Copper(I) cyanide is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula CuCN. This off-white solid occurs in two
polymorph
Polymorphism, polymorphic, polymorph, polymorphous, or polymorphy may refer to:
Computing
* Polymorphism (computer science), the ability in programming to present the same programming interface for differing underlying forms
* Ad hoc polymorphi ...
s; 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 chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
in the preparation of
nitrile
In organic chemistry, a nitrile is any organic compound that has a functional group. The prefix ''cyano-'' is used interchangeably with the term ''nitrile'' in industrial literature. Nitriles are found in many useful compounds, including met ...
s.
[H. Wayne Richardson "Copper Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005. ]
Structure
Copper cyanide is a
coordination polymer
A coordination polymer is an inorganic or organometallic polymer structure containing metal cation centers linked by ligands. More formally a coordination polymer is a coordination compound with repeating coordination entities extending in 1, 2, o ...
. 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 a ...
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. 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 with sodium bisulfite at 60 °C, followed by the addition of
sodium cyanide to precipitate pure LT-CuCN as a pale yellow powder.
: 2 CuSO
4 + NaHSO
3 + H
2O + 2 NaCN → 2 CuCN + 3 NaHSO
4
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:
: 2 CuSO
4 + 4 NaCN → 2 CuCN + (CN)
2 + 2 Na
2SO
4
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
pseudohalide. 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 reagents 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 ...
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