Experimental thermochemical study of three monosubstituted pyrazines

The phase relationship between the pyrazinamide polymorphs α and γ

“…The specific volume of different polymorphs of PZA in the literature is shown in Table 2. Lavor et al, 2012) 420.4(5) 13.3(2) 5 ) 420.65 11.35 5 (Baaklini et al, 2015 d®g 408(5) 17(2) 10 (Castro et al, 2009) 404.35 13.5 5 (Cherukuvada et al, 2010) d®a 395(1) ∆H > 0 b 10 (Castro et al, 2009) b®g 368.15 ∆H > 0 b 10 (Castro et al, 2009) 372.55 6.3 5 (Cherukuvada et al, 2010) PZA®vap 829(18) c (Ribeiro da Silva et al, 2005) a®vap 915(13) d (Blokhina et al, 2015a) a®vap 715(44) e (Negoro, 1959;Negoro, 1960) a Values from the literature reported in °C or in J mol -1 are adjusted by adding 273.15 K or are divided by 123.11 g mol -1 , respectively; an average value is used in this table when multiple values have been reported in the same paper; values are rounded to the number of reported digits in the respective reference. b Enthalpy values have not been mentioned in the reference (Castro et al, 2009), but DSC curves in the figures indicate endothermic transitions with increasing temperature.…”

Thermochemical study of cyanopyrazines: Experimental and theoretical approaches

“…b The standard molar enthalpy of formation of cyanopyrazine was taken from reference [7]. The experimental values of the enthalpies of formation of auxiliary molecules were taken from reference [32].…”

“…The experimental values of the enthalpies of formation of auxiliary molecules were taken from reference [32]. b The standard molar enthalpy of formation of cyanopyrazine was taken from reference [7]. These reactions were chosen to be of the isodesmic type, that is, the number of bonds of any formal type is conserved in each side of the equations and are likely to largely cancel the correlation errors in reactants and products, thus leading to reliable estimates of the reaction energies.…”

“…The thermochemical study of pyrazine derivatives has been a continuing interest of researchers in our laboratory, in order to establish relationships among the structural and energetical properties in this kind of compounds [1][2][3][4][5][6][7]. It is our aim with this paper to enlarge the thermochemical database as well as to predict theoretically thermochemical parameters for other compounds whose experimental study is impossible due to difficulties in their synthesis and/or in obtaining them pure in the needed quantity.…”

“…We have performed the experimental study of cyanopyrazine [7] and in the present work we report the standard molar enthalpy of formation of 2,3-dicyanopyrazine (2, in the gaseous phase, obtained from measurements of the combustion energy using a static bomb calorimeter and from the enthalpy of sublimation of the compound measured by microcalorimetry Calvet. Experimental determinations for tri-and tetracyanopyrazine were precluded due to the impossibility to obtain pure samples of the compounds in the needed quantity.…”