Preparation
Cuprous cyanide is commercially available and is supplied as the low-temperature polymorph. It can be prepared by the reduction of copper(II) sulfate with sodium bisulfite at 60 °C, followed by the addition of sodium cyanide to precipitate pure LT-CuCN as a pale yellow powder.
- 2 CuSO4 + NaHSO3 + H2O + 2 NaCN → 2 CuCN + 3 NaHSO4
On addition of sodium bisulfite the copper sulfate solution turns from blue to green, at which point the sodium cyanide is added. The reaction is performed under mildly acidic conditions. Copper cyanide has historically been prepared by treating copper(II) sulfate with sodium cyanide, in this redox reaction, copper(I) cyanide forms togther with cyanogen:
- 2 CuSO4 + 4 NaCN → 2 CuCN + (CN)2 + 2 Na2SO4
Because this synthetic route produces cyanogen, uses two equivalents of sodium cyanide per equivalent of CuCN made and the resulting copper cyanide is impure it is not the industrial production method. The similarity of this reaction to that between copper sulfate and sodium iodide to form copper(I) iodide is one example of cyanide ions acting as a pseudo halide. It also explains why copper(II) cyanide, Cu(CN)2, has not been synthesised.
Read more about this topic: Copper(I) Cyanide
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