Influence de la structure sur l'hydrolyse des N-pyrrolylmethylene-2 anilines

Hydrolysis of the imine function of a series of Schiff bases derived from pyrrole-2-carboxaldehyde and substituted anilines (X = H, p-OCH₃, p-OC₂H₅, p-CH₃, p-Cl, p-Br, m-CN, m-NO₂, p-NO₂) was studied in all of the pH ranges. The hydrolysis curves log k_abs (mn^?1) = f(pH) were established in buffered aqueous methanol by polarography or amperometry. The shapes of the curves obtained for pH > 5 indicates that N-pyrrolylmethylene-2 anilines hydrolyse according to the same mechanism as N-benzylidene anilines. The particular stability of these products for pH < 5 permits one to obtain complete hydrolysis curves in acid media. A very good Hammett correlation (k_obs = + 1,73) has been established from the maxima which appear for strong acidity. This stability is interpreted as due to the specific electron-donating effect of the pyrrole nucleus. The influence of the structural parameter X on the morphology of the curves log k_abs = f(pH) and on the hydrolysis mechanism of the imine function is discussed in all of the pH ranges.     

Bending Stiffness of Damaged Cross-Ply Laminates

Mechanics of Composite Materials - The bending stiffness of carbon/epoxy and glass/epoxy cross-ply laminates with intralaminar cracks in the surface 90° plies and local delaminations were...     

Sur la ribosylation de divers mercapto-2 benzoazoles

A comparative study of the ribosylation reaction of various 2-mercaptobenzazoles using the three more usual techniques was performed: acid-catalyzed fusion, reaction of the silylated aglycones with 1-acetoxy and 1-halogeno sugars, respectively. For all the various 2-mercaptobenzazoles the N-nucleosides were obtained and fully characterized. The reactivity of 2-mercapto-benzimidazole is quite particular as we have noticed the formation of the corresponding N₁, N₃-diriboside and of an unusual 2-2-anhydro nueleoside.     

Effect of sodium diisopropylnaphthalene sulfonate on Zn-Mn alloys electrodeposition

Journal of Solid State Electrochemistry - A novel additive sodium diisopropylnaphthalene sulfonate (SDIPNS) was investigated in Zn-Mn electrodeposition on steel from chloride bath. To this end,...     

Solving multi-criteria scheduling flow shop problem through compromise programming and satisfaction functions

The multi-criteria scheduling problem is one of the main research subjects in the field of multiple objectives programming. Several procedures have been developed to deal with this type of problem where some conflicting criteria have to be optimized simultaneously. The aim of our paper is to propose an aggregation procedure that integrates three different criteria to find the best sequence in a flow shop production environment. The compromise programming model and the concept of satisfaction functions will be utilized to integrate explicitly the manager’s preferences according to the deviations between the achievement and the aspiration levels of the following criteria: Makespan, total flow time and total tardiness.     

Structure and Characterization of the [Rbx (NH4)1-x]2TeCl6 Tellurate Family at Room Temperature

The crystal structure of rubidium-ammonium hexachlorotellurate [Rb_0.94(NH₄)_0.06]₂TeCl₆ was determined by X-ray single crystal analysis at room temperature. The space group is Fm3m with the lattice parameter a = 10.2503(5) ? and Z = 4. The refinement converged to R(F) = 0.015 and wR(F ²) = 0.032. As in the studied [Rb0.94(NH₄)₀.06]2TeCl6 family, this compound has an antifluorite-type arrangement. Tellurium atoms are surrounded by an octahedron of chlorine atoms. The Rb or N atoms are located between TeCl₂⁶ octahedra ensuring the stabilization of the structure by ionic and hydrogen bonding contacts N-HCl. The substitution of rubidium by ammonium groups does not affect the structural arrangement, but it leads to a decrease in the a lattice cell dimension. IR and Raman spectroscopic studies at room temperature were performed to confirm the X-ray crystallographic results.     

