Izvorni znanstveni članak

Proton Transfer Chemistry in the Gas Phase. Is a Spontaneous 'Neutralization' Reaction a Myth or a Reality?

Ewa D. Raczyńska ; Department of Chemistry, Warsaw University of Life Sciences, 02-776 Warsaw, Poland
Jean-François Gal orcid.org/0000-0002-5500-5461 ; Laboratoire de Radiochimie, Sciences Analytiques et Environnement, Institute of Chemistry of Nice (FR CNRS 3037), University of Nice - Sophia Antipolis, 06108 Nice Cedex 2, France
Pierre-Charles Maria ; Laboratoire de Radiochimie, Sciences Analytiques et Environnement, Institute of Chemistry of Nice (FR CNRS 3037), University of Nice - Sophia Antipolis, 06108 Nice Cedex 2, France
Małgorzata Szeląg ; Interdisciplinary Department of Biotechnology, Warsaw University of Life Sciences, 02-726 Warsaw, Poland

Sažetak

Relying on physicochemical knowledge, the proton cannot be spontaneously transferred from a gaseous mineral acid (HF, HCl, HBr, HI, HNO₃, H₂SO₄, or HClO₄) to a gaseous nitrogen base (NH₃, alkylamine, aniline, pyridine, amidine, or guanidine). For example, the full proton-transfer from HCl to NH₃, followed by the separation of Cl- and NH₄+ requires more than 500 kJ mol-1. The same is true for a spontaneous intramolecular proton-transfer for gaseous amino acids, aminophenols and other amphiprotic compounds. From the gas-phase acidity parameter of COOH and the gas-phase basicity parameter of NH₂ (or other more basic group in the side chain), it appears that proton transfer is endothermic or endergonic. For arginine, an amino acid with a highly basic guanidine function, this difference is still larger than about 300 kJ mol-1. Only solvation of the acid-base system by neutral species (e.g., one or more water molecules), complexation by ions (e.g., ionic acids or bases, metal cations) or even electrons may reduce the
energetic barrier and facilitate the proton-transfer. Recent extension of the gas-phase acidity-basicity scale toward superacids and superbases, and recent development of spectroscopic techniques adapted to the gas phase for less volatile organic compounds give some perspectives for observing the full intermolecular proton-transfer between a molecular Brønsted-Lowry superacid and a molecular Brønsted-Lowry superbase.

Ključne riječi

acid-base chemistry; gas phase; acidity-basicity scale; proton-transfer; 'neutralization' reaction; superacids; superbases; amino acids; zwitterions

Hrčak ID:

38626

URI

https://hrcak.srce.hr/38626

Datum izdavanja:

30.6.2009.

Posjeta: 4.772 *