Center for Magnetic Resonance

E.A. Krylova, M.G. Shelyapina, P. Nowak, H. Harańczyk, M. Chislov, I.A. Zvereva, A.F. Privalov, M. Becher, M. Vogel, V. Petranovskii

“Mobility of water molecules in sodium- and copper-exchanged mordenites: Thermal analysis and 1H NMR study”

Microporous and Mesoporous Materials, 2018, 265, 132-142
DOI:10.1016/j.micromeso.2018.02.010

Comprehensive research of water behavior in Na- and Cu-mordenites with different Na/Cu ratio was done. Several steps of dehydration process were detected and analyzed, taking into account difference in chemical composition of the samples, reaction models and corresponding kinetic equations. Activation energies for these steps were calculated. It was shown that the majority of dehydration steps for all zeolite samples studied might be associated with chemical reaction mechanism corresponding to the second order kinetic model, except for the most high-temperature step for Cu-mordenite, for which the third-order model has the higher correlation coefficient. A detailed analysis of rehydration processes was studied by proton NMR spectroscopy. The obtained results allow one to distinguish different types of water and to associate them with a certain localization of water molecules in zeolite voids: the main channel for both Na and Cu-mordenites; a side pocket of Na-mordenite; molecules coordinated with Cu2+ cations in Cu-mordenite. The diffusion measurements carried out using static field gradient NMR technique proved that the water diffusion character below 300 K is essentially intracrystalline, whereas above 300 K it becomes intercrystalline. The activation energy of intercrystalline diffusion is about 28 kJ/mol and does not depend on the Na/Cu ratio. That allows us to suppose that in the studied zeolites the intercrystalline diffusion is governed by the morphology of the sample mainly.

Y.M. Zhukov, M.G. Shelyapina, I.A. Zvereva, A.Y. Efimov, V. Petranovskii

“Microwave assisted versus convention Cu2+ exchange in mordenite”

Microporous and Mesoporous Materials, 2018, 259, 220-228
DOI:10.1016/j.micromeso.2017.10.013

Sodium mordenite was Cu²⁺-exchanged by conventional methods at ambient temperature (accepted as 20 °C) and with microwave radiation at 100 ± 1 °C. To increase the copper content, we repeat the exchange procedure several times. Both the degree of Cu²⁺ exchange and the environment of the Cu²⁺ ions depend on the method of exchange. Neither conventional, nor microwave methods do not destruct the topology of mordenite framework. XRD pattern of the mordenite persists, but slight elastic deformation and some dealumination of the surface layer occurs. For all the studied samples, all the copper ions are in Cu²⁺ state, neither Cu¹⁺ nor Cu⁰ were detected. All the copper ions play the role of charge-balancing counter-cations. Their placement into the interior of zeolite causes the channel contraction due to electrostatic interactions of double charged cations with [AlO₄]^δ– units. The increase of copper content is accompanied by increasing of number of water molecules per unit cell. In fully hydrated samples the copper cations are effectively separated from the zeolite framework and are fully surrounded by a water ligand shell.

M. S. Ledovskaya, K. S. Rodygina, V. P. Ananikov

“Calcium-mediated one-pot preparation of isoxazoles with deuterium incorporation”

Org. Chem. Front., 2018, 5, 226-231
DOI:10.1039/C7QO00705A

In this work, a novel synthetic methodology for the one-pot preparation of isoxazoles directly from the reaction of calcium carbide with aldoximes is reported. Calcium carbide acts as a safe and inexpensive acetylene source and, in addition, as a source of the Ca(OH)₂ base to enable the generation of nitrile oxide. Various 3-substituted isoxazoles were synthesized from the corresponding aldoximes in good yields (up to 95%) and a series of new deuterated 4,5-dideuteroisoxazoles were prepared.