THERMODYNAMIC PROPERTIES AND IDEAL-GAS ENTHALPIES OF FORMATION FOR CYCLOHEXENE, PHTHALAN (2,5-DIHYDROBENZO-3,4-FURAN), ISOXAZOLE, OCTYLAMINE, DIOCTYLAMINE, TRIOCTYLAMINE, PHENYL ISOCYANATE, AND 1,4,5,6-TETRAHYDROPYRIMIDINE

The results of a study aimed at improvement of the group-contribution methodology for estimation of thermodynamic properties of organic subs tances are reported. Specific weaknesses where particular group-contri bution terms were unknown, or estimated because of lack of experimenta l data, are addressed by experimental studies of enthalpies of combust ion in the condensed phase, vapor-pressure measurements, and different ial scanning calorimetric (dsc) heat-capacity measurements. Ideal-gas enthalpies of formation of cyclohexene, phthalan (2,5-dihydrobenzo-3,4 -furan), isoxazole, octylamine, dioctylamine, trioctylamine, phenyl is ocyanate, and 1,4,5,6-tetrahydropyrimidine are reported. Two-phase (li quid + vapor) heat capacities were determined for phthalan, isoxazole, the three octylamines, and phenylisocyanate. Liquid-phase densities a long the saturation line were measured for phthalan and isoxazole in t he temperature range 298 K to 425 K. The critical temperature and crit ical density of octylamine were determined from the dsc results and a critical pressure derived from the fitting procedures. Fitting procedu res were used to derive critical temperatures, critical pressures, and critical densities for cyclohexene (pressure and density only), phtha lan, isoxazole, dioctylamine, and phenylisocyanate. Group-additivity p arameters or ring-correction terms useful in the application of the Be nson group-contribution correlations are derived.