Exploring CO2-Philicity: Effects of Stepwise Fluorination

Abstract

It is well-known that, in general, fluorocarbons are highly soluble in liquid and supercritical CO2 and fluorine substitution has been widely utilized as a method to make otherwise insoluble organic compounds more CO2-philic. In this work, we investigate the CO2-philicity of fluorinated compounds with varying numbers of fluorine atoms in the system by using simple quantum chemical calculations. We explore the fundamental nature of fluorocarbon and hydrocarbon interactions with CO2 by examining the effects of stepwise fluorination on methane using correlated ab initio calculations. The results suggest an optimum density of fluorine atoms that can be viewed as a maximum CO2-philicity. As a charge-separated molecule, CO2 is observed to act as a weak Lewis acid as well as a weak Lewis base in intermolecular interactions. In this work, we present evidence that CO2−fluorocarbon and CO2−hydrocarbon interactions are fundamentally different, although energetically comparable. Fluorocarbons interact through the carbon atom of CO2, while hydrocarbons interact through the oxygen atoms. The results indicate that in the case of partially fluorinated hydrocarbons, there is a specific fluorine atom−CO2 interaction. In these systems, the C−H bonds may also contribute to CO2-philicity through weak C−H···O interactions. The effect of fluorine substitution on the CO2-philicity of carbonyl containing CO2-philes is also investigated.