Gibbs energies of transfer of the proton from water into mixtures of water with chain multiple ethers: Equilibria involving changes of solvation of the proton

Abstract

The solvent reorganisation around the proton has been investigated in mixtures of water with the dimethyl ethers of diethylene glycol and triethylene glycol using spectrophotometric observations on dilute solutions of 4-nitroaniline. The protonation occurs at only one basic site on the multiple ethers and the equilibrium constant is much greater than for simple ethers and alcohols. The Gibbs energy of transfer of the proton from water into the mixture is calculated. Comparing ΔG^o_t(H⁺) with those for simple ethers and alcohols, it is concluded that the end ether group is the preferred basic site in the multiple ethers. ΔG^o_t(H⁺) from this method are compared with ΔG^o_t(H⁺) determined using the TATB method for a range of co-solvents: good agreement is obtained, except where enhanced structure is found in the water + co-solvent mixtures.