Sublimation thermodynamics of indoline and benzoxazine based spiropyrans

Sublimation of 1,3,3,6'-tetramethyl-8'-formyl-spiroindoline-2,2'-[2H] -chromene (SP-1) and 3,6'-dimethyl-8'formyl-spiro (4-oxo-3,4-dihydro-2H-1,3-benzoxazine)-2,2'-[2H] -chromene (SP-2) was studied by Knudsen effusion mass spectrometry in the temperature range 309-363 K and 331-384 K, respectively. It has been shown that, in the temperature range under study, both spiropyrans are thermally stable and sublime congruently in the form of monomeric molecules. The dependences of the saturated vapor pressure (Pa) on temperature are described by the equations: lg p (SP-1) = - (6.239 +/- 0.093)center dot 10(3)center dot T-1 + (15.832 +/- 0.278), lg p (SP-2) = - (6.625 +/- 0.111)center dot 10(3)center dot T-1 + (15.459 +/- 0.312). The sublimation enthalpies have been evaluated by the second law method as Delta H-s degrees (298.15 K) = 119 +/- 5 kJ.mol(-1) (SP-1) and Delta H-s degrees(298.15 K) = 128 +/- 5 kJ.mol(-1) (SP-2). The enthalpies of formation of spiropyran molecules in the ideal gas state, Delta H-f degrees(g)(298.15 K) = 199 +/- 9 kJ.mol(-1) (SP-1) and Delta H-f degrees(g)(298.15 K) = -296 +/- 10 kJ.mol(-1) (SP-2), have been calculated using isodesmic reactions method implying quantum chemical calculations. Combining the latter values with the corresponding sublimation enthalpies the enthalpies of formation for crystalline state spiropyrans were determined: Delta H-f degrees(cr)(298.15 K) = 80 +/- 10 kJ.mol(-1) (SP-1) and Delta H-f degrees(cr)(298.15 K) = -424 +/- 11 kJ.mol(-1) (SP-2).

Automated summary

The sublimation properties of two spiropyrans, SP-1 and SP-2, were studied in the temperature range of 309-363 K and 331-384 K, respectively. It was found that both spiropyrans are thermally stable and sublime congruently in the form of monomeric molecules within the studied temperature range. The sublimation enthalpies and enthalpies of formation for both spiropyrans were evaluated and determined using Knudsen effusion mass spectrometry and quantum chemical calculations.