期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：1
DOI：10.1073/pnas.2111938119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Methanediol [CH
2(OH)
2] represents a pivotal atmospheric volatile organic compound and plays a fundamental role in aerosol growth. Although sought for decades, methanediol has never been identified due to the inherent dehydration tendency of two adjacent hydroxyl groups (OH) at the same carbon atom. Here, we prepare and identify methanediol via processing of low-temperature ices followed by sublimation into the gas phase. These findings open up a concept to synthesize and characterize unstable geminal diols—critical organic transients in Earth’s atmosphere. The excited state dynamics of oxygen may also lead to methanediol in methanol-rich interstellar ices in cold molecular clouds, followed by sublimation in star-forming regions and prospective detection of these reactive intermediates in the gas phase by radiotelescopes.
Geminal diols—organic molecules carrying two hydroxyl groups at the same carbon atom—have been recognized as key reactive intermediates by the physical (organic) chemistry and atmospheric science communities as fundamental transients in the aerosol cycle and in the atmospheric ozonolysis reaction sequence. Anticipating short lifetimes and their tendency to fragment to water plus the aldehyde or ketone, free geminal diols represent one of the most elusive classes of organic reactive intermediates. Here, we afford an exceptional glance into the preparation of the previously elusive methanediol [CH
2(OH)
2] transient—the simplest geminal diol—via energetic processing of low-temperature methanol–oxygen ices. Methanediol was identified in the gas phase upon sublimation via isomer-selective photoionization reflectron time-of-flight mass spectrometry combined with isotopic substitution studies. Electronic structure calculations reveal that methanediol is formed via excited state dynamics through insertion of electronically excited atomic oxygen into a carbon–hydrogen bond of the methyl group of methanol followed by stabilization in the icy matrix. The first preparation and detection of methanediol demonstrates its gas-phase stability as supported by a significant barrier hindering unimolecular decomposition to formaldehyde and water. These findings advance our perception of the fundamental chemistry and chemical bonding of geminal diols and signify their role as an efficient sink of aldehydes and ketones in atmospheric environments eventually coupling the atmospheric chemistry of geminal diols and Criegee intermediates.
