Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide, an Isoprene-Derived Criegee Intermediate, with Formic Acid: Experiment and Theory

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity not well understood. This study identifies the functionalized hydroperoxide species, 1-hydroperoxy-2-methylallyl formate (HPMAF), generated reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr 13.3 hPa). Electronic structure calculations indicate proceeds via an energetically favorable 1,4-addition mechanism. The formation HPMAF observed by rapid appearance fragment ion at m/z 99, consistent proposed mechanism and characteristic loss HO2 upon functional hydroperoxides. identification confirmed comparison energy theoretical predictions threshold. results are compared to analogous studies on methyl vinyl ketone (MVK-oxide), other four-carbon in ozonolysis.