摘要:

Chitosan has been reductively N-alkylated with a 6-O-substituted galactose derivative bearing an iminodiacetate residue, to give a chitosan derivative having a hydrophilic branch and a metal chelating group. The Cu(II) binding capacity of the derivative was comparable to native chitosan, but showed better ion-exchange ability. The product was water soluble, giving viscous 1% aqueous solutions that showed decreased viscosity upon addition of Cu(II) ions.Keywords: chitosan, derivative, chelation, solubilization, viscosity.

ISSN:0008-4042    

DOI:10.1139/v91-088

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The desulfurization of benzo[b]thiophene1with aqueous transition metal species in the presence of various hydrocarbons at elevated temperatures is described. Mechanistic studies have shown that treatment of1with solutions of RuCl3and other platinum metal species results in the formation of 2,3-dihydrobenzo[b]thiophene2and ethylbenzene3as major products. Metal coordinated species are probable intermediates in the formation of2and hydrocarbon products.2readily coordinates to PdCl2to form square-planartrans-dichlorobis(2,3-dihydrobenzo[b]thiophene) palladium(II), which decomposes to ethylbenzene at 300 °C. The crystal structure of the complex was determined by a single crystal X-ray diffraction study. The complex crystallized in the monoclinic space groupC2/cwith Z = 8 in a cell of dimensionsa = 23.057 (3),b = 9.711 (1),c = 15.227 (2) Å and β = 99.74(1)°. The structure was solved by the Fourier method and was refined by full-matrix least-squares calculations toR = 0.042 for 2537 observed data withI > 2.5σ(I).Keywords: benzo[b]thiophene, desulfurization, platinum metal species.

ISSN:0008-4042    

DOI:10.1139/v91-089

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

A study of the two polarographic prewaves of the Ni(II)–thiourea system has been made. The results were analysed by determining Koutecky's parameter from the ratio of the limiting current of the prewaves and the main wave. This parameter is considered an experimental rate constant and the influence of different variables on its value was analyzed. An electrochemical study of the prewaves was also made. Two formal mechanisms to explain both prewaves are proposed.Keywords: polarographic prewaves, electrochemical kinetics, reaction mechanisms.

ISSN:0008-4042    

DOI:10.1139/v91-090

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

An electrochemical technique has been employed to study the ionization of the iodine complexes of (C6H5)3As, (C6H5)3Sb, and pyridine. Several different ionization mechanisms are proposed depending on the chemical nature and concentration of the reactants. A new ionic complex, (C6H5)3MI22+is postulated for the interaction of iodine with (C6H5)3As and (C6H5)3Sb at high iodine concentrations. Equilibrium constants have been calculated from the emf data for the various ionization steps.Keywords: triphenylarsine, triphenylstibine, iodine, complex formation, ionization.

ISSN:0008-4042    

DOI:10.1139/v91-091

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Reaction of aqueous silicate with ammonium molybdate at pH 1.5 affords the β form of silicomolybdic acid. The latter can be precipitated by the addition of a variety of quaternary ammonium salts. The precipitated silicomolybdate can then be decomposed to silica in a two-step combustion process (at 350 and 1000 °C). Recoveries of Si are nearly complete, but the starting silicate solution must be made strongly basic prior to the reaction with molybdate. The overall process can be utilized for the recovery of silicon isotopes and as a method of silica purification.Keywords: silica, silicate, silicomolybdate, silicon-29.

ISSN:0008-4042    

DOI:10.1139/v91-092

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Several 9-substituted 9-(o-methylthiomethylphenyl)fluorenes and their oxidation products, 9-substituted 9-(o-methylsulfinylmethylphenyl)fluorenes, were prepared. Each equilibrium constant at room temperature or at low temperature was investigated and the conformational equilibriaof these compounds are discussed by comparing them with those of the corresponding 9-substituted 9-(o-methylthiophenyl)fluorenes and 9-substituted 9-(o-methylsulfinylphenyl)fluorenes in which theo-substituents were one CH2unit shorter than those of the title compounds. Kinetic data for the internal rotation of several compounds are also given.Keywords: conformational isomerism, restricted rotation, 9-arylfluorenes.

