Extraction of copper ions using silica gel with chemically modified surface

The applicability of silica gels for the application in solid-phase extraction was tested. Silica was modified with ketoimine groups. Surface characteristics of the modified silica were determined by elemental analysis, NMR spectra of solid phases (²⁹Si CP MAS NMR), analysis of pore size distribution of the silica support, and nitrogen adsorption-desorption. Newly proposed sorbents with ketoimine groups were applied in the preconcentration of trace amounts of the Cu (II) ions from lake water, post-industrial water, and demineralized water unburdened back to the lake. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

A new mesogenic mixture with antiferroelectric phase only at a broad temperature range

New compounds (S)-4?-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[3-(2,2,3,3,4,4,5,5,5-nonafluoropentyloxy)prop-1-oxy]benzoates were synthesised and characterised. Their mesomorphic properties were tested by means of polarising optical microscopy and differential scanning calorimetry. The multicomponent antiferroelectric high tilt mixture with long pitch has been also formulated and characterised. The helical pitch of prepared mixture was estimated with selective reflection method.     

Preparation of Allylstannanes and Distannanes Using Zinc in Liquid Ammonia

Abstract

Barbier-type reductive coupling of allylic bromides and organotin compounds can be carried out in liquid ammonia (?33°C) using commercial zinc powder. This procedure provide a new simple and environment-friendly method for the synthesis of allylstannanes and distannanes.     

Chiral benzisoselenazolones: conformational analysis based on experimental and DFT calculated Se NMR

A series of new enantiomeric N-substituted benzisoselenazol-3(2H)-ones were prepared from 2-(chloroseleno)benzoyl chloride and 9-amino-deoxyquinine (both 9-native and 9-epi) as well as the other chiral primary amines. The ⁷⁷Se NMR parameters for the obtained benzisoselenazolones were measured and theoretically calculated at the DFT level of theory using B97-2 hybrid functional and cc-pVTZ basis set. The DFT ⁷⁷Se chemical shifts for the lowest energy conformers were in agreement with the experimental data, while the conformers of higher energy showed markedly worse fit. Interestingly, the preferred conformation for 2-(1-arylalkyl)-benzisoselenazolones is the gauche type (Se–N–C–H≈±180°), and it is in agreement with those observed in crystals (X-ray). The calculation predicts a much higher sensitivity for the ⁷⁷Se chemical shift of the conformation than for the corresponding ¹³C data. In the ⁷⁷Se NMR spectra of chiral benzisoselenazolones with added racemic or l-N-Boc-phenylglycine, chiral discrimination could not be observed mostly due to signal broadening. In the ¹H NMR spectra, the benzisoselenazole derived from epi-9-amino-deoxyquinine induced splittings of the amino acid signals, thus allowing for discrimination of the enantiomers.     

Boronate Covalent and Hybrid Organic Frameworks Featuring PIII and P=O Lewis Base Sites

Two covalent organic frameworks comprising Lewis basic P^III centers and Lewis acidic boron atoms were prepared by poly-condensation reactions of newly obtained tris(4-diisopropoxyborylphenyl)phosphine with 2,3,6,7,10,11-hexahydroxytriphenylene and 2,3,6,7-tetrahydroxy-9,10-dimethylanthracene. Obtained materials exhibit significant sorption of dihydrogen (100 cm³ g⁻¹ at 1 bar at 77 K), methane (20 cm³ g⁻¹ at 1 bar at 273 K) and carbon dioxide (50 cm³ g⁻¹ at 1 bar at 273 K). They were exploited as solid-state ligands for coordination of Pd⁰ centers. Alternatively, in a bottom-up approach, boronated phosphine was treated with Pd₂dba₃ and poly-condensated, yielding hybrid materials where the polymer networks are formed by means of covalent boronate linkages and coordination P−Pd bonds. In addition, the analogous materials based on phosphine oxide were synthesized. The DFT calculations on framework–guest interactions revealed that the behavior of adjacent boron and phosphorus/phosphine oxide centers is reminiscent of that found in Frustrated Lewis Pairs and may improve sorption of selected molecules.     

Electrochemical Sensing of Pb2+ and Cd2+ Ions with the Use of Electrode Modified with Carbon-Covered Halloysite and Carbon Nanotubes

A novel voltammetric method for the sensitive and selective determination of cadmium and lead ions using screen-printed carbon electrodes (SPCEs) modified with carbon-deposited natural halloysite (C_Hal) and multi-walled carbon nanotubes (MWCNTs) was developed. The electrochemical properties of the proposed sensor were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), while the morphology and structure were established by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). A two-factorial central composite design (CCD) was employed to select the composition of the nanocomposite modifying the electrode surface. The optimal measuring parameters of differential pulse anodic stripping voltammetry (DPASV) used for quantitative analysis were established with the Nelder–Mead simplex method. In the analytical investigation of Cd(II) and Pb(II) ions by DPASV, the MWCNTs/C_Hal/Nafion/SPCE exhibited a linear response in the concentration range of 0.1–10.0 µmol L⁻¹ (for both ions) with a detection limit of 0.0051 and 0.0106 µmol L⁻¹ for Pb(II) and Cd(II), respectively. The proposed sensor was successfully applied for the determination of metal ions in different natural water and honey samples with recovery values of 96.4–101.6%.     

