Simultaneous determination of Cd(II), Cu(II) and Pb(II) in surface waters by solid phase extraction and flow injection analysis with spectrophotometric detection

A method for heavy metal monitoring using spectrophotometric detection is presented. Traces of Cu(II), Pb(II) and Cd(II) at the low microg l(-1) level can be determined simultaneously after both selective removal of metal interferences and preconcentration using 'extraction chromatographic resins'. Lewatit TP807'84, which contains di(2,4,4-trimethylpentyl)phosphinic acid as active component, was used as solid adsorbent. Two minicolumns containing this resin were used: one at pH 3.2 for the removal of interferences, such as Zn(II) and Fe(III), and the other at pH 5.5 for the selective preconcentration of the target analytes. Spectrophotometric determination used FIA methodology with sulfarsazene as chromogenic reagent and partial least-squares multivariate calibration. The method was successfully applied to the analysis of surface waters from the Llobregat river and ground water samples from wells in the Guadiamar basin. Accuracy, expressed in terms of recoveries, was in the range 80-120% and relative standard deviations were below 10%.     

Reactions of 6‐aminopyrimidines with 2‐dimethylaminomethylenetetralone. Regiospecific Synthesis Of 5,6‐Dihydrobenzo [h]pyrimido [4,5‐b] quinolines

Benzo[h]pyrimido[4,5‐b]quinolines ( 3 ) have been synthesized via a regiospecific cyclocondensation reaction between 6‐aminopyrimidines ( 1 ) and 2‐dimethylaminomethylentetralone hydrochloride ( 2 ). The linear structure of the final compounds were determined by nmr measurements, especially by ¹H,¹H, ¹H,¹³C COSY and DEPT experiments.     

Effect of the comonomer content on the mechanical parameters and microhardness values in poly(ethylene‐co‐1‐octadecene) synthesized by a metallocene catalyst

Stress–strain and microhardness measurements were carried out on a series of copolymers of ethylene and 1‐octadecene with different comonomer contents in the corresponding homopolymer of ethylene, synthesized with a metallocene catalyst. The different mechanical properties, deduced from the stress–strain curves (Young's modulus, yield stress, deformation at break, and energy to break) are interpreted in terms of the crystallinity and molecular weight of the samples because these two characteristics show considerable variations with the comonomer content. The microhardness values are explained in terms of these properties, and they are also correlated with Young's moduli and yield stresses deduced from the stress–strain curves. Linear relations are found between microhardness and yield stress and between the logarithm of the microhardness and the logarithm of the elastic modulus. The properties deduced from these lines are compared with literature values. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 277–285, 2001     

Diethyl 2-[cyano(toluene-4-sulfinyl)methylene]propanedioate and its Diels–Alder adduct with cyclopentadiene

The thermal Diels–Alder cyclo­additon reaction of diethyl 2-­[cyano­(toluene-4-sulfinyl)­methyl­ene]­propane­dioate, C₁₆H₁₇­NO₅S, with cyclo­penta­diene gave the pure racemates of two of the four possible diastereomers, with a complete π-facial selectivity and a high (80:20) endo/exo-sulfinyl selectivity. X-ray diffraction studies of diethyl 2-[cyano­(toluene-4-sulfinyl)­methyl­ene]­propane­dioate and the major isomer of the cyclo­addition product, namely diethyl 3-cyano-3-(toluene-4-sulfinyl)­bi­cyclo­[2.2.1]­hepta-5-ene-2,2-di­carboxyl­ate, C₂₁H₂₃­NO₅S, reveal that the conformation of the substituents on the acrylo­nitrile moiety produces both steric and electronic effects, which affect the stereoselectivity of the reaction.     

Investigation of the C−H Activation Potential of [Hydrotris(1H‐pyrazolato‐κN1)borato(1−)]iridium (IrTpx) Fragments Featuring Aromatic Substituents x at the 3‐Position of the Pyrazole Rings,The Choice of the Precursor

A series of pyrazole‐substituted [hydrotris(1H‐pyrazolato‐κN¹)borato(1−)]iridium complexes of the general composition [Ir(Tp^x)(olefin)₂] (Tp^x=Tp^Ph and Tp^Th) and their capability to activate C−H bonds is presented. As a test reaction, the double C−H activation of cyclic‐ether substrates leading to the corresponding Fischer carbene complexes was chosen. Under the reaction conditions employed, the parent compound [Ir(Tp^Ph)(ethene)₂] was not isolable; instead, (OC‐6‐25)‐[Ir(Tp^PhκC^Ph,κ³N,N′,N″)(ethyl)(η²‐ethene)] ( 1 ) was formed diastereoselectively. Upon further heating, 1 could be converted exclusively to (OC‐6‐24)‐[Ir(Tp^Phκ²C^Ph,C^Ph,κ³N,N′,N″)(η²‐ethene)] ( 2 ). Complex 1 , but not 2 , reacted with THF to give (OC‐6‐35)‐[Ir(Tp^Phκ³N,N′,N″)H(dihydrofuran‐2(3H)‐ylidene)] ( 3 ), a cyclic Fischer carbene formed by double C−H activation of THF. Accordingly, complexes of the general formula [Ir(Tp^x)(butadiene)] (see 4 – 6 ; butadiene=buta‐1,3‐diene, 2‐methylbuta‐1,3‐diene (isoprene), 2,3‐dimethylbuta‐1,3‐diene) reacted with THF to yield 3 or the related derivative 9 . The reaction rate was strongly dependent on the steric demand of the butadiene ligand and the nature of the substituent at the 3‐position of the pyrazole rings.     

