Energetics of the N−O Bonds in 2-Hydroxyphenazine-di-N-oxide

Abstract

The standard enthalpy of formation and the enthalpy of sublimation of crystalline 2-hydroxyphenazine-di-N-oxide, at T ) 298.15 K, were determined from isoperibol static bomb combustion calorimetry and from Knudsen effusion experiments, as -76.7 ( 4.2 kJ‚mol -1 and 197 ( 5 kJ‚mol -1 , respectively. The sum of these two quantities gives the standard enthalpy of formation in the gas-phase for this compound, ∆ f H°m(g) ) 120 ( 6 kJ‚mol -1 . This value was combined with the gas-phase standard enthalpy of formation for 2-hydroxyphenazine retrieved from a group estimative method yielding the mean (N-O) bond dissociation enthalpy, in the gas-phase, for 2-hydroxyphenazine-di-N-oxide. The result obtained with this strategy is 〈DH°m (N -O)〉 ) 263 ( 4 kJ‚mol -1 , which is in excellent agreement with the B3LYP/6-311+G(2d,2p)// B3LYP/6-31G(d) computed value, 265 kJ‚mol -1 .

Thermochemical properties of 4-N,N-dialkylamino-7-nitrobenzofurazan derivatives (alkyl=methyl, ethyl)

“…During the last two decades, our Research Group has been involved in a systematic study of the dissociation enthalpy of terminal N-O bonds in heterocyclic compounds [1][2][3][4][5][6][7][8][9][10][11][12]. These studies are a contribution to the understanding of the chemical behavior of those organic compounds, particularly as oxidizing agents, enabling the ordering of them on a reactivity scale [1].…”

“…These studies are a contribution to the understanding of the chemical behavior of those organic compounds, particularly as oxidizing agents, enabling the ordering of them on a reactivity scale [1]. Several classes of compounds with N-O terminal bonds have been studied, with particular attention devoted to quinoxaline N,N-dioxides [2][3][4][5][6][7], pyrazine N,N-dioxides [1,8,9], phenazine N,N-dioxides [10], benzofurazan N-oxides [1], pyridine N-oxides [11] and dipyridil N-oxides [12]. We have extended recently these studies to 4-nitro-2,1,3-benzothiadiazoles [13] and Miranda et al also have published studies on the structure, energetics and aromaticity of 2,1,3-benzothiadiazole [14,15].…”

Thermochemical Studies on 3-Methyl-quinoxaline-2-carboxamide-1,4-dioxide Derivatives: Enthalpies of Formation and of N−O Bond Dissociation

“…10,12,[32][33][34][35] Here, the use of this computational approach is quite difficult, since the experimental enthalpies of formation for key species, such as C 6 H 5 N(sH)C(dO)sX, where X is a methyl group or, even more interesting, an aromatic ring, are not available in the literature. Therefore, from our experience, large errors are to be expected if the present computational approach is used to estimate the gas-phase enthalpies of formation for compounds 1b and c without the knowledge of thermochemical data for similar compounds.…”

“…This notation has also been used in previous works. [10][11][12][13]38 The B3LYP/6-311+G(2d,2p)//B3LYP/6-31G(d) computed dissociation enthalpies for 1a are reported in Figure 2. The enthalpies computed for the removal of a single oxygen atom from compound 1a show that the weakest bond is that nearby the carboxamide group.…”

“…This approach has been employed successfully in the past with an excellent agreement between computed and experimental results. [10][11][12] Then, using the computed enthalpies for the reaction of dissociation of the two N-O bonds together with the standard molar gas-phase enthalpies of formation of the oxygen atom and of compounds 1a-c, the enthalpy of formation of compounds 2a-c were estimated.…”