Metal Complexes with Macrocyclic Ligands. XI. Ring size effect on the complexation rates with transition metal ions

The 12-16 membered tetraazamacrocycles 1 - 6 were synthesized, their protonation constants and complexation kinetics measured at 25° and I = 0.50. The results of Table 1 Show that pK is strongly influenced by the ring size whereas pK and pK are relatively insensitive to it. This can be understood in terms of electrostatic interactions of the positive charges when located on adjacent amino groups. The kinetics of complex formation between the macrocyclic ligands and several transition metal ions have been studied by pH-stat and stopped-flow techniques and the results have been analyzed as bimolecular reactions between the metal ion and the different protonated species of the ligands. The rate constants, given in Table 2, show that the macrocycles react less rapidly than analogous open chain amines. However, for a given protonated species of the ligand the rate of complexation follows the order Cu²⁺ > Zn²⁺ > Co2⁺ > Ni²⁺ which parallels the sequence of their water exchange rates. For the diprotonated tetraamines LH reacting with Cu²⁺ the slower rates seem to be mainly a consequence of electrostatic interactions, since a correlation between logk and pK exists. For LH⁺, however, the complexation rates of a metal ion with the different macrocycles are all in one order of magnitude and do not depend in a regular way on the ring size or the basicity of the ligand. It is therefore suggested that in this case other factors such as unfavourable preequilibria must be considered as important.     

Stereochemistry of planarchiral compounds,part XII: Absolute chiralities and X-ray crystal structures of 2,2′-Bi(1,6-methano[10]annulenyl)s

Summary The absolute chirality of the dextrorotatory main rotamer of 10,10-dibromo-2,2-bi(1,6-methano[10]annulenyl) (1 b), obtained by low temperature chromatography or by crystallisation of the (+)-enantiomer of1 b, was established by observation of anomalous X-ray diffraction as (+)-(R) _p (R) _a (R) _p -1b. This result was confirmed by reduction of (+)-1 b to a dextrorotatory 2,2-bi(1,6-methano[10]annulenyl) (1 a), which in turn was accessible by coupling of (–)-2-Bromo-1,6-methano[10]annulene (3) of known chirality (S) _p and, moreover, by enantioselective chromatography of1 a on triacetyl cellulose in ethanol. This correlation determines also the chirality of (+)-1 a as (S) _p (S) _p .According to the X-ray analyses the main rotamer of (+)-1 b and the meso-form (2 b) adopt crystal structures in which the bromine atoms come close to the CH₂-bridges. The torsional angles around the 2,2-bonds vary between 33°, 53° and 65° for (+)-1 b, racem.1 b and the mesoform2 b, respectively.Dedicated to Prof. Dr. G. Snatzke (Bochum) with cordial wishes on the occasion of the 60th anniversary of his birthday     

Kinetics of crosslinking reactions. 2. Reaction rates of intermolecular and intramolecular crosslinkings by using a soluble microgel

Soluble microgels with several pendant vinyl groups were synthesised by radical copolymerization of methyl methacrylate (MMA) with p-divinyl benzene (p-DVB). The competitive reactions of intermolecular and intramolecular crosslinkings of these microgels were carried out at 40°C in the presence of 1-buten-3-ol as a degradative chain transfer agent. The rate constant of intermolecular crosslinking (k) was estimated by GPC (gel permeation chromatography) analysis on the polymer produced from intermolecular propagation between bimolecules. The k depended strongly on the internal structure of microgels. Network formation was discussd inclusive of informations for the rate constant of intramolecular crosslinking (k).     

