dichlorine monoxide

The earliest method of synthesis was to treat mercury(II) oxide with chlorine gas. However, this method is expensive, as well as highly dangerous due to the risk of mercury poisoning.

:2 Cl₂ + HgO → HgCl₂ + Cl₂O

A safer and more convenient method of production is the reaction of chlorine gas with hydrated sodium carbonate at 20–30 °C.

:2 Cl₂ + 2 Na₂CO₃ + H₂O → Cl₂O + 2 NaHCO₃ + 2 NaCl

:2 Cl₂ + 2 NaHCO₃ → Cl₂O + 2 CO₂ + 2 NaCl + H₂O

This reaction can be performed in the absence of water but requires heating to 150–250 °C; as dichlorine monoxide is unstable at these temperatures{{cite journal|last=Hinshelwood|first=Cyril Norman|author2=Prichard, Charles Ross|title=CCCXIII.—A homogeneous gas reaction. The thermal decomposition of chlorine monoxide. Part I|journal=Journal of the Chemical Society, Transactions|year=1923|volume=123|pages=2730–2738|doi=10.1039/CT9232302730}} it must therefore be continuously removed to prevent thermal decomposition.

:2 Cl₂ + Na₂CO₃ → Cl₂O + CO₂ + 2 NaCl

The structure of dichlorine monoxide is similar to that of water and hypochlorous acid, with the molecule adopting a bent molecular geometry (due to the lone pairs on the oxygen atom) and resulting in C_2V molecular symmetry. The bond angle is slightly larger than normal, likely due to steric repulsion between the bulky chlorine atoms.

File:H2O 2D labelled.svg

File:Hypochlorous-acid-2D-dimensions.svg

File:Dichlorine-oxide-2D-dimensions.png

In the solid state, it crystallises in the tetrahedral space group I4₁/amd, making it isostructural to the high pressure form of water, ice VIII.{{cite journal|last=Minkwitz|first=R.|author2=Bröchler, R. |author3=Borrmann, H. |title=Tieftemperatur-Kristallstruktur von Dichlormonoxid, Cl₂O|journal=Zeitschrift für Kristallographie|date=1 January 1998|volume=213|issue=4|pages=237–239|doi=10.1524/zkri.1998.213.4.237|bibcode=1998ZK....213..237M }}

Dichlorine monoxide is highly soluble in water,{{cite journal|last=Davis|first=D. S.|title=Nomograph for the Solubility of Chlorine Monoxide in Water|journal=Industrial & Engineering Chemistry|year=1942|volume=34|issue=5|pages=624|doi=10.1021/ie50389a021}} where it exists in an equilibrium with HOCl. The rate of hydrolysis is slow enough to allow the extraction of Cl₂O with organic solvents such as CCl₄, but the equilibrium constant ultimately favours the formation of hypochlorous acid.{{cite book|last1=Aylett|first1=founded by A.F. Holleman; continued by Egon Wiberg; translated by Mary Eagleson, William Brewer; revised by Bernhard J.|title=Inorganic chemistry|date=2001|publisher=Academic Press, W. de Gruyter.|location=San Diego, Calif. : Berlin|isbn=9780123526519|page=442|edition=1st English ed., [edited] by Nils Wiberg.}}

:2 HOCl ⇌ Cl₂O + H₂O K (0 °C) = 3.55x10⁻³ dm³/mol

Despite this, it has been suggested that dichlorine monoxide may be the active species in the reactions of HOCl with olefins and aromatic compounds,{{cite journal|last=Swain|first=C. Gardner|author2=Crist, DeLanson R.|title=Mechanisms of chlorination by hypochlorous acid. The last of chlorinium ion, Cl+|journal=Journal of the American Chemical Society|date=1 May 1972|volume=94|issue=9|pages=3195–3200|doi=10.1021/ja00764a050}}{{cite journal|last=Sivey|first=John D.|author2=McCullough, Corey E. |author3=Roberts, A. Lynn |title=Chlorine Monoxide (Cl₂O) and Molecular Chlorine (Cl₂) as Active Chlorinating Agents in Reaction of Dimethenamid with Aqueous Free Chlorine|journal=Environmental Science & Technology|date=1 May 2010|volume=44|issue=9|pages=3357–3362|doi=10.1021/es9038903|pmid=20302364 |bibcode=2010EnST...44.3357S }} as well as in the chlorination of drinking water.{{cite journal|last=Powell|first=Steven C.|title=The active species in drinking water chlorination: the case for Cl₂O|journal=Environmental Science & Technology|date=1 May 2010|volume=44|issue=9|pages=3203|doi=10.1021/es100800t|pmid=20302368 |bibcode=2010EnST...44.3203P }}

Dichlorine monoxide reacts with metal halides, with the loss of Cl₂, to form unusual oxyhalides.{{cite journal|last=Oppermann|first=H.|title=Untersuchungen an Vanadinoxidchloriden und Vanadinchloriden. I. Gleichgewichte mit VOCl3, VO2Cl und VOCl2|journal=Zeitschrift für anorganische und allgemeine Chemie|year=1967|volume=351|issue=3–4|pages=113–126|doi=10.1002/zaac.19673510302}}{{cite journal|last=Dehnicke|first=Kurt|title=Titan(IV)-Oxidchlorid TiOCl2|journal=Zeitschrift für anorganische und allgemeine Chemie|year=1961|volume=309|issue=5–6|pages=266–275|doi=10.1002/zaac.19613090505}}

