Hydrolysis of (CH3)3Sn+ in Various Salt Media

The hydrolysis of trimethyltin(IV) has been studied by potentiometry (H⁺ -glass electrode) and calorimetry in various salt media (NaNO₃, NaCl, KCl, Na₂SO₄, and NaNO₃—NaCl mixtures). The effect of ionic strength on the hydrolysis constants is accounted for by a simple Debye–Hückel type equation and by Pitzer equations. The results allow us to obtain H for hydrolysis and the temperature dependence of the Pitzer parameters. The resulting coefficients can be used to examine the speciation of (CH₃)₃Sn⁺ in multicomponent electrolyte solutions, such as natural waters, over a wide range of temperature and ionic strength.     

Reactions of carbethoxycarbene with enaminones. Formation of unexpected pyrroles

The reactions of carbethoxycarbene (:CH₂-CO₂Et, 2) with several acyclic enaminones (RCOCH=CR¹NHR², 3) lead to the unexpected formation of 2-Me, 3-CO₂Et, 4-H, 5-R¹-pyrroles 4 . Structural variations of the enaminones show that the structural fragments C(3)-CO₂Et and C(2)-Me are provided by 2 and that the fragment C(5)-R¹NHR² originates from the enaminones 3 , while the RCO group from 3 is eliminated during the course of reaction. Reactions with cyclic and nitrogen-hindered enaminones do not lead to pyrrole formation but occur by simple insertion of 2 to the Cα-H bond.     

Molecular ion rearrangements of benzenesulfonylhydrazides

The mass spectra of a series of substituted benzenesulfonylhydrazides are discussed. The main fragmentation mode of these compounds corresponds to rearrangement of the molecular ion with subsequent loss of N₂H˙ and/or N₂H₂. These fragmentations are confirmed by mass analysed ion kinetic energy spectra. Simple cleavage of the S? N bond with retention of the charge on nitrogen is observed for all the hydrazides studied but is favoured by electron withdrawing substituents. This latter fragmentation could not be confirmed by mass analysed ion kinetic energy spectra as it is probably very rapid and occurs mainly in the source.     

Acid–Base Properties, Solubility, Activity Coefficients and Na+ Ion Pair Formation of Complexons in NaCl(aq) at Different Ionic Strengths

The protonation constants and solubilities of three complexons [ethylenediamine-N,N′-disuccinic acid (EDDS), ethylene glycol bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA) and 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CDTA)] are reported in aqueous solutions of NaCl with different ionic strength values (0 ≤ I ≤ 4.8 mol·L^?1) and, in the case of CDTA, in (CH₃)₄NCl (0.1 ≤ I ≤ 2.7 mol·L^?1). The dependence on ionic strength of the protonation constants of these three complexons and four other complexons that were previously reported (NTA, EDTA, DTPA and TTHA), is analyzed in NaCl solution; the ionic strength influences quite strongly the protonation constants (as an example for CDTA, log₁₀ K ₁ = 10.54 and 9.25 at I = 0.1 and 1 mol·L^?1, respectively), while the effect of (CH₃)₄NCl concentration is lower. Based on the total solubility S ^T and the protonation constant data at different salt concentrations, the solubility of the neutral species S ⁰ and the solubility products K _S0 are obtained. The Setschenow coefficients k _m and the solubility values S ₀ ⁰ in pure water are also reported (S ₀ ⁰  = 0.55, 0.21 and 0.75 mmol·kg^?1 for EDDS, EGTA and CDTA, respectively). The dependence of the protonation constants on ionic strength is also interpreted in terms of ion pair formation, and the formation constants of Na⁺ species are reported.     

QuEChERS sample preparation for the determination of pesticides and other organic residues in environmental matrices: a critical review

Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) is an extraction and clean-up technique originally developed for recovering pesticide residues from fruits and vegetables. Since its introduction, and until December 2013, about 700 papers have been published using the QuEChERS technique, according to a literature overview carried out using SciFinder, Elsevier SciVerse, and Google search engines. Most of these papers were dedicated to pesticide multiresidue analysis in food matrices, and this topic has been thoroughly reviewed over recent years. The QuEChERS approach is now rapidly developing beyond its original field of application to analytes other than pesticides, and matrices other than food, such as biological fluids and non-edible plants, including Chinese medicinal plants. Recently, the QuEChERS concept has spread to environmental applications by analyzing not only pesticides but also other compounds of environmental concern in soil, sediments, and water. To the best of our knowledge, QuEChERS environmental applications have not been reviewed so far; therefore, in this contribution, after a general discussion on the evolution and changes of the original QuEChERS method, a critical survey of the literature regarding environmental applications of conventional and modified QuEChERS methodology is provided. The overall recoveries obtained with QuEChERS and other extraction approaches (e.g., accelerated solvent extraction, ultrasonic solvent extraction, liquid/solid extraction, and soxhlet extraction) were compared, providing evidence for QuEChERS higher recoveries for various classes of compounds, such as biopesticides, chloroalkanes, phenols, and perfluoroalkyl substances. The role of physicochemical properties of soil (i.e., clay and organic carbon content, as well as cation exchange capacity) and target analytes (i.e., log K_OW, water solubility, and vapor pressure) were also evaluated in order to interpret recovery and matrix effect data.     

Interaction of methyltin(IV) compounds with carboxylate ligands. Part 2: formation thermodynamic parameters,predictive relationships and sequestering ability

Thermodynamic data of mono‐, di‐ and tri‐methyltin(IV)‐carboxylate complexes (acetate, malonate, succinate, oxydiacetate, diethylenetrioxydiacetate, malate, citrate, 1,2,3‐tricarballylate, 1,2,3,4‐butanetetracarboxylate, 1,2,3,4,5,6‐benzenehexacarboxylate) in aqueous solution are reported at t = 25 °C and I = 0 mol l⁻¹. Thermodynamic parameters obtained were analysed to formulate empirical predictive relationships as a function of different parameters, such as the number of carboxylate groups of the ligand and the charge of the alkyltin(IV) cation. Sequestration diagrams of citrate and 1,2,3‐tricarballylate towards alkyltin(IV) cations at different pH values are also reported and discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

A heuristic algorithm for a chance constrained stochastic program

A chance constrained stochastic program is considered that arises from an application to college enrollments and in which the objective function is the expectation of a linear function of the random variables. When these random variables are independent and normally distributed with mean and variance that are linear in the decision variables, the deterministic equivalent of the problem is a nonconvex nonlinear knapsack problem. The optimal solution to this problem is characterized and a greedy-type heuristic algorithm that exploits this structure is employed. Computational results show that the algorithm performs well, especially when the normal random variables are approximations of binomial random variables.     

Uranium(VI) sequestration by polyacrylic and fulvic acids in aqueous solution

Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate ( \textUO₂²⁺ {{\text{UO}}_{2}}^{2+} –FA) and uranyl–polyacrylate ( \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the two systems investigated: (i) UO₂(FA₁), UO₂(FA₁)(FA₂), UO₂(FA₁)(FA₂)(H) for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –fulvate (where FA₁ and FA₂ represent the carboxylic and phenolic fractions, respectively, both present in the structure of FA), and (ii) UO₂(PAA), UO₂(PAA)(OH), (UO₂)₂(PAA)(OH)₂ for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –polyacrylate. By using the stability data obtained for all the complex species formed, the uranium(VI) sequestration by PAA and FA was expressed by the pL₅₀ parameter [i.e. the −log(total ligand concentration) necessary to bind 50% of uranyl ion] at different pH values. A comparison between pL₅₀ values of FA and PAA and some low molecular weight carboxylic ligands toward uranyl ion is also given.