Synthesis and thermochemical study of quinoxaline-N-oxides: enthalpies of dissociation of the N-O bond

The synthesis of three new quinoxaline mono‐N‐oxides derivatives, namely, 2‐tert‐butoxycarbonyl‐3‐methylquinoxaline‐N‐oxide, 2‐phenylcarbamoyl‐3‐ethylquinoxaline‐N‐oxide, and 2‐carbamoyl‐3‐methylquinoxaline‐N‐oxide, from their corresponding 1,4‐di‐N‐oxides is reported. Samples of these compounds were used for a thermochemical study, which allowed derivation of their gaseous standard molar enthalpies of formation, ΔfHmo(g), from their enthalpies of formation in the condensed phase, ΔfHmo(cr), determined by static bomb combustion calorimetry, and from their enthalpies of sublimation, ΔcrgHmo, determined by Calvet microcalorimetry. Finally, combining the ΔfHmo(g) for the quinoxaline‐N‐oxides derived in this work with literature values for the corresponding 1,4‐di‐N‐oxides and atomic oxygen, the bond dissociation enthalpies for cleavage of the first N−O bond in the di‐N‐oxides, DH1(N–O), were obtained and compared with existing data. Copyright © 2011 John Wiley & Sons, Ltd. The first N‐O bond dissociation enthalpy of three quinoxaline derivatives is obtained from the experimental gas‐phase standard molar enthalpies of formation at T = 298.15 K determined for three novel N‐oxide derivatives and available literature data.