azpcpXX - 8-8-2015 at 07:32
Hi all!
I found very easy way to prepare metal cyanides in solution without high temperatures and gaseos HCN. The reaction between ferrocyanide solution and
nitrite salt produces cyanide acording to the euqation:
[Fe(CN)6]4− + H2O + NO2− → [Fe(CN)5(NO)]2− + CN− + 2 OH−(wikipedia)
This reaction ends with solution of nitroprusside salt and hydroxide. I have no idea how to isolate pure cyanide from this solution. Maybe metal
cyanides are soluble in immisible with water solvents? Can someone help me?
Thanks!
kecskesajt - 8-8-2015 at 08:43
Add to 2x of its volume of alcohol.
azpcpXX - 8-8-2015 at 09:10
I think its no way becouse hydroxides are soluble in alcohols, alcohols are soluble in water and it all will end with homogenos mixture.
On another side the reaction can be performed in anhydrous ethanol. Cyanoferrates and nitroferrates are insoluble in alcohol but potassium nitrite is.
They will precitipate and after evaporation leave me with mixture of KCN and KOH. Maybe suitable solvent can disslove only one of the solids and leave
sediment.
Boffis - 8-8-2015 at 09:51
This reaction is used to prepare nitroprusside but since the hydroxide ions destroy the product a compound to mop up the hydroxide ions must be added.
This usually means that the cyanide ions get protonated in the process and the HCN expelled as a gas (so back to square one!). There is a book on the
forum library with full details but I can't remember which one off the top of my head.
But also this is a very inefficient way of making cyanides.
azpcpXX - 8-8-2015 at 10:04
What hydroxide ions destroy, the cyanide or nitroprusside? The reaction produces low amount of cyanide but its done in solution and is safe for lab
scale.
Dan Vizine - 11-8-2015 at 19:41
By definition it isn't a simple way if isolation is difficult.
You will probably never find a method better than collecting stabilized HCN and adding it to a cold stirred aqueous/alcoholic metal hydroxide
solution.
AJKOER - 14-8-2015 at 07:38
Comments from atomistry.com (link: http://carbon.atomistry.com/hydrocyanic_acid.html ) that you may find helpful if you decide to consider a gaseous route:
"Hydrogen cyanide is generally prepared, however, from potassium ferrocyanide or a simple cyanide. In either case it is synthetic in origin, for
ferrocyanide was originally made by heating together a mixture of potassium carbonate, iron, and nitrogenous organic matter, whilst cyanide is
obtained either from the hydrogen cyanide formed synthetically in gas manufacture or by passing ammonia over a heated mixture of alkali carbonate, and
carbon (Beilby's process). When powdered potassium ferrocyanide is distilled with dilute sulphuric acid (1 part H2SO4 to 2 parts water) hydrocyanic
acid is evolved according to the reaction:
2K4Fe(CN)6 + 3H2SO4 = 6HCN + K2Fe[Fe(CN)6] + 3K2SO4.
The vapour may be dried by passing it through calcium chloride tubes kept at 30° C. by immersion in warm water, and then condensed in a freezing
mixture; or the vapour may be at once passed into water if only a solution of the acid is required. "
[Edited on 14-8-2015 by AJKOER]