An exploration of the mechanisms for the formation of 3,4-bis(4-aminofurazan-3-yl)-furoxan by density functional theory

Formation of 3,4-bis(4-aminofurazan-3-yl)-furoxan from 4-aminofurazan-3-carboxamidoxime has been theoretically investigated with the density functional theory (DFT) method to clarify the reaction mechanism. The formation reaction has been examined in three successive courses. In the first course, chloroxime furazan is formed from amidoxime furazan via electrophilic substitution and diazotization followed by N2 elimination. In the second course, chloroxime furazan undergoes a dehydrochlorination process to give the nitrile oxide species. In the third course, dimerization of nitrile oxides leads to the formation of tricyclic furoxan, 3,4-bis(4-aminofurazan-3-yl)-furoxan. The theoretical calculation indicates that a catalyzed water molecule accelerates the hydrogen transfer and dehydrochlorination in the first and second reaction courses. The computational results also suggest that the dimerization is stepwise process in which intermediates and transition states (TSs) show strong diradical character. The dimerization occurs with a large exothermicity, and its rate-determining step corresponds to CC bond formation.