Catalytic Coupling of Free Radical Oxidation and Electrophilic Chlorine Addition by Phase-Transfer Intermediates in Liquid Aerosols

Abstract

While examining the heterogeneous reaction of chlorine atoms with alkenes, in the presence of Cl2, we have observed an unexpectedly large enhancement of reactivity and the predominance of chlorinated reaction products even under high O2 conditions, where Cl atom recycling is expected to be minimal. These observations cannot be explained by known free radical oxidation or cycling mechanisms, but rather we find evidence for the multiphase catalytic coupling of free radical oxidation with electrophilic Cl2 addition. The mechanism entails the production of oxygenated reaction intermediates, which act as gas–liquid phase-transfer catalysts (gl-PTCs) by promoting the accommodation of gas-phase Cl2 by the aerosol, thereby enhancing electrophilic addition. Although the majority of PTCs typically couple chemistry between two immiscible liquid phases (aqueous/organic), there are few examples of PTCs that couple gas–liquid reactions. This work shows how multiphase reaction schemes of aerosols can be reimagined for understanding catalytic reaction mechanisms.

A Molecular Dynamic Study of the Effects of Surface Partitioning on the OH Radical Interactions with Solutes in Multicomponent Aqueous Aerosols

“…Aqueous aerosols are known to control cloud nucleation − and to affect the climate, air quality, and human health. − A complete understanding of their role in atmospheric phenomena remains challenging as the properties of nanometric aqueous particles differ greatly from those of a bulk solution. − The chemical evolution of atmospheric aerosols as well as their ability to initiate cloud formation is mostly controlled by the properties of the gas–water interface. , Phenomena such as microconfinement, high surface electric field, preferred molecular orientation, ,,, and lower water densities at the interface , affect reaction rates , and photochemical processes, thus enhancing certain reaction channels while suppressing others. − Because atmospheric aerosols contain a wide range of solutes, it has become important to improve our understanding of how chemical composition changes surface reactivity …”