Contributions to the Chemistry of Silicon—Sulphur Compounds. 66. Synthesis,crystal and molecular structure of bis(tri-tert-butoxysilanethiolato)(acetonitrile)cobalt(II)[(t-C4H9O)3SiS]2Co(NCCH3)

The title compound [(t-C₄H₉O)₃SiS]₂Co(NCCH₃)] 1 was obtained by reaction of anhydrous cobalt(II) chloride with tri-tert-butoxysilanethiol and triethylamine in acetonitrile as a solvent. The compound crystallizes as deep-blue orthorhombic plates with a = 17.779(4), b = 45.363(9), c = 9.096(2) Å, space group Fdd2 and Z = 8. The structure was solved by Patterson synthesis and refined to the R value of 0.0343. The crystal consists of mononuclear complexes in which the cobalt atom is five-fold coordinated to two sulphurs, two oxygens and one nitrogen in a distorted trigonal bipyramidal arrangement. The relevant bond distances and angles are: Co? S, 2.2680(7); Co? N, 2.065(4); Co? O1, 2.283(2); S? Si, 2.0666(8) Å; S? Co? S′, 119.14(4); N? Co? S, 120.43(2); O1? Co? O1′, 178.81(10)°.     

Beiträge zur Chemie der Silicium-Schwefelverbindungen. XXXVIII. Hexa-(tri-t-butoxy)disiloxan und Hexa-(tri-t-butoxy)disilthian

Contributions to the Chemistry of Silicon Sulfur Compounds. XXXVIII. Hexa(tri-t-butoxy)disiloxane and Hexa(tri-t-butoxy)disilthiane Hexa(tri-t-butoxy)disiloxane 1 and Hexa(tri-t-butoxy)disilthiane 2 were prepared by reaction of R₃SiONa with R₃SiCl and R₃SiSNa with R₃SiCl (R = tri-t-butoxy), respectively. The mass spectra show characteristic series of fragments. A large ²⁹Si n.m.r. chemical shift of about —103.55 ppm is observed with 1 , whereas the value of 2 is —75.99 ppm. The crystal structure analysis of 1 result first in a colinear molecule (Si? ;O? ;Si = 180°) with 1 symmetry and relative short mean bond lengths of about d(Si? ;O) = 155.6 pm, but with large and strong anisotropic ellipsoids. Their quantitative rigid body analyses yield decisive corrections, namely a bent molecule with an Si? ;O? ;Si angle of 144.0° and d?_corr = 163.5 pm. Molecule 2 is also bent as expected (Si? ;S? ;Si = 110.5°, d?(Si? ;S) = 211.9 pm and after rigid body correction 108.0° and d_corr = 215.2 pm, respectively). The results of our investigations will be discussed corresponding to the energy differences of the varying configurations at the bridging atoms.     

Hyperbranched polyethers by ring‐opening polymerization: Contribution of activated monomer mechanism

Propagation in the cationic ring‐opening polymerization of cyclic ethers involves nucleophilic attack of oxygen atoms from the monomer molecules on the cationic growing species (oxonium ions). Such a mechanism is known as the active chain‐end mechanism. If hydroxyl groups containing compounds are present in the system, oxygen atoms of HO? groups may compete with cyclic ether oxygen atoms of monomer molecules in reaction with oxonium ions. At the proper conditions, this reaction may dominate, and propagation may proceed by the activated monomer mechanism, that is, by subsequent addition of protonated monomer molecules to HO? terminated macromolecules. Both mechanisms may contribute to the propagation in the cationic polymerization of monomers containing both functions (i.e., cyclic ether group and hydroxyl groups) within the same molecule. In this article, the mechanism of polymerization of three‐ and four‐membered cyclic ethers containing hydroxymethyl substituents is discussed in terms of competition between two possible mechanisms of propagation that governs the structure of the products—branched polyethers containing multiple terminal hydroxymethyl groups. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 457–468, 2003     

CNDO/2 molecular orbital calculations of dewar structures or pyrazine,pyrimidine and pyridazine

CNDO/2 molecular orbital calculations have been carried out on the Dewar structures of pyrazine, pyrimidine and pyridazine in order to determine the configurations of minimum energy.