Add time:09/10/2019         Source:sciencedirect.com

The reactions of O−.2 with alkyl and aryl esters of benzenedicarboxylic acids have been studied under negative-ion chemical ionization (NICI) conditions via a conventional chemical ionization source. Reaction mechanisms have been elucidated by using ion isolation techniques on a Fourier transform ion cyclotron resonance mass spectrometer. In addition, 18O−.2 has been used as the reagent and the products of competitive reactions that involve the mixed esters of benzenedicarboxylic acids have been studied. O−.2 reactions with the alkyl esters of 1,2- and 1,3-benzenedicarboxylic acids are attributed to SN2 displacement at the O-alkyl carbon. The spectra of mixed alkyl esters show that O−.2 attack is reduced at sterically hindered alkyl groups. In contrast with the spectra of 1,2- and 1,3-benzenedicarboxylic acids, the spectra of 1,4-benzenedicarboxylic acids are dominated by M−. production. Reactions of O−.2 with phenyl benzoates and the aryl esters of benzenedicarboxylic acids proceed via addition-elimination pathways. Experiments with mixed alkyl-aryl benzenedicarboxylic acid esters show that the addition-elimination reaction pathway is preferred over O-alkyl SN2 displacement. The O2/Ar-NICI mass spectra show features that can be used to distinguish 1,2-, 1,3-, and 1,4-benzenedicarboxylic acid esters. Molecular and fragment ions provide structural information complementary to that generated under electron ionization and chemical ionization conditions.

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