Rearrangements in the Molecular Ions of Some ortho-Substituted Schiff Bases

Abstract

Under electron ionization conditions, the ortho-substituted Schiff bases N-benzylidene-o-toluidine (1a), N-(o-methylbenzylidene)aniline (1b), N-salicylideneaniline (1c) and N-(o-methoxybenzylidene)aniline (1d) give fragment ions which have been shown by collision-activated mass-analysed ion kinetic energy spectra to have the structure of the protonated molecular ions of indole (2), benzofuran (3), and 1,2-benzisoxazole (4). The molecular ion of N-(o-methylbenzylidene)-o-toluidine (1f) gives as fragment ions not only the protonated molecular ion (2) of indole and the tropylium ion but also the molecular ion of anthracene. Attempts to find supporting evidence for a mechanism for this rearrangement by deuterium labelling of a methyl group in (1b), such as (1g), have been unsuccessful.

Differentiation of isomeric methylanilines by imidization and gas chromatography/mass spectrometry analysis

“…EI‐MS analysis of the imidization derivatives has been reported previously . Herein, further EI‐MS analysis of the three derivatives was carried out for the isomeric differentiation.…”

“…EI-MS analysis of the imidization derivatives has been reported previously. 22,23 Herein, further EI-MS analysis of the three derivatives was carried out for the isomeric differentiation. As shown in Figure 3, there are several abundant peaks at m/z 195, 194, 118, 91 and 65 observed in the mass spectra.…”