Energies of combustion and enthalpies of formation of 5-methyl-5-phenylhydantoin and 5,5-diphenylhydantoin

Abstract

The standard molar energies of combustion D c U°(cr, 298.15 K) of 5-methyl-5-phenylhydantoin and 5,5-diphenylhydantoin were obtained by static-bomb combustion calorimetry. The calorimeter was re-calibrated in order to determine the energy equivalent, and the valued obtained was e (calor) = (10,150.8 ± 1.2) J K -1 . The heat capacities and purities of the compounds studied in present work were determined using a differential scanning calorimeter. The molar combustion energies obtained for 5-methyl-5-phenylhydantoin and 5,5-diphenylhydantoin were: -(4984.61 ± 0.87) and -(7391.36 ± 1.34) kJ mol -1 , respectively. From these combustion energy values, the standard molar enthalpies of formation (D f H°) in the crystalline phase at T = 298.15 K were obtained as: -(378.40 ± 1.58) and -(223.80 ± 2.38) kJ mol -1 , respectively. Additionally, and with comparative proposes, the enthalpies of formation in the gas phase were determined using the experimental data and predicted values of the enthalpies of sublimation by using standard methods described in specialized literature.

Thermochemical Study of 1-Methylhydantoin

“…For example, El-Sayed [16] reported the enthalpies of combustion and formation of hydantoin; Silva et al [17] described a comprehensive computational and experimental energy study on hydantoin and 2-thiohydantoin. Recently, our research group has carried out thermochemical studies on the enthalpies of sublimation and enthalpies of formation in the condensed and gas phase of 5-methylhydantoin, 5-methyl-5-phenylhydantoin, and 5,5-diphenylhydantoin [18,19]. Nogueira et al [20] conducted a study on the spectroscopic characterization and thermal behavior of 1-methylhydantoin.…”