Cuprous cyanide

Copper(I) cyanide
Identifiers
CAS number 544-92-3 YesY
PubChem 11009
ChemSpider 10543 YesY
EC number 208-883-6
RTECS number GL7150000
Jmol-3D images Image 1
Properties
Molecular formula CuCN
Molar mass 89.563 g/mol
Appearance off-white / pale yellow powder
Density 2.92 g/cm3[1]
Melting point

474 °C, 747 K, 885 °F

Solubility in water negligible
Solubility insoluble in ethanol, cold dilute acids;
soluble in NH4OH, KCN
Hazards
MSDS Oxford MSDS
EU Index 006-007-00-5
EU classification Very toxic (T+)
Dangerous for the environment (N)
R-phrases R26/27/28, R32, R50/53
S-phrases (S1/2), S7, S28, S29, S45, S60, S61
NFPA 704
0
4
0
Flash point Non-flammable
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Copper(I) cyanide is an inorganic compound with the formula CuCN. This off-white solid occurs in two polymorphs; impure samples can be green due to the presence of Cu(II) impurities. The compound is useful as a catalyst, in electroplating copper, and as a reagent in the preparation of nitriles.[2]

Structure

Copper cyanide is a coordination polymer. It exists in two polymorphs both of which contain -[Cu-CN]- chains made from linear copper(I) centres linked by cyanide bridges. In the high-temperature polymorph, HT-CuCN, which is isostructural with AgCN, the linear chains pack on a hexagonal lattice and adjacent chains are off set by +/- 1/3 c, Figure 1.[3] In the low-temperature polymorph, LT-CuCN, the chains deviate from linearity and pack into rippled layers which pack in an AB fashion with chains in adjacent layers rotated by 49 °, Figure 2.[4]

LT-CuCN can be converted to HT-CuCN by heating to 563 K in an inert atmosphere. In both polymorphs the copper to carbon and copper to nitrogen bond lengths are ~1.85 Å and bridging cyanide groups show head-to-tail disorder.[5]

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.[6]

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 together with cyanogen:[7]

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.

Reactions

Copper cyanide is insoluble in water but rapidly dissolves in solutions containing CN- to form [Cu(CN)3]2- and [Cu(CN)4]3-, these ions are trigonal planar and tetrahedral respectively. This is in contrast to both silver and gold cyanides which form [M(CN)2]- ions in solution. [8] The coordination polymer KCu(CN)2 contains [Cu(CN)2]- units which link together forming helical anionic chains.[9]

Copper cyanide is also soluble in 0.88 aqueous ammonia, pyridine and N-methylpyrrolidone.

Applications

Cuprous cyanide is used for electroplating copper.[2] The compound is useful reagent in organic synthesis, for example in the regioselective and stereoselective allylation and conjugate addition of N-Boc-2-lithiopyrrolidine and N-Boc-2-lithiopiperidine,[10] or the copper cyanide catalyzed palladium coupling of α-lithio amines and aryl iodides.[11]

References

External links

  • National Pollutant Inventory - Cyanide compounds fact sheet
  • National Pollutant Inventory - Copper and compounds fact sheet
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