Studies on Solute−Solvent Interactions in Gaseous and Supercritical Carbon Dioxide by High-Pressure 1H NMR Spectroscopy

Abstract

A newly designed high-pressure NMR flow cell has been developed for studies of supercritical fluids. By using the high-pressure cell, 1H chemical shifts of nonpolar (n-hexane and benzene) and polar (dichloromethane, chloroform, acetonitrile, water, methanol, and ethanol) solute molecules in gaseous and supercritical carbon dioxide were measured in the wide pressure range between 2 and 30 MPa at 313.3 K. The chemical shifts of hydroxyl protons of water, methanol, and ethanol in carbon dioxide at 20.0 MPa were shifted to higher frequency due to intermolecular hydrogen bonding with increasing concentration. A comparison of the concentration dependence with relevant data in carbon tetrachloride indicated a specific interaction between alcohol and carbon dioxide molecules. The corrected 1H chemical shifts of nonpolar and polar solute molecules at infinite dilution, where the bulk magnetic susceptibility contribution was subtracted, were shifted to higher frequency with increasing density of carbon dioxide. The...