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Author: Subject: Preparation of Cyanide Salts
mbrown3391
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[*] posted on 26-10-2011 at 20:02
Preparation of Cyanide Salts


I am going to attempt this synthesis:

A concentrated solution is made with 100g photographer's grade potassium ferricyanide in water. An excess of 80% sulfuric acid (>30ml) is added to this solution, and the resulting solution poured into a flask, which is heated in a water bath. HCN is evolved, and bubbled through a concentrated solution of 75g sodium hydroxide in water, forming sodium cyanide. When the reaction ceases, the sodium cyanide solution is allowed to evaporate, then the resulting crystals are washed with ethanol to remove any remaining sodium hydroxide.

If this reaction is performed outside, will the HCN gas that escapes pose a health threat, or will concentrations be negligible?
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woelen
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[*] posted on 26-10-2011 at 22:38


This method hardly will give you any NaCN. A solution of NaCN quickly hydrolyses in water and your yield will be low. Almost all wet methods for making NaCN use a solution in alcohol. Please search the forums for more information, there is a lot of info on this.

Coming back to your question, if you do this outside, then wait for a breezy day and ALWAYS stay with your back pointed towards the wind and the reaction vessel in front of you. Also assure that in down-wind direction there are no people nearby, e.g. houses of neightbours, a path where people can be walking.

I'm also not sure whether a solution of ferricyanide (red prussiate of potash) will give good yields of HCN. Normally the ferrocyanide (yellow prussiate of potash) is used. I can imagine that in ferricyanide there will be internal oxidation of part of the cyanide by the iron(III), but I am not sure about this.

[Edited on 27-10-11 by woelen]




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simba
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[*] posted on 27-10-2011 at 05:01


https://www.sciencemadness.org/whisper/viewthread.php?tid=23
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mbrown3391
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[*] posted on 27-10-2011 at 13:00


I chose potassium ferricyanide because it is significantly easier to find, being a photographic chemical, but from what i've read you are correct: yield will be lower than with the ferrocyanide. I hadn't thought of using a solution of hydroxide in alcohol... i will definitely try that instead. thanks.
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cyanureeves
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[*] posted on 27-10-2011 at 14:37


i had no trouble finding potassiumferrocyanide nor ferricyanide but the ferricyanide was way more expensive,about 10x more expensive by weight. i tried that method but without all the water and i believe i ended up with cyanate which turned to ammonia in about a day. i have phosphoric acid that i will be using instead of sulfuric but i am not ready yet to make the synthesis. i am now kinda wary of HCN. use ethanol and hydroxide as the recipient for the HCN. i do love,love this stuff that makes the pretty blue.careful with the HCN mbrown3391 and i hope you succeed.
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