copper(II) chloride

Anhydrous copper(II) chloride adopts a distorted cadmium iodide structure. In this structure, the copper centers are octahedral. Most copper(II) compounds exhibit distortions from idealized octahedral geometry due to the Jahn-Teller effect, which in this case describes the localization of one d-electron into a molecular orbital that is strongly antibonding with respect to a pair of chloride ligands. In {{chem2|CuCl2*2H2O}}, the copper again adopts a highly distorted octahedral geometry, the Cu(II) centers being surrounded by two water ligands and four chloride ligands, which bridge asymmetrically to other Cu centers.{{Cite book |last=Wells |first=A.F. |title=Structural Inorganic Chemistry |publisher=Clarendon Press |year=1984 |isbn=0-19-855370-6 |location=Oxford |page=253}}

Copper(II) chloride is paramagnetic. Of historical interest, {{chem2|CuCl2*2H2O}} was used in the first electron paramagnetic resonance measurements by Yevgeny Zavoisky in 1944.{{cite book|url=https://books.google.com/books?id=FldqbSffUMgC&pg=PA167|page=167|title=Mechanochemistry in Nanoscience and Minerals Engineering|author=Peter Baláž|publisher=Springer|year=2008|isbn=978-3-540-74854-0}}{{cite book|url=https://books.google.com/books?id=l3F9yUSk-rgC&pg=PA3|page=3|title=Electron paramagnetic resonance: a practitioner's toolkit|author=Carlo Corvaja|publisher=John Wiley and Sons|year=2009|isbn=978-0-470-25882-8}}

{{multiple image

| align = center

| width = 200

| footer = Structures of the forms of copper(II) chloride

| image1 = Tolbachite-3D-balls.png

| alt1 =

| caption1 = Anhydrous
{{legend|rgb(256, 128, 80)|Copper, Cu}}{{legend|red|Oxygen, O}}{{legend|lime|Chlorine, Cl}}{{legend|white|Hydrogen, H}}

| image2 = Copper(II)-chloride-dihydrate-xtal-3D-balls.png

| alt2 =

| caption2 = Dihydrate}}

File:CuCl2 equilibrium.JPG

Aqueous solutions prepared from copper(II) chloride contain a range of copper(II) complexes depending on concentration, temperature, and the presence of additional chloride ions. These species include the blue color of {{chem2|[Cu(H2O)6](2+)}} and the yellow or red color of the halide complexes of the formula {{chem2|[CuCl_{2+x}]^{x−}|}}.Greenwood, N. N. and Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. p. 1183–1185 {{ISBN|0-7506-3365-4}}.

When copper(II) chloride solutions are treated with a base, a precipitation of copper(II) hydroxide occurs:

:{{chem2|CuCl2 + 2 NaOH → Cu(OH)2 + 2 NaCl}}

Partial hydrolysis gives dicopper chloride trihydroxide, {{chem2|Cu2(OH)3Cl}}, a popular fungicide. When an aqueous solution of copper(II) chloride is left in the air and isn't stabilized by a small amount of acid, it is prone to undergo slight hydrolysis.

