Application of Molecular Connectivity Indices to the Design of Supercritical Carbon Dioxide‐Soluble Metal Ion Extractants: SC‐CO₂ Solubilities of Symmetrically Substituted Alkylenediphosphonic Acids

Abstract

Using a dynamic flow method, the supercritical carbon dioxide (SC‐CO₂) solubilities of two series of symmetrically substituted alkylenediphosphonic acids, bearing 2‐ethylhexyl and 3‐trimethylsilyl‐1‐propyl ester groups, respectively, were determined as a function of the number of methylene groups separating the two phosphorus atoms. An even–odd effect, similar to that observed previously for the aggregation of these compounds in nonpolar diluents, was observed, with compounds that form more highly aggregated species in nonpolar diluents exhibiting lower solubility in SC‐CO₂. Differences in the relative solubilities of analogous members of these series prompted the study of the SC‐CO₂ solubilities of symmetrically substituted methylenediphosphonic acids bearing seven‐ and eight‐carbon ester groups of various degrees of branching to determine the relative importance of steric and electronic effects in determining SC‐CO₂ solubilities. When molecular connectivity indices were used to quantify the extent of branching in the ester groups, a remarkable correlation between these molecular descriptors and SC‐CO₂ solubility was observed.

^#Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy under contract number W‐31‐109‐ENG‐38.

^‡The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W‐31‐109‐ENG‐38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Keywords:

• SC‐CO₂
• Solubility
• Diphosphonic acid
• Seven‐ and eight‐carbon ester
• Molecular connectivity

Acknowledgments

This work was performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences (SC‐CO₂ studies) and the Environmental Management Sciences Program of the Offices of Science and Environmental Management (extractant syntheses), US Department of Energy, under grant number DE‐FG07‐98ER14928 (LUC) and W‐31‐109‐ENG‐38 (ANL). The authors thank Loyola University Chicago for Dissertation Fellowship support (JAD and DCS) and the Department of Education for support through a GAANN Fellowship (DRM and PRZ). The authors also thank Dr. Joan Brennecke (Department of Chemical Engineering, University of Notre Dame) for helpful advice and discussions.

Notes

^#Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy under contract number W‐31‐109‐ENG‐38.

^‡The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W‐31‐109‐ENG‐38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.