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 Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

, in electroplating copper, and as a reagent in the preparation of nitriles.H. Wayne Richardson "Copper Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.

Structure

Copper cyanide is a coordination polymer. It exists in two polymorphs both of which contain - u-CN chains made from linear copper(I) centres linked by

cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

bridges A bridge is a structure built to span a physical obstacle (such as a body of water, valley, road, or rail) without blocking the way underneath. It is constructed for the purpose of providing passage over the obstacle, which is usually someth ...

. 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. 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. File:Structure of HT-CuCN (dissorderd CN).jpg, Figure 1: The structure of HT-CuCN showing the chains running along the c axis. Key: copper = orange and cyan = head-to-tail disordered cyanide groups. File:Structure of LT-CuCN (dissorderd CN).jpg, Figure 2: The structure of LT-CuCN showing sheets of chains stacking in an ABAB fashion. Key copper = orange and cyan = head-to-tail disordered cyanide groups. 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.

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 Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered h ...

with sodium bisulfite at 60 °C, followed by the addition of

sodium cyanide Sodium cyanide is a poisonous compound with the formula Na C N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its hi ...

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

with

, in this redox reaction, copper(I) cyanide forms together with

cyanogen Cyanogen is the chemical compound with the formula ( C N)2. It is a colorless and highly toxic gas with a pungent odor. The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups – analogous to diatomic halogen molecu ...

: : 2 CuSO₄ + 4 NaCN → 2 CuCN + (CN)₂ + 2 Na₂SO₄ Because this synthetic route produces

, 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

pseudohalide Pseudohalogens are polyatomic analogues of halogens, whose chemistry, resembling that of the true halogens, allows them to substitute for halogens in several classes of chemical compounds. Pseudohalogens occur in pseudohalogen molecules, inorganic ...

. 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 u(CN)₃sup>2− and u(CN)₄sup>3−, which exhibit trigonal planar and tetrahedral coordination geometry, respectively. These complexes contrast with those of silver and gold cyanides, which form (CN)₂sup>− ions in solution. The coordination polymer KCu(CN)₂ contains u(CN)₂sup>− units, which link together forming helical anionic chains.Housecroft, Catherine E.; Sharpe, Alan G. (2008) Inorganic Chemistry (3rd ed.), Pearson: Prentice Hall. ISBN 978-0-13-175553-6. Copper cyanide is also soluble in concentrated aqueous ammonia, pyridine and N-methylpyrrolidone.

Applications

Cuprous cyanide is used for electroplating copper.

Organic synthesis

CuCN is a prominent reagent in organocopper chemistry. It reacts with

organolithium reagent In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...

s to form "mixed cuprates" with the formulas Li CuCNand Li₂ ₂CuCN The use of CuCN revolutionized the deployment of simpler organocopper reagents of the type CuR and LiCuR₂, the so-called

Gilman reagent A Gilman reagent is a lithium and copper ( diorganocopper) reagent compound, R2CuLi, where R is an alkyl or aryl. These reagents are useful because, unlike related Grignard reagents and organolithium reagents, they react with organic halides to ...

s. In the presence of cyanide, these mixed cuprates are more readily purified and more stable. The mixed cuprates Li CuCNand Li₂ ₂CuCNfunction as sources of the carbanions R⁻, but with diminished reactivity compared to the parent organolithium reagent. Thus they are useful for conjugate additions and some displacement reactions. CuCN also forms silyl and stannyl reagents, which are used as sources of R₃Si⁻ and R₃Sn⁻. CuCN is used in the conversion of aryl halides to nitriles.Steven H. Bertz, Edward H. Fairchild, Karl Dieter, "Copper(I) Cyanide" in Encyclopedia of Reagents for Organic Synthesis 2005, John Wiley & Sons. CuCN has also been introduced as a mild electrophilic source of nitrile under oxidative conditions, for instance secondary amines as well as sulfides and disulfides have been efficiently cyanated using this methodology. This last methodology has been then introduced in a domino 3 component reaction, leading to 2-aminobenthiazoles.

References

External links

National Pollutant Inventory - Cyanide compounds fact sheet
{{Authority control Copper compounds Cyanides Inorganic insecticides Fungicides