title: Thermodynamic investigations of methyl tert-butyl ether and water mixtures.
abstract: Interactions between methyl tert-butyl ether (MTBE) and water have been investigated by scanning calorimetry, isothermal titration calorimetry, densitometry, IR-spectroscopy, and gas chromatography. The solubilization of MTBE in water at 25 °C at infinite dilution has ΔH° = -17.0 ± 0.6 kJ mol(-1); ΔS° = -80 ± 2 J mol(-1) K(-1); ΔC(p) = +332 ± 15 J mol(-1) K(-1); ΔV° = -18 ± 2 cm(3) mol(-1). The signs of these thermodynamic functions are consistent with hydrophobic interactions. The occurrence of hydrophobic interaction is further substantiated as IR absorption spectra of MTBE-water mixtures show that MTBE strengthens the hydrogen bond network of water. Solubilization of MTBE in water is exothermic whereas solubilization of water in MTBE is endothermic with ΔH° = +5.3 ± 0.6 kJ mol(-1). The negative mixing volume is explained by a large negative contribution due to size differences between water and MTBE and by a positive contribution due to changes in the water structure around MTBE. Henry's law constants, K(H), were determined from vapor pressure measurements of mixtures equilibrated at different temperatures. A van't Hoff analysis of K(H) gave ΔH(H)° = 50 ± 1 kJ mol(-1) and ΔS(H)° = 166 ± 5 J mol(-1) K(-1) for the solution to gas transfer. MTBE is excluded from the ice phase water upon freezing MTBE-water mixtures.
authors.affiliation: Dept. of Life Science, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark. tbn@bio.aau.dk
authors.forename: Troels Bach
authors.initials: TB
authors.lastname: Nielsen
authors.forename: Søren
authors.initials: S
authors.lastname: Hvidt
authors.forename: Søren Rud
authors.initials: SR
authors.lastname: Keiding
authors.forename: Christian
authors.initials: C
authors.lastname: Petersen
authors.forename: Peter
authors.initials: P
authors.lastname: Westh
authors.forename: Kristian
authors.initials: K
authors.lastname: Keiding
mesh_terms: D002152:Calorimetry, Differential Scanning; D002849:Chromatography, Gas; D003720:Densitometry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008738:Methyl Ethers / Q000737:chemistry*; D013055:Spectrophotometry, Infrared; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D008738:Methyl Ethers; D014867:Water; C043243:methyl tert-butyl ether