TITLE:
A Proton Nuclear Magnetic Resonance (1H NMR) Investigation of NaCl-Induced Phase Separation of Acetonitrile-Water Mixtures
AUTHORS:
Ruizhi Wen, Muqian Yu, Le Jiang, Lili Feng, Wenjie Deng, Bo Chen
KEYWORDS:
1H NMR, NaCl, Phase Separation, Acetonitrile-Water Mixtures, Hydrogen Bond
JOURNAL NAME:
American Journal of Analytical Chemistry,
Vol.8 No.10,
October
27,
2017
ABSTRACT: The microscopic properties of NaCl-induced phase
separation of acetonitrile (ACN)-water mixtures have been studied by proton
nuclear magnetic resonance (1H NMR). Acetonitrile-rich phase
increases with increasing NaCl concentration (cNaCl) at xACN ≈ 0.25. 1H chemical shift of water for
acetonitrile-rich phase rapidly decreases with decreasing NaCl mole
concentration and that for water-rich phase quickly increases with increasing cNaCl. However, 1H chemical shift of acetonitrile has
nothing to do with the molar concentration of NaCl, and it keeps relatively
stable for all solutions (±0.002). These results reveal that Na+ and Cl- are
rapidly hydrated by water, not by acetonitrile. The change of 1H
chemical shift of water has shown that the number of hydrogen bond increases or
hydrogen bond strengths with increasing NaCl molarity in mixtures. But hydrogen
bond is broken or weaken with the temperature rising. 1H chemical
shifts of pure water and the water in acetonitrile-rich phase have been investigated
at 293 K, 298 K and 303 K. The hydration number of Na+ (6.05) in water-rich
phase is determined by an empirical equation involving 1H chemical
shift, temperature and NaCl molarity, which is in good agreement with the literatures.