Gas-Phase Proton Affinity of Nitric Acid and Its Esters. A Mass Spectrometric and ab Initio Study on the Existence and the Relative Stability of Two Isomers of Protonated Ethyl Nitrate

Abstract

The protonation of C 2 H 5 ONO 2 has been studied in the gas phase by the joint application of mass spectrometric and ab initio theoretical methods. The MIKE and CAD spectra of (C 2 H 5 ONO 2 )H + ions from various sources and their reactivity toward selected nucleophiles, investigated by FT-ICR mass spectrometry, point to the existence of two protomers, the C 2 H 5 OHNO 2 + ion-dipole complex (1c) and the covalently bound C 2 H 5 -ONOOH + species (2c), and to the tendency of the latter to isomerize into 1c in the presence of neutral C 2 H 5 -ONO 2 . The BE of NO 2 + to C 2 H 5 OH, independently measured by the kinetic and the equilibrium methods, amounts to 22.2 ( 2 kcal mol -1 at 298 K, leading to a PA of C 2 H 5 ONO 2 of 178.4 ( 2.6 kcal mol -1 , referred to the protonation at the ethereal oxygen. The computational results at the G2(MP2) level of theory show that protomers 1c and 2c have the same stability at 298 K and that at the same temperature the 2c f 1c isomerization is characterized by a ∆G°change of ca. -3 kcal mol -1 . The PA of C 2 H 5 ONO 2 is computed to be 177 ( 2 kcal mol -1 at 298 K, irrespective of whether protonation occurs at the ethereal O or at the NO 2 group, in excellent agreement with the experimental value. The results are discussed in connection with the general problem concerning the preferred protonation site and the PA trend along the RONO 2 homologous series. It is shown that entirely different factors control the local PA of the RO and the NO 2 groups.

Proton affinity of peroxyacetyl nitrate sampled by membrane introduction mass spectrometry

“…However, we have compensated for these difficul- ties by making measurements with a large number of reference compounds and are confident that the estimated PA is correct, within the estimated 3 kcal/mol uncertainty. The estimated proton affinity for PAN is higher than the values reported in the literature for the esters of nitric acid 50 and related compounds 50,51 which are in the range 175-177 kcal/mol. On the other hand, it is similar to the values for carbonyl compounds such as formate esters.…”

Fabrication of Micrometer‐Scale Anatase‐Phase TiO2 Congeries Assembled with Hollow Spheres

“…The shells of the hollow spheres obviously became thinner and looser after calcination, which might be due to the removal of carbon and hydrogen in the form of carbon dioxide and water during the transformation from Ti 2 O 2 (C 2 O 4 )(OH) 2 ·H 2 O to anatase‐phase TiO 2 .Based on the above observations, a possible mechanism to form micrometer‐scale anatase‐phase TiO 2 congeries of hollow spheres is proposed. In our system, nitric acid reacts with ethanol at 0°C to form nitric acid ethyl ester, 26 which is subsequently heated in the acid medium and decomposes to generate ethene 27 . The generated ethene is immediately oxidated, first by nitric acid to glycol, 28 which is then further oxidated in the nitric acid solution to oxalic acid 29 .…”

“…In our system, nitric acid reacts with ethanol at 01C to form nitric acid ethyl ester, 26 which is subsequently heated in the acid medium and decomposes to generate ethene. 27 The generated ethene is immediately oxidated, first by nitric acid to glycol, 28 which is then further oxidated in the nitric acid solution to oxalic acid. 29 At the same time, the nitric acid is reduced to nitrogen monoxide.…”

Gaseous [N2O5]H+, [N2O4]H+, and Related Species from the Addition of NO2+ and NO+ Ions to Nitric Acid and Its Derivatives

“…Gas-phase positive ion chemistry of nitric acid and related molecules is the focus of sustained interest, owing to its intrinsic fundamental interest and the relevance to atmospheric chemistry. − Particular attention has been devoted to protonated nitric acid, both in the isolated state and in water clusters, − and the investigation has been extended to its derivatives, i.e., protonated alkyl nitrates − and nitramide, leading to the construction of a scale of NO 2 + binding energies (BE) …”