Advances in gas-phase electrophilic aromatic substitution reaction

Recent advances in the gas - phase reaction of aromatics with cationic electrophiles are reviewed. The overall substitution reaction is analyzed in terms of its elementary steps. Mechanistic studies have been focused on the structure and reactivity of covalent and non - covalent ionic intermediates, which display a rich chemistry and provide benchmark reactivity models. Particular attention has been devoted to proton transfer reactions, which may occur intra or intermolecularly in arenium intermediates.

Investigation of the electrocatalytic effect of polyaniline on the redox reaction of 2,5-dimercapto-1,3,4-thiadiazole by cyclic voltammetry

Electrochemical polymerized polyaniline(PAn) film electrode was used to investigate the electrocatalytic effect of PAn on the electrochemical redox reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT), PAn film electrode was electrochemically treated or immersed in DMcT solution before it was scanned in 1.0 mol/L HCl electrolyte. The cyclic voltammograms of PAn film electrode in 1.0 mol/L HCl solution changed with the above treatment, implying the electrocatalytic effect of PAn on the redox reaction of DMcT, The formation of electron-donor-acceptor adducts through the interaction between thiol or disulfide groups of DMcT and amine or imine groups of PAn during the treatment was probably the reason of the catalysis, The electrochemical properties of the adduct were different from those of PAn and DMcT, The adduct possessed a higher electrochemical activity and a better electrochemical reversibility than DMcT or PAn used alone.

Formation of ordered arrays of gold nanoparticles from CTAB reverse micelles

In this presentation, a reverse micelle technique was described to create colloid gold nanoparticles and their self-organization into superlattices. Gold nanoparticles were prepared by the reduction of HAuCL4 in CTAB/octane + 1-butanol/H2O reverse micelle system using NaBH4 as reducing agent. Dodecanethiol (C12H25SH) was used to passivate the gold nanoparticles immediately after formation of the gold colloid. After re-dispersing in toluene under ultrasonication, a supernatant containing nearly monodispersed dodecanethiol-capped gold nanoparticles was obtained. Self-organization of the gold nanoparticles into 1D, 2D and 3D superlattices was observed on the carbon-coated copper grid by TEM. UV-vis absorption spectra were also used to characterize the gold colloids with and without dodecanethiol capping. (C) 2001 Elsevier Science B.V. All rights reserved.

Reaction and formation of crystalline silicon oxynitride in Si-O-N systems under solid high pressure

Oxidized amorphous Si3N4 and SiO2 powders were pressed alone or as a mixture under high pressure (1.0-5.0 GPa) at high temperatures (800-1700 degreesC). Formation of crystalline silicon oxynitride (Si(2ON)2) was observed from amorphous silicon nitride (Si3N4) powders containing 5.8 wt% oxygen at 1.0 GPa and 1400 degreesC, The Si2ON2 coexisted with beta -Si3N4 with a weight fraction of 40 wt%, suggesting that all oxygen in the powders participated in the reaction to form Si2ON2. Pressing a mixture of amorphous Si3N4 of lower oxygen (1.5 wt%) and SiO2 under 1.0-5.0 GPa between 1000 degrees and 1350 degreesC did not give Si2ON2 phase, but yielded a mixture of alpha,beta -Si3N4, quartz, and coesite (a high-pressure form of SiO2). The formation of Si2ON2, from oxidized amorphous Si3N4 seemed to be assisted by formation of a Si-O-N melt in the system that was enhanced under the high pressure.

Scanning electrochemical microscopy study of electron transfer across the water/1,2-dichloroethane interface induced by common ions

In this work, we report the reverse electron transfer reaction between TCNQ in 1, 2-dichloroethane (DCE) and ferrocyanide in water. This process is a thermodynamic unfavorable reaction and the reverse electron transfer reaction can only be obtained by scanning electrochemical microscopy(SECM) in the presence of suitable potential-determining ions, which govern the interfacial potential difference. In our case, the potential determining ions are tetrabutylammonium ion(TBA(+)) and tetraphenylarsonium ion (TPAs+). The effects of the concentrations of TBA(+) and TPAs+ in two phases and other parameters have been studied in detail. The apparent heterogeneous rate constants(k(i)) were obtained under different values of K-p(K-p=c(i)(w)/c(i)(o)) for both cases by fitting the SECM approach curves with theoretical ones and the results showed that they were controlled by the interfacial potential differences. The relationship between apparent heterogeneous rate constants and the interfacial potential differences obeys Butler-Volmer theory.

