Thermochemical study of dichloromethylpyrimidine isomers

• Published in: The Journal of chemical thermodynamics Vol. 100; pp. 148 - 155
• Main Authors: Szterner, Piotr, Amaral, Luísa M.P.F., Morais, Victor M.F., Ribeiro da Silva, Maria D.M.C., Ribeiro da Silva, Manuel A.V.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.09.2016
• Subjects: Calorimetry; Combustion; Dichloromethylpyrimidines; Enthalpy; Enthalpy of formation; Enthalpy of sublimation/vaporization; Formations; G3 theoretical calculations; Isomers; Vaporization; Enthalpy of formation; Enthalpy of sublimation/vaporization; Dichloromethylpyrimidines; G3 theoretical calculations
• ISSN: 0021-9614; 1096-3626
• DOI: 10.1016/j.jct.2016.04.011

•Enthalpies of formation were derived by rotating-bomb combustion calorimetry.•Enthalpies of phase transition were determined by Calvet microcalorimetry.•Gaussian-3 theory for calculation of enthalpies of formation for all the isomers.•Structure and energy correlations were established. The standard (po=0.1MPa) molar enthalpies of formation in the condensed phase, ΔfHmo, of 2,4-dichloro-5-methylpyrimidine, 2,4-dichloro-6-methylpyrimidine, 4,6-dichloro-2-methylpyrimidine and 4,6-dichloro-5-methylpyrimidine were derived from the standard molar energies of combustion, ΔcUmo, in oxygen, to yield CO2 (g), N2 (g) and HCl·600H2O (l), at T=298.15K, measured by rotating bomb combustion calorimetry. The standard molar enthalpies of vaporization or sublimation, Δcr,lgHmo, for these compounds, at T=298.15K were determined by high temperature Calvet microcalorimetry. Combining these values, the following enthalpies of formation in the gas phase, at T=298.15K, were then derived: 2,4-dichloro-5-methylpyrimidine, (79.6±4.1)kJmol−1, 2,4-dichloro-6-methylpyrimidine, (70.5±3.0)kJmol−1, 4,6-dichloro-2-methylpyrimidine, (68.7±3.3)kJmol−1, and 4,6-dichloro-5-methylpyrimidine, (78.1±2.5)kJmol−1. The gas-phase enthalpies of formation were also estimated by G3 theoretical calculations, which were extended to the computation of gas-phase enthalpies of formation of the other dichloromethylpyrimidine isomers, namely, 2,5-dichloro-4-methylpyrimidine, 4,5-dichloro-2-methylpyrimidine and 4,5-dichloro-6-methylpyrimidine, whose experimental study was not performed.