3 of the solution.
I'm not sure what the fluffy solid is, but it definatly isn't fake blood. An iron compound maybe?
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microcosmicus
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According to Fownes, isocyanate may be relieved of its oxygen by
ignition with charcoal in a covered crucible. (Cyanate will
automatically isomerize to isocyanate upon heating; in fact what
you produce by heating is likely already isocyanate.) Once you have
the cyanide, you can then try to add the suphur directly or
make ferrocyanide and proceed as above.
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CyrusGrey
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Yes, there is a thread on the forums detailing that proccess. I was hoping that I could skip the cyanide step in the hopes that it would give a more
cyanide free product, but thats probably not going to happen.
I don't think I'm really experienced enough to be comfortable handling cyanides, and I'm beginning to think that it would not really be a good idea to
smear this on my arm as a prank.
[Edited on 31-3-2008 by CyrusGrey]
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MagicJigPipe
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Well, in that case, fake blood is easily obtained from "party stores". Around here it's called Party City.
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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garage chemist
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You can easily make a melt containing small amounts of cyanide by melting together urea, sodium carbonate and charcoal (all powdered and premixed) and
briefly raising the temperature to red heat under exclusion of air (lightly stoppered test tube).
After it has cooled down, add sulfur and heat again to generate thiocyanate.
Then leach with water and add iron(III) solution.
The good thing is: If you simply add iron(III) in excess, it will bind any residual cyanide by forming nontoxic hexacyanoferrate.
Less desirable is that the latter could produce some prussian blue if you're unlucky, interfering with the desired color. But prussian blue is
insoluble, just let it settle (takes some time) and decant.
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microcosmicus
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Whether you prepare it the way garage_chemist described or the
way I described, extraction with alcohol is a good way to
purify your thiocyante because the cyanide or freeocyanide
does not dissolve in alcohol.
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CyrusGrey
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Argh! I ground together sodium carbonate, cyanuric acid, and charcoal into a fine powder. I then heated this with a propane torch for about 20 minutes
(Broke two crucibles doing this!  Don't buy crucibles from Cynmar). I then added
sulfur and heated again for about 10 minutes. I let the crucible cool down and broke as much as I could out of it and dissolved the bits in methanol.
This gave me a yellow solution. As the methanol evaporated the solution turned colorless (!?) and I started getting needle-like crystals.
When I added FeCl3 to a little bit of the methanol solution I get a red-orange color that doesn't look enough like blood to fool anyone. I was going
to evaporate the solution and try again with just water and the crystals but its getting too late. Oh well, maybe next April Fools.
Any ideas on what the (volatile?) yellow compound was?
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garage chemist
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Did you at least cover the crucible? Cyanides are very air-sensitive when hot.
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CyrusGrey
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Yes I covered it. The first crucible broke though, so I took it off the heat and then moved it to a second one, which only cracked. Stupid crucibles.
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garage chemist
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Hmm, if that doesn't work then you need to purchase some potassium ferrocyanide. That method is as amateur-friendly as it gets, avoiding any toxic
compounds.
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CyrusGrey
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I think I just need better crucibles. I wasn't able to heat the second crucible to near the amount that I did with the first and it STILL cracked.
They were brand new and unused, and they were my only two.
The crucible I had before these lasted for months and about a dozen reactions. I think I broke it by dropping it or something.
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microcosmicus
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You might also want to do as I often do and use an iron pipe cap for a crucible.
Since the reaction with sulphur takes place at the melting point of the sulphur,
you could do that in a glass container so as to avoid producing sulphide from
the iron container. (Although the problem may not be so bad should you carry
out the second step in the iron crucible since the sulphide would likely only
form a layer on the outside and, being quite insoluble, not contaminate your
product to an appreciable degree.) For a cover, you could use a plug which
screws into the pipe cap.
[Edited on 1-4-2008 by microcosmicus]
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meaniac
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Apologies for resurrecting an old thread:
I am interested in an OTC route to Thiocyanates, and where I am, the Ferrocyanides are not readily available.
Assuming we go the Urea+Alkali+Charcoal route, could the sulfur be added before the melt cooled? The idea is to dump sulfur in and replace the lid
immediately. How vigorous is the reaction between sulfur and cyanides? I assume it would need stirring at least after a while.
Then cool , break up and extract with acetone (I believe thiocyanate is the only substance there that's soluble in acetone).
From the CRC Handbook it seems as though the sodium salt is more soluble in acetone.
Anyone have an opinion? (esp Polverone and Garage Chemist!)
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Pyridinium
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Quote: Originally posted by CyrusGrey  | I think I just need better crucibles. I wasn't able to heat the second crucible to near the amount that I did with the first and it STILL cracked.
They were brand new and unused, and they were my only two.
The crucible I had before these lasted for months and about a dozen reactions. I think I broke it by dropping it or something. |
Crucibles, being porcelain, have a nonzero coefficient of thermal expansion. The best way to heat them is by gradually bringing them up to
temperature. First, wave the flame across the underside a few times, in a sort of oscillation. Gradually decrease the amplitude and frequency of the
oscillation until the flame is spending more and more time underneath the crucible.
I fairly routinely heat thin-walled, Made in China crucibles up to orange heat with no problems. I think the only time I ever broke one was when I
quenched the contents with water while it was still hot.
I promise you I'm not intending to be brusque here, but it seems highly likely that your long-surviving crucible was just a matter of chance. Any
glass or porcelain item can break catastrophically if subjected to thermal stresses. Because there is some randomness involved, that failure could be
five seconds from now or five months from now.
[Edited on 15-4-2012 by Pyridinium]
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