Thermochemical behaviour of straight-chain ethers CH 3O(CH 2CH 2O) nCH 3 ( n = 1–4) in aqueous and tetrachlormethane solutions

Abstract

The enthalpies of solution Δ sol H m of straight-chain polyethers CH 3O(CH 2CH 2O) n CH 3 ( n = 1–4) have been measured in water and tetrachlormethane as inert reference solvent at temperature of 298.15 K. The enthalpic coefficients of pairwise interaction and enthalpies of solvation were determined. The interaction between ether molecules in inert solvent are dominated by electrostatic forces resulting in the negative coefficients of interaction. In water the coefficients of interaction are positive. This is because the partial destruction of hydrophobic and hydrophilic shells becomes the predominant contribution to the coefficient. The enthalpy of solvation of one ethane oxide group in water is more negative than in tetrachlormethane by −7.4 kJ mol −1 that was related to the prevailing contribution of hydrogen bonding between ether and water molecules. The comparison of enthalpic characteristics was performed for the open-chain and cyclic ethers. The more exothermic effect of hydration of CH 2CH 2O group is observed for cyclic ethers. The distinction is connected with strengthening of hydrogen-bond bridges between adjacent ether oxygen atoms in cyclic molecule.