[MgAl][CO3] hydrotalcites were prepared by aqueous precipitation and crystallization procedures. The basic potential of these solids was studied by the knoevenagel model reaction. The most basic precursor was impregnated by a cobalt phtalocyanine and tested in light oil sweetening process for mercaptan oxidation. It reveals an important activity and a good selectivity confirming our interest to hydrotalcites.
L. Chatti, A. Ghorbel, P. Grange, J.M. Colin
Hydrotalcite, cobalt phtalocyanine, mercaptan oxidation, Knoevenagel reaction
Pages 1599-1606
A rapid and simple flow injection system with gas diffusion separation and spectrophotometric detection is described for the determination of acid dissociable cyanide in natural and wastewater samples. The proposed method is based on the diffusion of cyanide (as hydrogen cyanide) through a microporous PTFE membrane wall from a hydrochloric acid donor stream into a bromothymol blue acceptor stream. The transferred cyanide was then reacted with bromothymol blue and the changes in the reagent colour was monitored spectrophotometrically at 630 nm. The working conditions of the flow injection system (donor stream concentration, acceptor stream concentration and pH, sample loop volume, flow rates...etc.) were optimised. The calibration graph is linear from 1 to 25 μgml-1 cyanide (R2 = 0.998), the detection limit is 0.5 μgml-1, the sampling rate is 25 samples h-1 and the precision was 1.85% RSD. The method is simpler and quicker than other published flow injection methods.
L. Monser, N. Adhoum
Cyanide, Bmmothymol blue, Flow injection, Gas diffusion, Spectophotometry
Pages 1607-1613
The electrochemical behavior of 4-chloroguaiacol (4-CG) on pre-treated gold electrodes was investigated by cyclic voltammetry. Electrolytic solutions are water-acetone mixtures with 0 - 40 vol % acetone and containing 0.5 mol dm-3 of sulfuric acid. The cyclic voltammogram shows one irreversible anodic peak and a pre-peak. The effect of experimental conditions on the ratio of these two peaks was examined. The proposed mechanism is based on the hypothesis of a two-electron discharge leading to three phenoxonium cation mesomers, which hydrolysis would lead to 4-chlorocatechol, methoxyhydroquinone and 5-chloro-3-methoxycatechol. The process of electrode passivation during 4-CG electrooxidation at the gold electrode was studied with respect to 4-CG concentration and for different conditions of the electrode pre-treatment. Preliminary study shows that 4-CG is quantitatively oxidized by electrolysis at PbO2 anode in sulfuric acid aqueous solutions (pH = 2). Maleic, fumaric, formic and oxalic acids are among the formed products.
Y. Samet, R. Abdelhedi, A. Savall
4-chloroguaiacol, electrochemical oxidation, gold electrode, PbO2 anode
Pages 1615-1624
The basic hydrolysis of Baygon or o-isopropoxyphenyl-N-methylcarbamate has been studied, in aqueous media, by reversed phase Liquid Chromatography and UV Spectrophotometry. The pseudo-first order rate constant of hydrolysis reaction of Baygon were determined by measurements of the increase UV absorption of o-iso-propoxyphenol versus time, in buffer solutions with pH displayed from 9 to 12. The obtained positive activation enthropy ΔS = + 63,45 J mol-1 K-1, indicates an ElcB hydrolytic mechanism involving unimolecular decomposition of Baygon via a methylisocyanate intermediate.This elimination process is confirmed by the position corresponding to the Baygon point on the Hammett and Brõnsted line, determined by Williams for a serie of substituted N-methyl-carbamates whose decomposition has been established to follow the ElcB mechanism.
N. Ben Hamida, M. Smaali, S. Sabbah
Baygon, kinetic, mecanism, hydrolysis, HPLC, UV Spectrophotometry
Pages 1625-1640
In this work, the air gap membrane distillation is used in order to desalinize synthetic waters having temperature and concentration comparable to those of geothermal and brackish waters from the South of Tunisia. An experimental laboratory apparatus is built up. Different operating parameters have been investigated, such as the feed flow rate, the sodium chloride concentration, the temperature and the air gap width. The obtained results are in a good agreement with those found in literature, The AGMD is adapted to desalt waters having a sensible heat (e.g. geothermal waters).
S. Bouguecha, A. El- Amali, M. Dhabhi
Hydrophobic membrane, Membrane distillation, PTPE membrane, Air Gap Membrane Distillation, Desalination
Pages 1641-1648
Cathodic reduction of several N-Arylsulfonyl-N-phényl hydrazonates of a typical structure (schemel) has been investigated by cyclic voltammetry and controlled potential electrolysis at mercury electrode in aprotic solvent. Quantitative results for preparative electrolysis show the occurrence of reductive cleavage of the carbon-sulfur bond leading to the formation of N-phenylhydrazonates in good yields. For all the investigated compounds values of the kinetic solution electron transfer are reported.
T. Saied, M. L. Benkhoud, K. Boujlel
Elydrazonates, cyclic voltammetry, redox catalysis, rate constant of solution electron transfer
Pages 1649-1656
The title compound, strontium tetraphosphate Sr3P4O13 was prepared by solid-state methods, This compound crystallizes in the triclinic system, space group P-1 with a = 6.9122(9) Å, b = 7.7190(8) Å, c = 5.525(1) Å, α = 104.22(2)°, β = 109.46(2)°. γ = 83.275(9)° and Z = 1. Its structure is composed of infinite chains of edge-sharing Sr(2)O7 polyhedra. These chains are linked together by edge-sharing and corner-sharing Sr(l)O8 polyhedra. The structure cohesion is insured by centrosymmetric P4O136- groups forming a three dimensional framework.
M. Graia, A. Driss, T. Jouini
Preparation, structure, tetraphosphate, strontium, P4O136-
Pages 1657-1663
The sodium tetranickel triarsenate NaNi4(AsO4)3 crystallizes in the tetragonal system, space group I 4 2d (N° 122). The parameters of the unit cell are: a = 6.7863(2)Å, c = 18.682(2)Å, Z = 4, ρc = 5.208 Mg.m-3. The structure consists of a three-dimensional framework made of AsO4 tetrahedra and NiO6 octahedra sharing edges and corners. This closed framework delimits cavities wherein Na ions are located. The double NaNi4(PO4)3 orthophosphate although analogous in composition, is fundamentally different in structure from the arsenate studied. The later compound exhibits the Namg4(VO4)3 structure.
R. Ben Smail, M.F. Zid, T. Jouini
Arsenate, nickel, crystal structure
Pages 1665-1673
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