Measurement and Prediction of the Monocarboxylic Acids Thermochemical Properties

The standard molar enthalpies of vaporization or sublimation of 2-methylpropanoic, butanoic, 2-methylbutanoic, 3-methylbutanoic, pentanoic, 2,2-dimethylpropanoic, 3,3-dimethylbutanoic, hexanoic, heptanoic, and octanoic acids were measured by the transpiration method. The enthalpies of vaporization of ethanoic, propanoic, 2-methylpropanoic, and butanoic acids were measured using correlation gas chromatography. The enthalpies of the phase transitions of 2,2-dimethylpropanoic acid were measured using differential scanning calorimetry. The values of of the compounds studied were taken as a basis for the development of a group-additivity predictive scheme. The standard molar enthalpies of formation Δ f (g) at the temperature T = 298.15 K of monocarboxylic acids were derived using the data for Δ f (l or cr) from the literature and the present results for the enthalpies of vaporization or sublimation. The improved group-contribution method was used for the estimation of the gaseous enthalpies of formation of monocarboxylic acids.