Thermodynamic properties of indoline and benzoxazine based spiropyrans studied by Knudsen effusion mass spectrometry

An approach including thermal analysis and Knudsen effusion mass spectrometry was used to investigate the thermal stability range and the thermodynamic properties of sublimation for four indoline and benzoxazine based spiropyrans: 1,3,3-trimethyl-6 '- (tert-butyl) - 8 '-formyl-spiro [indoline-2,2 '-2H-chromene] (1), 1,3,3,8 ' tetramethyl-6 '-formyl-spiro [indoline-2,2 '-2H-chromene] (4), 1,3,3-trimethyl-8 '-methoxy-6 '-formyl-spiro [indoline-2,2 '-2H-chromene] (7), and 3-methyl-6 '-methoxy-8 '-formyl-spiro [1,3-benzoxazin-4-one-2,2 '-2H-chromene] (9). The melting and decomposition temperatures as well as the melting enthalpies were obtained by thermal analysis. The electron ionization mass spectra as well as the ionization efficiency curves were measured. Schemes of the formation of the main ions in the mass spectra were suggested. The temperature dependencies of vapor pressures were used to obtain the sublimation enthalpies. All data were obtained for the first time.