A comparative study between three main methods for the preparation of α,β-unsatured epoxides is presented. We show, in particular, that from bromhydrines, the dehydrobromation in the presence of phase transfer catalyst enables to double the yields obtained in homogenous phase. These yields remain higher than those provided by other methods.
A. Baklouti, A. Hedhli
Reaction of amines with 2-acetoxymethylcyclohexenones in mild conditions, give α-aminomethylcyclohexenones in good yields.
F. Rezgui, M.M. El Gaied
Chromia-Aluminia mixed oxides are prepared by the "sol-gel" method. This method involves the hydrolysis and polycondensation of an homogeneous mixture of metallic alkoxides. The gelification occurs in acetic medium by varying the molar ratio k = [acetic acid] / [alkoxide] between 0.5 and 3. The structural and catalytic properties of the xerogels obtained by calcination up to 440°C depend on the molar k, the quantity of chromium and the temperature of calcination. Very selective catalysts in partial oxidation and ammoxidation of paraxylene are obtained by acting on these parameters.
S. Sam-Rezgui, A. Ghorbel
Titania pillared montmorillonite was prepared by the reaction of Na-Montmorillonite with polymeric Ti cations, formed by partial hydrolysis of TiCl4 in HCl. The resulting TiO2-cross-linked montmorillonite has a surface area of 316 m2/g and pore volume of about 0.17 cm3/g and is thermally stable up to 500°C. The pillar heights of the product heated at a temperature > 100°C was 17-15 Å. The uptake of TiO2 by the montmorillonite depends on the ratio H+/Ti in the solution.
L Khalfallah-Boudali, A Ghorbel, D Tichit, F Figuéras
The addition of the Ce3+ and Eu3+ in the nickel zeolithe faujasite X systems affects the reducibility of Ni2+ ions and leads to a highly dispersed metallic state of Ni°. This influence seems to be related on the one hand to the localization of cation present in different cristallographic sites of zeolite and to oxydo-reducing properties of such systems. The preferential localization of the trivalent cations, with high electrostatic fields, in the zeolite have for consequence a location of the Ni2+ ions more accessible sites to the reducing agent, this easing their reduction. Besides, the oxydo-reducing properties of the zeolite are modified in the presence of cerium-europium ions with an electro-yielding character. Theses modifications lead to, the existence of high interaction between the metal and the support, and the stabilization of a highly-dispersed metallic state.
S. Djemel, A. Ghorbel, J. Jeanjean, M.F. Guilleux
Copper corrosion by natural water from the South of Tunisia has been studied and several organic molecules have been tested to asses their inhibiting efficiency. Electrochemical investigations were followed by surface analysis techniques such as I.R, XPS, EXAFS, SEM which allowed the identification of surface compounds. Phenylthiol is the more efficient by building-up an inhibiting film based on a polymeric Cu(I) complex.
H. Chelli-Ferjani, E. Triki, J.P. Labbé. M. Delamar