Chemical Ionization of TNT and RDX with Trimethylsilyl Cation

摘要

Fourier transform ion cyclotron resonance mass spectrometry has been used to examine the reactions of Si(CH3)3+ with nitrobenzene, TNT, and RDX. With nitrobenzene, the only reaction observed is adduct formation which generates the C↓(6)H↓(5)NO↓(2)Si(CH↓(3))↓(3)↑(+) ion.. The bimolecular rate constant for the reaction of Si(CH3)3+ with nitrobenzene is measured to be 1.8 × 10↑(-9) cm↑(3) s↑(-1) molecule↓(-1).. With TNT, fragmentation and adduct formation were observed. The bimolecular rate constant for the reaction of Si(CH↓(3))↓(3)↑(+) with TNT is measured to be 0.85 x 10↑(-9) cm↑(3) s↑(-1) molecule↑(-1) With RDX, the dominant reaction observed is adduct formation, but some fragmentation is seen as a minor reaction pathway. The bimolecular rate constant for the reaction of Si(CH↓(3))↓(3)↑(+) with RDX is estimated to be similar to that observed with TNT (~0.7 × 10↑(-9) cm↑(3) s↑(-1) molecule↑(-1). Collision-induced dissociation experiments performed on both the TNT-Si(CH↓(3))↓(3)↑(+) and the RDX-Si(CH↓(3))↓(3)↑(+) adducts using off-resonance collisional activation show the same fragmentation pattern that is observed during adduct formation. This fragmentation pattern appears to be a "fingerprint" for both adducts. These reactions appear to be driven by the high affinity of Si for oxygen and the attraction of the Si(CH↓(3))↓(3)↑(+) ion to the formal negative charge of oxygen in a nitro group. A reaction coordinate diagram for reactions of RDX with Si(CH↓(3))↓(3)↑(+)is derived (from known thermochemistry and ab initio calculations on the reactive intermediates) and its implications are discussed. Reactions of this type could be useful as a detection scheme for common explosives.