Micellar-catalyzed reactions for flow-injection systems : Determination of pyridoxal

The advantages of applying the solubilization and catalytic properties of aqueous micelle solutions to reactions taking place in flow-injection systems are demonstrated. The reaction of pyridoxal (a B₆ vitamin) with cyanide was investigated in both aqueous and micellar cetyltrimethylammonium bromide (CTAB) solution. Higher sensitivities and lower limits of detection were obtained for the micellar carrier, with the pseudo-first-order reaction rate increasing by a factor of two in 0.05 M CTAB relative to water carrier. Because the micellar aggregates also increase fluorescence quantum yields, use of fluorescence detection gave further signal enhancement, with the limit of detection lowered by a factor of three. Measurement of dispersion in the two systems was also investigated and compared. A new method of characterizing dispersion in flow-injection systems, based on moment analysis of exponentially modified Gaussian peak shapes, is described.     

Mixed-Ligand Complex Formation Equilibria of Vanadium(III) with 2,2′-Bipyridine and the Amino Acids Glycine, Proline, α-Alanine and β-Alanine Studied in 3.0 mol?dm?3 KCl at 25 °C

We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2??-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), ??-alanine (H??Ala), and ??-alanine (H??Ala) by means of electromotive forces measurements emf(H) using 3.0?mol?dm^?3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V₂O(Bipy)(B)]³⁺, [V₂O(Bipy)₂(B)₂]²⁺, [V(OH)(Bipy)(B)₂] and [V(OH)₂(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.     

Ageing of polyethylene at raised temperature in contact with chlorinated sanitary hot water. Part I - Chemical aspects

In France, hot water quality control inside buildings is occasionally assured by disinfection treatments using sodium hypochlorite (between 0.5 and 1 ppm residual free chlorine). This disinfectant is a strong oxidizer and it could interact with metallic and polymer pipes used in hot water systems. To assess the long-term performance of these pipes, it is then necessary to study the impact of these treatments on the material behaviour, in particular for polymeric materials, even at relatively low disinfectant concentrations as used in potable water treatments. The objective of this work was to study the influence of sodium hypochlorite concentration on PERT/Al/PERT (PolyEthylene Raised Temperature) pipe degradation. Pipe samples were filled with chlorinated water solutions (concentrations ranging between 0 and 100 ppm) and maintained in static conditions during 270 days at 70 °C. The antioxidant depletion profile through a PERT wall was monitored using the oxidation induction time (OIT) method, which is a conventional technique of Differential Scanning Calorimetry. Chemical changes on the aged polymer were checked by Infrared Spectrometry. OIT change showed that the PERT stabilizing system was rapidly chemically consumed by the action of chlorinated water at 25 and 100 ppm concentrations. However, PERT degradation was strictly confined to the immediate inner wall. Only a 0.3 mm thick layer (inner part of the pipe) showed significant antioxidant depletion. An increase of the OH and C-O-C infrared bands was also observed on inner part of any samples during ageing which characterize the oxidation of the PERT on the inner wall.     

Hydrogen‐bonded assembly in six closely related pyrazolo[3,4‐b]pyridine derivatives; a simple chain,three types of chains of rings and a complex sheet structure

Six closely related pyrazolo[3,4‐b]pyridine derivatives, namely 6‐chloro‐3‐methyl‐1,4‐diphenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₄ClN₃O, (I), 6‐chloro‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O, (II), 6‐chloro‐4‐(4‐chlorophenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃Cl₂N₃O, (III), 4‐(4‐bromophenyl)‐6‐chloro‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃BrClN₃O, (IV), 6‐chloro‐4‐(4‐methoxyphenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O₂, (V), and 6‐chloro‐3‐methyl‐4‐(4‐nitrophenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃ClN₄O₃, (VI), which differ only in the identity of a single small substituent on one of the aryl rings, crystallize in four different space groups spanning three crystal systems. The molecules of (I) are linked into a chain of rings by a combination of C—H...N and C—H...π(arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space group P, are each linked by two independent C—H...O hydrogen bonds to form chains of edge‐fused rings running in different directions through the three unit cells; the molecules of (III) are linked into complex sheets by a combination of two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond; finally, the molecules of (VI) are linked by a single C—H...O hydrogen bond to form a simple chain.