New class of substances detected in atmospheric chemistry

An international research team has succeeded in detecting hydrotrioxides (ROOOH) for the first time under atmospheric conditions. Until now, there was only speculation about the existence of these organic compounds with the unusual OOOH group. In laboratory experiments, their formation during the oxidation of important hydrocarbons, such as isoprene and alpha-pinene, has been clearly demonstrated. By means of quantum chemical calculations and computational models, important data on this new class of substances have been estimated. About 10 million metric tons per year of them are formed in the Earth’s atmosphere by the oxidation of isoprene. The lifetime of ROOOH is estimated between a few minutes and a few hours. Hydrotrioxides represent a hitherto unnoticed class of substances in the atmosphere whose effects on health and the environment need to be studied, write the researchers led by the Leibniz Institute for Tropospheric Research (TROPOS) in the current issue. of the scientific journal SCIENCE.

The lower layer of the Earth’s atmosphere is a large chemical reactor in which several hundred million metric tons of hydrocarbons are converted each year, ultimately leading to the formation of carbon dioxide and water. These hydrocarbons are emitted by forests or anthropogenic sources. A wide variety of oxidation processes occur, only some of which are well understood. A recent axis of atmospheric research concerns hydrotrioxides (ROOOH). They are gaseous substances with a group consisting of three consecutive oxygen atoms “O” and one hydrogen atom “H”, which is bonded to an organic residue (R). Hydroperoxides (ROOH) with two oxygen atoms have been known and proven for a long time. In the literature, it has already been speculated that there could be substances in the atmosphere carrying not only two oxygen atoms (ROOH) but also three oxygen atoms (ROOOH). In organic synthesis, hydrotrioxides are used to form special oxidation products when reacting with alkenes. However, these reactive and thermally unstable hydrotrioxides are produced there in organic solvents at very low temperatures around -80°C and then react. Whether this class of substances also exists as gases in the atmosphere at significantly higher temperatures was unknown until now.

In their study, researchers from the Leibniz Institute for Tropospheric Research (TROPOS), the University of Copenhagen and the California Institute of Technology (Caltech) were able to provide direct evidence for the first time that the formation of hydrotrioxides also takes place. under atmospheric conditions of the reaction of peroxy radicals (RO2) with hydroxyl radicals (OH). The laboratory investigations were mainly carried out at TROPOS in Leipzig in a free-jet tube at room temperature and 1 bar air pressure – combined with the use of highly sensitive mass spectrometers. Additional experimental information, including on the stability of hydrotrioxides, has been provided by Caltech investigations. Quantum chemical calculations have been performed by the University of Copenhagen to describe the reaction mechanisms as well as the temperature and photostability of hydrotrioxides. TROPOS’ global simulations with the ECHAM-HAMMOZ chemistry-climate model have enabled an initial assessment of the effects on the Earth’s atmosphere.

“It is really exciting to show the existence of a new universal class of compounds formed from precursors present in the atmosphere (RO2 and OH radicals)”, reports Professor Henrik G. Kjærgaard from the University of Copenhagen. . “It is very surprising that these interesting molecules are so stable with such a high oxygen content. Further research is needed to determine the role of hydrotrioxides for health and the environment”, emphasizes Dr. Torsten Berndt from TROPOS. “Our study has shown that direct observation of hydrotrioxides using mass spectrometry is feasible. This means that it is now possible to further study these compounds in different systems, including, perhaps, quantification of their abundance in the environment.” explains Professor Paul O. Wennberg of Caltech.

The importance of the first successful detection of this new class of “hydrotrioxide” substances will only become clear in the next few years. However, with experimental evidence and current knowledge, the study by Berndt et al. laid the first milestones which should also arouse the interest of other research groups.

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