Copper(II) chloride is a mild oxidant. It starts to decompose to copper(I) chloride and chlorine gas around {{convert|400|C}} and is completely decomposed near {{convert|1000|C}}:{{Cite book|title=Ullmann's Encyclopedia of Industrial Chemistry|author1=Zhang, J. |author2=Richardson, H. W.|year=2016|isbn=978-3-527-30673-2|chapter=Copper Compounds|pages=1–31 |doi=10.1002/14356007.a07_567.pub2}}{{cite journal |author1=Shuiliang Zhou |author2=Shaobo Shen |author3=Dalong Zhao |author4=Zhitao Zhang |author5=Shiyu Yan |title=Evaporation and decomposition of eutectics of cupric chloride and sodium chloride |journal=Journal of Thermal Analysis and Calorimetry |date=2017 |volume=129 |issue=3 |pages=1445–1452 |doi=10.1007/s10973-017-6360-y |s2cid=99924382 |language=en}}{{Cite book|title=Kirk-Othmer Encyclopedia of Chemical Technology|last=Richardson|first=H. W.|year=2003|isbn=0471238961|chapter=Copper Compounds|doi=10.1002/0471238961.0315161618090308.a01.pub2}}{{cite journal |author1=Z. Wang |author2=G. Marin |author3=G. F. Naterer |author4=K. S. Gabriel |title=Thermodynamics and kinetics of the thermal decomposition of cupric chloride in its hydrolysis reaction |journal=Journal of Thermal Analysis and Calorimetry |date=2015 |volume=119 |issue=2 |pages=815–823 |doi=10.1007/s10973-014-3929-6 |s2cid=93668361 |url=https://research.library.mun.ca/13446/1/2015-JTAC.pdf |language=en}}

:{{chem2|2 CuCl2 → 2 CuCl + Cl2}}

The reported melting point of copper(II) chloride of {{convert|498|C}} is a melt of a mixture of copper(I) chloride and copper(II) chloride. The true melting point of {{convert|630|C}} can be extrapolated by using the melting points of the mixtures of CuCl and {{chem2|CuCl2}}.{{cite journal |author1=Wilhelm Biltz |author2=Werner Fischer |title=Beiträge zur systematischen Verwandtschaftslehre. XLIII. Über das System Cupro-/Cuprichlorid |journal=Zeitschrift für anorganische und allgemeine Chemie |date=1927 |volume=166 |issue=1 |pages=290–298 |doi=10.1002/zaac.19271660126 |language=de}}{{cite book |author1=A. G. Massey |author2=N. R. Thompson |author3=B. F. G. Johnson |title=The Chemistry of Copper, Silver and Gold |date=1973 |publisher=Elsevier Science |isbn=9780080188607 |language=en |page=42}} Copper(II) chloride reacts with several metals to produce copper metal or copper(I) chloride (CuCl) with oxidation of the other metal. To convert copper(II) chloride to copper(I) chloride, it can be convenient to reduce an aqueous solution with sulfur dioxide as the reductant:

:{{chem2|2 CuCl2 + SO2 + 2 H2O → 2 CuCl + 2 HCl + H2SO4}}

{{chem2|CuCl2}} reacts with HCl or other chloride sources to form complex ions: the red {{chem2|[CuCl3]−}} (found in potassium trichloridocuprate(II) {{chem2|K[CuCl3]}}) (it is a dimer in reality, {{chem2|[Cu2Cl6](2−)}}, a couple of tetrahedrons that share an edge), and the green or yellow {{chem2|[CuCl4](2−)}} (found in potassium tetrachloridocuprate(II) {{chem2|K2[CuCl4]}}).{{cite book|author=Naida S. Gill |author2=F. B. Taylor |series=Inorganic Syntheses |year=1967 |volume=9 |pages=136–142 |doi=10.1002/9780470132401.ch37 |title=Tetrahalo Complexes of Dipositive Metals in the First Transition Series |isbn=978-0-470-13240-1}}

:{{chem2|CuCl2 + Cl- ⇌ [CuCl3]-}}

:{{chem2|CuCl2 + 2 Cl- ⇌ [CuCl4](2-)}}

Some of these complexes can be crystallized from aqueous solution, and they adopt a wide variety of structures.

Copper(II) chloride also forms a variety of coordination complexes with ligands such as ammonia, pyridine and triphenylphosphine oxide:{{cite journal |author1=W. Libus |author2=S. K. Hoffmann |author3=M. Kluczkowski |author4=H. Twardowska |title=Solution equilibriums of copper(II) chloride in pyridine and pyridine-diluent mixtures |journal=Inorganic Chemistry |date=1980 |volume=19 |issue=6 |pages=1625–1632 |doi=10.1021/ic50208a039 |language=en}}

:{{chem2|CuCl2 + 2 C5H5N → [CuCl2(C5H5N)2]}} (tetragonal)

:{{chem2|CuCl2 + 2 (C6H5)3P\dO → [CuCl2((C6H5)3P\dO)2]}} (tetrahedral)

However "soft" ligands such as phosphines (e.g., triphenylphosphine), iodide, and cyanide as well as some tertiary amines induce reduction to give copper(I) complexes.

