Publications

Abstract A procedure for the estimation of the number and values of acidity constants from variations observed in aqueous Fourier transform infrared spectra of compounds containing carboxylic groups, including fulvic acids, with increasing pH, by using principal component analysis and evolving factor analysis, has been studied. The validation of the procedure was made by treating simulated data without and with random noise and data obtained in experiments with simple carboxylic compounds (acetic, shikimic, maleic, malonic and succinic acids) and binary mixtures of these compounds. The results for fulvic acids show two different types of carboxylic groups with pK(a) values of 2.8 and 4.6.

Abstract The standard (p° = 0.1 MPa) molar enthalpies of combustion at 298.15 K were measured by static-bomb calorimetry and the standard molar enthalpies of sublimation at 298.15 K were measured by microcalorimetry for the following aromatic nitriles and aromatic nitrile N-oxides: (2, 4, 6 - Trimethylbenzonitrile 5530.7 ± 0.9 82.9 ± 1.6; 2, 4, 6 - Trimethylbenzonitrile N -oxide 5563.1 ± 0.8 77.5 ± 3.7; 2, 4, 6 - Trimethoxybenzonitrile 5150.0 ± 0.9 112.6 ± 2.0; 2, 4, 6 - Trimethoxybenzonitrile N -oxide 5187.1 ± 1.6 91.9 ± 1.9; 2, 6 - Dimethylbenzonitrile 4890.1 ± 1.0 83.9 ± 2.8). From the standard molar enthalpies of formation of the gaseous compounds, the molar dissociation enthalpies of the (N{single bond}O) bonds were derived: D(N{single bond}O)/(kJ·mol-1) trimethylbenzonitrile N-oxide, (222.2 ± 4.6); trimethoxybenzonitrile N-oxide, (232.8 ± 3.8). © 1991 Academic Press Limited All rights reserved.

Abstract Enthalpies of dissolution in water of dialkylsulphides: CH3(CH2)v{single bond}S{single bond}(CH2)vCH3, v = 0, 1, and 2, and dialkyldisulphides: CH3(CH2)v{single bond}S{single bond}S{single bond}(CH2)vCH3, v = 0 and 1, were determined by microcalorimetry at the temperatures (288.15, 298.15, 308.15, and 328.15) K. Molar enthalpies of solvation and partial molar heat capacities at 298.15 K were derived for the infinitely dilute solutions. The partial molar heat capacities are discussed in terms of an empirical group scheme.

Abstract Thermopile heat conduction calorimeters normally have high time constants. Multistep titration experiments involving fast processes may then require several hours to perform. It is demonstrated that such experiments can be conducted about 10 times faster, without loss of accuracy, by use of a "dynamic correction method". For a new small vessel thermopile conduction calorimeter, injections can be made at 1.5-min intervals.

Abstract Cis/trans isomers of ferulic and isoferulic acids and their corresponding coumarins, scopoletin and isoscopoletin, were separated by isocratic High Performance Liquid Chromatography using RP-8 (5-mu-m) as a stationary phase and aqueous methanol or aqueous acetonitrile as a mobile phase. The UV spectrum of cis-isoferulic acid was obtained by a photodiode array detector.

Abstract The standard (po = 0.1 MPa) molar enthalpies of formation were derived from the standard molar enthalpies of combustion, in oxygen, at 298.15 K, measured by static bomb calorimetry for 2-hydroxyquinoline (2HOQ), 4-methyl-2-hydroxyquinoline (4Me-2HOQ), 4-hydroxyquinoline (4HOQ), and 2-methyl-4-hydroxyquinoline (2Me-4HOQ); the vapour pressures of the crystals were measured as functions of temperature by the Knudsen-effusion technique, and the standard molar enthalpies of sublimation, at 298.15 K, were derived by the Clausius-Clapeyron equation. {A table is presented}. © 1990.