engleski

Thermal E-Z Isomerization of Aromatic Azodioxides in Solid State

Most of the investigations of solid-state E-Z isomerizations have been focused on photoreactions. Thermal solid-state isomerizations of double bonds in organic molecules are very rare and not studied in details. In our previous works we have developed the approach to the study of the solid-state reaction mechanisms by using the dimerizations and dissociations of the aromatic C-nitroso compounds as models. The E-Z isomerizations of azodioxides in solution exclusively follow the pathway through the formation of the nitroso monomer intermediates. Direct “torsional” E-Z isomerization has not yet been observed. Here we demonstrate that the azodioxide Z-E isomerization in solid state can occur without the formation of the free nitroso molecule. The reaction is studied by measuring the kinetics of isomerizations of 3-chloro- and 3-bromonitrosobenzene dimers. The mechanism is discussed on the basis of the measured activation parameters, DSC, and time-resolved XPRD. It is proposed that the two concurrent reactions, the azodioxide E-Z isomerization, and the dimerization of C-nitroso molecules, respectively, occur through the same type of the transition state.

activation parameters; aromatic azodioxides; kinetics of reaction; thermal solid-state E-Z isomerization

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