Copper(II) chloride is prepared commercially by the action of chlorination of copper. Copper at red heat (300-400°C) combines directly with chlorine gas, giving (molten) copper(II) chloride. The reaction is very exothermic.{{cite book |author1=H. Wayne Richardson |title=Handbook of Copper Compounds and Applications |date=1997 |publisher=CRC Press |isbn=9781482277463 |language=en |pages=24–68}}

:{{chem2|Cu(s) + Cl2(g) → CuCl2(l)}}

A solution of copper(II) chloride is commercially produced by adding chlorine gas to a circulating mixture of hydrochloric acid and copper. From this solution, the dihydrate can be produced by evaporation.

Although copper metal itself cannot be oxidized by hydrochloric acid, copper-containing bases such as the hydroxide, oxide, or copper(II) carbonate can react to form {{chem2|CuCl2}} in an acid-base reaction which can subsequently be heated above {{convert|100|C}} to produce the anhydrous derivative.

Once prepared, a solution of {{chem2|CuCl2}} may be purified by crystallization. A standard method takes the solution mixed in hot dilute hydrochloric acid, and causes the crystals to form by cooling in a calcium chloride ({{chem2|CaCl2}}) ice bath.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. 220–223, Wiley, New York, 1738.{{cite book|title = Purification of Laboratory Chemicals|author1=W. L. F. Armarego |author2=Christina Li Lin Chai |pages = 461|url = https://books.google.com/books?id=PTXyS7Yj6zUC&pg=PA461|format = Google Books excerpt|edition = 6th|isbn = 978-1-85617-567-8|publisher = Butterworth-Heinemann|date = 2009-05-22}}

There are indirect and rarely used means of using copper ions in solution to form copper(II) chloride. Electrolysis of aqueous sodium chloride with copper electrodes produces (among other things) a blue-green foam that can be collected and converted to the hydrate. While this is not usually done due to the emission of toxic chlorine gas, and the prevalence of the more general chloralkali process, the electrolysis will convert the copper metal to copper ions in solution forming the compound. Indeed, any solution of copper ions can be mixed with hydrochloric acid and made into a copper chloride by removing any other ions.{{cite journal |author1=J. Ji |author2=W. C. Cooper |title=Electrochemical preparation of cuprous oxide powder: Part I. Basic electrochemistry |journal=Journal of Applied Electrochemistry |date=1990 |volume=20 |issue=5 |pages=818–825 |doi=10.1007/BF01094312 |s2cid=95677720 |language=en}}

A major industrial application for copper(II) chloride is as a co-catalyst with palladium(II) chloride in the Wacker process. In this process, ethene (ethylene) is converted to ethanal (acetaldehyde) using water and air. During the reaction, Palladium(II) chloride reduced to Pd, and the {{chem2|CuCl2}} serves to re-oxidize this back to {{chem2|PdCl2}}. Air can then oxidize the resultant CuCl back to {{chem2|CuCl2}}, completing the cycle.{{cite journal |author1=Nicholas D. P. Cosford |author2=Pauline Pei Li |author3=Thierry Ollevier |title=Copper(II) Chloride |journal=Encyclopedia of Reagents for Organic Synthesis |date=2015 |pages=1–8 |doi=10.1002/047084289X.rc214.pub3 |isbn=9780470842898 |language=en}}

1. {{chem2|C2H4 + PdCl2 + H2O → CH3CHO + Pd + 2 HCl}}
2. {{chem2|Pd + 2 CuCl2 → 2 CuCl + PdCl2}}
3. {{chem2|4 CuCl + 4 HCl + O2 → 4 CuCl2 + 2 H2O}}

