Trioxidane

Trioxidane, hydrogen trioxide or dihydrogen trioxide (H2O3 or HOOOH) is an unstable molecule, a type of hydrogen polyoxide, which in water undergoes a retro- 2+2+2 decomposition to form two water molecules and singlet oxygen. The reverse reaction typically does not occur due to the scarcity of singlet oxygen and the difficulty of assembling three molecules into the appropriate transition structure. In biological systems, however, ozone is known to be generated from singlet oxygen, and the presumed mechanism is an antibody-catalyzed production of trioxidane from singlet oxygen.



Preparation
It can be obtained in small, but detectable, amounts in various reactions of ozone and hydrogen peroxide, or by the electrical dissociation of water. Larger quantities have been prepared by the reaction of ozone with organic reducing agents at low temperatures in a variety of organic solvents, and it is also formed during the decomposition of organic hydrotrioxides (ROOOH).

The reaction of ozone with hydrogen peroxide is known as the "Peroxone process"; this mixture has been used for some time for treating groundwater contaminated with polycyclic organic compounds etc; The reaction seems to proceed via an intermediate ring containing two hydrogen atoms and five oxygens.

For a review on the preparation, characterization, structure (1H, 17O NMR, IR, quantumchemical methods), and decomposition of HOOOH, see: Božo Plesničar, Progress in the Chemistry of Dihydrogen Trioxide (HOOOH). ''Acta Chim. Slov''. 2005, 52, 1-12 and references cited therein.

Structure
Spectroscopic analysis has shown the molecule to have a skewed linear structure H-O-O-O-H, with the O-O bond length being shorter than that in hydrogen peroxide. Various dimeric and trimeric forms also seem to exist. It is slightly more acidic than hydrogen peroxide, dissociating into H+ and OOOH-

Reactions
It readily decomposes into water and singlet oxygen, with a half-life of about 16 minutes in organic solvents at room temperature, but only milliseconds in water. It reacts with organic sulfides to form sulfoxides, but little else is known of its reactivity.

Recent research found that dihydrogen trioxide is the active ingredient responsible for the antimicrobial properties of the well known ozone / hydrogen peroxide mix. Because these two compounds are present in biological systems as well it is argued that an antibody in the human body can generate dihydrogen trioxide as a powerful oxidant against invading bacteria. The source of the compound in biological systems is the reaction between singlet oxygen and water (which proceeds in either direction, of course, according to concentrations), with the singlet oxygen being produced by immune cells.

In 2005 dihydrogen trioxide was observed experimentally by microwave spectroscopy in a supersonic jet. The molecule exists in a trans configuration with oxygen-oxygen bond lengths of 142.8 picometer compared to 146.4 picometer for hydrogen peroxide. Computational chemistry predicts that more oxygen chain molecules or hydrogen polyoxides exist and that even infinite oxygen chains can exist in a low temperature gas. With this spectroscopic evidence a search for these type of molecules can start in interstellar space.