Sampling of aryldiazonium, anilino, and aryl radicals by membrane introduction mass spectrometry: Thermolysis of aromatic diazoamino compounds

Membrane introduction mass spectrometry (MIMS) is used to sample free radicals generated by thermolysis at atmospheric pressure. This is done by heating the solid sample in a custom-made probe that is fitted with a silicone membrane to allow selective and rapid introduction of the pyrolysates into the ion source of a triple quadrupole mass spectrometer. Phenyldiazonium radical (C 6H 5N 2) and some of its ring-substituted analogs, the methoxy anilino radical CH 3OC 6H 4NH, and aryl radicals are generated by gas phase thermolysis of symmetrical aryl diazoamino compounds (ArNH-N 2Ar). The radicals are identified by measurement of their ionization energies (IE) using threshold ionization efficiency data. A linear correlation between the ionization energy of the phenyldiazonium radicals and their Brown σ + values is observed, and this confirms the formation of these species and validates the applicability of MIMS in sampling these radicals. The ionization energies of the aryldiazonium radicals are estimated as IE ( p-CH 3O-C 6H 4N 2 ·), 6.74 ± 0.2 eV; IE ( p-CH 3-C 6H 4N 2 ·), 7.72 ± 0.2 eV; IE (C 6H 5N 2 ·), 7.89 ± 0.2 eV; IE ( m-Cl-C 6H 4N 2 ·), 7.91 ± 0.2 eV; IE ( p-F-C 6H 4N 2 ·), 8.03 ± 0.2 eV; and IE ( m-NO 2-C 6H 4N 2 ·), 8.90 = 0.2 eV. The ionization energies of the aryl radicals are estimated as IE ( p-CH 3O-C 6H 4 ·), 7.33 ± 0.2 eV; IE ( p-CH 3-C 6H 4 ·), 8.31 ± 0.2 eV; IE (C 6H 5 ·), 8.44 ± 0.2 eV; IE ( m-Cl-C 6H 4 ·), 8.50 ± 0.2 eV and IE ( p-F-C 6H 4), 8.54 ± 0.2 eV. Also, the ionization energy of the p-methoxyanilino radical ( p-CH 3O-C 6H 4NH ·) is estimated as 7.63 ± 0.2 eV.