Ion Pair Formation in Solutions of Alkali Halides in Dimethyl Sulfoxide: Ultrasonic Absorption Studies

Abstract

The ultrasonic absorption of dimethyl sulfoxide solutions of several alkali halides has been studied in the frequency range 1.5 to 52 MHz. An excess absorption, relaxing between 3 and 8 MHz, was observed. The relaxation was assigned to the final step in the stepwise formation of a contact ion pair, with the relaxation frequency controlled by the rate of movement of a solvent molecule rather than an ion. Data on the system water – dimethyl sulfoxide are also presented and the effect of water on the relaxation discussed.

Titrations in nonaqueous solvents

“…Dimethyl Sulfoxide. This substance has been used pure (27,66,74,122,161,193,194) and mixed with water (10,74,192) and alcohols (10) as a solvent for titration using potentiometric (27,66,161,193,194), indicator (10,193,194), and conductometric (122,192) methods. A potentiometric method for detecting thio and sulfide impurities in DMSO has been developed (144).…”

“…Spectroscopic studies on solvent-solute interactions for halide ions (285,286) indicate that the preferential solvation did not occur in DMS0-H20 mixtures. Contact ion pairs were detected for solutions of alkali halides in DMSO from ultrasonic absorption studies (74). Cryoscop-ic measurements indicated that H2C2O4, CI3CCO2H, and picric acid were 100% ionized; CI2CHCO2H, 50% ionized; and C6H5CO2H, CICH2CO2H, salicyclic, tartaric, succinic, maleic, fumeric, and phthalic acids were less than 10% ionized in DMSO (3).…”