Molecular structure and Synthesis of Copper(I) cyanide

Copper(I) cyanide is a monovalent copper salt. At room temperature and under atmospheric pressure, it appears as an off-white to green solid powder and has a certain degree of hygroscopicity. It is poorly soluble in water and ether-type organic solvents but is soluble in alcohol-type organic solvents. Copper(I) cyanide is primarily used as a basic raw material in fine chemical production. According to literature reports, it can be used in electroplating of copper and its alloys, as a raw material for anti-tuberculosis drugs and other pharmaceuticals in medicine, as well as in the manufacture of insecticides, antifouling paints, and other products.

Figure1: Picture of Copper(I) cyanide

Molecular structure

Copper(I) Cyanide is an important reagent in organic, organometallic, and supramolecular chemistry due to both its copper center and the versatile cyanide ligand. In the solid phase, Copper(I) Cyanide and many of its derivatives exhibit oligomeric or polymeric structures, a characteristic shared with other metal cyanides. It is often difficult to determine the orientation of the cyano ligand in an X‑ray structure. A gas‑phase reaction between copper vapor and cyanogen (NCCN) clearly produces Copper(I) Cyanide as CuCN, rather than CuNC. The precise structure of the Copper(I) Cyanide thus produced was determined using millimeter/submillimeter‑wave spectroscopy. Because of the highly efficient synthesis and the presence of significant amounts of two copper isotopes, such strong signals were observed that natural‑abundance materials allowed the detection of transitions for four isotopomers—⁶³Cu¹²C¹⁴N, ⁶⁵Cu¹²C¹⁴N, ⁶³Cu¹³C¹⁴N, and ⁶³Cu¹²C¹⁵N—and the determination of the ro, rs, and rm(2) structures. All data unequivocally show a linear geometry and that the carbon of the cyanide ligand is bound to copper, with a Cu−C distance of 1.82962(4) Å in the rm(2) structure, which is likely to be the closest to the equilibrium geometry. [2]

Synthesis

Researchers have reported a preparation process for Copper(I) Cyanide. In this process, metallic copper, crystalline copper sulfate, and sodium chloride are mixed with an appropriate amount of water and reacted at a temperature of 80–120 °C for 3–4 hours to produce a monovalent copper salt, namely a complex solution formed by cuprous chloride and sodium chloride. This complex solution is then reacted with sodium cyanide at room temperature to generate a precipitate of Copper(I) Cyanide. The obtained precipitate is subsequently washed with acid and water, and dried at 110 °C to yield pure, white, monoclinic crystalline Copper(I) Cyanide. The reported process is characterized by simple equipment, a short process flow, easy control, low cost, and high product quality, making it suitable for large-scale industrial production.

Oxidation of Copper(I) Cyanide

In the gold mining industry, copper(I) cyanide (Cu(CN)₄³⁻) presents the biggest concern in cyanide management because it is significantly more stable than free cyanide. Copper(I) cyanide is highly toxic to aquatic life; therefore, environmentally friendly techniques are required for its removal from gold mine effluent. The oxidation of copper(I) cyanide by iron(VI) (FeVIO₄²⁻, Fe(VI)) and iron(V) (FeVO₄³⁻, Fe(V)) was studied using stopped-flow and premix pulse radiolysis techniques. The stoichiometry of the reaction with Fe(VI) was determined to be: 5HFeO₄⁻ + Cu(CN)₄³⁻ + 8H₂O → 5Fe(OH)₃ + Cu²⁺ + 4CNO⁻ + 3/2O₂ + 6OH⁻. The rate law for the oxidation of copper(I) cyanide by Fe(VI) was found to be first-order with respect to each reactant. The reaction rates decreased with increasing pH, which was mostly attributed to a decrease in the concentration of the reactive protonated Fe(VI) species, HFeO₄⁻. A mechanism is proposed that agrees with the observed reaction stoichiometry and rate law. The rate constant for the oxidation of copper(I) cyanide by Fe(V) was determined at pH 12.0 to be 1.35 (±0.02) × 10⁷ M⁻¹·s⁻¹, which is approximately three orders of magnitude larger than that for Fe(VI). The results indicate that Fe(VI) is highly efficient for the removal of cyanides from gold mill effluent. [1]

Toxicity

Copper(I) Cyanide exhibits toxicity similar to that of hydrocyanic acid. Chronic exposure to Copper(I) Cyanide may lead to symptoms such as headache, weight loss, disorders of sexual function and libido, autonomic neurasthenia, anemia, and leukopenia, as well as elevated levels of aminotransferase and cyanomethemoglobin.

Reference

[1] Sharma V K, Burnett C R, Yngard R A, et al. Iron (VI) and iron (V) oxidation of copper (I) cyanide[J]. Environmental science & technology, 2005, 39(10): 3849-3854.

[2] Grotjahn D B, Brewster M A, Ziurys L M. The first precise molecular structure of a monomeric transition metal cyanide, copper (I) cyanide[J]. Journal of the American Chemical Society, 2002, 124(20): 5895-5901.