:VOCl₃ + Cl₂O → VO₂Cl + 2 Cl₂

:TiCl₄ + Cl₂O → TiOCl₂ + 2 Cl₂

:SbCl₅ + 2 Cl₂O → SbO₂Cl + 4 Cl₂

Similar reactions have also been observed with certain inorganic halides.{{cite journal|last=Dehnicke|first=Kurt|title=Über die Oxidchloride PO2Cl, AsO2Cl und SbO2Cl|journal=Chemische Berichte|date=1 December 1964|volume=97|issue=12|pages=3358–3362|doi=10.1002/cber.19640971215}}{{cite journal|last=Martin|first=H.|title=Kinetic Relationships between Reactions in the Gas Phase and in Solution|journal=Angewandte Chemie International Edition in English|date=1 January 1966|volume=5|issue=1|pages=78–84|doi=10.1002/anie.196600781}}

:AsCl₃ + 2 Cl₂O → AsO₂Cl + 3 Cl₂

:NOCl + Cl₂O → NO₂Cl + Cl₂

Dichlorine monoxide is an effective chlorinating agent. It can be used for either the side-chain or ring chlorination of deactivated aromatic substrates.{{cite journal|last=Marsh|first=F. D.|author2=Farnham, W. B. |author3=Sam, D. J. |author4= Smart, B. E. |title=Dichlorine monoxide: a powerful and selective chlorinating reagent|journal=Journal of the American Chemical Society|date=1 August 1982|volume=104|issue=17|pages=4680–4682|doi=10.1021/ja00381a032}} For activated aromatics such as phenols and aryl-ethers it primarily reacts to give ring halogenated products.{{cite journal|last=Sivey|first=John D.|author2=Roberts, A. Lynn|title=Assessing the Reactivity of Free Chlorine Constituents Cl₂, Cl₂O, and HOCl Toward Aromatic Ethers|journal=Environmental Science & Technology|date=21 February 2012|volume=46|issue=4|pages=2141–2147|doi=10.1021/es203094z|pmid=22211432 |bibcode=2012EnST...46.2141S }} It has been suggested that dichlorine monoxide may be the active species in the reactions of HOCl with olefins and aromatic compounds.

Dichlorine monoxide undergoes photodissociation, eventually forming O₂ and Cl₂. The process is primarily radical based, with flash photolysis showing radical hypochlorite (ClO·) to be a key intermediate.{{cite journal|last=Basco|first=N.|author2=Dogra, S. K.|title=Reactions of Halogen Oxides Studied by Flash Photolysis. II. The Flash Photolysis of Chlorine Monoxide and of the ClO Free Radical|journal=Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences|date=22 June 1971|volume=323|issue=1554|pages=401–415|doi=10.1098/rspa.1971.0112|bibcode=1971RSPSA.323..401B |s2cid=98084403 }}

:2 Cl₂O → 2 Cl₂ + O₂

Dichlorine monoxide is explosive, although there is a lack of modern research into this behaviour. Room temperature mixtures with oxygen could not be detonated by an electric spark until they contained at least 23.5% Cl₂O{{cite journal|last1=Cady|first1=George H.|last2=Brown|first2=Robert E.|title=Minimum Explosive Concentration of Chlorine Monoxide Diluted with Oxygen|journal=Journal of the American Chemical Society|date=September 1945|volume=67|issue=9|pages=1614–1615|doi=10.1021/ja01225a501}} which is an exceedingly high minimum explosive limit. There are conflicting reports of it exploding on exposure to strong light.{{cite journal|last1=Iredale|first1=T.|last2=Edwards|first2=T. G.|title=Photoreaction of Chlorine Monoxide and Hydrogen|journal=Journal of the American Chemical Society|date=April 1937|volume=59|issue=4|pages=761|doi=10.1021/ja01283a504}}{{cite journal|last=Wallace|first=Janet I.|author2=Goodeve, C. F.|title=The heats of dissociation of chlorine monoxide and chlorine dioxide|journal=Transactions of the Faraday Society|date=1 January 1931|volume=27|pages=648|doi=10.1039/TF9312700648}} Heating above 120 °C, or a rapid rate of heating at lower temperatures also apparently lead to explosions.

Liquid dichlorine monoxide has been reported to be shock-sensitive.{{cite journal|last1=Pilipovich|first1=Donald|last2=Lindahl|first2=C. B.|last3=Schack|first3=Carl J.|last4=Wilson|first4=R. D.|last5=Christe|first5=Karl O.|title=Chlorine trifluoride oxide. I. Preparation and properties|journal=Inorganic Chemistry|volume=11|issue=9|year=1972|pages=2189–2192|issn=0020-1669|doi=10.1021/ic50115a040}}

{{Reflist}}

{{Chlorine compounds}}

{{Oxides}}

Category:Chlorine oxides

Category:Gases with color

Category:Explosive chemicals

Category:Chlorine(I) compounds