Reaction of CO3−• with trinitrotoluene (TNT) in CO2 plasma: Experimental and theoretical study on the formation of [TNT + O]−• and its fragmentation pathways

Abstract

It has previously been demonstrated that 2,4,6-trinitrotoluene (TNT) exhibits characteristic reactivity with negative reactant ions generated in air or O2 during atmospheric-pressure chemical ionization (APCI). For instance, the reaction products were TNT−• (m/z 227) for O2−•, [TNT−H•]− (m/z 226) for NO3−, and [TNT − OH•]− (m/z 210) and [TNT − NO•]− (m/z 197) for O3−•. In this work, reactions of TNT in atmospheric pressure CO2 plasma were examined. [TNT + O]−• (m/z 243) was found as the major ion in addition to TNT−•, [TNT + O − OH•]− (m/z 226), [TNT + O − O2H•]− (m/z 210), [TNT + O − NO•]− (m/z 213), and [TNT + O − NO2•]− (m/z 197). Because CO3−• was detected as the only reactant ion in CO2 plasma, it was concluded that [TNT + O]−• was formed by the reaction of CO3−• with TNT. To elucidate the structure of [TNT + O]−•, tandem mass spectrometry analysis for [TNT + O]−• was performed and the fragmentation pathways were examined by density functional theory. It was proposed that the methyl group of TNT migrates flexibly in the ring to afford the observed fragment anions. In the terminal product ion of C7H3O4− (m/z 151), π orbital electrons in the ring are most delocalized by forming four carbonyl (CO) bonds and an exo cyclic methylene (CCH2) group.