Dichlorine Heptoxide is a chemical compound with
the formula Cl2O7. Dichlorine heptoxide is the anhydride
of perchloric acid and is related to perchlorates
in general. It is produced by the careful distillation of
perchloric acid in the presence of a dehydrating agent
such as phosphorus pentoxide:
2HClO4＋P4O10→Cl2O7＋H2P4O11
It is also produced by the careful distillation of
perchloric acid that has been dehydrated with P2O5. It may also be formed by illumination of mixtures of
chlorine and ozone. It slowly hydrolyzes back to
perchloric acid, if allowed to contact moisture in any
way. Dichlorine heptoxide melts at 91.5°C and boils
at 82°C. It is highly explosive and can be set off with
flame, mechanical shock, and on contact with organic
substances. Cl2O7 is an endothermic molecule, which
means that it is intrinsically unstable:
2Cl2O7→2Cl2＋7O2 (DH＝＋135 kJ/mol).
