Etude du Systeme Ternaire Se-Te-Sn

This work is a part of the systematic study of the ternary based chalcogenides systems. The aim is to determine the phase equilibrium, and to determine the limits of the phase area. This is done in view to perfecting knowledge of elaboration conditions for new materials and to study of their physical properties. Few works have been devoted to the study of the ternary system Se-Te-Sn, only the cross section SnSe-SnTe has been studied [1] and [2]. The experimental study by DTA, DSC and X-ray diffraction on powder performed at room temperature, exhibits a miscibility gap in the liquid state which narrows as it goes through the Sn-Se binary system. Three cross sections behave as ‘quasi-binary‘ system and six ternary invariants have been exhibited: three ternary eutectics and three ternary quasi-peritectics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Novel coated-graphite membrane sensor based on N,N′-dimethylcyanodiaza-18-crown-6 for the determination of ultra-trace amounts of lead

A novel selective membrane electrode for determination of ultra-trace amount of lead was prepared. The PVC membrane containing N,N′-dimethylcyanodiaza-18-cown-6 (DMCDA18C6) directly coated on a graphite electrode, exhibits a Nernstian response for Pb²⁺ ions over a very wide concentration range (from 1.0×10⁻² to 1.0×10⁻⁷ M) with a limit of detection of 7.0×10⁻⁸ M (∼14.5 ppb). It has a fast response time of ∼10 s and can be used for at least 2 months without any major deviation in potential. The electrode revealed very good selectivity with respect to all common alkali, alkaline earth, transition and heavy metal ions. The proposed sensor was used as an indicator electrode in potentiometric titration of lead ions and in determination of lead in edible oil, human hair and water samples. The proposed sensor was found to be superior to the best Pb²⁺-selective electrodes reported in terms of detection limit and selectivity coefficient.     

Catalytic Method for Synthesis of Aspirin by a Green,Efficient and Recyclable Solid Acid Catalyst (Preyssler's Anion) at Room Temperature

Synthesis of aspirin at room temperature via O‐acetylation of salicylic acid in the presence of Preyssler type heteropolyacids has been investigated in order to contribute toward clean technology, which is the most important need of the society. All of the catalysts are recyclable and reusable.     

The synthesis of unsymmetrically N-substituted chiral 1,4,7-triazacyclononanes

A number of chiral unsymmetrically N-substituted 1,4,7-triazacyclononane ligands have been prepared by modular methods. The key step in the synthesis centres on the macrocyclisation of three tertiary amide precursors under standard Richman-Atkins conditions which allows for subsequent N-functionalisation.     

Synthesis,Characterization and Crystal Structures of new Palladium(II) Complexes and the first Platinum(III) Complex Containing ATT (ATT = 6‐Aza‐2‐thiothymine)

Treatment of the ligand 6‐aza‐2‐thiothymine (ATT, HL, 1 ) with palladium chloride in methanol forms the ionic complex [(HL)₄Pd]Cl₂·8MeOH ( 2 ), while its reaction with palladium iodide in same solvent produces the neutral complex trans‐[(HL)₂PdI₂]·2MeOH ( 3 ) in high yields. The reaction of 1 with Na₂[PdCl₄] in the presence of sodium acetate in a molar ratio of 2:1:2 and with platinum(II) chloride in presence of sodium acetate led to the dimer tetranuclear complexes [(L₄Pd₂)NaCl]₂·8MeOH ( 4 ) and [L₄Pt₂Cl₂]·6MeOH·H₂O ( 5 ). The latter is the first Pt^III complex of the ligand. All complexes were characterized by elemental analyses and IR spectroscopy and the crystal structures of 2 , 3 , 4 and 5 are determined by single‐crystal X‐ray diffraction. Crystal data for 2 at ?80 °C: triclinic space group , a = 1006.6(1), b = 1006.9(1), c = 1158.1(1) pm, α = 85.20(1)°, β = 83.84(1)°, γ = 88.91(1)°, Z = 1, R₁ = 0.0278; for 3 at ?80 °C: triclinic space group , a = 490.5(1), b = 977.2(2), c = 1116.8(2) pm, α = 90.26(1)°, β = 102.33(1)°, γ = 96.08(1)°, Z = 1, R₁ = 0.0394; for 4 at ?80 °C: orthorhombic space group Ccca, a = 1791.7(2), b = 1874.1(2), c = 2044.0(1) pm, Z = 4, R₁ = 0.0341 and for 5 at ?80 °C: monoclinic space group P2₁/c, a = 1464.3(1), b = 2003.7(1), c = 1368.5(1) pm, β = 95.66(1)°, Z = 4, R₁ = 0.0429.     

