Chlorine oxides

Chlorine oxides are chemical compounds between the halogen chlorine and oxygen . According to its oxidation states, chlorine forms a number of oxides which generally and particularly easily decompose when heated. In the presence of oxidizable matter, chlorine oxides tend to explode , they are all unstable compounds and therefore very reactive and strong oxidizing agents.

Overview

	Oxidation number
	I.	II	III	IV	V	VI	VII
ClO x		ClO		ClO 2		ClO 3
Cl 2 O y	Cl 2 O	Cl 2 O 2	Cl 2 O 3	Cl 2 O 4	Cl 2 O 5 *	Cl 2 O 6	Cl 2 O 7

^* Dichloropentaoxide (Cl ₂ O ₅ ) is so far unknown.

Structural formulas of some chlorine oxides. Dichlorotrioxide (Cl ₂ O ₃ ) exists as chlorine chlorate (Cl – OClO ₂ ); In the liquid and gaseous state, dichlorohexaoxide (Cl ₂ O ₆ ) has the structure of a covalent chlorine perchlorate (O ₂ Cl – OClO ₃ ) ( a ), in the solid phase it has an ionic structure ( b ).

properties

Chlorine dioxide

Only chlorine dioxide (ClO ₂ ) is technically important . At standard temperature it is a yellow-reddish gas with a molar mass of 67.46 g / mol. When heated, it decomposes explosively into Cl ₂ and O ₂ .

Dichloro oxide

Dichloroxide ( dichloromonoxide , Cl ₂ O) is a yellow-brown gas with a molar mass of 86.91 g / mol. At standard temperature it has a density of 3.89 g / l. Dichloro monoxide freezes at −116 ° C, boils at 4 ° C and is explosive . Dichloroxide is the anhydride of hypochlorous acid .

Cl ₂ O can be obtained by passing chlorine over fresh mercury (II) oxide :

${\displaystyle \mathrm {2\ Cl_{2}+2\ HgO\rightarrow \ Cl_{2}O+HgO\cdot HgCl_{2}} }$

Chlorine monoxide

Chlorine monoxide (ClO), a radical, plays an important role in creating the ozone hole in the stratosphere when chlorine is present. It is formed, for example, by photolysis or microwave discharge of chlorine / oxygen mixtures. Alternatively, it can arise from the reaction of elemental chlorine with ozone or dichloromonoxide.

${\displaystyle \mathrm {Cl\ +\ O_{3}\rightarrow \ ClO+O_{2}} }$

Dichlorine dioxide

Dichloro dioxide (Cl ₂ O ₂ , dichlor peroxide, sometimes referred to as chlor peroxide) is produced by the dimerization of two chlorine monoxide radicals according to:

${\displaystyle \mathrm {2\ ClO\rightarrow \ Cl_{2}O_{2}+73kJ} }$

Thermally it breaks down into chlorine and oxygen, photochemically into chlorine atoms. These also catalyze the breakdown of ozone in the atmosphere.

Chloroperoxide

Chloroperoxide (ClOO) is a short-lived isomer of chlorine dioxide. It can arise from the rearrangement of chlorine dioxide after it has been split up by light or from a chlorine radical and oxygen and has a lifespan of only 0.3–0.4 nanoseconds .
Dichloro dioxide is also sometimes referred to as chloroperoxide, but because of the short lifespan of ClOO there is hardly any risk of confusion.

Dichloro trioxide

Dichlorotrioxide (Cl ₂ O ₃ ) is a metastable, dark brown solid at -78 ° C, which decomposes slowly at -45 ° and explosively at around 0 ° C to form Cl ₂ and O ₂ . Dichlorotrioxide can be viewed as chlorine chlorate (Cl – OClO ₂ ). Dichlorotrioxide has a molar mass of 118.91 g / mol. It can arise from chlorine dioxide through low-temperature photolysis:

${\displaystyle \mathrm {ClO+ClO_{2}\rightleftarrows \ Cl_{2}O_{3}+46kJ} }$

Dichlorotetraoxide

Dichlorotetraoxide (Cl ₂ O ₄ ) can be regarded as chloroperchlorate (Cl – OClO ₃ , chlorine (I, VII) oxide). It can be represented photochemically from chlorine dioxide as well as by chlorination of perchlorates with chlorofluorosulfonate.

Chlorine trioxide

Chlorine trioxide (ClO ₃ ) has a pyramidal structure. When exposed to radiation, it splits off oxygen atoms.

Chlorine tetraoxide

Chlorine tetraoxide (ClO ₄ ) is a radical. It only exists as an intermediate reaction product and is also formed during the thermolysis of Cl ₂ O ₆ .

Dichlorohexoxide

Dichlorohexaoxide (Cl ₂ O ₆ ) is a black-red, oily liquid with a density of 2.02 g / ml and a molar mass of 166.91 g / mol. It freezes at 3.5 ° C and boils at 203 ° C. It is a strong oxidizing agent and reacts with many reducing substances when it explodes. As a gas and liquid, it is present as covalent chlorine perchlorate (chlorine (V, VII) oxide, mixed anhydride from chloric and perchloric acid), as a solid with isolated ClO ₂ ⁺ and ClO ₄ ^- ions.

It can be represented by oxidizing chlorine dioxide with oxygen-thinned ozone.

${\displaystyle \mathrm {2\ ClO_{2}+2\ O_{3}\rightarrow \ Cl_{2}O_{6}+2\ O_{2}} }$

Reaction with water produces perchloric acid and chloric acid , with ozone slowly dichloroheptaoxide.

${\displaystyle \mathrm {Cl_{2}O_{6}+H_{2}O\rightleftarrows \ HClO_{3}+HClO_{4}} }$

Dichloroheptoxide

Dichloroheptaoxide (Cl ₂ O ₇ ) is a colorless oil with a density of 1.86 g / ml. It freezes at −92 ° C, boils at 82 ° C and has a molar mass of 182.91 g / mol. The molecule has no mirror plane, the two ClO ₃ groups are rotated by 15 degrees against each other. Dichlorheptaoxide is explosive, but it is still the most persistent chlorine oxide.

Dichlorheptaoxide is the anhydride of perchloric acid ; accordingly, it can be prepared by dehydrating perchloric acid with phosphorus pentoxide with a subsequent vacuum distillation:

${\displaystyle \mathrm {4\ HClO_{4}+P_{4}O_{10}\rightarrow \ 2\ Cl_{2}O_{7}+\ 4\ HPO_{3}} }$

literature

• AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 102nd edition. Walter de Gruyter, Berlin 2007, ISBN 978-3-11-017770-1 , pp. 482-487.