The overall process is:

:{{chem2|2 C2H4 + O2 → 2 CH3CHO}}

Copper(II) chloride has some highly specialized applications in the synthesis of organic compounds. It affects the 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:{{cite journal |author1=C. E. Castro |author2=E. J. Gaughan |author3=D. C. Owsley |year=1965 |title=Cupric Halide Halogenations |journal=Journal of Organic Chemistry |volume=30 |issue=2 |pages=587 |doi=10.1021/jo01013a069}}

:File:CuCl2 alpha chlorination.png

This reaction is performed in a polar solvent such as dimethylformamide, often in the presence of lithium chloride, which accelerates the reaction.

{{chem2|CuCl2}}, in the presence of oxygen, can also oxidize phenols. The major product can be directed to give either a quinone or a coupled product from oxidative dimerization. The latter process provides a high-yield route to 1,1-binaphthol:{{cite journal |author1=J. Brussee |author2=J. L. G. Groenendijk |author3=J. M. Koppele |author4=A. C. A. Jansen |year=1985 |title=On the mechanism of the formation of s(−)-(1, 1'-binaphthalene)-2,2'-diol via copper(II)amine complexes |journal=Tetrahedron |volume=41 |issue=16 |pages=3313 |doi=10.1016/S0040-4020(01)96682-7}}

:File:CuCl2 naphthol coupling.png

Such compounds are intermediates in the synthesis of BINAP and its derivatives.

Copper(II) chloride dihydrate promotes the hydrolysis of acetonides, i.e., for deprotection to regenerate diols{{cite journal |last=Chandrasekhar |first=M. |author2=Kusum L. Chandra |author3=Vinod K. Singh |year=2003 |title=Total Synthesis of (+)-Boronolide, (+)-Deacetylboronolide, and (+)-Dideacetylboronolide |journal=Journal of Organic Chemistry |volume=68 |issue=10 |pages=4039–4045 |doi=10.1021/jo0269058 |pmid=12737588}} or aminoalcohols, as in this example (where TBDPS = tert-butyldiphenylsilyl):{{cite journal |last=Krishna |first=Palakodety Radha |author2=G. Dayaker |year=2007 |title=A stereoselective total synthesis of (−)-andrachcinidine via an olefin cross-metathesis protocol |journal=Tetrahedron Letters |publisher=Elsevier |volume=48 |issue=41 |pages=7279–7282 |doi=10.1016/j.tetlet.2007.08.053}}

:File:CuCl2 DeprotectionOfAminoAlcohol.png

{{chem2|CuCl2}} also catalyses the free radical addition of sulfonyl chlorides to alkenes; the alpha-chlorosulfone may then undergo elimination with a base to give a vinyl sulfone product.

Copper(II) chloride is used as a catalyst in a variety of processes that produce chlorine by oxychlorination. The Deacon process takes place at about 400 to 450 °C in the presence of a copper chloride:

:{{chem2|4 HCl + O2 → 2 Cl2 + 2 H2O}}

Copper(II) chloride catalyzes the chlorination in the production of vinyl chloride and dichloromethane.

Copper(II) chloride is used in the copper–chlorine cycle where it reacts with steam into copper(II) oxide dichloride and hydrogen chloride and is later recovered in the cycle from the electrolysis of copper(I) chloride.