Pyrazine Complexes of Octacyanometallates of Mo(IV) and W(IV) With 8-hydroxyquinoline: Synthesis,characterisation and thermal studies

The complexes formed by photosubstitution of pyrazine (Pz) in octacyanomolybdate(IV) and -tungstate(IV) with 8-hydroxyquinoline have been assigned the formulae [Mo(CN)₂(OH)₂(Pz)₂(OX)] and [W(CN)₂(OH)₂(Pz)₂(OX)·1.5H₂O]. Coordination of Pz as an unidentate ligand by donating a lone pair of electron from nitrogen is shown by an absorption peak between 8–11 µ. Mechanism for the thermal decomposition of the complexes has been given. The formation of tungsten metal as residue in case of II has been confirmed by XRD analysis. The kinetic and thermodynamic parameters like activation energy (E _a), pre-exponential factor (A) and entropy of activation (S ^#) were calculated employing different integral methods of Doyle, Coats and Redfern and Arrhenius.H for each stage of decomposition was obtained from DSC.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preconcentration and Determination of Chromium Species Using Octadecyl Silica Membrane Disks and Flame Atomic Absorption Spectrometry

A novel and selective method for the fast determination of trace amounts of chromium species in water samples has been developed. The procedure is based on the selective formation of chromium diethyldithiocarbamate complexes at different pH in the presence of Mn(II) as an enhancement agent of chromium signals followed by elution with organic eluents and determination by atomic flame absorption spectrometry. The maximum capacity of the employed disks was found to be (396±3) µg and (376±2) µg for Cr(III) and Cr(VI), respectively. The detection limit of the proposed method is 49 and 43 ng·L^?1 for Cr(III) and Cr(VI), respectively. The proposed method was successfully applied for determination of chromium species Cr(III) and Cr(VI) in different water samples.     

Titanium-dioxide-mediated photocatalysis reaction of three selected pesticide derivatives

The photocatalysis reaction of three selected pesticide derivatives, namely methoxychlor (1), chlorothalonil (2) and disulfoton (3), has been investigated in an acetonitrile/water mixture in the presence of titanium dioxide and oxygen. The change as a function of irradiation time has been monitored using the UV spectroscopic analysis technique. An attempt has been made to identify the product formed during the photooxidation process through GC/MS analysis technique. The photolysis of methoxychlor (1) led to the formation of methoxychlor olefin (4) and 4,4-dimethoxybenzophenone (9), whereas chlorothalonil (2) gave rise to 2,3,4,5-tetrachlorophenol (17) as the only product. On the other hand, the photolysis of disulfoton (3) under analogous conditions gave disulfoton sulfoxide (25) and phosphorodithioic acid (21). All the products have been identified by comparing the molecular ion and mass fragmentation peaks of the products with those reported in the library. A probable mechanism for the formation of the products has been proposed.     

Electron transfer reactions. Reaction of tetracyclone,tetraphenylfuran and related substrates with potassium

The reaction of tetracyclone (1) with potassium in THF gave a mixture of benzoic acid (4), tetraphenylfuran (5) and cis-1,2-dibenzoylstilbene (6). The reaction of 1 with potassium in oxygen-saturated THF gave a mixture of 2-hydroxy-2,4,5-triphenyl-3(2H)furanone (3), 4, 5 and 6, whereas the reaction of 1 with potassium superoxide gave a moderate yield of 3,4,5,6-tetraphenyl-2-pyrartone (7), besides 3, 4, 5, and 6. The reaction of tetraphenylfuran (5) itself with potassium in THF gave a mixture of 6, 1,2,3,4-tetraphenylbutan-1-one (9), 2,3-diphenyl-1-indenone (10) and 2,3-epoxy-4-hydroxy-2,3,4-tnphenyltetralone-l (11), whereas practically no reaction occurred on treatment of 5 with potassium superoxide. Treatment of 10 with potassium in THF, however, gave a mixture of 4, dibenzo[a,c]-13-fluorenone (13), 2,3-diphenyl-2-hydroxyl-1-indanone (14) and 2,3-diphenylbenzofuran (15). A similar mixture of products consisting of 4, 13, 14 and 15 was obtained when the reaction of 10 with potassium was carried out in oxygen-saturated THF or when 10 was treated with potassium superoxide. Treatment of 2,3-diphenyl-2,3-epoxy-1-indanone (16) with potassium on the other hand, gave 10 in excellent yield. Cyclic voltammetric studies have been carried out to measure the reduction potentials of 1, 5, 10 and 16 in the generation of their radical anions. The radical anions of 1, 5, 10 and 16 were also generated pulse radiolytically in methanol and their spectra showed absorption maxima in the region 320–380 nm.     

A reliable treatment of Abel’s second kind singular integral equations

The central idea of this paper is to construct a new mechanism for the solution of Abel’s type singular integral equations that is to say the two-step Laplace decomposition algorithm. The two-step Laplace decomposition algorithm (TSLDA) is an innovative adjustment in the Laplace decomposition algorithm (LDA) and makes the calculation much simpler. In this piece of writing, we merge the Laplace transform and decomposition method and present a novel move toward solving Abel’s singular integral equations.