Proton transfer reactions between nitric acid and acetone, hydroxyacetone, acetaldehyde and benzaldehyde in the solid phase

Abstract

The heterogeneous and homogeneous reactions of acetone, hydroxyacetone, acetaldehyde and benzaldehyde with solid nitric acid (HNO₃) films have been studied with Reflection–Absorption Infrared Spectroscopy (RAIRS) under Ultra-High Vacuum (UHV) conditions in the 90–170 K temperature range. In the bulk or at the surface of the films, nitric acid transfers its proton to the carbonyl function of the organic molecules, producing protonated acetone–H⁺, hydroxyacetone–H⁺, acetaldehyde–H⁺ and benzaldehyde–H⁺, and nitrate anions NO₃⁻, a reaction not observed when nitric acid is previously hydrated [J. Lasne, C. Laffon and Ph. Parent, Phys. Chem. Chem. Phys., 2012, 14, 697]. This provides a molecular-scale description of the carbonyl protonation reaction in an acid medium, the first step of the acid-catalyzed condensation of carbonyl compounds, fuelling the growth of secondary organic aerosols (SOA) in the atmosphere.