(18)O/(16)O isotope effect on miscibility of isobutyric acid with water |
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Authors: | Siporska Agnieszka Makowska Anna Szyd?owski Jerzy |
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Institution: | Faculty of Chemistry, University of Warsaw, Zwirki Wigury 101, 02-089, Warsaw, Poland. |
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Abstract: | The miscibility of isobutyric acid with water and the influence of the isotope substitution of oxygen (16O/18O) in water over a broad concentration range are reported. The system exhibits a phase diagram with an upper critical solution temperature (UCST) and a visible isotope effect thereon. The oxygen isotope substitution decreases the UCST, leading to better miscibility of isobutyric acid with water. The isotope shift, DeltaTc = Tc(18O) - Tc(16O), extrapolated to the 100% enrichment in 18O, is equal to -1.15 K; hence it is much smaller and opposite to that found for deuterium substitution. The origin of the observed miscibility isotope effect has been qualitatively discussed in terms of the condensed-phase isotope effect theory. |
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