H/D exchange reaction of cyclopropane derivatives in the ion system of CD3OD

The fragmentation properties of the product ions [M + 1](+), [M + 2](+) and [M + 3](+) formed by ion-molecule reaction of four cyclopropane derivatives with the ion system of CD3OD were investigated by using collision-induced dissocation technique. The experiment results indicated that the product ions were produced via the H/D exchange reaction between reactants and reactive reagent ions of CD3OD. There are two exchangable hydrogen atoms on the ring of compounds 1 and 2, and only one for compound 3 and 4.

Kinetic isotope effects of proton transfer reaction for amines by ultrasonic relaxation methods: Unexpected evidence from the results in ethylamine solutions

Ultrasonic absorption coefficients for ethylamine in heavy water (D2O) and in light water (H2O) have been measured in the frequency range from 0.8 to 220 MHz at 25 degrees C. A single relaxational process has been observed in these two kinds of solutions. From the concentration dependence of the ultrasonic relaxation parameters, and following the reaction mechanism proposed by Eigen et al. for ethylamine in H2O, the causes of the relaxations have been attributed to a perturbation of an equilibrium associated with a deuteron or proton transfer reaction. The rate and equilibrium constants have been estimated from deuterioxide or hydroxide ion concentration dependence of the relaxation frequency, and the kinetic isotope effects have been determined. In addition, the standard volume changes of the reactions have been calculated from the concentration dependence of the maximum absorption per wavelength, and the adiabatic compressibility has also been determined from the density and sound velocity for ethylamine in D2O and in H2O, respectively. These results are compared with those for propylamine and butylamine and are discussed in relation to the different kinetic properties between D2O and H2O, the reaction radii derived by Debye theory, and the structural properties of the reaction intermediate.

Isotope effect in proton-transfer and association-dissociation reactions for butylamine by ultrasonic relaxation methods

Ultrasonic absorption coefficients were measured for butylamine in heavy water (D2O) in the frequency range from 0.8 to 220 MHz and at concentrations from 0.0278 to 2.5170 mol dm(-3) at 25 degrees C; two kinds of relaxation processes were observed. One was found in relatively dilute solutions (up to 0.5 mol dm(-3)), which was attributed to the hydrolysis of butylamine. In order to compare the results, absorption measurements were also carried out in light water (H2O). The rate and thermodynamic parameters were determined from the concentration dependence of the relaxation frequency and the maximum absorption per wavelength. The isotope effects on the diffusion-controlled reaction were estimated and the stability of the intermediate of the hydrolysis was considered while comparing it with the results for propylamine in H2O and D2O. Another relaxation process was observed at concentrations greater than 1 mol dm(-3) in D2O. In order to examine the solution characteristics, proton NMR measurements for butylamine were also carried out in D2O. The chemical shifts for the gamma- and delta-proton in butylamine molecule indicate the existence of an aggregate. From profiles of the concentration dependence of the relaxation frequency and the maximum absorption per wavelength of sound absorption, the source of the relaxation was attributed to an association-dissociation reaction, perhaps, associated with a hydrophobic interaction. The aggregation number, the forward and reverse rate constants and the standard volume change of the reaction were determined. It was concluded from a comparison with the results in H2O that the hydrophobic interaction of butylamine in D2O is stronger than that in H2O. Also, the isotope effect on this reaction was interpreted in terms of the solvent structure.

