psyloxy (Hive Addict)
10-10-03 06:51
No 463729
      cyanides from thiocyanates     

NaCN is without doubt a useful reagent. Formylation of phenol ethers (with ZnCN made from ZnCl2/NaCN) and synthesis of phenylacetonitriles from benzylhalides comes to mind. The two preparations on Rh.ws have disadvantages. The synth starting from K4[Fe(CN)6]3 produces volatile HCN as intermediate. The alternative BaO + 3C + N2 ----> Ba(CN)2 + CO just doesn't look too appealing. A FSE session didn't turn up any hits where either KCN/KSCN or NaCN/NaSCN were mentioned together in the same post so I assume that topic was not discussed before though NaSCN __> NaCN seems like a favorable reaction. Here is a snipple from Patent DE89607 which claims to be an improvement of Patent US507753 :

97Kg KSCN and 65Kg Zn dust are heated (to 300-400°C) in an iron-pan with stirring. As soon as the mass begins to gleam the external heating is discontinued and one lets the reaction run till the end. The stripped alkaline solution is to contain 60Kg KCN, i.e. ~90% yield. 1-2% NaOH is said to help the reaction immensley.

Well, that's the only info I have available right now. I'd like to hear some opinions / additional knowledge on that reaction. After all it doesn't seem to be too uncommon.

--psyloxy--
 
 
 
 
    Rhodium
(Chief Bee)
10-10-03 10:57
No 463753
      Poison Gas Pyrotechnics     

The reaction Zn + S -> ZnS is very exothermic (very nice rocket fuel combination), so whatever bonds need to be broken to deconstruct NaSCN -> NaCN + S it will definitely be outweighed by the former reaction.

Someone please calculate the heat given off in the NaSCN + Zn -> NaCN + ZnS - I think it may be quite a lot, and may resemble thermite. No doubt about the fact that a lot of very poisonous gasses will be given off, and that the reaction should not be performed by just any amateur...
 
 
 
 
    psyloxy
(Hive Addict)
10-10-03 12:12
No 463762
      noxious gases ?     

The US patent says the reaction takes place at between 425°C and 480°C heats itself up up to 540°C. The same reaction with lead is reported to be much less violent.

Which gases could be produced, and how ? I guess any of H2S, HCN, SOx, NH3, NOx, CO, CO2 but I could only imagine some sort of bizarre high-temp chemistry taking place in contact with air.

I think everybody agrees no chemistry involving -CN should be practiced by amateurs.

--psyloxy--
 
 
 
 
    Rhodium
(Chief Bee)
10-11-03 15:32
No 463978
      never trust high-temp chemistry     

I could only imagine some sort of bizarre high-temp chemistry taking place in contact with air.

Exactly my thoughts - never trust high-temp chemistry, it is very unpredictable.