Copper(II) chloride
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{{Chembox new
| Name = Copper(II) chloride
| ImageFile = copper(II) chloride dihydrate.jpg
<!-- | ImageSize = 200px -->
| ImageName = copper(II) chloride dihydrate
| ImageFile1 = Tolbachite-3D-balls.png
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| ImageName1 = Crystal structure of anhydrous copper(II) chloride
| ImageFile2 = Tolbachite-3D-polyhedra.png
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| ImageName2 = Crystal structure of anhydrous copper(II) chloride
| IUPACName = Copper(II) chloride<br />Copper dichloride
| OtherNames = Cupric chloride
| Section1 = {{Chembox Identifiers
| CASOther = [7447-39-4] (ahydrous)<br />10125-13-0] (dihydrate)
| RTECS = GL7000000
}}
| Section2 = {{Chembox Properties
| Formula = CuCl<sub>2</sub>
| MolarMass = 134.45 g/mol (anhydrous)<br />170.48 g/mol (dihydrate)
| Appearance = blue-green solid (dihydrate)<br /> yellow-brown solid (anhydrous)
| Density = 3.386 g/cm³, solid
| Solubility = 70.6 g/100 mL (0 °C)<br />75.7 g/100 mL (25 °C)
| Solvent = [[methanol]]
| SolubleOther = 68 g/100 mL (15 °C)
| Solvent = [[ethanol]]
| SolubleOther = 53 g/100 mL (15 °C)
| MeltingPt = 100 °C (dehydration<br />of dihydrate)
| BoilingPt = decomposes at 993°C<br /> (anhydrous)
}}
| Section3 = {{Chembox Structure
| Coordination = [[Octahedron|Octahedral]]
| CrystalStruct = distorted [[Cadmium iodide#Structure|CdI<sub>2</sub> structure]]
}}
| Section7 = {{Chembox Hazards
| ExternalMSDS = [http://sciencelab.com/msds.php?msdsId=9923592 ScienceLab.com]
| EUClass = not listed
| FlashPt = nonflammable
}}
| Section8 = {{Chembox Related
| OtherAnions = [[Copper(II) fluoride]]<br />[[Copper(II) bromide]]<br />[[Copper(I) iodide]]<!-- this is not a typo, copper(II) iodide does not exist -->
| OtherCations = [[Copper(I) chloride]]<br />[[Silver chloride]]<br />[[Gold(III) chloride]]
}}
}}
'''Copper(II) chloride''' is the [[chemical compound]] with the [[chemical formula|formula]] CuCl<sub>2</sub>. This a yellow-brown solid which slowly absorbs moisture to form a blue-green [[hydrate|dihydrate]]. It occurs naturally as the very rare mineral [[eriochalcite]].
==Structure==
Anhydrous CuCl<sub>2</sub> adopts a distorted [[cadmium iodide]] structure. Most copper(II) compounds exhibit distortions from idealized octahedral geometry due to the [[Jahn-Teller effect]], which in this case describes the localisation of one d-electron into a [[molecular orbital]] that is strongly antibonding with respect to a pair of ligands. In CuCl<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> the copper can be described as a highly distorted octahedral complex, the Cu(II) center being surrounded by two water ligands and four chloride ligands, which [[bridging ligand|bridge]] asymmetrically to other Cu centers.<ref>Wells, A.F. (1984) Structural Inorganic Chemistry, Oxford: Clarendon Press. ISBN 0-19-855370-6.</ref>
==Properties==
Copper(II) chloride dissociates in aqueous solution to give the blue color of [Cu(H<sub>2</sub>O)<sub>6</sub>]<sup>2+</sup> and yellow or red color of the halide complexes of the formula [CuCl<sub>2+x</sub>]<sup>x-</sup>. Concentrated solutions of CuCl<sub>2</sub> appear green because of the combination of these various chromophores. The color of the dilute solution depends on temperature, being green around 100 °C and blue at room temperature.<ref>Alfred Swaine Taylor; Robert Eglesfeld Griffith. On Poisons, in Relation to Medical Jurisprudence and Medicine. Lea & Blanchard, 1848, p. 378.</ref> When Copper(II) Chloride burns, it emitts a green-blue colour.
It is a weak [[Lewis acid]], and a mild [[Redox|oxidizing agent]]. It has a crystal structure consisting of polymeric chains of flat CuCl<sub>4</sub> units with opposite edges shared. It decomposes to [[Copper(I) chloride|CuCl]] and [[Chlorine|Cl<sub>2</sub>]] at 1000 °C:
:2 CuCl<sub>2</sub>([[solid|s]]) → 2 [[Copper(I) chloride|CuCl]]([[solid|s]]) + [[Chlorine|Cl<sub>2</sub>]]([[gas|g]])
In its reaction with HCl (or other [[chloride]] sources) to form the complex ions CuCl<sub>3</sub><sup>-</sup> and CuCl<sub>4</sub><sup>2-</sup>.<ref>Gill, N. S.; Taylor, F. B., "Tetrahalo Complexes of Dipositive Metals in the First Transition Series", Inorganic Syntheses, 1967, volume 9, pages 136-142.</ref>
[[Image:CuCl2 chloride equilibria.png|400px|''Equilibria of CuCl2 with chloride ion'']]
Some of these complexes can be crystallized from aqueous solution, and they adopt a wide variety structural types (Fig. 1).
