Dichlorine monoxide 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

molecular formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

Cl₂O. It was first synthesised in 1834 by Antoine Jérôme Balard, who along with

Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778 – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt), for two laws ...

also determined its composition. In older literature it is often referred to as chlorine monoxide, which can be a source of confusion as that name now refers to the neutral species ClO. At room temperature it exists as a brownish-yellow gas which is soluble in both water and organic solvents. Chemically, it is a member of the

chlorine oxide Chlorine and oxygen can bond in many ways: * chlorine monoxide, , chlorine (II) oxide * chlorine peroxide, , dimer of chlorine (II) oxide * chlorine dioxide, , chlorine (IV) oxide * chloroperoxyl, *chlorine trioxide, ClO3, chlorine (VI) oxide * ...

family of compounds, as well as being the

anhydride An organic acid anhydride is an acid anhydride that is an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the pa ...

hypochlorous acid Hypochlorous acid (HClO, HOCl, or ClHO) is a weak acid that forms when chlorine dissolves in water, and itself partially dissociates, forming hypochlorite, ClO−. HClO and ClO− are oxidizers, and the primary disinfection agents of chlorine so ...

. It is a strong oxidiser and chlorinating agent.

Preparation

The earliest method of synthesis was to treat

mercury(II) oxide Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, is the inorganic compound with the formula Hg O. It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. The mineral form montroydite is v ...

with

chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...

gas. However, this method is expensive, as well as highly dangerous due to the risk of

mercury poisoning Mercury poisoning is a type of metal poisoning due to exposure to mercury. Symptoms depend upon the type, dose, method, and duration of exposure. They may include muscle weakness, poor coordination, numbness in the hands and feet, skin rashe ...

. :2 Cl₂ + HgO → HgCl₂ + Cl₂O A safer and more convenient method of production is the reaction of

gas with hydrated

sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...

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 it must therefore be continuously removed to prevent

thermal decomposition Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes. The reaction is usually endothermic as heat is req ...

. :2 Cl₂ + Na₂CO₃ → Cl₂O + CO₂ + 2 NaCl

Structure

The structure of dichlorine monoxide is similar to that of water and

, with the molecule adopting a

bent molecular geometry In chemistry, molecules with a non-collinear arrangement of two adjacent bonds have bent molecular geometry, also known as angular or V-shaped. Certain atoms, such as oxygen, will almost always set their two (or more) covalent bonds in non-colline ...

(due to the

lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...

s on the oxygen) and resulting in C_2V

molecular symmetry Molecular symmetry in chemistry describes the symmetry present in molecules and the classification of these molecules according to their symmetry. Molecular symmetry is a fundamental concept in chemistry, as it can be used to predict or explain m ...

. The

bond angle Bond or bonds may refer to: Common meanings * Bond (finance), a type of debt security * Bail bond, a commercial third-party guarantor of surety bonds in the United States * Chemical bond, the attraction of atoms, ions or molecules to form chemical ...

is slightly larger than normal, likely due to

steric repulsion Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape ( conformation) and reactivity of ions ...

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 In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it unchan ...

I4₁/amd, making it isostructural to the high pressure form of water, ice VIII.

Reactions

Dichlorine monoxide is highly soluble in water, 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 The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...

ultimately favours the formation of hypochlorous acid. :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 compound Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...

s, as well as in the chlorination of drinking water.

With inorganic compounds

Dichlorine monoxide reacts with

metal halide Metal halides are compounds between metals and halogens. Some, such as sodium chloride are ionic, while others are covalently bonded. A few metal halides are discrete molecules, such as uranium hexafluoride, but most adopt polymeric structures, ...

s, with the loss of Cl₂, to form unusual

oxyhalide In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), chlor ...

s. : VOCl₃ + Cl₂O → VO₂Cl + 2 Cl₂ : TiCl₄ + Cl₂O → TiOCI₂ + 2 Cl₂ : SbCI₅ + 2 CI₂O → SbO₂CI + 4 Cl₂ Similar reactions have also been observed with certain inorganic halides. : AsCI₃ + 2 CI₂O → AsO₂CI + 3 Cl₂ : NOCl + Cl₂O → NO₂Cl + Cl₂

With organic compounds

Dichlorine monoxide is an effective chlorinating agent. It can be used for either the side-chain or ring chlorination of deactivated

aromatic In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...

substrates. For activated aromatics such as

phenol Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it req ...

s and aryl-ethers it primarily reacts to give ring halogenated products. It has been suggested that dichlorine monoxide may be the active species in the reactions of HOCl with olefins and aromatic compounds.

Photochemistry

Dichlorine monoxide undergoes

photodissociation Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...

, eventually forming O₂ and Cl₂. The process is primarily

radical Radical may refer to: Politics and ideology Politics *Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...

based, with

flash photolysis Flash photolysis is a pump-probe laboratory technique, in which a sample is first excited by a strong pulse of light from a pulsed laser of nanosecond, picosecond, or femtosecond pulse width or by another short-pulse light source such as a fla ...

showing radical hypochlorite (ClO·) to be a key intermediate. :2 Cl₂O → 2 Cl₂ + O₂

Explosive properties

Dichlorine monoxide is explosive, although there is a lack of modern research into this behaviour.

Room temperature Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...

mixtures with oxygen could not be detonated by an electric spark until they contained at least 23.5% Cl₂O which is an exceedingly high minimum explosive limit. There are conflicting reports of it exploding on exposure to strong light. 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.

References

{{Oxides Chlorine oxides Nonmetal halides Gases with color Explosive chemicals Chlorine(I) compounds