Thermal Rearrangement of 1,4-Dinitroimidazole to 2,4-Dinitroimidazole: Characterization and Investigation of the Mechanism by Mass Spectrometry and Isotope Labeling

Article abstract of DOI:10.1021/j100014a022

The thermal rearrangement of 1,4-dinitroimidazole to 2,4-dinitroimidazole has been investigated by differential scanning calorimetry and mass spectrometry techniques.When mixtures of independently prepared deuterium- and (15)N-labeled samples of the 1,4-isomer were subjected to thermal rearrangement, the resulting 2,4-dinitroimidazole failed to show isotope-scrambled molecular ions in its mass spectrum, suggesting that the reaction was intramolecular in nature.This was interpreted to mean that the mechanism was of the (1,5)-sigmatropic type rearrangement.Extensive NMR measurements were used to obtain unequivocal evidence for the identity of the assumed structures of the isomeric dinitroimidazoles.Two byproducts (4-nitroimidazole and a trinitroimidazole), formed during the rearrangement reaction, have also been identified.Plausible mechanisms for their formation are discussed.