JOURNAL of the Tunisian Chemical Society

serving the Research, the Education and the Industry

Mécanisme réactionnel et corrélations structure-réactivité des anilines para-x-substituées dans les réactions de SNAr

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The reaction of 2,4,6-tris(trifluorométhanesulfonyl) anisole with a series of aniline para-X-substituted (X = OCH3, CH3, H, F, Cl) was studied kinetically in the acétonitrile with 20°C. The mechanism and the nature of rate limiting have been proposed. The kinetic findings collected, completed with the analysis of the electronic effects of the substituent X (σ) on the constants of bimolecular rate (k1) have enabled us to establish an excellent correlation of Hammett, with negative ρ value (ρ = -1,82). Besides, good linear relationships was obtained from plots of log k1 against basicity of anilines, with the Brönsted coefficient βNu = 0,41.

N. Elguesmi, R. Goumont, T. Boubaker

SNAr, Brönsted, Hammett

Pages 97-107

Carbohydrates from Moricandia arvensis growing in Tunisia

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β-D-Glucopyranosyl-2-methylbutanoate, β-D-glucopyranosyl-2-methylpropanoate, 2-O-methyl-α-D-fructofuranose, 2-O-methyl-β-D-fructofuranose, and sucrose were isolated from the flowers of Moricandia arvensis, and characterized by spectroscopic methods.

H. Braham, H. Ben Jannet, Z. Mighri, P.M. Abreu

Moricandia arvensis, β-D-Glucopyranosyl-2-methylbutanoate, β-D-glucopyranosyl-2-methylpropanoate, 2-O-methyl-α-D-fructofuranose, 2-O-methyl-β-D-fructofuranose

Pages 109-113

Synthèse d’isoxazolines et de spiro-isoxazolines par réaction de cycloaddtion dipolaire-1,3

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1,3-dipolar cycloaddition of arylnitriloxydes 1 on N-alkylmaleimides 2 realized in refluxing toluene leads to the corresponding isoxazolines. The synthesis of a new series of spiro-isoxazolines, by cycloaddition of arylnitriloxydes with les (E)-arylidène-N-arylsuccinimides 6 is reported. We also devoted a particular interest to the structural elucidation of such heterocyclic compounds.

N. Ben Hamadi, M. Msaddek

arylnitriloxides, 1,3-dipolar cycloaddition, isoxazoline, spiro-isoxazoline

Pages 115-120

Étude cinétique de la dégradation hydrolytique d’un insecticide : le Bendiocarb

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This paper deals with the kinetic hydrolysis mecanism of Bendiocarb or 2,2-dimethyl-1,3-benzodioxol-4-yl-Nmethylcarbamate in aqueous media. This work is carried out by reversed phase Liquid Chromatography and UV Spectrophotometry. The determination of 2,2-dimethyl-1,3-benzodioxol-4-ol, as the main product of Bendiocarb hydrolysis gives evidence for the significant reactivity of this insecticide in aqueous media. Temperature effects were determined by measuring the base hydrolysis rate constant for Bendiocarb. The obtained positive entropy + 112 Jmol-1K-1, indicates an E1cB hydrolytic mechanism involving unimolecular decomposition of Bendiocarb via a methylisocyanate intermediate. This elimination process is confirmed by the position of the point corresponding to the Bendiocarb on the Brönsted and Hammett lines wich has been determined by Williams for a serie of substituted N-methylcarbamate whose decomposition has been established to follow the E1cB mechanism.

F. Boujelbane, N. Ben Hamida

Bendiocarb, kinetic, mechanism, HPLC, spectrophotometric UV

pages 121-132

Déminéralisation des eaux saumâtres du sud Tunisien par électrodialyse ou par osmose inverse

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The contribution of membrane techniques with the aim of producing potable water from brackish water without using chemical reactants has become a reality e.g. the supply of the towns of Gabes and Zarzis (south of Tunisia). The utilization of selective membranes CMX/ACS (selective to monovalent ions) allows one to reduce the contents of monovalent ions ( Na+ and Cl- which are responsible for the salinity of water) while reducing only slightly the contents of divalent ions. Experiment shows that low mobility of divalent ions in the membrane phase plays a determining role in ion extraction. A pilot equipped with a filmTec RO membrane (Nanomax 95) alimented with brackish water collected from Zarzis town was operated at 15 bars, 25°C, and up to a water recovery ratio of 50%. The results showed that the RO is actually efficient since it highly reduced the content of inorganic matter present in raw waters (rejection > 95% for the divalent ions and 85% for the monovalent ones ).

