Enthalpies of transfer of the CH 2 moiety into aqueous acetonitrile mixtures; comparison of values from n-alcohols and tetraalkylammonium ions; effect of temperature variation

Abstract

The enthalpies of solution of ethanol, n-butanol, n-pentanol and n-octanol into aqueous acetonitrile mixtures at T = (288.2 and 283.2) K are reported. These data are combined with literature values for the n-alcohols at T = 298.2 K and for a range of tetraalkylammonium bromides at several temperatures to allow determination of the enthalpy of transfer of CH 2 moieties, Δ t H ∘(CH 2), from acetonitrile to the aqueous mixed solvents. It is found that the Δ t H ∘(CH 2) values pass through minima at intermediate solvent compositions, with the minimum becoming deeper with decreasing temperature and with increasing chain length. It is proposed that these minima originate from microphase formation of the aqueous acetonitrile mixtures.