Linear free energy relationships between stability of complex and basicity of ligands: V. The stability of complex formed from 1,10-phenanthroline,N-(p-substituted phenyl) glycines with copper(II), nickel(II), cobalt(II) and zinc(II)

The formation constants (log K ) of ternary mixed ligand complex formed from 1,10-phenanthroline (A, phen) and N-(p-substituted phenyl) glycines,R NHCH₂COOH (B, p RPhG, CH₃, H, CL), with copper (II), nickel (II), cobalt (II) and zinc (II) were determined by pH method at 25°C in 30% (V/V) ethanol solution in presence of 0.1 M NaClO₄. It was found that linear free energy relationships exist between the stability of M(II)-phen-p-RPhG ternary complex and the base strengths of the ligands p-RPhG, conforming to the equation log K = α pK_B +C. The factors influencing the stability of the ternary complex have been discussed. The enhancement of stability of ternary complex was explained in terms of formation of π back bonding between metal ion and the ligand phen. In contrast to the binary system, the ternary ni (II) and zn (II) complexes showed higher stability which could be accounted for by the formation of π back bonding and by intramolecular ligand-ligand interaction, possibly aromatic-ring stacking.     

Pneumatik in der Gas-Chromatographie

Zusammenfassung Einfache pneumatische Geräte zur Programmierung des Eingangsdrucks einer gas-chromatographischen Kolonne werden beschrieben. Der Druck wächst — in guter Näherung — exponentiell oder nach einer Tangenshyperbolicus-Funktion mit der Zeit. Ein Absinken des Drucks mit der Zeit ist ebenfalls möglich, falls erwünscht. Das Gerät arbeitet voll automatisch, keine Teile müssen mechanisch bewegt werden. Dieses System zur Druckprogrammierung kann ohne Schwierigkeiten in Verbindung mit einem beliebigen gas-chromatographischen Gerät benutzt werden. Die Reproduzierbarkeit des Druckprogramms ist besser als ±1%. Das Programm kann kontinuierlich verändert werden. Eine rechnerische Behandlung der Vorgänge wird im Anhang dieser Veröffentlichung gegeben.

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Summary Simple pneumatical equipmens are described to program the inlet pressure of a gas-chromatographic column. The pressure increases, in a good approximation, as an exponential or tangens hyperbolicus function of the time. If wanted, the pressure may drop with time too. The equipment works fully automatically, no parts have to be moved mechanically. The pressure-programming system can be adjusted without any difficulties to a given gas-chromatographic equipment. The reproducibility of the pressure program is better than ±1%. The program is changeable continuously. Mathematical treatment of the processes is given in the appendix.

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Symbolverzeichnis c /RT - j Druckkorrekturfaktor definiert in. Gl. (2) - k Verteilungskoeffizient - k Kapazitätsverhältnis, für isobare und isotherme Analysen, definiert in Gl. (1) - m Massenstrom eines Gases. (Durch einen Querschnitt in der Strömung tretende Masse Gas in der Zeiteinheit) - p Druck, allgemein - p ₀ Druck am Ausgang eines Strömungswiderstands, Kolonnenausgangsdruck - p ₁ Druck vor dem Regelventil in Abb. 1 - p ₂ Druck auf der Steuerseite der Membran des Regelventils in Abb. 1 - p ₃ Ausgangsdruck des Regelventils in Abb. 1, als Eingangsdruck der Kolonne verwendet - p ₂₀ Anfangswert von p ₂ bei t = 0 des abfallenden Druckprogramms - p ₂₁ Anfangswert von p ₂ bei t = 0 des steigenden Druckprogramms nach Abb. 5 - p ₃₀ Anfangswert von p ₃ bei t = 0 des steigenden Druckprogramms nach Abb. 1 - p _i Eingangsdruck eines Strömungswiderstands, Kolonneneingangsdruck - p _A atmosphärischer Druck - p _F Federdruck auf die Membran des Regelventils in Abb. 1 - _p p _i p ₀ = Druckabfall an der Kolonne - q ₀ freier Gasquerschnitt am Ausgang eines Strömungswiderstands - t ₀ Durchbruchszeit eines Inertgases - t _R Retentionszeit definiert in Gl. (1) - t _R Nettoretentionszeit definiert in Gl. (1) - t _R Abstand benachbarter Peaks - L/t ₀ = zeitgemittelte lineare Trägergasgeschwindigkeit in der Kolonne - B 2L/Kq ₀ c - D 2p_F/cBV Druckrate = relativer Anstieg von p ₃ pro Zeit bei exponentiellem Druckprogramm - E 1/cBV - K spezifische Gaspermeabilität - L Länge eines Strömungswiderstands, Kolonnenlänge - M Masse des Gases im Volumen V - R Gaskonstante des idealen Gasgesetzes - T Temperatur - V Inhalt des Volumens V - W Strömungswiderstand definiert in Gl. (3) - Viscosität - Molmasse - Dichte eines strömenden Gases bei dem Druck p - ₀ Dichte eines Gases am Ausgang eines Strömungswiderstands bei dem Druck p ₀ II. Mitt.: Deininger, G., u. I. Halász: diese Z. 228, 241 (1967).Die Autoren bedanken sich bei der Deutschen Forschungsgemeinschaft, Bad Godesberg, die uns zu dieser Arbeit finanzielle Unterstützung gewährte.     

