:Copper(I) cyanide

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.{{cite journal |author1=S. J. Hibble |author2=S. M. Cheyne |author3=A. C. Hannon |author4=S. G. Eversfield | title = CuCN: A Polymorphic Matirial. Structure of One Form from Total Neutron Diffraction | journal = Inorg. Chem. | year = 2002 | volume = 41 | issue = 20 | pages = 8040–8048 | doi = 10.1021/ic0257569|pmid=12354028 }} 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.{{cite journal |author1=S. J. Hibble |author2=S. G. Eversfield |author3=A. R. Cowley |author4=A. M. Chippindale | title = Copper(I) Cyanide: A Simple Compound with a complicated Structure and Surprising Room-Temperature Reactivity | journal = Angew. Chem. Int. Ed. | year = 2004 | volume = 43 | issue = 5 | pages = 628–630 | doi = 10.1002/anie.200352844|pmid=14743423 }}

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.{{cite journal |author1=S. Kroeker |author2=R. E. Wasylishen |author3=J. V. Hanna | title = The Structure of Solid Copper(I) Cyanide: A Multinuclear Magnetic and Quadrupole Resonance Study. | journal = Journal of the American Chemical Society | year = 1999 | volume = 121 | issue = 7 | pages = 1582–1590 | doi = 10.1021/ja983253p}}

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.{{cite journal | author = H. J. Barber | title = Cuprous Cyanide: A Note on its Preparation and Use | journal = J. Chem. Soc. | year = 1943 | page = 79 | doi=10.1039/JR9430000079 }}

: 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:{{OrgSynth | author = J. V. Supniewski and P. L. Salzberg | title = Allyl Cyanide | collvol = 1 | collvolpages = 46 | year = 1941 | prep = CV1P0046}}

: 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 pseudohalide. It also explains why cupric cyanide (copper(II) cyanide, Cu(CN)₂), has not been synthesised.

Copper cyanide is insoluble in water but rapidly dissolves in solutions containing CN⁻ to form [Cu(CN)₃]²⁻ and [Cu(CN)₄]³⁻, which exhibit trigonal planar and tetrahedral coordination geometry, respectively. These complexes contrast with those of silver and gold cyanides, which form [M(CN)₂]⁻ ions in solution.{{cite book|last=Sharpe|first=A. G.|title=The Chemistry of Cyano Complexes of the Transition Metals|year=1976|publisher=Academic Press|isbn=0-12-638450-9|pages=265}} The coordination polymer KCu(CN)₂ contains [Cu(CN)₂]⁻ 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.

Cuprous cyanide is used for electroplating copper.

CuCN is a prominent reagent in organocopper chemistry. It reacts with organolithium reagents to form "mixed cuprates" with the formulas Li[RCuCN] and Li₂[R₂CuCN]. The use of CuCN revolutionized the deployment of simpler organocopper reagents of the type CuR and LiCuR₂, the so-called Gilman reagents. In the presence of cyanide, these mixed cuprates are more readily purified and more stable.

The mixed cuprates Li[RCuCN] and Li₂[R₂CuCN] function 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⁻.Dieter, R. K. In Modern Organocopper Chemistry; Krause, N., Ed.; Wiley-VCH: Mörlenback, Germany, 2002; Chapter 3.

CuCN is used in the conversion of aryl halides to nitriles in the Rosenmund–von Braun reaction.Steven H. Bertz, Edward H. Fairchild, Karl Dieter, "Copper(I) Cyanide" in Encyclopedia of Reagents for Organic Synthesis 2005, John Wiley & Sons. {{doi|10.1002/047084289X.rc224.pub2}}

CuCN has also been introduced as a mild electrophilic source of nitrile under oxidative conditions, for instance secondary amines{{Cite journal|last1=Teng|first1=Fan|last2=Yu|first2=Jin-Tao|last3=Jiang|first3=Yan|last4=Yang|first4=Haitao|last5=Cheng|first5=Jiang|date=2014|title=A copper-mediated oxidative N-cyanation reaction|url=http://xlink.rsc.org/?DOI=c4cc03439b|journal=Chemical Communications|language=en|volume=50|issue=61|pages=8412–8415|doi=10.1039/c4cc03439b|pmid=24948488|issn=1364-548X|url-access=subscription}} as well as sulfides and disulfides{{Cite journal|last1=Castanheiro|first1=Thomas|last2=Gulea|first2=Mihaela|last3=Donnard|first3=Morgan|last4=Suffert|first4=Jean|date=2014|title=Practical Access to Aromatic Thiocyanates by CuCN-Mediated Direct Aerobic Oxidative Cyanation of Thiophenols and Diaryl Disulfides|url=http://onlinelibrary.wiley.com/doi/10.1002/ejoc.201403279/abstract|journal=European Journal of Organic Chemistry|language=en|volume=2014|issue=35|pages=7814–7817|doi=10.1002/ejoc.201403279|s2cid=98786803 |issn=1099-0690}} have been efficiently cyanated using this methodology. This last methodology has been then introduced in a domino 3 component reaction, leading to 2-aminobenthiazoles.{{Cite journal|last1=Castanheiro|first1=Thomas|last2=Suffert|first2=Jean|last3=Gulea|first3=Mihaela|last4=Donnard|first4=Morgan|date=2016|title=Aerobic Copper-Mediated Domino Three-Component Approach to 2-Aminobenzothiazole Derivatives|journal=Organic Letters|volume=18|issue=11|pages=2588–2591|doi=10.1021/acs.orglett.6b00967|pmid=27192105|issn=1523-7060|doi-access=free}}

{{Reflist|30em}}

{{Commons category|Copper(I) cyanide}}

• [http://www.npi.gov.au/database/substance-info/profiles/29.html National Pollutant Inventory - Cyanide compounds fact sheet]
• [http://www.npi.gov.au/database/substance-info/profiles/27.html National Pollutant Inventory - Copper and compounds fact sheet]

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