Croissance urbaine et réduction des espaces agricoles au Maghreb. Analyse diachronique de quelques exemples en Algérie

Dagorne Andrée, Fenet B. Croissance urbaine et réduction des espaces agricoles au Maghreb. Analyse diachronique de quelques exemples en Algérie. In: Cahiers de la Méditerranée, n°51, 1, 1995. Villes intermédiaires en Méditerranée. Tome 2. pp. 145-146

Oran, Métropole de l'Ouest algérien, d'hier à aujourd'hui

Dagorne Andrée, Fenet B. Oran, Métropole de l'Ouest algérien, d'hier à aujourd'hui. In: Cahiers de la Méditerranée, n°51, 1, 1995. Villes intermédiaires en Méditerranée. Tome 2. pp. 147-161

Formation mechanisms and yields of small imidazoles from reactions of glyoxal with NH4+ in water at neutral pH

SSCI-VIDE+ATARI+AMX:BNO:HMEInternational audienceImidazoles have numerous applications in pharmacology, chemistry, optics and electronics, making the development of their environmentally-friendly synthetic procedures worthwhile. In this work, the formation of imidazole, imidazole-2-carboxaldehyde, and 2,2-bis-1H-imidazole was investigated in the self-reaction of glyoxal and its cross-reactions with each of these compounds in aqueous solutions of inorganic ammonium salts at pH = 7. Such conditions are relevant both as cheap and environmentally-friendly synthetic procedures and for the chemistry of natural environments where NH4+ is abundant, such as in atmospheric aerosols. These reactions were investigated both by H-1-NMR and UV-Vis absorption spectroscopy at room temperature with the objective to determine the formation pathways of the three imidazoles and the parameters affecting their yields, to identify the optimal conditions for their synthesis. The results show that only the simplest imidazole is produced by the self-reaction of glyoxal and that imidazole-2-carboxaldehyde and 2,2-bis-1H-imidazole are produced by cross-reactions of glyoxal with imidazole and imidazole-2-carboxaldehyde, respectively. The yields of imidazole-2-carboxaldehyde and 2,2-bis-1H-imidazole formed by the cross-reactions were close to unity, but the yield of imidazole formed by the self-reaction of glyoxal, Y-Im, was small and varied inversely with the initial glyoxal concentration, [G](0): Y-Im > 10% only for [G](0) < 0.1 M. The latter result was attributed to the kinetic competition between the imidazole-forming condensation pathway and the acetal/oligomer formation pathway of the glyoxal self-reaction and constitutes a bottleneck for the formation of higher imidazoles. Other parameters such as pH and the NH4+ concentration did not affect the yields. Thus, by maintaining small glyoxal concentrations, high imidazole yields can be achieved in environmentally-friendly aqueous ammonium solutions at neutral pH. Under the same conditions, higher yields are expected expected from substituted carbonyl compounds, regardless of their concentration, as they produce less acetals

iminium-catalysed hydrolysis of epoxides by nh4+ in water: importance for atmospheric and green chemistry

SSCI-VIDE+ATARI+AMX:BNO:LFI:CFEInternational audienceIminium catalysis, which was known for a long time to be mediated by amines and amino acids, was also recently shown to be mediated by inorganic ammonium ions, NH4+. Iminium catalysis by NH4+ is potentially of great interest both for green chemistry in water and in atmospheric aerosols where these ions are abundant. In this work we investigate the hydrolysis of epoxides such as 1,2-epoxybutane, cis-2,3-epoxybutane, 2,3-dimethyl-2,3-epoxybutane, and the âisoprene-derivedâ cis- and trans-(2-methyloxirane-2,3-diyl)dimethanol (or âIEPOXâ 3 and 4, respectively) in aqueous solutions at pH = 5-8 in the presence of NH4+. The products and kinetics of each reaction have been studied with a combination of GC/MS, GC/FID and 1H-NMR and by comparison with authentic standards. The results showed that each epoxide produced the expected diol or tetrol in large yield and that the reaction rate was much larger than when catalyzed by base or acid, confirming that NH4+ is an efficient catalyst for the hydrolysis of epoxides. Iminium catalysis by NH4+ thus provides a cheap and green alternative for the manufacturing of diols and glycols in water. In tropospheric aerosols, the hydrolysis of epoxides by NH4+ catalysis should be much faster than by acid catalysis for pH 3-4, thus in many regions except the most polluted ones

PGFSE-NMR study of the self diffusion of sucrose fatty acid monoesters in water

The micellization of pure monosubstituted sucrose fatty acid esters in water, namely sucrose octanoate, sucrose decanoate, sucrose laurate, sucrose dodec-5-cis-enoate, sucrose myristate, and sucrose palmitate, has been investigated by means of two NMR methods, pulsed field gradient spin-echo NMR (PFGSE–NMR), giving access to the self-diffusion coefficients of free molecules and micelles in solution, and the ERETIC method (electronic reference to access in vivo concentrations) for the measurement of concentrations by external calibration of a synthetic NMR signal. The early micellar regions and, when possible, the premicellar regions were investigated. By this method, we obtained the hydrodynamic radii of micelles, displaying a linear progression in relation to the chain length and an accurate determination of critical micellar concentration (CMC) for each sucrose ester. The effect of the regiochemistry of fatty chain grafting has been investigated, showing special behavior for -O-sucrose palmitate

Concentration measurements of sucrose and sugar surfactants solutions by using the 1H NMR ERETIC method

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Conformational study of aminocalixarenes

Chiral calix[4]arenes bearing (R) - (+) or S - (-) (methoxymethyl)-pyrrolidin groups (MMP) on the upper ring are synthesized. The conformation is studied by 2D 1H NMR and by High Temperature Annealed Molecular Dynamics Simulations. A new conformation due to the hydrogen bond between the OH phenolic group and the oxygen atom of the methoxy group is found. These calixarenes exhibit circular dichroism with split Cotton effects as a result of exciton chirality induction. The optical activity is in agreement with the conformation studied by MD simulations which indicate that the MMP groups are twisted forming, with the aromatic nucleus, the beginning of an helix

The hydrolysis of epoxides catalyzed by inorganic ammonium salts in water: kinetic evidence for hydrogen bond catalysis

International audienceNaturally-occurring inorganic ammonium ions have been recently reported as efficient catalysts for some organic reactions in water, which contributes to the understanding of the chemistry in some natural environments (soils, seawater, atmospheric aerosols, …) and biological systems, and is also potentially interesting for green chemistry as many of their salts are cheap and non-toxic. In this work, the effect of NH4+ ions on the hydrolysis of small epoxides in water was studied kinetically. The presence of NH4+ increased the hydrolysis rate by a factor of 6 to 25 compared to pure water and these catalytic effects were shown not to result from other ions, counter-ions or from acid or base catalysis, general or specific. The small amounts of amino alcohols produced in the reactions were identified as the actual catalysts by obtaining a strong acceleration of the reactions when adding these compounds directly to the epoxides in water. Replacing the amino alcohols by other strong hydrogen-bond donors, such as trifluoroethanol (TFE) or hexafluoroisopropanol (HFIP) gave the same results, demonstrating that the kinetics of these reactions was driven by hydrogen-bond catalysis. Because of the presence of many hydrogen-bond donors in natural environments (for instance amines and hydroxy-containing compounds), hydrogen-bond catalysis is likely to contribute to many reaction rates in these environments