Collision-induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene.
Upon activation in the gas phase, protonated benzoic acid (m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide (H - O+═ C ≡ O, m/z 45), or a molecule of carbon dioxide to yield protonated benzene (m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO2or benzene loss, protonated benzoic acid transfers the charge-imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion-neutral complex between benzene and protonated CO2. The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans-cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO2within the ion-neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd.
Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030.
Sihang
S
Xu
Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030.
Julius
J
Pavlov
Center for Mass Spectrometry, Department of Biomedical Engineering, Chemistry and Biological Sciences, Stevens Institute of Technology, 1 Castle Point on the Hudson, Hoboken, NJ, USA, 07030.
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