ISSN:0008-4042    

DOI:10.1139/v91-093

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The proximate coupling constants,5J, betweenorthoand methyl protons in thioanisole and 18 of its derivatives are discussed as conformational indicators. On the assumption that5Jvaries as cos4θ, for 0° ≤ θ ≤ 90°, θ being the angle by which the methyl group twists out of the aromatic plane,5Jfor θ = 0° follows as −0.43 (2) Hz from the known internal barrier in thioanisole in solution. A measurement of5Jinmeta- orpara-substituted thioanisole derivatives then yields an approximate value for the twofold barrier to rotation about the Csp2—S bond. For derivatives containing anorthosubstituent,5Jyields an estimate of the torsion angle for the thiomethyl moiety. In some instances these angles are compared with those derived from long-range1H,13C and13C,13C coupling constants. The size of theorthosubstituent appears to have only a small effect on the magnitude of5J. The major determinant of the latter appears to be the manner in which the substituent perturbs the mobile bond order of the Csp2—S bond.Keywords: spin–spin coupling constants, thioanisole derivatives;1H NMR, thioanisole derivatives; conformations, thioanisole derivatives; conformations, torsional motion of SCH3group.

ISSN:0008-4042    

DOI:10.1139/v91-094

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

Two series of isoxazoles substituted by long alkyl or alkenyl chains in the α position with respect to the oxygen atom or in the α position with respect to the two heteroatoms have been synthesized. Starting from 3,5-dimethylisoxazole, the regioselective metalation/alkylation on the α-O methyl group was a very convenient route to a large variety of "α-O substituted isoxazoles". When applied to α-O methylated isoxazoles bearing an α-N alkenyl chain the same method provides an original unequivocal approach to 3,5-dialkenyl isoxazoles. An alternative route to these compounds, despite the formation of di-isoxazoline as by-product and an additional step corresponding to the oxidation of the intermediate isoxazoline, is the 1,3-dipolar cycloaddition, by using terminal dienes as dipolarophiles with alkenyl dipoles. Nevertheless, the cycloaddition between monoalkylated alcynes and alkylated dipoles remains the most straightforward synthesis of 3,5-dialkyl isoxazoles.Keywords: isoxazoles, alkenyl side chains, metalation–alkylation, regioselectivity.

ISSN:0008-4042    

DOI:10.1139/v91-095

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

The molecular structure, interaction energy, and infrared spectrum of the linearly hydrogen bonded 1:1 molecular complex of water and ammonia have been predicted by means of a series ofabinitiomolecular orbital calculations, at the level of second order Møller–Plesset perturbation theory, using the 6-31G** basis set. The calculated wavenumbers and intensities have been compared with those calculated earlier for the respective monomers, and the wavenumber shifts and intensity changes rationalized in terms of the hydrogen bond interaction responsible for the stability of the complex.The calculated hydrogen bond energy of the complex has been compared with those of the linear water and ammonia dimers, reported in a previous publication, and the relative strengths of interaction of the three aggregates have been rationalized on the basis of the electron donor/acceptor capacities of the respective monomer units.Keywords:abinitio, infrared spectrum, water, ammonia.

ISSN:0008-4042    

DOI:10.1139/v91-096

出版商:NRC Research Press    

年代:1991

数据来源: NRC

摘要:

New aspects of the theory of ideal associated mixtures related to a differentiation between formed cyclic and linear dimers are discussed. A mathematical analysis is presented for the dimerization model, A + B + A2, the continuous association (Mecke–Kempter) model,, both coupled with the cyclic dimmer → linear dimer transformation and for the unsymmetrical (mixed) dimer formation model, A + B + A2 + B2 + AB. Introduction of the standard reaction enthalpies and volumes associated with transformations of dimers leads to a considerable change in behavior and symmetry properties of the excess thermodynamic functions. In terms of the modified Mecke–Kempter model, a consistent representation of the excess Gibbs energy of mixingGE, heat of mixingHE, and excess molar volumeVEis reported for the acetic acid – water system at 298.15 K.Keywords:association, dimerization, linear dimers, cyclic dimers, hydrogen bonding, carboxylic acids, alcohols, aqueous solutions.

ISSN:0008-4042    

DOI:10.1139/v91-097

出版商:NRC Research Press    

年代:1991

数据来源: NRC