Dichlorine heptoxide

Dichlorine heptoxide
Dichlorine heptoxide
Identifiers
CAS number 10294-48-1 YesY
PubChem 123272
ChemSpider 109884 YesY
ChEBI CHEBI:52356 YesY
Jmol-3D images Image 1
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]
 YesY heptoxide (verify) (what is: YesY/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.

Contents

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. 

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