摘要:

A literature survey on the homogeneous gas-phase oxidation of light alkanes shows that despite a rather high number of papers there are still, even in the case of isobutane, an important number of unresolved questions, which makes the writing of a reaction scheme rather difficult. To obtain more reliable experimental data, we have studied the homogeneous gas-phase oxidation of isobutane in a conventional static system, at 310 and 340 °C and subatmospheric pressure. This investigation is chiefly aimed at identifying and measuring the major primary products of the reaction. A chain radical scheme based on the primary products and on estimation of the rate constants of the elementary steps by the methods of Thermochemical Kinetics is put forward to interpret our experimental results. Two major reaction routes appear, one corresponding to the formation of isobutene and the other to the formation of isobutene oxide. The conclusions of the present investigation and suggestions for further developments are also mentioned.Keywords: oxidation, chemical kinetics, reaction mechanism, isobutane.

ISSN:0008-4042    

DOI:10.1139/v89-115

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The structures of four new drimane-type sesquiterpenes1–4produced in liquid cultures of the fairy ring fungus,Marasmiusoreades, have been determined by a combination of chemical and spectroscopic methods. The structure assigned to one of these sesquiterpenes (1) has been confirmed by an X-ray crystallographic study. An unprecedented feature of all four sesquiterpenes is the biosynthetic elaboration of C8–C12 and C15 of the drimane skeleton to a dioxabicyclooctane moiety. In addition, two of the sesquiterpenes possess an uncommon α orientation of the hydroxyl groups at C3.Keywords: sesquiterpenes, fungal metabolites, drimanes, fairy ring mushroom, crystal structure.

ISSN:0008-4042    

DOI:10.1139/v89-116

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Samples of all three of the expected bisphenols, 4,4′,5,5′-tetrachloro-2,2′-methylenebisphenol (1) and the 3,4,4′,5′-(2) and 3,3′,4,4′-tetrachloro (3) isomers, and of a minor by-product, 5,5′,6,6′-tetrachloro-8,8′-methylenebis(4H-benzo-1,3-dioxin) (4), have been isolated from the mixture formed by acid-catalyzed condensation of 3,4-dichlorophenol with one half of a molar equivalent of formaldehyde. In addition, the structures and solid state conformations of all four compounds, and of an ethanol solvate of1, have been revealed by X-ray crystallographic studies. The three bisphenols (1,2,3) all crystallize in space group, as centrosymmetric hydrogen-bonded dimers, while the solvate,1•EtOH, although it also belongs to space group, forms relatively open infinite bands of hydrogen-bonded molecules. Crystals of4belong to space groupFdd2 and the molecules have twofold crystallographic symmetry.Keywords: X-ray crystallography, bisphenols, tetrachloro-2,2′-methylenebisphenols, tetrachloro-8,8′-methylenebis(4H-benzo-1,3-dioxin).

ISSN:0008-4042    

DOI:10.1139/v89-117

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

A complete kinetic study of the N-chlorination, in aqueous medium, of dimethylamine and diethylamine by a stopflow spectrophotometric method is presented. In neutral or basic medium our experimental results can be interpreted by two kinetically indistinguishable mechanisms; the reactions between protonated amine (R2NH2+) and hypochlorite ion (ClO−) and the reaction between R2NH and hypochlorous acid (ClOH) are equivalent because of the fast equilibrium of proton exchange existing between the two groups of possible reactants. In acid medium, in the presence of chloride ions, we observed a reaction by aqueous chlorine (Cl2) on the amine (Cl2 + R2NH → chloramine).Keywords: kinetics, N-chlorination, amines, aqueous medium.

ISSN:0008-4042    

DOI:10.1139/v89-118

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

A medium solvent isotope effect of Φ = 0.827 ± 0.013 was determined for transfer of isobutyrophenone from H2O to D2O. This result, in conjunction with the average solvent isotope effect on hydration of a number of carbonyl compounds, leads toas the fractionation factor for the hydroxyl group hydrogens of the hydration reactions'gem-diol products, which is consistent with the expectation that fractionation factors for uncharged hydroxyl groups should be unity.Keywords: isobutyrophenone, fractionation factors, solvent isotope effects, deuterium oxide.

ISSN:0008-4042    

DOI:10.1139/v89-119

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Diastereoselective reduction of 2-propionyl-6-methyl-3,4-dihydropyran and its ring opened derivatives, followed by acidic work-up, gives mixtures rich (>9:1) of eitherexo- orendo-brevicomin.Keywords:exo- andendo-brevicomin, diastereoselective ketone reduction.

ISSN:0008-4042    

DOI:10.1139/v89-120

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Metal complexes containing the ligand 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazatetradecane were synthesized and characterized using electron impact (EI) and fast atom bombardment (FAB). The FAB mass spectra were obtained in positive and negative ion mode. FAB in the positive ion mode proved to be the most successful technique for the identification of these compounds. The majority of the FAB spectra obtained were structurally informative, although not all showed molecular (M+) or quasimolecular ([M + H]+) ions. The fragmentations observed were characteristic of the ligands and the metal, and were interpreted based on the chemical and spectroscopic properties of these compounds.Keywords: FAB mass spectroscopy, tetraazacyclotetradecane complexes.

ISSN:0008-4042    

DOI:10.1139/v89-121

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Dielectric absorption measurements are reported at radio and microwave frequencies (at six different wavelengths) for acetylacetone and benzoylacetone solutions in benzene, in a temperature range 25–60 °C. Analysis of dielectric data in terms of Cole–Cole arc plots and multiple relaxation processes reveals that, at higher temperatures, overall molecular relaxation is the dominant relaxation mechanism in these β-diketones. The observed relaxation times, distribution parameters, and dipole moments are in reasonable agreement with the few data reported for some temperatures, in the literature. The activation energy parameters are also evaluated assuming dielectric relaxation to be a rate process. Molar polarization vs. weight fraction (concentration) plots show anomalous behaviour for acetylacetone.Keywords: dielectric properties, dielectric losses, relaxation times, dipole moment, dielectric absorption and dispersion, microwave measurements.

ISSN:0008-4042    

DOI:10.1139/v89-122

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H2, D2, N2, CH4, C2H4, C2H6, CF4, SF6, and CO2) in 2-methylcyclohexanone at 273.15–303.15 K and a partial pressure of gas of 101.32 kPa are reported. Thermodynamic functions (Gibbs energy, enthalpy, and entropy) for the solution process at 298.15 K and 101.32 kPa partial pressure of gas are evaluated. Use is made of the Scaled Particle Theory applied to gas solubility for determining Lennard-Jones (6, 12) pair-potential parameters and temperature dependence of the effective hard-sphere diameter of the solvent. The values that this theory predicts for the solution thermodynamic functions are also calculated.Keywords: 2-methylcyclohexanone, gas solubility, thermodynamic functions of solution, Henry coefficient, scaled particle theory.

ISSN:0008-4042    

DOI:10.1139/v89-123

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

H–D exchange of 2-methylbenzofuran (1), 2-methylindole (2), 2-methylbenzimidazole (3), 2-methylbenzothiazole (4), and 2-methylbenzoxazole (5) has been studied in neutral D2O at elevated temperatures. While1,2,3, and4can be specifically labelled and4can be perlabelled at 255 °C,5undergoes facile hydrolysis in D2O at 115 °C to 2-acetamidophenol (8) with the incorporation of deuterium into the methyl group.Keywords: H–D exchange, heterocycles, D2O, elevated temperatures.

ISSN:0008-4042    

DOI:10.1139/v89-124

出版商:NRC Research Press    

年代:1989

数据来源: NRC