Characteristic operators and unitarily invariant decomposition of hermitian operators

A set of characteristic operators {F} is proposed for performing the decomposition of p-particle Hermitian operators {D^p} to constitute irreducible components {D} of the unitary group D = FD^p, q = 0,1,2,…,p. For a deeper expolration of the properties of the characteristic operators, a few theorems are presented. As an illustration, the expected values for symmetric p-particle Hermitian operators are obtained as a number of terms having invariant group-theoretical meaning.     

Hydrolysis of 2-aminoethanethiolsulfate ions

The kinetics of the acid catalyzed hydrolysis of 2-aminoethanethiolsulfate (AETS) ions were investigated. The dependence of the hydrolysis rate constant on acidity and temperature was determined. The hydrolysis rate equation can be expressed as where H_o is the Hammett acidity function. The rate constant, k, can be expressed as The pK_a's for the compound were measured and literature value of pK_a was found to be in error. The values determined in this study are pK_a1 < ?0.5 and pK_a2 = 9.1 ± 0.1. General acid catalysis of the hydrolysis reaction was found not to proceed to a significant degree. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Metallocene–methylaluminoxane catalyst for olefin polymerization. II. Bis-η5-(neomenthyl cyclopentadienyl)zirconium dichloride

Bis(neomenthyl cyclopentadienyl)zirconium dichloride/methyl aluminoxane (η⁵-(NMCp)₂ZrCl₂/MAO) catalyst has been investigated for ethylene polymerization. About 51% of the Zr forms active sites more or less instantaneously according to quenching with tritiated methanol. There is an initial drop of rate of polymerization, R_p, of about 30% which remains constant thereafter. The catalytic activity increases monotonically with temperature; it is proportional to [MAO]^1.75 at a constant [Zr] = 1.5 μM and proportional to [Zr]^?1.2 at a constant [MAO] = 64.5 mM. At very large [MAO]/[Zr], the catalyst has extremely high activity; κ_p = 5 × 10³ (Ms)^?1 at 50°C. There is also facile chain transfer to aluminum, κ = 0.14 s^?1 at 50°C. Both κ_p and κ are about 30 times greater than the corresponding rate constants for MgCl₂ supported TiCl₃ catalysts. The TiCl₃/MgCl₂ and (NMCp)₂/MAO catalysts have nearly the same activation energy for propagation (ca. 7 kcal/mol^?1). The higher activity of the latter is due to its larger preexponential factor in κ_p. The dependence of catalytic activity on the [MAO]/[Zr] ratio may be explained by rapid association-dissociation equilibria of MAO involving acid-base and/or electron deficient bridge complexation.     

Methanol adsorption by amorphous silica alumina in the critical temperature range

The methanol adsorption capacity of an amorphous silica-alumina was measured using an equilibrium technique. The experimental temperature range was of 140 to 260°C and the pure methanol pressure range was 0.1 to 1.2 MPa. A multilayer adsorption was found, also for temperatures above the critical temperature of the adsorbate. Based on the Jovanovic adsorption model, the mean residence times of the adsorbed molecules were calculated. Surprisingly, the heat of adsorption was found to be independent of the temperature in the multilayer adsorption range.Symbols Units a parameter defined by Equation (7) - a parameter defined by Equation (10) Pa - a(T) parameter in the Peng-Robinson equation Pa/(mol/m³)² - b parameter defined by Equation (8) - b parameter defined by Equation (11) Pa^–1 - b(T) parameter in the Peng-Robinson equation m³ mol^–1 - c constant in the BET equation - k Boltzmann constant, being 1.3806 · 10^–23 JK^–1 - K characteristic constant in the Peng-Robinson equation - m mass of one adsorbate molecule kg - p pressure Pa - q adsorption capacity g/g - Q heat of adsorption J mol^–1 - R gas constant, being 8.314 J mol^–1 K^–1 - T absolute temperature K - V molar volume m³ mol^–1 - x relative pressure (=p/p ₀) - active molecule area m² - residence time s - acentric factor     