<!--notice that the charge is incorrect in some drawings-->
[[Image:CuCl2 chloride complexes.png|480px|''Structure of some chloride complexes of CuCl2'']]
Copper(II) chloride also forms a rich variety of other [[complex (chemistry)|coordination complexes]] with [[ligand]]s such as [[pyridine]] or [[triphenylphosphine oxide]]:
:CuCl<sub>2</sub> + 2 [[pyridine|C<sub>5</sub>H<sub>5</sub>N]] → [CuCl<sub>2</sub>(C<sub>5</sub>H<sub>5</sub>N)<sub>2</sub>] (tetragonal)
:CuCl<sub>2</sub> + 2 [[triphenylphosphine oxide|(C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>P=O]] → [CuCl<sub>2</sub>((C<sub>6</sub>H<sub>5</sub>)<sub>3</sub>P=O)<sub>2</sub>] (tetrahedral)
However "soft" ligands such as [[phosphine]]s (e.g., [[triphenylphosphine]]), iodide, and cyanide as well as some tertiary [[amines]] cause [[Redox|reduction]] to give copper(I) complexes. To convert copper(II) chloride to copper(I) derivatives it is generally more convenient to reduce an aqueous solution with the reducing agent [[sulfur dioxide]]:
:2 CuCl<sub>2</sub>(aq) + [[sulfur dioxide|SO<sub>2</sub>]] → 2 CuCl(s) + 2 [[hydrochloric acid|HCl]]([[aqueous|aq]]) + [[Sulfuric acid|H<sub>2</sub>SO<sub>4</sub>]](aq)
CuCl<sub>2</sub> can simply react as a source of Cu<sup>2+</sup> in precipitation reactions for making insoluble copper(II) salts, for example copper(II) hydroxide, which can then decompose above 30 °[[celsius|C]] to give [[copper(II) oxide]]:
:CuCl<sub>2</sub>([[aqueous|aq]]) + 2 [[sodium hydroxide|NaOH]]([[aqueous|aq]]) → Cu(OH)<sub>2</sub>([[Solid|s]]) + 2 [[sodium chloride|NaCl]]([[aqueous|aq]])
Followed by
:Cu(OH)<sub>2</sub>([[Solid|s]]) → [[Copper(II) oxide|CuO]]([[Solid|s]]) + [[water (molecule)|H<sub>2</sub>O]]([[liquid|l]])
==Preparation==
Copper(II) chloride is prepared by the action of [[hydrochloric acid]] on [[copper(II) oxide]], copper(II) hydroxide or [[copper(II) carbonate]], for example:
:[[Copper(II) oxide|CuO]]<sub>([[Solid|s]])</sub> + 2 [[hydrochloric acid|HCl]]<sub>([[aqueous|aq]])</sub> → CuCl<sub>2</sub><sub>(aq)</sub> + [[water (molecule)|H<sub>2</sub>O]]<sub>([[liquid|l]])</sub> Anhydrous CuCl<sub>2</sub> may be prepared directly by union of the elements, copper and [[chlorine]].
CuCl<sub>2</sub> may be purified by crystallisation from hot dilute [[hydrochloric acid]], by cooling in a [[Calcium chloride|CaCl<sub>2</sub>]]-ice bath<sup>[7]</sup>.
==Uses==
A major industrial application for copper(II) chloride is as a co-catalyst (along with [[palladium(II) chloride]]) in the [[Wacker process]]. In this process, [[ethene]] (ethylene) is converted to [[ethanal]] (acetaldehyde) using water and air. In the process [[Palladium(II) chloride|PdCl<sub>2</sub>]] is [[Redox|reduced]] to [[Palladium|Pd]], and the CuCl<sub>2</sub> serves to re-oxidise this back to PdCl<sub>2</sub>. Air can then oxidise the resultant [[Copper(I) chloride|CuCl]] back to CuCl<sub>2</sub>, completing the cycle.
