HYDRATION OF PROPIONALDEHYDE, ISOBUTYRALDEHYDE, AND PIVALALDEHYDE . THERMODYNAMIC PARAMETERS, BUFFER CATALYSIS, AND TRANSITION STATE CHARACTERIZATION

Values of the thermodynamic parameters ΔG°, ΔH°, and ΔS° for the reversible hydrations of propionaldehyde isobutyraldehyde, and pivalaldehyde were determined using a spectrophotometric method. Short extrapolations of absorbancy to time zero allow the accurate determination of the molar extinction coefficient for the n-π* absorption of the unhydrated aldehydes in water solvent. Kinetic data on the hydronium ion, acetic acid, acetate ion, dihydrogen phosphate ion, monohydrogen phosphate ion, diethylmalonate dianion, hydroxide ion, and water catalysis are presented for all three aldehydes. The data are shown to be consistent with a concerted mechanism of hydration-dehydration.