Laser Doppler anemometry under plasma conditions. Part II. Measurements in an inductively coupled r.f. plasma

Laser Doppler anemometry is used for the measurements of the plasma and particle velocity profiles in the coil region of an inductively coupled r.f. plasma. Results are reported for a 50 mm i.d. induction plasma torch operated at atmospheric pressure with argon as the plasma gas. The oscillator frequency is 3 MHz and the plate power is varied between 4.6 and 10.5 kW. Plasma velocity measurements are obtained using a fine carbon powder as a tracer. Measurements are also given for larger silicon particles ( ) centrally injected into the discharge under different operating conditions.Nomenclature d _p particle diameter - P ₀ plasma power - Q ₁ powder carrier gas flow rate - Q ₂ plasma gas flow rate - Q ₃ sheath gas flow rate - r distance in the radial direction - V axial plasma velocity - V _p axial particle velocity - Z distance in the axial direction - standard deviation     

Scaled AMO calculations on the hydrogen molecule. III. The 1s2s 3∑ state

The potential energy curve for the 1s2s ³∑ state of the hydrogen molecule is calculated in a scaled version of the AMO approximation. Deviations from a simple potential curve occur. The agreement with experimental data is found to be better for the present state than for the 1sσ2pσ ¹∑ state studied in a previous paper.     

Kinetics of reactions of methyl α-eleostearate with cresols

The kinetics of addition reactions between methyl α-eleostearate which forms the main chain of tung oil and cresols when catalyzed by an acid, p-toluene sulfonic acid, have been studied. The addition reactions, carried out with any one of the o-, m-, and p-cresols were shown to be first order with regard to both methyl α-eleostearate and cresol concentrations. The reactions were additions of two cresol molecules to one methyl α-eleostearate molecule, and it was presumed that they proceed in the two steps given below in which the first step in rate-determining. (1) (2) (E: methyl/α-eleostearate, C: cresols) The apparent reaction rate constants (L/mol min) were found to be 0.046 for o-cresol, 0.038 for m-cresol, and 0.033 for p-cresol. The apparent activation energies (kcal/mol) were found to be 0.95, 3.66, and 4.05, in the cases of o-, m-, and p-cresols, respectively.     

Radical polymerization in the presence of complexing agents. VI. Effect of low concentrations of ZnCl2 on the overall rate of copolymerization of methyl methacrylate with ethyl acrylate

Overall rates for the free-radical copolymerization of methyl methacrylate with ethyl acrylate in the presence of low concentrations of ZnCl₂ have been determined at 50°C. The rate of copolymerization R_p depends on both the ZnCl₂ concentration and the monomer feed composition. Relative copolymerization rates R_p/R where R is the rate of copolymerization in the absence of complexing agent in the reaction mixture, show a minimum for intermediate feed compositions, independently of the ZnCl₂ concentration. On the basis of the results obtained, a conventional copolymerization mechanism is proposed for this system in which free and complexed species of both acrylic monomers participate.     

