Concerted HO2 Elimination from α-Aminoalkylperoxyl Free Radicals: Experimental and Theoretical Evidence from the Gas-Phase NH2(•)CHCO2(-) + O2 Reaction.
We have investigated the gas-phase reaction of the α-aminoacetate (glycyl) radical anion (NH2(•)CHCO2(-)) with O2 using ion trap mass spectrometry, quantum chemistry, and statistical reaction rate theory. This radical is found to undergo a remarkably rapid reaction with O2 to form the hydroperoxyl radical (HO2(•)) and an even-electron imine (NHCHCO2(-)), with experiments and master equation simulations revealing that reaction proceeds at the ion-molecule collision rate. This reaction is facilitated by a low-energy concerted HO2(•) elimination mechanism in the NH2CH(OO(•))CO2(-) peroxyl radical. These findings can explain the widely observed free-radical-mediated oxidation of simple amino acids to amides plus α-keto acids (their imine hydrolysis products). This work also suggests that imines will be the main intermediates in the atmospheric oxidation of primary and secondary amines, including amine carbon capture solvents such as 2-aminoethanol (commonly known as monoethanolamine, or MEA), in a process that avoids the ozone-promoting conversion of (•)NO to (•)NO2 commonly encountered in peroxyl radical chemistry.
†Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia.
Gabriel
G
da Silva
‡ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, NSW 2522, Australia.
Benjamin B
BB
Kirk
‡ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, NSW 2522, Australia.
Celli
C
Lloyd
‡ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, NSW 2522, Australia.
Adam J
AJ
Trevitt
‡ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, School of Chemistry, University of Wollongong, NSW 2522, Australia.
Stephen J
SJ
Blanksby
RRKM; amine oxidation; glycine; kinetics; mass spectrometry; peroxyl radicals