Copper(II) chloride is used in pyrotechnics as a blue/green coloring agent. In a flame test, copper chlorides, like all copper compounds, emit green-blue light.{{cite web | title = Flame Tests | url = http://www.chemguide.co.uk/inorganic/group1/flametests.html | first = Jim | last = Clark | date = August 2018 | website = chemguide.co.uk | archive-url = https://web.archive.org/web/20201127013520/http://www.chemguide.co.uk/inorganic/group1/flametests.html | url-status = live | archive-date = November 27, 2020 | access-date = January 10, 2021}}

In humidity indicator cards (HICs), cobalt-free brown to azure (copper(II) chloride base) HICs can be found on the market.{{cite patent| number =US 20150300958 A1| title =Adjustable colorimetric moisture indicators | pubdate=2015| inventor =Evan Koon Lun Yuuji Hajime| url =https://www.google.com/patents/US20150300958?cl=en}} In 1998, the European Community classified items containing cobalt(II) chloride of 0.01 to 1% w/w as T (Toxic), with the corresponding R phrase of R49 (may cause cancer if inhaled). Consequently, new cobalt-free humidity indicator cards containing copper have been developed.{{cite web |title=Cobalt dichloride |url=https://echa.europa.eu/substance-information/-/substanceinfo/100.028.718 |website=European Chemicals Agency |publisher=ECHA |access-date=30 May 2023}}

Copper(II) chloride is used as a mordant in the textile industry, petroleum sweetener, wood preservative, and water cleaner.{{cite book |author1=B.H. Patel |editor1-last=Clark |editor1-first=M. |title=Handbook of Textile and Industrial Dyeing |date=2011 |publisher=Woodhead Publishing |isbn=9781845696955 |pages=412–413 |url=https://www.sciencedirect.com/book/9781845696955/handbook-of-textile-and-industrial-dyeing |access-date=2 June 2023 |language=en |chapter=11 - Natural dyes}}

Copper(II) chloride is also used in high school demos, such as reacting with aluminum to create aluminum chloride and copper, and learning how to measure moles.{{Cite web |last=Flinn Scientific, Inc. |date=2016 |title=Aluminum and Copper Demonstration and Inquiry |url=https://www.flinnsci.com/api/library/Download/4a4b759462d74590b1ce25d1dcb6cfe6?srsltid=AfmBOopW6xB-Z-_V17IFrXDeFdZfFO5PC4hlFkivyNe3xmSxSVNHKCRe |access-date=Jan 14, 2025 |website=Flinn Scientific}}

File:Eriochalcite-88986.jpg

Copper(II) chloride occurs naturally as the very rare anhydrous mineral tolbachite and the dihydrate eriochalcite.Marlene C. Morris, Howard F. McMurdie, Eloise H. Evans, Boris Paretzkin, Harry S. Parker, and Nicolas C. Panagiotopoulos (1981) Copper chloride hydrate (eriochalcite), in ''[https://nvlpubs.nist.gov/nistpubs/Legacy/MONO/nbsmonograph25-18.pdf Standard X-ray Diffraction Powder Patterns] National Bureau of Standards, Monograph 25, Section 18; page 33. Both are found near fumaroles and in some copper mines.{{cite web |title=Tolbachite |url=https://www.mindat.org/min-3990.html |website=mindat.org |access-date=24 August 2023 |language=en}}{{cite web |title=Eriochalcite |url=https://www.mindat.org/min-1398.html |website=mindat.org |access-date=24 August 2023}}{{cite web |title=The New IMA List of Minerals |url=http://cnmnc.units.it/imalist.htm |website=Università degli studi di Trieste |publisher=International Mineralogical Association |access-date=24 August 2023 |language=en}} Mixed oxyhydroxide-chlorides like atacamite ({{chem2|Cu2(OH)3Cl}}) are more common, arising among Cu ore beds oxidation zones in arid climates.{{cite web |title=Atacamite |url=https://www.mindat.org/min-406.html |website=mindat.org |access-date=30 May 2023}}

