HYDRATION AND AGGREGATION NEUTRAL OXYGEN-DONOR EXTRACTANTS HYDRATION AND AGGREGATION OF MONOFUNCTIONAL SULFOXIDE AND OTHER NEUTRAL OXYGEN-DONOR EXTRACTANTS: THE D1(2-ETHYLHEXYL) SULFOXIDE, DODECANE, WATER SYSTEM

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Abstract
The nature of the hydration and aggregation of di(2-ethylhexyl) sulfoxide (DEHSO) dissolved in wet dodecane at 25 °C has been characterized using Fourier transform infrared (FTIR) spectrophotometry, Karl Fischer titrations, and tritium-tracer equilibrium measurements. Least-squares computer modeling of the water content of 0.01-to-0.4 M DEHSO solutions equilibrated with water (optionally containing nonextractable CaCl2 to adjust the water activity ay in the range 0.28 to 1.0) indicates that the expected 1:1 species DEHSO H20 predominates at low DEHSO concentration (K11 = {DEHSO H20} / ({DEHS0]aw.) = 0.12 ± 0.01) with additional formation of hyarated dimeric species at the higher DEHSO concentrations. Analysis of the water vibrational bands in the FTIR spectra of 0.01-to-0.4 M DEHSO solutions in equilibrium with pure water supports the formation of both the 1:1 species and a dimer, identified by its spectral characteristics as the 2:1 dimer monohydrate. By reference to the available literature on the hydration of weak bases, the results suggest that at least part of the ‘nom'deaiityrsquo; of solutions of weak-base extractants in wet nonpolar diluents may be explained by formation of the discrete 1:1 and 2:1 monohydrate species.

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