Free‐radical copolymerization of styrene with butyl acrylate. II. Elemental kinetic copolymerization step predictions from homopolymerization data

The free‐radical copolymerization of styrene and butyl acrylate has been carried out in benzene at 50 °C. The lumped k _p/k parameter (where k _p and k _t are the average copolymerization propagation and termination rate constants, respectively) has been determined. Applying the implicit penultimate unit model for the overall copolymerization propagation rate coefficient and the terminal unit effect for the overall copolymerization termination rate coefficient and using the homopolymerization kinetic coefficients, we have found good qualitative agreement between the experimental and theoretical k _p/k values. The variation of the copolymerization rate in solution with respect to the values previously found in bulk has been ascribed to a chain length effect on the copolymerization termination rate coefficient. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 130–136, 2004     

Magnesium chloride supported high mileage catalysts for olefin polymerization. XIII. Effect of external Lewis base on ethylene polymerization

The effect of external Lewis base (B_e) on the polymerization of ethylene by the MgCl₂/ethyl benzoate/p-cresol/AlEt₃/TiCl₄ catalyst was studied by activation with AlEt₃ alone without the use of methyl-p-toluate. The initially formed active site concentration, [Ti], is about doubled in the absence of B_e; at 50°C about 93% of the total titanium became catalytic. The same increment of [Ti] was observed without B_e. The rate constants of propagation are not appreciably affected by B_e; the values are the same at 50° with and without B_e. At other temperatures the k_p values are somewhat smaller without B_e. One major effect was the very large k values for chain transfer with aluminum alkyls in the absence of B_e as compared to those with B_e. This can be attributed to the greater monomeric AlEt₃ concentration in the former, but in much smaller amounts in the presence of B_e due to complexation. The rate constants of chain transfer with hydrogen are not much affected by B_e. However, the termination rate constants are generally much smaller when Lewis base is not present.     

The torsional barrier in aromatic carbonyl compounds. V. Carbon-13 DNMR study of stable protonated p-substituted acetophenones

The barrier to internal rotation around the phenyl–carbonyl bond in a series of stable protonated p-substituted acetophenones has been determined by means of low temperature ¹³C NMR and total bandshape analysis resulting in a value of ΔG = 48.1 kJ mol^?1 for the unsubstituted protonated compound. The energy results and the ¹³C chemical shifts are in good agreement with the quasi-planarity of the ground state in p-substituted protonated acetophenones. The barrier heights are discussed in terms of contributions from steric and resonance effects.     

Spectrophotometric microdetermination of uranium with m- and p-carboxyphenylazo-chromotropic acid

Summary A simple and rapid method for the spectrophotometric determination of uranium usingm- andp-carboxyphenylazo-chromotropic acid is given. The optimum conditions favouring the formation of the two complexes are reported. The molecular structure was found to be 1 1 and 1 2 of uranium to them- or thep-compound. Beer's law is obeyed for the ranges 2–16 and 2–18 ppm of uranium in the case of them- andp- compound respectively.

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Zusammenfassung Eine spektrophotometrische Methode zur Bestimmung von Uran mit Hilfe vonm-bzw.p-Carboxyphenylazochromotropsäure wurde beschrieben. Die besten Arbeitsbedingungen für die Bildung der beiden Komplexe wurden angegeben. Die Zusammensetzung entspricht dem Verhältnis 1 1 bzw. 1 2 von Uran zurm-bzw. zurp-Verbindung. Das Beer'sche Gesetz ist für die Bereiche 2–16 bzw. 2–18 ppm Uran im Falle derm-bzw. derp- Verbindung erfüllt.

     

On the Basicity of Triarylmethylamines in Solution

The pK of 11 triarylmethylamines (tritylamines), eight of which are new, and some related bases were measured in methylcellosolve/water 80:20 (MCS); some were also measured in dioxane/water 60:40 (Dx), acetonitrile (An), nitrobenzene (Nb) and acetic acid (Ac). (1) The influence of the aryl groups on the basicity is essentially additive; (2) In different solvents, similar linear free energy relationships were found, with differences in p* characteristic of solvation; (3) The influence on basicity of substituents of the aryl groups follows Hammett's relationship. These results indicate a preponderance of inductive effects. N, N-Dimethyltritylamine (3b) (pK=3.40) shows a marked crowding effect, absent in the isomeric tertiary amines 13 and 14 . Tri-p-nitrotritylamine (10a) (pK=3.10), N, N-dimethyl-tri-p-nitrotritylamine (10b) (pK=0.50), and 3b are particularly weak bases; the base-weakening effect of the trinitrotrityl group is similar to that of the cyanomethyl and trifluoroethyl groups.