Thermodynamic Study on the Sublimation of Six Substituted Quinoxalines

Abstract

The Knudsen mass-loss effusion technique was used to measure the vapor pressures at different temperatures of the following substituted quinoxalines: 2-hydroxyquinoxaline, between 383.17 K and 399.15 K; 2-hydroxy-3-methylquinoxaline, between 375.16 K and 391.15K; 2,3-dichloroquinoxaline, between 313.15 K and 329.15 K; 2,3,6,7-tetrachloroquinoxaline, between 347.16 K and 361.17 K; 2,3-dimethylquinoxaline between 294.14 K and 308.14 K; 2,3-bis(bromomethyl)quinoxaline, between 351.14 K and 365.14 K. From the temperature dependence of the vapor pressure, the standard molar enthalpies of sublimation at the mean temperature of the experimental range were derived by the Clausius−Clapeyron equation. From these results the standard molar enthalpies, entropies, and Gibbs functions of sublimation at T = 298.15 K were calculated. An empirical equation for estimating vapor pressure−temperature data from enthalpies of sublimation values is presented.

Energetics of LOHC: Structure-Property Relationships from Network of Thermochemical Experiments and in Silico Methods

“…The enthalpies of sublimation for 2,3dimethylquinoxaline compiled in Table 1 also agree within the combined experimental uncertainties. Vapor pressures for this compound measured in this work by the transpiration method are in agreement (see Figure S1) with those measured by the Knudsen mass-loss effusion technique [29]. Thus, the weighted average value ∆ g cr H o m (298 K) = (85.4 ± 0.7) kJ•mol −1 was derived and applied for further thermochemical calculations.…”

“…Standard molar enthalpies of formation of pyrazines and quinoxalines are required for the thermodynamic analysis of the hydrogenation/dehydrogenation reactions according to the Hess's Law (Equation (5)) or according to Equation (6). The thermochemistry of pyrazine and quinoxaline derivatives has been studied intensively in established laboratories in Porto [26,28,29,43,44]. The available experimental results together with our new measurements are compiled in Table 4.…”

The influence of the halogen atoms and acetyl group on vapour pressures and related properties of the p -haloacetophenones

“…Our research group has been developing equations correlating thermodynamic properties of sublimation and vaporisation of organic compounds for a period of time [1][2][3][4][5][6][7][8][9]. These correlations are very useful to test the internal coherency of the experimental results and to predict results for compounds not studied experimentally.…”

Thermochemical study of chloropyrazines and chloroquinoxalines

“…For 2,3-dichloroquinoxaline and 2,3,6,7-tetrachloroquinoxaline Monte and Hillesheim [26] reported the standard molar enthalpies of sublimation at T ¼ 298:15 K, respectively, D g cr H m ¼ ð93:1 AE 0:9Þ kJ Á mol À1 and D g cr H m ¼ ð108:2AE 1:9Þ kJ Á mol À1 measured by the Knudsen effusion method, which agree within the associated uncertainties with our results for these compounds.…”