Mechanism study of base-catalyzed cyclization of 2-nitrophenylhydrazine in aqueous solution

The mechanism of cyelizalion of 2-nitrophenylhydrazine to 1-hydroxybenztriazole in alkaline aqueous solutions is studied. Kinetic parameters, product distribution and activation parameters are determined. A mechanism involving direct attack of the β-hydrazino nitrogen on the nitrogen ol the nilro group with elimination of water is postulated. Substituted 2-nitrophenylhydrazines are synthesized and studied under the same conditions.     

Intramolecular nucleophilic cyclization of a carboxylic acid hydrazide under mild acid conditions

Phthaloyl-2′-nitrophenylhydrazide undergoes ring closure involving nucleophilic attack of the hydrazide on the carboxylic acid in dilute aqueous acid solution to form the corresponding N-substituted phthalimide. Structure of the resulting phthalimide was unequivocally confirmed by ¹³C-nmr.     

Numerical solution for viscous flow for two-dimensional domains using orthogonal coordinate systems

A method to generate two-dimensional orthogonal grids in simply and doubly connected domains is given. The method not only generates the grids but also finds the modulus of the domain simultaneously. Also, the Navier0Stokes equations are solved is some doubly connected domains. The insteady vorticity stream function approach is used. The stream function on one of the boundaries has to be updated at every time step. Comparisons are made between numerical and experimental results; quite good agreement can be achieved.     

Selective reagents in chemical ionization mass spectrometry: Tetramethylsilane

Mixtures of 50% tetramethylsilane (TMS) and methane have been found to give [M+73]⁺ adduct ions and structurally useful fragment ions for many oxygen- and nitrogen-containing organic compounds. All of the reagent ions in TMS react with polar compounds. The high-pressure TMS chemical ionization spectra of many simple oxygenated compounds are in agreement with predictions from ion chemistry of (CH₃)₃Si⁺ obtained by ion cyclotron resonance experiments at very low pressures, but differences are noted. Sensitivities for oxygen-, nitrogen-, and sulfur-containing compounds with TMS as the reagent gas appear to be approximately the same.     

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Diffusion based analysis in a sheath flow microchannel: the sheath flow T-sensor

This paper describes a microfluidic channel that allows for diffusion-based analysis of adsorbing species without passivation of the channel surfaces. The sheath flow configuration was used to measure the diffusion coefficient of fluorescently labeled species from their spatial distribution within the microchannel by analyzing the derivative of the intensity profile at the interface between two distinct core fluids. Measurements for both a small molecule (rhodamine B) and an intermediate-sized protein (wheat germ agglutinin) were made, demonstrating the utility of the sheath flow T-sensor.     

Association reactions of trimethylsilyl ions

Adduct ions, [M + (CH₃)₃Si]⁺, were produced by bimolecular association reactions of trimethylsilyl ions, (CH₃)₃Si⁺, with acetone, cydohexaoone, anisole, dimethyl ether, 2,5-dimethylfuran, 2-methylfuran and furan in ion cyclotron resonance experiments at 300 K and at pressures of ～10^?7 Torr (1 Torr = 133.3 Pa). The rate constants, k_a, for the association reactions varied from 100% to 2% of the collision rate constants, k_c. The rate constants were independent of pressure, except for furan. Measurements were also made of bond dissociation energies for these adduct ions, D[(CH₃)₃Si⁺–X], from equilibrium measurements. The association efficiency, k_a/k_c, increased with increasing bond dissociation energy and with increasing numbers of degrees of freedom, in qualitative agreement with theoretical predictions. Observations pertinent to the dependence of k_a on reactant temperature and relative kinetic energy are discussed. The possibility of determining ion-neutral complex binding energies from radiative association rate constants is considered.