Cyclic voltammetric and in situ Fourier transform infrared spectroelectrochemical studies on the reaction of Cd2+ on the plussian blue/platinum modified electrode

Plussian blue(PB)/Pt modified electrode Tvas studied in the CdCl2 electrolyte solution by cyclic voltammetry and in situ FTIR spectroelectrochemistry. It was found that Cadmium ion was capable of substituting the high-spin iron of PB in an electrochemically induced substitution reaction and hexacyanoferrate cadmium (CdHCF) can be formed in the PB film. But PB and CdHCF in mixture film showed their own electrochemistry properties without serious effect on each other. The mechanism of substitution reaction has been given in detail.

Study on the regulation of diorganogermanium compounds on the Maillard reaction of histidine and glycine by fluorescence spectrum

The suppression of diorganogermanium compounds on the Maillard reaction of histidine (His) and glycine (Gly) with glucose has been determined by fluorescence spectrum under physiological conditions. The title compounds show inhibition for the fluorescence intensity (FI) of glycosylated amino acids stronger than Ge-132.

Redox reaction of disulfide polyaniline in aqueous solution

The cleavage and formation of the di sulfide bond of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) were examined in an aqueous solution of pH value from 0 to 14 with and without polyaniline (PAn), The redox reaction of DMcT was accelerated by PAn in acidic condition. The cell using this anodic material was set-up and characterized in aqueous electrolyte.

The suppression of Ge-132 on the Maillard reaction of BSA by fluorescence spectrum

The fluorescences of BSA and glycosylated BSA were observed respectively. The lambda(cm) of BSA was 340 nm; while the lambda(cm) of glycosylated BSA was 436 nm. Because the fluorescence spectra of them were different greatly, we can observe the suppression of Ge-132 on the Maillard reaction of BSA without any interference of itself. It was showed that the fluorescence intensity of glycosylated BSA increased continuously with the cultured time, Ge-132 may suppress the Maillard reaction of BSA greatly, and the suppressing efficicency would be 32 %. The key site of the Maillard reaction of BSA is free amino groups of alanine residues on N-terminal amino group, besides the epsilon-amino groups of intrachain Lysine residues.

The characterization of the interfacial reaction in polyamide 1010 poly(propylene)-graft-(glycidylmethacrylate) blends

Binary blends of polyamide 1010/poly(propylene) and polyamide 1010 (PA1010)/poly(propylene)-graft-(glycidyl methacrylate) (PP-g-GMA) were prepared. The epoxy groups in PP-g-GMA react with the amino end-groups in PA1010, thus a PA1010-graft-PP copolymer is formed and acts as a compatibilizer between PA1010 and PP-g-GMA. The reaction was confirmed by electron spectroscopy for chemical analysis (ESCA) and attenuated total reflection (ATR)-FTIR spectroscopic analysis, and also evaluated by the stability of the suspension obtained by dissolving the blends in formic acid and by the morphologies of the blends.

Reaction of halfsandwich iridium polychalcogenide complexes with dimethyl acetylenedicarboxylate. Molecular structure of Cp*Ir[S2C2(COOMe)(2)]

The pentamethylcyclopentadienyl iridium complexes Cp*Ir(PMe3)(E-n) (E = S, n = 4, 5 or 6; E = Se, n = 2 or 4 E = Te, n = 2) react with dimethyl acetylenedicarboxylate to give Cp*Ir(PMe3)[E2C2(COOMe)(2)] compounds which tend to lose the trimethylphosphine ligand; the molecular structure of the dithiolene derivative, Cp*Ir[S2C2(COOMe)(2)], has been determined.

Studies on the product of ion-molecule reaction of halogeno-benzene in gas phase by MS/MS

The fragmentations of the product ions produced by the ion-molecule reaction of the halogeno-benzene (chlorobenzene, bromobenzene and iodobenzene) were studied using the collision-induced dissociation, The main product ions of the ion-molecule reaction of three kinds of halogeno-beneze include the dimeric ions, m/z(2M-X) ions and m/z(2M-2X) ions, The CID spectra of these ions were compared with that of the protonated bromodiphenyl and biphenyl, The formation mechanism and the structure of the product ions were obtained.