Aggregation and micelle formation of ionic liquids in aqueous solution

Association of ionic liquids possessing n-octyl moiety either in the cation or in the anion has been studied in aqueous solution with conductivity and turbidity measurements as well as using 2-hydroxy-substituted Nile Red solvatochromic probe. 1-Butyl-3-methylimidazolium octyl sulfate was found to act as a surfactant above 0.031 M critical micelle concentration. In contrast, 1-methyl-3-octylimidazolium chloride produced inhomogeneous solution of larger aggregates, which were dissolved on the addition of more than 2:1 molar excess of sodium dodecyl sulfate (SDS) due to mixed micelle formation. Even small amount (<10 mM) of ionic liquids could markedly reduce the polarity of the Stern layer of SDS micelle.     

Typical data of a new microporous material obtained from gels with titanium and silicon

The aim of this work is the synthesis and the characterization of a microporous material obtained from gels with titanium and silicon: NTS (titanosilicate). The structure of NTS zeotype is similar to that of AM-1 and JDF-L1 (titanosilicates). The synthesis were carried out with gels of composition: 3.5Na₂O–yTiO₂–4.48HCl–xSiO₂–110H₂O with 1.0≤x≤12.0 and 0.2≤y≤0.7. The temperature of reaction was 190±2°C.     

Initiated oxidation of polyenes formed in the thermal degradation of PVC

Polyenes formed in the thermal degradation of PVC are readily oxidized in the liquid phase in the presence of a radical initiator. In pure oxygen at a constant rate of initiation, different length polyenes are consumed by a first-order reaction: the rate of consumption is proportional to the polyene length and to the square root of initiator concentration. Applying the relationships given by the theory of chain reactions, we determined the ratio of the rate constant of chain propagation calculated for one double bond k₂ to the square root of the chain-termination rate constant k₄. The value obtained, which is relatively high in comparison to other unsaturated hydrocarbons, reflects very well the high reactivity of polyenes of the degraded PVC sample towards oxidation. Intramolecular chain propagation steps are also likely to play a role in the oxidation of polyenes.     

Competitive bromination kinetics of CH3Br and CH2ClBr

The relative-rate method with gas-chromatographic product analysis was applied to study the kinetics of the reactions Br + CH₃Br → CH₂Br + HBr (1) and Br + CH₂ClBr → CHClBr + HBr (2) The rate coefficient ratio of k ₁/ k ₂ = (1.6 ± 0.2) exp[(-15.2 ± 0.3) kJ mol^-1/ RT] was determined in the temperature range of 353 - 410 K. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis of Enantiomerically Pure 2-Isoxacephems

Summary. (R,6R,7R)-7-(1-Acetoxyethyl)-3-methyl-2-isoxacephem-4-carboxylic acid and its enantiomer have been prepared. The ring systems were formed from the corresponding enantiomerically pure N-unsubstituted -lactams. The reduction of methyl [(R,2S,3R)-3-(1-acetoxyethyl)-1-(4-methoxyphenyl)-4-oxoazetidine-2-carboxylate] has been solved via a hemi-acetal. The structure and the configuration of a new stereogenic center in this intermediate was predicted by using 2D NMR technique and unambiguously proven by x-ray.     

Continuous-time random-walk theory of interfering diffusion and chemical reaction with an application to electrochemical impedance spectra of oxidized Zr-1%Nb

A microscopic theory is developed for the interplay of diffusion and chemical reaction and the results are compared with electrode impedance measurements on an oxide electrode. The theory is based on the ideas of continuous-time random walk and accounts for the interference of diffusion and recombination of the charge carriers in the oxide. The treatment results in a dispersive diffusivity with two time constants, one of them corresponding to the random walk, the other to the reaction. Combining this diffusivity with the Warburg electrode admittance expression, which refers to cases where the rate-limiting step is diffusion in a semi-infinite medium bounded by a plane, an admittance function is obtained. The phase angle is found to be higher than 45 degrees distinguishing it from the Gerischer impedance which was developed for a related problem. The oxides were produced by hydrothermal oxidation of Zr-l%Nb alloy, a metal used as cladding material for nuclear fuel elements. The electrode impedance spectra of Zr/Zr-oxide electrodes in aqueous SO(3) (2-) solutions were taken at various anodic voltages between 1 Hz and 100 kHz and temperatures between 278 and 333 K. The theoretical admittance functions could be successfully compared with the observed spectra. Both the functional forms and the fitted parameter values support our theory which is also in keeping with Macdonald's point-defect model.     

Kinetics of radical polymerization—XLIII. Investigation of the polymerization of methyl acrylate in solution by the rotating sector method

The solvent effect on the chain propagation (k?₂) and chain termination (k₄) rate constants was studied for the polymerization of MA in benzene at 50°. Absolute values of the rate constants were determined from the classical polymerizations published earlier and from rotating sector measurements. The value of k₄ was found constant within the limits of experimental error, while k?₂ greatly depends on the monomer concentration, its variation can be quantitatively described in terms of the hot radical theory.     

Chemical origin of the sustained-like pattern formation observed in the bromate — Dual substrate — Dual catalyst oscillatory batch system

The BrO ₃ ⁻ — BrAc — Ru(bpy) ₃ ²⁺ subsystem is shown to represent the core oscillator that serves as source of the long lasting temporal and spatial periodic behaviors observed in the BrO ₃ ⁻ — H₂PO ₂ ⁻ — acetone — Mn²⁺ — Ru(bpy) ₃ ²⁺ — acid “double substrate-double catalyst” oscillatory batch system. The BrAc — the substrate of the core oscillator — is formed and accumulated in the reactions taking place in the six-component system. BrAc was produced in a separate experiment with bromide, acetone, acid and excess bromate and the mixture was used for bringing about patterns in the thin solution layer after adding the Ru(bpy) ₃ ²⁺ catalyst. The two-dimensional reaction-diffusion patterns that appear in the subsystem and its parent system are very similar in wave speed, wavelength, color and in the duration of the pattern evolution, therefore a common chemical origin is supposed to exist in their formation. The role that the BrAc may play in the mechanism of the BrO ₃ ⁻ — reductant — acetone — catalyst type oscillators (∼ 30 variants) is also pointed out.     

Structural defects in poly(vinylchloride)—III. Degradation of vinyl chloride-phenylacetylene copolymers in solution

Vinylchloride-phenylacetylene copolymers have been prepared and characterized. A known amount of defined defect sites, viz. double bonds, has been introduced into the main chain of the polymer. Thermal degradation behaviour of the copolymers has been studied in trichlorobenzene solution. A strong dependence of the kinetics of dehydrochlorination and polyene formation on the defect concentration has been found. Rate constants and activation parameters have been determined. The effects of different structures have been compared.     

A.c. conductivity and optical absorption in chalcogenide glasses

The energy levels of a simple model describing the doubly occupied defect states in chalcogenide glasses are calculated when strong electron-phonon interaction is supposed. The Kubo formula is used to get a.c. conductivity. The model implies a connection between the power dependence of a.c. conductivity ^s and between the low-energy exponential absorption tail.I would like to thank Dr. E. Majerníková for advice and encouragement throughout this work.