Investigation of Geometrical and Conformational Isomers of Cobalt(II) Bis(diphenylacetato)-bis(γ-picolinate) by Dynamic NMR Spectroscopy and Molecular Mechanics

Cobalt(II) bis(diphenylacetato)-bis(-picolinate) is synthesized and its geometrical and conformational isomers are investigated using dynamic NMR and molecular mechanics methods. The complex in the solution is shown to exist as cis and trans isomers, which are detected at 263 K in the course of a slow intermolecular ligand exchange. At T < 223 K, the intramolecular rotation of the phenyl radicals about the ^–O₂C–CH(Ph)₂ and ^–O₂CCH(Ph)–Ph bonds slows, which results in the formation of different conformers. The energies of the retarded intermolecular exchange and of the retarded rotation of the phenyl radicals were calculated from ¹H NMR and molecular mechanics data.     

On the Synthesis and Selective Deprotection of Low‐Generation Dendrons with Orthogonally Protected Peripheral Amine Groups and a Possible Impact of the Deprotection Conditions on the Stability of Dendronized Polymers' Skeletons

The synthesis of first‐ and second‐generation dendrons with defined ratios of orthogonally protected amine groups in the periphery ((benzyloxy)carbonyl (Cbz) and (tert‐butoxy)carbonyl (Boc) protection) and the degree to which they can be selectively removed are described. The reaction conditions required for these deprotections were applied to methacrylic acid (= 2‐methylprop‐2‐enoic acid) based dendronized polymers carrying the same peripheral protecting groups to investigate whether they have any detrimental interference with the polymer skeleton. Specifically it was explored whether dendrons attached to the backbone could possibly be cleaved off as a whole (de‐dendronization). Finally it was investigated how de‐dendronizations can be used for quantifying both the dendron‐structure perfection and the polymer‐backbone configurations.     

Ferrocene-cyclam: a redox-active macrocycle for the complexation of transition metal ions and a study on the influence of the relative permittivity on the coulombic interaction between metal cations

The reaction of 1,1'-ferrocene-bis(methylenepyridinium) salt with 1,4,8,11-tetraazacyclotetradecane-5,12-dione, followed by LiAlH4 reduction results in the formation of FcCyclam. Metal complexes of FcCyclam with M2+ = Co2+, Ni2+, Cu2+, and Zn2+ were synthesized from FcCyclam and the respective metal triflates. The complexation of Cu2+ and FcCyclam in CH3CN is preceeded by a rapid electron transfer, followed by a slower complex formation reaction and a reverse electron transfer. The protonation constants of FcCyclam and the stability constants for the Cu2+ complex of FcCyclam (logK = 9.26(4) for the formation of the [Cu(FcCyclam)]2+ complex) were determined in 1,4-dioxane/water 70:30 v/v, 0.1 moldm(-3), KNO3, 25 degrees C. By using FcCyclam one can selectively sense the presence of Cu2+ ions in the presence of Ni2+, Zn2+, Cd2+, Hg2+, and Pb2+ with a very large deltaE approximately 200 mV, depending on pH. The X-ray crystal structures of FcCyclam and of complexes with Co2+, Ni2+, Cu2+, and Zn2+ were determined and Fe-M2+ distances obtained: Fe-Co2+ 395.9, Fe-Ni2+ 385.4, Fe-Cu2+ 377.7, and Fe-Zn2+ 369.0 pm. The redox potential of FcCyclam is influenced in a characteristic manner by the complexation of M2+. A linear correlation of 1/r approximately/= deltaE [r = distance Fe-M2+ from crystal data, deltaE=-E1/2([M(FcCyclam)]2+) - E1/2(FcCyclam)] was found; this is indicative of a mainly Coulomb type interaction between the two metal centers. The nature of the Fe...M2+ interaction was also investigated by determining deltaE in several solvents (mixtures) of different dielectric constants epsilon. The expected relation of deltaE approximately/= 1/epsilon was only found at very high values of epsilon. At epsilon < 40 increased ion-pairing appears to reduce the effective positive charge at M2+ leading to progessively smaller values of deltaE with lowered epsilon. The dependence of deltaE and epsilon can be calculated semiquantitatively by combining the Fuoss ion-pairing theory with the Coulomb model.     

Synthesis and reactions of 2-[α-(3,4-disubstituted phenacyl)-p-substituted styryl]-4H-3,1-benzoxazin-4-ones

Science Department, Faculty of Teachers, P.O.Box 2313, Al Hasa, 31982, Saudi Arabia Faculty of Engineering, Ain Shames University, EgyptChemistry Department, Faculty of Science, Ain Shames University, Egypt     

Extraction-separation of mercury with 1-nephthylthiocarbamide

The extraction of mercury(II) has been studied from mineral acid solution using 1-nephthylthiocarbamide (ANTU) in chloroform-acetone mixture (9:1). The variables such as the concentration of acid and extractant have been optimized. The extractability of some other elements at the optimum conditions for mercury is also studied in order to establish the separation procedure. The probable composition of the extracted species has been deduced from log data. Effect of a number of foreign metal ions and anions has also been studied.     

