Protonated nitric acid. Structure and relative stability of isomeric H2NO3+ ions in the gas phase

Gong

et al. 2013

Sci Rep

Selective activation of benzene has been mainly limited to the C-H activation. Simple replacement of one carbon in benzene with another atom remains unresolved due to the high dissociation energy. Herein, we demonstrate a direct breakage of the particularly strong C = C bond in benzene through ion-molecule reaction in a low-temperature plasma, in which one carbon atom was replaced by one atomic nitrogen with the formation of pyridine. The mechanism for the formation of pyridine from benzene has been proposed based on the extensive investigation with tandem mass spectrometry. The reaction pathway also works to other aromatics such as toluene and o-xylene. This finding provides a new avenue for selective conversion of aromatics into nitrogen-containing compounds.

Section: Discussionmentioning

confidence: 87%

Observation of Replacement of Carbon in Benzene with Nitrogen in a Low-Temperature Plasma

Gong

et al. 2013

Sci Rep

“…[6][7][8][9][10] Application of structurally diagnostic mass spectrometric techniques has demonstrated the existence of two types of protonated adducts, namely, ion-molecule complexes 1 formed by nitronium ion with water or alcohols and ions 2, protonated at the nitro group, showing that ions of type 1 are more stable for R ) H, CH 3 . 11,12 Both findings were confirmed by high-level ab initio studies whose results revealed, in addition, a peculiar and counterintuitive trend, namely, the higher proton affinity (PA) of nitric acid than of methyl nitrate, 182.5 ( 3 vs 176.9 kcal mol -1 . 13,14 The theoretical prediction is supported by the most recent experimental results, in that flowing-afterglow (FA-SIFT) measurements assign a PA of 177.7 ( 2.3 and 175.0 ( 2.5 kcal mol -1 to HNO 3 and CH 3 ONO 2 , respectively, 15 and the corresponding values from Fourier-transform ion cyclotron resonance (FT-ICR) experiments are 182.0 ( 2.3 16 and 178.0 ( 2.0 kcal mol -1 .…”

Section: Introductionmentioning

confidence: 86%

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

et al. 1996

Self Cite

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.

Proc. Natl. Acad. Sci. U.S.A.

“…The conceivable formation of clusters-e.g., proton-bound dimers of the same m/z ratio but structurally different from nitronium ion-bound dimers-has required preliminary selection of the species suitable for application of the kinetic method. Fortunately a systematic survey has allowed identification of many (Li, L2, NO2)+ clusters whose metastable fragmentation occurs exclusively via the competing processes k[ L1(NO+)L2 k3 L1NO+ +L2, [3] suggesting that the dissociating species has the structure of a L1(NO+)L2 nitronium ion-bound dimer, as in the representative examples illustrated in Fig. 2.…”

Section: Methodsmentioning

confidence: 99%

“…The spectra were recorded at temperatures ranging from 400 to 50°C, as measured by a thermocouple inserted into the source block, using gaseous mixtures of NO2 and the two ligands (L1 and L2), whose composition was optimized to obtain the highest intensity of the L1(NO')L2 dimers, at total pressures in the 0.1-to 0. The study of the complexes formed in the gas phase by NO2 is currently the focus of considerable fundamental interest (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and, in addition, has a direct bearing on areas ranging from mechanistic organic chemistry (12)(13)(14)(15)(16)(17)(18)(19) to atmospheric chemistry, clustering and nucleation phenomena, intracluster reactivity (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30), etc. In view of the considerable interest of the problem and of the scant experimental information currently available (31-33), we have undertaken a systematic study of the binding energy (BE) of NO+ to representative ligands, aimed at the construction of a gas-phase nitronium ion-affinity scale.…”

mentioning

confidence: 99%

Gas-phase nitronium ion affinities.

Cacace

Petris

Pepi

et al. 1995

Evaluation of nitronium ion-transfer equilibria, L1NO' + L2 = L2NO' + L1 (where L1 and L2 are ligands 1 and 2, respectively) by Fourier-transform ion cyclotron resonance mass spectrometry and application of the kinetic method, based on the metastable fragmentation of L1(NO+)L2 nitronium ion-bound dimers led to a scale of relative gas-phase nitronium ion affinities. ligands, aimed at the construction of a gas-phase nitronium ion-affinity scale.To this end, we have applied the Fourier-transform ion cyclotron resonance mass spectroscopy equilibrium method largely used in proton affinity (PA) measurements (34) to NO' transfer reactions and extended the kinetic method, so far used exclusively in PA and gas-phase acidity determinations (35,36), to nitronium ion-bound dimers. MATERIALS AND METHODSAll chemicals were obtained as research-grade products from Aldrich and were used without further purification. The gases were purchased from Matheson with a stated purity >99.95 mol %, except NO2, for which purity was >99.5 mol %, and were used L,NO+ + L2 = L2NO2 + Ll, [1] allows direct determination of the corresponding free energy change, AG', provided that the equilibrium constant can be accurately measured, which requires attainment of true equilibrium, unperturbed by significant side reactions. In the specific application, CH3O(NO2)2, the nitrating reagent, is prepared in the external chemical ionization source of a Fourier transform ion cyclotron resonance mass spectrometer and driven into the resonance cell, where it nitrates both ligands, present in a known concentration ratio. One of the nitrated complexes is isolated by selective-ejection techniques and allowed to equilibrate in the mixture of the ligands. Application of the method is prevented in many cases by incursion of fast proton-transfer reactions that perturb the equilibrium-e.g., the nitronium ion transfer, [C2H5OH-NO2]+ + NH3 = [H3N-NO2]+ + C2H5OH, [la] undergoes competition by proton transfer to ammonia from both nitrated complexes, which react as the conjugate acids of ethyl nitrate and of nitramide. Furthermore, in the case of ligands of low ionization potential the study of equilibrium 1 Abbreviations: PA, proton affinity; BE, binding energy; RP, reference pair; MIKE, mass analyzed ion kinetic energy. tTo whom reprint requests should be addressed.The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 8635