Nitrosobenzene Dimerizations as a Model System for Studying Solid-State Reaction Mechanisms

Abstract

Thermal dimerization of nitroso compounds in the solid state was investigated by using para-substituted nitrosobenzenes as model compounds. A mechanism that includes the interplay of topochemical reaction trajectories and phase transfer was proposed on the basis of FT-IR spectroscopic kinetics, time-resolved powder diffraction, and low-temperature X-ray structure determination. From shapes of the kinetic curves analyzed on the basis of the Avrami model, it was found that phase transfer could be triggered by a dimerization reaction of para-substituted nitrosobenzene to azodioxide, which, in turn, can be caused by different packing factors such as disorder in the starting nitroso monomer crystals. Since the represented model can be extended to a broad series of compounds, we propose it as a general method for investigations of solid-state reaction mechanisms.

Polymerization of 1,4-dinitrosobenzene: Kinetics and Submicrocrystal Structure

“…[1][2][3] They exist in two different forms, as nitroso compounds (monomers), and E-or Zazodioxy compounds (dimers or polymers). [4,5] In the solid state, most aromatic C-nitroso compounds appear in the azodioxy form, but can be converted to stable or metastable monomeric forms by dissolution in organic solvents, heating, or by UV irradiation at cryogenic temperatures.…”

“…[3] It appears that monomers are more randomly distributed after cryogenic deposition, while after photolysis of the polymer the orientation of monomer molecules is more conserved, which is convenient for repolymerization. [1,2] Also, repolymerization after photolysis depends on the regularity of the crystal structure of the starting polymer. [1] In this work, we present a morphological investigation of the polymeric material, complemented with isothermal determination of activation energies for the polymerization under cryogenic conditions.…”

Aromatic C-Nitroso Compounds and Their Dimers: A Model for Probing the Reaction Mechanisms in Crystalline Molecular Solids

“…Kinetics of the solid-state dimerization of p-bromonitrosobenzene followed by (a) time-resolved IR spectroscopy (exponential kinetic curve) and by (b) time-resolved XRPD (sigmoidal kinetic curve). Reproduced with permission from [13]. Copyright 2004 American Chemical Society.…”

“…In the experiments with aromatic C-nitroso compounds, these two processes have been measured by two independent methods [13]. While the chemical reaction was followed by time-resolved IR spectroscopy, the corresponding phase transformation was monitored by the time-resolved X-ray powder diffraction (XRPD) [13].…”

“…In the experiments with aromatic C-nitroso compounds, these two processes have been measured by two independent methods [13]. While the chemical reaction was followed by time-resolved IR spectroscopy, the corresponding phase transformation was monitored by the time-resolved X-ray powder diffraction (XRPD) [13]. In cases of some substituted nitrosobenzenes, the studied processes afford the diverse kinetic behaviours: typically, the chemical reaction is characterized by the exponential kinetic curve, and the phase transformation mostly follows the sigmoid kinetic curve (Figure 1).…”