Thermochemical and Theoretical Studies of 2-Hydroxyquinoxaline, 2,3-Dihydroxyquinoxaline, and 2-Hydroxy-3-methylquinoxaline

Abstract

The standard (p°) 0.1 MPa) molar enthalpies of formation for crystalline 2-hydroxyquinoxaline, 2,3-dihydroxyquinoxaline, and 2-hydroxy-3-methylquinoxaline were derived from the standard molar enthalpies of combustion, in oxygen, at T ) 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpies of sublimation, at T ) 298.15 K, of the three compounds were measured by Calvet microcalorimetry. The derived standard molar enthalpies of formation in the gaseous phase are 45.9 ( 4.3 kJ‚mol -1 for 2-hydroxyquinoxaline, -(179.2 ( 5.3) kJ‚mol -1 for 2,3-dihydroxyquinoxaline, and -(8.8 ( 4.9) kJ‚mol -1 for 2-hydroxy-3-methylquinoxaline. In addition, theoretical calculations using the density functional theory and the B3LYP/6-311G** hybrid exchange-correlation energy functional were performed for these molecules in order to obtain the most stable geometries and to access their relative stability. The theoretical results are in general good agreement with experimental findings.

Experimental thermochemical study of three monosubstituted pyrazines

“…The thermochemical study of nitrogen heterocyclic molecules derived from pyridine and pyrazine, as well as the study of the corresponding bicyclic systems generated when a benzene ring fuses to those species, resulting quinoline and quinoxaline derivatives, has been one of the main interests of researchers in our laboratory, in order to contribute to the interpretation of their behaviour, establishing relationships among of the energetical, structural, and reactivity characteristics [2][3][4][5][6][7][8][9][10][11][12][13]. On the other hand, we have been involved over the last decade in the development of studies on the energetics of the (N-O) bonds in some classes of Noxide derivatives, namely pyridine N-oxide, pyrazine N-oxide, quinoline N-oxide, and quinoxaline N-oxide derivatives.…”

Thermochemical study of chloropyrazines and chloroquinoxalines

“…In previous work, we have studied the thermochemistry of benzodiazines [1], chloropyridines [2], methyldiazines [3], hydroxyquinoxalines [4], ethylpyridines and ethylpyrazines [5]. In the present work, we continue with the study of pyrazine and quinoxaline derivatives as the thermochemical database for aromatic heterocyclic compounds is still too scarce.…”

Experimental and computational thermochemistry of the dihydroxypyridine isomers

“…Recently, we have reported experimental and theoretical studies on hydroxyquinoxalines [1], hydroxypyridines and hydroxypyridines N-oxide [2]. In this work, we continue with the study of dihydroxypyridines with the purpose of extending the thermochemical database still too scarce for nitrogen heterocycles and for a better understanding of the effect of the hydroxyl group on the energetics of pyridine.…”