Desproporcionamento de tolueno sobre zeólitas tipo mordenita - atividade e seletividade na obtenção de xilenos

A sodium mordenite zeolite (Na-MOR) was synthesized and modified by dealumination with chloridric acid solution (H-MOR). X-Ray Diffraction (XRD), Inductive Coupled Plasm (ICP) and Scanning Electron Micrograph (SEM) techniques were used for sample characterization. The zeolite catalytic behavior was evaluated through toluene disproportionation at 435°C. It was verified that mordenites were very selective for the disproportionation reaction and the samples with higher aluminum content showed larger initial activity, however, these samples showed too a higher deactivation velocity due to a blockage of the unidimensional porous system of the zeolite by coke deposits. The selectivity to xylene isomers was practically not influenced by the Si/Al ratio and changed with the time on stream, due to coke formation. Transition state shape selectivity inside the mordenite pores is also discussed.

Utilização de endoperóxidos de derivados de naftaleno como fontes químicas de oxigênio singlete em sistemas biológicos

Molecular oxygen, in the first excited state (singlet oxygen, ¹O2), has a substantial reactivity towards electron-rich organic molecules, such as biological targets, including unsaturated fatty acids, proteins, RNA and DNA. Considering the complexity of biological systems and the great variety of reactive species generated by photochemistry, efforts have been devoted to develop suitable ¹O2 generators based on the thermolysis of water soluble naphthalene endoperoxides. These compounds are chemically inert and have been employed as versatile sources of ¹O2. The synthesis is based on structural modifications in position 1,4 of dimethylnaphtalene, grafting hydrophilic substituents. The correspondent endoperoxide can be generated using photochemical method, or molybdate-catalyzed disproportionation of hydrogen peroxide.

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

Estudo por espectrometria de massas de soluções de hidróxi(tosilóxi)iodobenzeno: propostas para mecanismos de desproporção

Solutions of [hydroxy(tosyloxy)iodo]benzene (HTIB or Koser's reagent) in acetonitrile were analyzed using high resolution electrospray ionization mass spectrometry (ESI-MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS) under different conditions. Several species were characterized in these analyses. Based on these data, mechanisms were proposed for the disproportionation of the iodine(III) compounds in iodine(V) and iodine(I) species.