Dichlorine heptoxide

Dichlorine heptoxide
IUPAC name Dichlorine heptoxide
Other names Chlorine(VII) oxide; Perchloric anhydride; (Perchloryloxy)chlorane trioxide
Identifiers
CAS number	10294-48-1 Y
PubChem	123272
ChemSpider	109884 Y
ChEBI	CHEBI:52356 Y
Jmol-3D images	Image 1
SMILES O=Cl(=O)(=O)OCl(=O)(=O)=O
InChI InChI=1S/Cl2O7/c3-1(4,5)9-2(6,7)8 Y Key: SCDFUIZLRPEIIH-UHFFFAOYSA-N Y InChI=1/Cl2O7/c3-1(4,5)9-2(6,7)8 Key: SCDFUIZLRPEIIH-UHFFFAOYAG
Properties
Molecular formula	Cl2O7
Molar mass	182.901 g/mol
Appearance	colorless oil
Density	1900 kg m-3
Melting point	−91.5 °C
Boiling point	82 °C
Hazards
Main hazards	oxidizer, contact explosive[1]
Y heptoxide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Dichlorine heptoxide is the chemical compound with the formula Cl₂O₇. This chlorine oxide is the anhydride of perchloric acid. It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:^[1]

2 HClO₄ + P₄O₁₀ → Cl₂O₇ + H₂P₄O₁₁

The chlorine(VII) oxide can be distilled off from the mixture.

It may also be formed by illumination on mixtures of chlorine and ozone.^[2] It slowly hydrolyzes back to perchloric acid, which is also hazardous when anhydrous.

Structure

Cl₂O₇ is an endothermic molecule, which means that it is intrinsically unstable.

2 Cl₂O₇ → 2 Cl₂ + 7 O₂ (ΔH = -135 kJ/mol)

Cl₂O₇ is bent with Cl-O-Cl angle of 118.6° giving the molecule C₂ symmetry. The terminal Cl-O distances are 1.709 Å and the Cl=O distances are 1.405 Å.^[1] In this compound, chlorine exists in its highest formal oxidation state of +7, although the bonding in this molecule is significantly covalent.

Chemistry

Dichlorine heptoxide reacts with primary and secondary amines in carbon tetrachloride solution to yield N-perchloryls:^[3]

2 RNH₂ + Cl₂O₇ → 2 RNHClO₃ + H₂O

2 R₂NH + Cl₂O₇ → 2 R₂NClO₃ + H₂O

It also reacts with olefins to give alkyl perchlorates. For example, it reacts with propene in carbon tetrachloride solution to yield isopropyl perchlorate and 1-chloro-2-propyl perchlorate.^[4]

Safety

Although it is the most stable chlorine oxide, Cl₂O₇ is a strong oxidizer as well as an explosive that can be set off with flame or mechanical shock, or by contact with iodine.^[5] Nevertheless, it is less strongly oxidising than the other chlorine oxides, and does not attack sulfur, phosphorus, or paper when cold.^[1] It has the same effects on the human body as elemental chlorine, and requires the same precautions.^[6]

References

1. ^ ^{a b c d} Holleman, Arnold F.; Wiberg, Egon (2001). Inorganic chemistry. Translated by Mary Eagleson, William Brewer. San Diego: Academic Press. p. 464. ISBN 0123526515. 
2. ^ Byrns, A. C.; Rollefson, G. K. (1934). Journal of the American Chemical Society 56 (5): 1250–1251. doi:10.1021/ja01320a506.  edit
3. ^ Beard, C. D.; Baum, K. (1974). "Reactions of dichlorine heptoxide with amines". Journal of the American Chemical Society 96 (10): 3237–3239. doi:10.1021/ja00817a034.  edit
4. ^ Baum, K. . (1976). "Reactions of dichlorine heptoxide with olefins". The Journal of Organic Chemistry 41 (9): 1663–1665. doi:10.1021/jo00871a048.  edit
5. ^ Lewis, Robert Alan (1998). Lewis' dictionary of toxicology. CRC Press. p. 260. ISBN 1566702232. 
6. ^ Jeanne Mager Stellman, ed (1998). "Halogens and their compounds". Encyclopaedia of occupational health and safety (4th ed.). International Labour Organization. p. 104.210. ISBN 9221098176.