Gas-phase reactions of O −.2 with alkyl and aryl esters of benzenedicarboxylic acids

Abstract

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 S N2 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 S N2 displacement. The O 2/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.