Carbon Dioxide Solubility Enhancement through Silicone Functionalization: “CO₂-philic” Oligo(dimethylsiloxane)-substituted Diphosphonates∗

Abstract

Abstract Carbon dioxide has received significant attention as a potential environmentally benign medium to replace hazardous organic compounds, but is a relatively poor solvent. The addition of siloxane substituents provides an attractive and inexpensive means to solubilize a wide variety of compounds in CO2. By synthesizing and testing a family of gem-diphosphonate ligands that have been rendered CO2-philic by incorporation of a number of related, discrete dimethylsiloxane oligomers, we show that small variations in substituents have a significant effect on the CO2-philicity of the ligand. To our knowledge, this is the first systematic study of the effect of siloxane substituent size, branching, and position on the affinity of a ligand for CO2. In addition, we present a general approach to the preparation of novel gem-diphosphonate ligands. Keywords: supercritical carbon dioxidesolubilitysilicone functionalization ACKNOWLEDGEMENTS This work was funded by the Environmental Management Sciences Program of the Offices of Science and Environmental Management, U. S. Department of Energy, under grant number DE-FGO7-98ER14928 (Loyola), grant number FG07–98ER14924 (Notre Dame), and contract number DE-AC02–06CH11357 (Argonne). Mass spectrometry was provided by the Washington University Mass Spectrometry Resource, an NIH Research Resource (Grant No. P41RR00954). ∗Work performed under the auspices of the United States Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences, under contract number DE-AC02–06CH11357. Notes