Copper(II) chloride can be toxic. Only concentrations below 1.3 ppm of aqueous copper ions are allowed in drinking water by the US Environmental Protection Agency.{{cite web |title=National Primary Drinking Water Regulations |url=https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations#Inorganic |website=EPA |date=30 November 2015 |access-date=29 May 2023}} If copper chloride is absorbed, it results in headache, diarrhea, a drop in blood pressure, and fever. Ingestion of large amounts may induce copper poisoning, CNS disorders, and haemolysis.{{cite web |title=Copper: Health Information Summary |work=Environmental Fact Sheet |publisher=New Hampshire Department of Environmental Services |id=ARD-EHP-9 |year=2005 |url=http://des.nh.gov/organization/commissioner/pip/factsheets/ard/documents/ard-ehp-9.pdf |archiveurl=https://web.archive.org/web/20170120014307/http://www.des.nh.gov/organization/commissioner/pip/factsheets/ard/documents/ard-ehp-9.pdf |archivedate=20 January 2017}}{{cite web |title=Safety Data Sheet |url=https://www.sigmaaldrich.com/US/en/sds/aldrich/203149 |website=Sigma Aldrich |access-date=30 June 2023}}

Copper(II) chloride has been demonstrated to cause chromosomal aberrations and mitotic cycle disturbances within A. cepa (onion) cells.{{cite journal | last1=Macar | first1=Tuğçe Kalefetoğlu | title=Resveratrol ameliorates the physiological, biochemical, cytogenetic, and anatomical toxicities induced by copper (II) chloride exposure in Allium cepa L. | url=https://link.springer.com/article/10.1007/s11356-019-06920-2 | journal=Environmental Science and Pollution Research | year=2020 | volume=27 | issue=1 | pages=657–667 | doi=10.1007/s11356-019-06920-2 | pmid=31808086 | s2cid=208649491| url-access=subscription }} Such cellular disturbances lead to genotoxicity. Copper(II) chloride has also been studied as a harmful environmental pollutant. Often present in irrigation-grade water, it can negatively affect water and soil microbes.{{cite journal | last1=Shiyab | first1=Safwan | title=Phytoaccumulation of copper from irrigation water and its effect on the internal structure of lettuce. | journal=Agriculture | year=2018 | volume=8 | issue=2 | pages=29 | doi=10.3390/agriculture8020029 | doi-access=free}} Specifically, denitrifying bacteria were found to be very sensitive to the presence of copper(II) chloride. At a concentration of 0.95 mg/L, copper(II) chloride was found to cause a 50% inhibition (IC50) of the metabolic activity of denitrifying microbes.{{cite journal | last1=Ochoa-Herrera | first1=Valeria | title=Toxicity of copper (II) ions to microorganisms in biological wastewater treatment systems. | url=https://www.sciencedirect.com/science/article/pii/S0048969711011065 | journal=Science of the Total Environment | year=2011 | volume=412 | issue=1 | pages=380–385 | doi=10.1016/j.scitotenv.2011.09.072 | pmid=22030247 | bibcode=2011ScTEn.412..380O| url-access=subscription }}

• Copper(I) chloride

{{Reflist}}

• {{Greenwood&Earnshaw|ref=none}}
• {{cite book |author=Lide, David R. |title=CRC handbook of chemistry and physics: a ready-reference book of chemical and physical data |url=https://archive.org/details/handbookofchemis00crcp |url-access=registration |publisher=CRC Press |location=Boca Raton |year=1990 |isbn=0-8493-0471-7|ref=none}}
• 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.
• 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

|ref=none}}

{{Commons category|Copper(II) chloride}}

• [http://www.periodicvideos.com/videos/mv_copper_chloride.htm Copper Chloride] at The Periodic Table of Videos (University of Nottingham)
• [https://web.archive.org/web/20150907141353/http://www.amazingrust.com/Experiments/background_knowledge/CuCl2.html Copper (II) Chloride – Description and Pictures]
• [https://web.archive.org/web/20130530211504/http://www.npi.gov.au/substances/copper/index.html National Pollutant Inventory – Copper and compounds fact sheet]

{{Copper compounds}}

{{Chlorides}}

Category:Copper(II) compounds

Category:Chlorides

Category:Metal halides

Category:Semiconductor materials

Category:Coordination complexes

Category:Pyrotechnic colorants