K. Walha, R. Ben Amar, F. Quemeneur, P. Jaouen

Brackish water, Desalination, Potable water, reverse Osmosis, Electrodialysis

Pages 133-142

Composé à nouvel polyanion hybride [(VO)2O(C204)3]2 (C5NH6)10 (NO3)4.4,44H2O

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A novel organic–inorganic hybrid vanadium [(VO)2O(C2O4)3]2(C5NH6)10(NO3)4.4,44H2O was synthesized at room temperature and characterized by IR spectrum and electron microscopy. Its crystal and molecular structure was determined by single crystal X-ray diffraction. This compound crystallizes in the triclinic system, space group Pī , with a = 10,645(3) Å, b = 14,373(2) Å, c = 15,370(3) Å , α = 110,08(1), β = 99,65(2), γ = 102,86(2)° and Z=1. The structure was solved and refined to R = 0.037, Rw = 0.077. The crystal structure is characterized by the cyclic and centrosymetric [(VO)2O(C2O4)3]26- anion. It consists of two binuclear mixed valence vanadium (IV) - vanadium (V) complexes [(VO)2O(C2O4)4] bridged by bis(bidentate oxalate) ligands. In this compound, each V atom is in a distorted octahedral coordination, being bonded to one terminal oxo-O atom, one bridging O atom, two O atoms from an oxalato ligand and two from an other oxalato bridging ligand. The structure cohesion is ensured by hydrogen-bonding and Vander Walls interactions, which form a three-dimensional framework.

R. Ksiksi, M. Graia, A. Driss

complex, vanadium, structure, IR absorption

Pages 143-156

Structural and magnetic properties of Sm2Fe17-xCox polycristalline compounds with 0≤x≤3

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Samples of Sm2Fe17-xCox (x = 0.5 - 3) arc-melted and subsequently annealed at a temperature 1225 K, were studied by X-ray diffraction (XRD), using the Rietveld method, coupled to Curie temperature Tc measurements. The as prepared compounds crystallize in a rhombohedral structure Th2Zn17-type. The Curie temperature increases linearly with "x" to reach 790 K for x = 3. The increase of Tc despite the low contraction of the cell volume can be explained by the strong exchange integrals JCo-Co and JFe-Co. The substitution of Co was assumed to contribute to complete the 3d sub band, reduce the negative interactions and induce the Curie temperature enhancement.

I. Nehdi, M. Abdellaoui, C. Djega-Mariadassou, H. Zarrouk

Rare earth compounds, Transition metal compounds, Crystal structure, Magnetic measurements

Pages 157-162

Application de la membrane liquide supportée à l'extraction du Cr(III) par le Lasalocide A

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The liquid-liquid extraction of Cr(III) ions has been investigated using lasalocid A as ionophore. Chromium extraction of 92 % of the initial chromium amount (2 mL 10-3 M) by 1 mL 5.10-3 M of Lasalocid A in 2- nitrophenyl octyl ether (NPOE) has been obtained at aqueous feed pH value of 5.5. Difficulties correlated to the stripping step were also studied because only 57 % of chromium was recovered by contact of the loaded organic phase with a solution of HCl at pH 0 was obtained. The incomplete stripping of the metal may be a result of the formation of stable species in the oragnic phase. The use of an acidic stripping solution made of HNO3 at pH 0 had permitted to surmount this hindrance and to obtain a stripped ratio of 89 %. The study of Cr(III) transport through a supported liquid membrane (SLM) and under the same optimum conditions, demonstrated a very low extraction ratio. The weakness of this ratio can he explained by a HNO3 leakage through the membrane, which in turn leads to a pH decrease in the source phase to acidic pH values where the extraction becomes impossible. This HNO3 leakage was confirmed by pH measurements and by circulating separately the source phase and the stripping phase successively (0.8 mL.min-1) through a hollow fibre SLM device (acting as a column system) where a recovery yield of 19 % was obtained after a circulation time of 24 h for each aqueous phase.

R. Tayeb, S. Tingry, M. Dhahbi, P. Seta

Chromium, Liquid-liquid extraction, Extraction efficiency, Supported liquid membrane (SLM)

Pages 187-194

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