Reaction of R-(+)-2-benzylideneaminobutan-1-ol with ethylene phosphorochloridite. Stereospecific formation of (3R,5R)-2-(2-chloroethoxy)-5-ethyl-2-oxo-3-phenyl-1,4,2-oxazaphosphorinane

The reaction of R-(+)-2-benzylideneaminobutan-1-ol with ethylene phosphorochloridite afforded phosphorus-epimeric (3R,5R)-2-(2-chloroethoxy)-5-ethyl-2-oxo-3-phenyl-1,4,2-oxazaphosphorinanes. The phosphorinane-ring closure proceeded stereospecifically and occurred only from one of the diastereofacial sides (re) of the C=N bond.     

A method for calculating the limiting activity coefficients of nonelectrolytes in mixed solvents based on associated solution theory

A method for calculating the limiting activity coefficients of liquid nonelectrolytes in binary solvents based on the associated solution + lattice model is suggested. The method can be used to calculate limiting activity coefficients in mixed solvents with the use of only molecular association parameters and mutual exchange energies ω_ij determined from the data on phase equilibria in mixed solvents.     

Vibrational spectroscopy of silver perchlorate and silver trifluoromethanesulfonate solutions in acrylonitrile

Solutions of silver trifluoromethanesulfonate (“triflate”) and silver perchlorate in acrylonitrile, over a range of concentrations between 0.5 and 4 mol.kg^-1 have been analyzed by dispersive infrared and Fourier-transform Raman spectroscopy. The spectral regions studied include the solvent v(C≡N) fundamental and several anion internal modes. The silver ion solvation number in the infinite dilution limit is 3 in both systems. This number falls when the salt concentration is increased because of the ionic pairing, which is slightly more intense for silver perchlorate solutions, with a calculated spectroscopic association constant 0.23 ±0.08 kg-mol^-1. For silver triflate solutions, the spectroscopic association constant is 0.17±0.05 kg-mol^-1. In both cases, the ionic pair structure is bidentate and silver ion preserves two molecules of acrylonitrile in its first solvation shell.     

Tetraalkylphosphonium-based ionic liquids

Ionic liquids are salts that are liquid at or near room temperature. Their wide liquid range, good thermal stability, and very low vapor pressure make them attractive for numerous applications. The general approach to creating ionic liquids is to employ a large, unreactive, low symmetry cation with and an anion that largely controls the physical and chemical properties. The most common cations used in ionic liquids are N-alkylpyridinium and N,N′-dialkylimidazolium. Another very effective cation for the creation of ionic liquids is tetraalkylphosphonium, [PR₁R₂R₃R₄]⁺. The alkyl groups, R_n, generally are large and not all the same. The halide salts of several phosphonium cations are available as starting materials for metathesis reactions used to prepare ionic liquids. The large phosphonium cations can combine with relatively large anions to make viscous but free flowing liquids with formula mass greater than 1000 g mol⁻¹. Some other more massive salts are waxes and glasses. The synthesis and the physical, chemical, and optical properties of phosphonium-ionic liquids having anions with a wide range of masses were measured and are reported here.     

Synthesis and evaluation of some polymeric surfactants for treating crude oil—Part II. Destabilization of naturally occurring water‐in‐oil emulsions by polyalkylphenol formaldehyde amine resins

In the present work, three polymeric surfactants were prepared and used as demulsifiers; polyalkyl phenol formaldehyde monoethanol amine ethoxylate, eo, 136(D1), polyalkyl phenol formaldehyde diethanol amine ethoxylate, eo, 37(D2) and polyalkyl phenol formaldehyde triethanol amine ethoxylate, eo, 21.5(D3). Their demulsification potency in breaking water‐in‐crude oil emulsions was investigated. In this respect, two naturally occurring Egyptian water‐in‐oil (w/o) emulsions, one of them was waxy and the other was asphaltenic, were used in order to study the demulsification power of these compounds. The data revealed that, the resolution of water from waxy crude emulsion was easier than asphaltenic crude emulsion. The demulsification efficiency increases with increasing demulsifier concentration, contact time and temperature. The interfacial tension (IFT) at the crude oil–water interface was measured, it was found that the concentration of demulsifiers required to cause a minimum IFT are always less than these indicating a maximum demulsification efficiency. All the results were discussed in relation to emulsifier chemical structure and crude oil composition. Copyright © 2002 John Wiley & Sons, Ltd.