A multi-objective production scheduling case study solved by simulated annealing

During several decades, research in production scheduling mainly concerns a single criterion to optimize. However, the analysis of the performance of a schedule often involves more than one aspect and therefore requires multi-objective analysis. Such situation appears in the real case study considered here.     

Structural Analysis of the Phase Transitions of (NH<Subscript>4</Subscript>)<Subscript>4</Subscript>HgBr<Subscript>6</Subscript>

Abstract Single crystal diffraction and differential scanning calorimetry DSC techniques have been used to investigate the different phases of (NH₄)₄HgBr₆, tetrammonium mercury hexabromide, from room temperature to 120 K. Two anomalies in thermal behaviour were detected for this compound at 190 and 268 K, by DSC experiment. X-ray diffraction measurements confirm these anomalies. At room temperature the structure is tetragonal P4/mnc (No. 128) with lattice parameters a = b = 9.25560(8) ?; c = 8.8657(11) ?; V = 759.49(9) ?³ and Z = 2. At T = 250 K the structure is orthorhombic Pnnm with lattice parameters a = 8.8436(8) ?; b = 9.2191(8) ?; c = 9.2232(7) ?; V = 751.97(11) ?³ and Z = 2. Below approximately 200 K the structure is monoclinic P2₁/n (No. 14) with: a = 8.8080(9) ?; b = 9.1608(8) ?; c = 9.1498(8) ?; β = 90.230(7)°; V = 738.28(12) ?³ and Z = 2 (T = 120 K). The structure of (NH₄)₄HgBr₆ consists of isolated HgBr₆-octahedra in the whole temperature range which are slightly compressed in c-direction. The ammonium groups are located between the octahedra ensuring the stability of the structure by hydrogen bonding contacts: N–H···Br. The structural phase transformations are described by a rotation of the [HgBr₆]²⁻ octahedra around the c-axis, and this behaviour is attributed to an orientational disorder of ammonium groups. Index abstract Structural analysis of the phase transitions of (NH₄)₄HgBr₆; M. Loukil, A. Kabadou, I. Svoboda, A. Ben Salah and H. Fuess; The phase transformations in (NH₄)₄HgBr₆ are explained by large rotation of [HgBr₆]²⁻ octahedra around the c-axis.      

Structure,atomic Hirshfeld surface,spectroscopic studies and magnetic and dielectric properties of new mixed solid solution (NH4)2Mn0.17Cu0.83Cl4⋅2H2O

The tetrachlorocupratmanganate dehydrate (NH₄)₂Mn_0.17Cu_0.83Cl₄?2H₂O has been prepared and characterized using various physicochemical techniques including Fourier transform infrared and Raman spectroscopies, differential scanning calorimetry and dielectric and magnetic measurements. A preliminary single‐crystal X‐ray diffraction structural analysis reveals that the title compound belongs to the tetragonal system with P4₍₂₎/mnm space group. The unit cell dimensions are: a = b = 7.5817(2), c = 7.9312(2) Å, with Z = 2. Its crystal structure was determined and refined down to R = 2%. The structure of this compound consists of discrete [Cu/MnCl₄?2H₂O]^2? octahedra interleaved with alkali cations. The cohesion and stabilization of the structure are provided by hydrogen bond interactions (N─H…Cl and O─H…Cl) between [NH₄]⁺ cation and [Cu/MnCl₄?2H₂O]^2? anion. Hirshfeld surface analysis has been performed to explore the behaviour of these weak interactions. Dielectric measurements confirm the transition temperatures determined using differential scanning calorimetry. The temperature dependence of the magnetic susceptibility was measured in the temperature range 10–300 K at various magnetic field intensities. Magnetic measurements reveal the occurrence of weak ferromagnetic behaviour at low temperature (T_c = 12 K). The ferromagnetic ordering is further confirmed by the presence of hysteresis loops.