Chemistry:Dichlorine heptoxide
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| Names | |
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| IUPAC name
Dichlorine heptoxide
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Other names
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| Identifiers | |
3D model (JSmol)
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PubChem CID
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| Properties[2] | |
| Cl2O7 | |
| Molar mass | 182.89 g·mol−1 |
| Appearance | colorless liquid, colorless gas |
| Density | 1.86 g/cm3 (0 °C (32 °F))[1] |
| Melting point | −91.5 °C (−132.7 °F; 181.7 K) |
| Boiling point | 82 °C (180 °F; 355 K) |
| hydrolyzes to form perchloric acid | |
| Vapor pressure | 23.7 mmHg (3.16 kPa) (0 °C (32 °F))[1] |
| Thermochemistry[citation needed] | |
Std enthalpy of
formation (ΔfH⦵298) |
275.7 kJ⋅mol−1 |
| Hazards | |
| Main hazards | oxidizer, contact explosive[3] |
| NFPA 704 (fire diamond) | |
| Related compounds | |
Related chlorine oxides
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Related compounds
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Perchloric acid |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Dichlorine heptoxide is the chemical compound with the formula Cl
2O
7. This chlorine oxide is the anhydride of perchloric acid.
Synthesis
It is produced by the careful distillation of perchloric acid in the presence of the dehydrating agent phosphorus pentoxide:[3]
- 2 HClO
4 + P
4O
10 → Cl
2O
7 + H
2P
4O
11
Cl
2O
7 can be distilled off from the mixture.
This preparation method also produces lower chlorine oxides unless the product gas is distilled through a copper tube containing copper(II) oxide (CuO) wire freshly reduced to copper. Alternately the P
2O
5 may be treated with ozone (Template:O3) for 0.5-3 hours prior to carrying out the reaction, followed by displacement of the ozone with oxygen gas (O2).[1]
It may also be formed by illumination of mixtures of chlorine and ozone with blue light.[4] It slowly hydrolyzes back to perchloric acid.
Structure
Cl
2O
7 is an endergonic molecule, meaning it is intrinsically unstable, decomposing to its constituent elements with release of energy:[5]
- 2 Cl
2O
7 → 2 Cl
2 + 7 O
2 (Template:DELTAH° = −132 kcal/mol (−550 kJ/mol)
Dichlorine heptoxide is a covalent compound consisting of two ClO
3 groups linked by an oxygen atom. It has an overall bent molecular geometry (C2 symmetry), with a Cl–O–Cl angle of 118.6°. The chlorine–oxygen bond lengths are 1.709 Å in the central region and 1.405 Å within each ClO
3 cluster.[3] In this compound, chlorine exists in its highest formal oxidation state of +7.
Chemistry
Dichlorine heptoxide reacts with primary and secondary amines in carbon tetrachloride solution to yield perchloric amides:[6]
- 2 RNH
2 + Cl
2O
7 → 2 RNH–ClO
3 + H
2O - 2 R
2NH + Cl
2O
7 → 2 R
2N–ClO
3 + H
2O
It also reacts with alkenes to give alkyl perchlorates. For example, it reacts with propene in carbon tetrachloride solution to yield isopropyl perchlorate and 1-chloro-2-propyl perchlorate.[7]
Dichlorine heptoxide reacts with alcohols to form alkyl perchlorates.[8]
- R–OH + O
3Cl–O–ClO
3 → R–O–ClO
3 + HClO
4
Dichlorine heptoxide is a strongly acidic oxide, and in solution it forms an equilibrium with perchloric acid.
Safety
Although it is the most stable chlorine oxide, Cl
2O
7 is a strong oxidizer as well as an explosive that can be set off with flame or mechanical shock, or by contact with iodine.[9] Nevertheless, it is less strongly oxidising than the other chlorine oxides, and does not attack sulfur, phosphorus, or paper when cold.[3] It has the same effects on the human body as elemental chlorine, and requires the same precautions.[10]
References
- ↑ 1.0 1.1 1.2 Schmeisser, M. (1963). "5. Chlorine, Bromine, Iodine - Dichlorine Heptoxide". Handbook of Preparative Inorganic Chemistry. 1 (2 ed.). New York, NY: Academic Press. pp. 305-6. https://archive.org/details/Handbook_of_Preparative_Inorganic_Chemistry_1_2_Brauer/page/n330/mode/1up.
- ↑ Template:RubberBible97th
- ↑ 3.0 3.1 3.2 3.3 Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils, ed., Inorganic Chemistry, San Diego/Berlin: Academic Press/De Gruyter, p. 464, ISBN 0-12-352651-5
- ↑ Byrns, A. C.; Rollefson, G. K. (1934). "The Formation of Chlorine Heptoxide on Illumination of Mixtures of Chlorine and Ozone". Journal of the American Chemical Society 56 (5): 1250-1. doi:10.1021/ja01320a506.
- ↑ Martin, Jan M. L. (2006-10-12). "Heats of Formation of Perchloric Acid, HClO4, and Perchloric Anhydride, Cl2O7. Probing the Limits of W1 and W2 Theory". The 7th Triennial Conference of the World Association of Theoretical and Computational Chemists (WATOC 2005). 771. 19-26. doi:10.1016/j.theochem.2006.03.035.
- ↑ Beard, C. D.; Baum, K. (1974). "Reactions of Dichlorine Heptoxide with Amines". Journal of the American Chemical Society 96 (10): 3237-9. doi:10.1021/ja00817a034.
- ↑ Baum, K. (1976). "Reactions of Dichlorine Heptoxide with Olefins". The Journal of Organic Chemistry 41 (9): 1663-5. doi:10.1021/jo00871a048.
- ↑ Baum, K.; Beard, C. D. (1974-05-01). "Reactions of Dichlorine Heptoxide with Alcohols" (in en). Journal of the American Chemical Society 96 (10): 3233-7. doi:10.1021/ja00817a033. ISSN 0002-7863.
- ↑ Lewis, Robert Alan (1998). Lewis' Dictionary of Toxicology. CRC Press. p. 260. ISBN 1-56670-223-2. https://archive.org/details/lewisdictionaryo0000lewi/page/260.
- ↑ Stellman, Jeanne Mager, ed (1998). "Halogens and their compounds". Encyclopaedia of occupational health and safety (4th ed.). International Labour Organization. p. 104.210. ISBN 92-2-109817-6. https://archive.org/details/encyclopaediaofo0003unse/page/104.
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