(1) [[ethene|C<sub>2</sub>H<sub>4</sub>]]([[gas|g]]) + PdCl<sub>2</sub>(aq) + H<sub>2</sub>O (l) → CH<sub>3</sub>CHO (aq) + Pd(s) + 2 [[hydrochloric acid|HCl]](aq)
(2) Pd(s) + 2 CuCl<sub>2</sub>(aq) → 2 CuCl(s) + PdCl<sub>2</sub>(aq)
(3) 2 CuCl(s) + 2 HCl(aq) +<sup>1</sup>/<sub>2</sub>[[Oxygen|O<sub>2</sub>]](g) → 2 CuCl<sub>2</sub>(aq) + H<sub>2</sub>O(l)
Overall process: C<sub>2</sub>H<sub>4</sub> +<sup>1</sup>/<sub>2</sub>O<sub>2</sub> → CH<sub>3</sub>CHO
Copper(II) chloride has a variety of applications in [[organic synthesis]]<sup>[7]</sup>. It can effect [[chlorination]] of [[aromatic hydrocarbons]]- this is often performed in the presence of [[aluminium oxide]]. It is able to chlorinate the alpha position of [[carbonyl]] compounds<sup>[8]</sup>:
[[Image:CuCl2 alpha chlorination.png|400px|''Alpha chlorination of an aldehyde using CuCl2'']]
This reaction is performed in a polar solvent such as [[Dimethylformamide|DMF]], often in the presence of [[lithium chloride]], which speeds up the reaction rate.
CuCl<sub>2</sub>, in the presence of [[oxygen]], can also oxidise [[phenols]]. The major product can be directed to give either a [[quinone]] or a coupled product from oxidative dimerisation. The latter process provides a high-yield synthesis of [[1,1-binaphthol]] (also called BINOL) and its derivatives, these can even be made as a single [[enantiomer]] in high [[enantiomeric excess]]<sup>[9]</sup>:
[[Image:CuCl2 naphthol coupling.png|400px|''Coupling of beta-naphthol using CuCl2'']]
Such compounds are valuable intermediates in the synthesis of [[BINAP]] and its derivatives, popular as [[chirality (chemistry)|chiral]] [[ligand]]s for asymmetric [[hydrogenation]] catalysts.
CuCl<sub>2</sub> also catalyses the [[free radical]] addition of [[sulfonyl chlorides]] to [[alkene]]s; the alpha-chlorosulfone may then undergo [[elimination]] with base to give a vinyl [[sulfone]] product.
Copper(II) chloride is also used in [[pyrotechnics]] as a blue/green coloring agent.
==Precautions==
Although copper is an essential element, all metal salts are potentially toxic if mishandled. See [[MSDS]].
==References==
<references/><!--too bad there are no titles for the journal articles, which are semi useless-->
# {{Greenwood&Earnshaw}}
# ''Handbook of Chemistry and Physics'', 71st edition, CRC Press, Ann Arbor, Michigan, 1990.
# ''The Merck Index'', 7th edition, Merck & Co, Rahway, New Jersey, USA, 1960.
# D. Nicholls, ''Complexes and First-Row Transition Elements'', Macmillan Press, London, 1973.
# A. F. Wells, '''Structural Inorganic Chemistry'', 5th ed., Oxford University Press, Oxford, UK, 1984.
# J. March, ''Advanced Organic Chemistry'', 4th ed., p. 723, Wiley, New York, 1992.
# S. H. Bertz, E. H. Fairchild, in ''Handbook of Reagents for Organic Synthesis, Volume 1: Reagents, Auxiliaries and Catalysts for C-C Bond Formation'', (R. M. Coates, S. E. Denmark, eds.), pp. 220-3, Wiley, New York, 1999.
# C. E. Castro, E. J. Gaughan, D. C. Owsley, ''Journal of Organic Chemistry'', '''30''', 587 (1965).
# J. Brussee, J. L. G. Groenendijk, J. M. Koppele, A. C. A. Jansen, ''Tetrahedron'', '''41''', 3313 (1985).
# ''Fieser & Fieser Reagents for Organic Synthesis'' Volume 5, p158, Wiley, New York, 1975.
# {{cite journal
| title = Chlorocuprates(II)
| author = D. W. Smith
| journal = Coordination Chemistry Reviews
| year = 1976
| volume = 21
| issue = 2-3
| pages = 93–158
| doi = 10.1016/S0010-8545(00)80445-2
}}
==External links==
*[http://www.amazingrust.com/Experiments/background_knowledge/CuCl2.html Copper (II) Chloride - Description and Pictures]
*[http://www.npi.gov.au/database/substance-info/profiles/27.html National Pollutant Inventory - Copper and compounds fact sheet]
[[Category:Copper compounds]]
[[Category:Chlorides]]
[[Category:Metal halides]]
[[Category:Semiconductor materials]]
[[Category:Coordination compounds]]
[[Category:Pyrotechnic colorants]]
[[ar:كلوريد نحاس ثنائي]]
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[[ja:塩化銅(II)]]
[[pl:Chlorek miedzi(II)]]
[[zh:氯化铜]]