11 September 2023
A better understanding of organic hydroperoxides
Published online 17 March 2023
Making and studying organic hydroperoxides will improve understanding of atmospheric chemistry and could help tackle vehicle exhaust pollution.
Organic hydroperoxides are reactive and hazardous chemicals that form when volatile organic compounds react with oxygen. They are released from burning vehicle fuels, by some processes of the chemical industry, and also occur naturally in the atmosphere. Some organic hydroperoxides are also detected in the very cold regions of interstellar space. An international research team has investigated the synthesis and properties of these hydroperoxides to better understand their chemistry and improve methods for quantifying their presence in air.
“Although they have been detected experimentally for a long time, the question of how to quantify these chemicals has always been challenging,” says chemist, Zhandong Wang, at the University of Science and Technology of China. The work is part of Wang’s continuing collaboration with chemical engineer, Mani Sarathy, at King Abdullah University of Science and Technology in Saudi Arabia.
The researchers developed a mild and environmentally friendly method to make a variety of organic hydroperoxides. These all share the reactive peroxide group (C-O-O-H), whose carbon atom is further bonded to various organic (carbon-based) groups. The reactivity of such compounds makes them a crucial link in forming a range of reactive chemicals in the atmosphere, including hazardous pollutants.
The new control gained over hydroperoxide synthesis allowed the researchers to reveal previously unknown details of how they react. It also allowed them to develop chemical methods to better quantify the presence of organic hydroperoxides. Until now the concentration of these hydroperoxides in the atmosphere has seldom been measured, while measurements that have been attempted have been subject to large uncertainties.
The availability of their variety of hydroperoxides also allowed the team to develop improved theoretical models of their chemical reactivity, especially reactions in the atmosphere triggered by sunlight. This work was focused on a feature of molecules called their photoionization cross-sections – essentially a measure of how readily a molecule will be ionized by a photon of light energy.
“Making such models more accurate gives improved guidance for the design of clean combustion engines and for emission controls,” says Wang.
“The paper highly impressed me,” comments theoretical and computational chemist, António Varandas, at the University of Porto, Portugal, who was not involved in the work. “Brought together, experiment and theory nicely validate each other.”
Wang and colleagues will now further probe the reactions of organic hydroperoxides, especially in collaboration with Donald Truhlar at the University of Minnesota, USA, who also worked on this study.
Hua, Z. et al. Elucidating the photodissociation fingerprint and quantifying the determination of organic hydroperoxides in gas-phase autoxidation. PNAS https://doi.org/10.1073/pnas.2220131120 (2023).