Chemical structure and surface activity. Part XIII. The effect of oxygen on surface properties of 2-(2-alkoxyethyl)-1,3-dioxacyclanes

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Solubility and surface tension measurements were performed for 2-(2-alkoxyethyl)-1,3-dioxolanes, 1, 2-(2-alkoxyethyl)-4-methyl-1,3-dioxolanes, 2, and 2-(2-alkoxyethyl)-1,3-dioxanes, 3, in 10 −4 M aqueous solution of sodium carbonate at 293.2 K. The alkyl substituent, R, in these compounds was varied from C 2H 5 to n-C 6H 13. From the solubility values, the standard free energies for transfer of the compounds from the aqueous solution to the pure liquid phase, Δ G 0 t, were calculated, as well as the contributions of individual parts of molecules to the Δ G 0 t values. The surface tension isotherms were used to calculate the efficiency of surface tension reduction, pC 20, the surface excess, Γ, the surface area per molecule in the adsorption layer, A, and the standard free energy of adsorption, Δ G 0 a,Π=20, as well as the contributions of given parts of molecules to the Δ G 0 a,Π=20 values. It was shown that the enlargement of 1,3-dioxacyclane ring by one methylene group does not significantly affect either the value of Δ G 0 t or Δ G 0 a,Π=20. The increment Δ G 0 t[−CH 3] of the methyl group at the C-4 carbon atom of the 1,3-dioxolane ring contributes with only ∼0.28 of the value of Δ G 0 t[CH 3−] for the alkyl substituent. Using known values of increments for five- and six-membered rings in 2-alkyl-1,3-dioxacyclanes, the increments Δ G 0 t[−OCH 2CH 2−] and Δ G 0 a [−OCH 2CH 2−] Π=20 for compounds 1–3 were calculated. These increments are in the range −0.1 to +0.9 kJ mol −1, indicating that the introduction of an ether-oxygen between the methylene groups β and γ ofthe alkyl chain at the C-2 carbon atom of the 1,3-dioxacyclane ring balances the hydrophobic character of the two methylene groups in positions α and β with respect to the ring.