engleski

Solid-state chemistry of p-iodonitrosobenzene

Aromatic C-nitroso compounds dominantly exist as Z- or E-azodioxides (dimers) in solid state [1]. Under cryogenic conditions, crystals of azodioxides can be photolysed to corresponding nitroso monomers, which again dimerize at elevated temperatures. Crystals of nitroso monomers can be also prepared by sublimation of azodioxides. By warming the sample to room temperature, sublimed monomers undergo dimerization reaction affording azodioxides. p-Iodonitrosobenzene can exist in two solid forms, as monomer and E-dimer. Solid-state chemistry of p-iodonitrosobenzene exhibits an interesting and somewhat different behavior when compared to other nitrosobenzene derivatives (e.g. p-bromonitrosobenzene). Dimerization reaction of p-iodonitrosobenzene after sublimation is very slow and ends in the early stage [2]. This can be explained by regular arrangements of molecules in the crystal lattice of p-iodonitrosobenzene with most of the nitroso groups near the iodine atoms rather than to each other. In addition, E-azodioxy dimer of p-iodonitrosobenzene, which can be isolated by crystallization from solution, reverts on heating to the crystals of monomers [3]. In the present work, we studied kinetics of solid-state thermal dissociation of E-azodioxy dimer of p- iodonitrosobenzene at different temperatures by IR spectroscopy. From the temperature dependence of the reaction rate constants, activation energy for thermal dissociation was calculated. In addition, we investigated solid-state photodissociation of E-dimers of p-iodonitrosobenzene under cryogenic conditions and kinetics of the subsequent re- dimerization reaction.

Aromatic C-nitroso compounds, dimerization, dissociation, solid state

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