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,Δ f H m o(g) , from their enthalpies of formation in the condensed phase,Δ f H m o(cr) , determined by static bomb combustion calorimetry, and from their enthalpies of sublimation,Δ cr g H m o , determined by Calvet microcalorimetry. Finally, combining theΔ f H m o(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, DH 1 (N–O), were obtained and compared with existing data. Copyright © 2011 John Wiley & Sons, Ltd.