Desvendando a alta eficiência do sistema peroxioxalato
A todas as pessoas que me concederam um pouco de sua amizade (você que lê está aqui!) porque eu certamente apreciei isso. , porque sem vocês quase nada valeria a pena. À Capes pelas bolsas concedidas. ABSTRACT Augusto, F. A. Unraveling the high efficiency of the peroxyoxalate system. 2016. 116p PhD Thesis -Graduate Program in Chemistry. The peroxyoxalate system has several analytical applications, mainly due to its high emission yields and relative simplicity. Here this system high efficiency
... s studied in several fronts, comparing it with similar systems, connecting it with an intramolecular efficient system, searching for the structure of its high-energy intermediate and investigating the steps in its production, trying to obtain experimental and theoretical information about this reaction. The peroxyoxalate system kinetics was studied using naphthalene as activator, an aromatic compound relatively simple, that allows the application of accurate theoretical calculations to this system. These theoretical study of charge transfer complexes between naphthalene and 1,2-dioxetane, 1,2-dioxetanone, and 1,2dioxetanedione have shown that the availability of excited states is directly related to the electronic properties of the involved peroxide. Studying the radical anion of these peroxides it was observed that an increase in the number of peroxide carbonyls makes it a better electron acceptor and that, specifically for 1,2-dioxetanone, the electron transfer can provide a barrierless decomposition path. Kinetic studies of the peroxyoxalate system using DBU as a nonnucleophilic strong base catalyst indicated the reaction feasibility in these conditions, despite its high rate. However, it was not possible to obtain kinetic results using phenolates as activators. Experiments of delayed addition of activator were made as well using a solvent that could facilitate the detection of the high-energy intermediate, observing accumulation of this intermediate in emission kinetics. Yet, it was not possible to detect this intermediate by mass spectroscopy. At last, it was verified that the initial steps of the system are exothermic, with exception of the four-membered ring formation. Studying this step in more detail, it was obtained for a step a Hammett ρ value similar to the one observed experimentally, indicating that this step should be the rate limiting step and that the high-energy intermediate should be the 1,2-dioxetanedione.