Gas-Phase Chemistry of NH_xCl_y⁺. 1. Structure, Stability, and Reactivity of Protonated Monochloramine

Abstract

The structure and the reactivity of gaseous NH3Cl+ ions obtained from direct protonation of aqueous monochloramine by CI/CH4 and from ionization of a Cl2 plasma containing trace amounts of ammonia have been investigated by FT-ICR mass spectrometry. The results characterized the NH3Cl+ ions arising from both experiments as having the NH3−Cl+ structure, consistent with the results of MO SCF calculations pointing to the higher basicity of the nitrogen than the chlorine atom of NH2Cl. The gas-phase basicity of monochloramine has been estimated to be 761 ± 5 kJ mol-1 from bracketing experiments according to the procedure based on the relationship between the efficiency and the standard free-energy difference of proton transfer. This value is consistent with those from theoretical calculations at the B3LYP and CCSD(T)/6-311++G(3df,3pd) level. In agreement with the protonation site, the NH3Cl+ ions behave as a protonating and chlorinating agent but addition is also observed.

Gas‐phase basicity of 2‐furaldehyde

“…The kinetic method, developed by Cooks and co‐workers, is based on the determination of the rates of competitive dissociations of mass‐selected cluster ions, which take place according to k and k i are the rate costants for the unimolecular dissociation of the ion‐bound cluster. Although other methods such as the bracketing or the equilibrium methods can be used for the measurement of the gas phase basicity, the kinetic method has a number of advantages. It is readily employed in commercial tandem mass spectrometers, gives good results for small amounts of sample and it is simple, fast and applicable to polar and non‐volatile samples without derivatization.…”

Tracking Monochloramine Decomposition in MIMS Analysis

“…The characteristic peaks of protonated monochloramine were at m/z 51.995 (NH 3 35 Cl + ) and 53.992 (NH 3 37 Cl + ). Ricci and Rosi found that these ions showed the NH 3 -Cl + structure [22,23]. In addition, the mass spectrum of NH 2 Cl solutions exhibited an intense peak at m/z 18.034, attributed to the NH 4 + ions.…”

“…However, the formation of these ions cannot be verified since the published mass spectra start at m It should be noted that disproportionation of monochloramine into dichloramine (NHCl 2 ) is possible at pH 7 [3,26]. However, no trace of characteristic NHCl 2 ions was found, even though its proton affinity (PA = 757.0 ± 10 kJ mol −1 ) is higher than that of water [22,23]. This is likely due to the fact that the NHCl 2 concentration in monochloramine solutions was below the MIMS detection limit.…”

“…Analysis was performed by chemical ionization using H 2 O as reagent. The proton affinity (PA) of monochloramine (PA = 797.05 kJ·mol −1 ) exceeds that of H 2 O (PA = 691.0 kJ mol −1 ), signifying that monochloramine might be able to undergo proton transfer reaction with H 3 O + , as shown in Equation (1) [22,23]. Hydronium ions were generated inside the ICR cell from water vapor pulses after electron ionization and molecular ion reactions.…”

The influence of Cu(II) on the decay of monochloramine

“…In acidic solutions, both proton transfer and Cl + transfer are known to occur (Snyder and Margerum, 1982;Ricci and Rosi, 1998). The reaction proceeds by nucleophilic attack of the unprotonated amine nitrogen on the chlorine of the protonated monochloramine and shifts to a rate-limiting step of electrophilic bond breaking in NH 3 Cl + as the amine nitrogen becomes more basic than ammonia.…”