Thermal stability of N-heterocycle-stabilized iodanes - a systematic investigation

The thermal stability of pseudocyclic and cyclic N-heterocycle-stabilized (hydroxy)aryl- and mesityl(aryl)-lambda(3)-iodanes (NHIs) through thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) is investigated. Peak decomposition temperatures (T-peak) were observed within a wide range between 120 and 270 degrees C. Decomposition enthalpies (Delta H-dec) varied from -29.81 to 141.13 kJ/mol. A direct comparison between pseudocyclic and cyclic NHIs revealed high T(peak )but also higher Delta H-dec values for the latter ones. NHIs bearing N-heterocycles with a high N/C-ratio such as triazoles show among the lowest T-peak and the highest Delta H-dec values. A comparison of NHIs with known (pseudo)cyclic benziodoxolones is made and we further correlated their thermal stability with reactivity in a model oxygenation.