Alcohol tracer diffusion, density, NMR and FTIR studies of aqueous ethanol and 2,2,2-trifluoroethanol solutions at 25°C

Abstract

New measurements have been made of the tracer diffusion coefficients of ethanol and 2,2,2-trifluoroethanol (TFE) in aqueous solution at 25°C across the whole composition range. The limiting values at infinite dilution of these alcohols and the series of primary alcohols from methanol to heptanol, the isomeric propanols and butanols and 2-butoxyethanol are found to vary as the alcohol limiting partial molar volume raised to the power -0.56. The self-diffusion coefficient of water lies on the same curve, suggesting that the rate-determining step for diffusion is the same for these alcohols at infinite dilution as it is for water. ¹H, ¹⁹F and ¹³C chemical shift and density measurements have been made and apparent molar volumes obtained from the latter. The composition dependence of the ν₂ bending vibration band of water in water–TFE at 1640 cm^-1 has been examined. The chemical shift and water IR measurements show that water–TFE behaves like other aqueous halogenoethanol solutions with water and hydroxyl proton shifts moving to higher field with increasing alcohol concentration. The results are consistent with thermodynamic data indicating some degree of microheterogeneity in the TFE-rich region of this system and a strengthening of water–TFE H-bonding on dilution of TFE. This is the opposite of what is observed for water–ethanol. We were unable to find any evidence from the diffusion data for the formation of water adducts to ethanol chains at high ethanol concentration in water–ethanol mixtures as has been suggested in the literature.