Heat of mixing profile, complexation curve and spectroscopic investigation of binary mixtures containing bicyclic Brønsted superbase DBN with hydrogen ethanoate

Highlights: • Binary mixtures of DBN with AcOH are strongly exothermic and highly non-ideal. • Superbase character of DBN, known in aqueous solution, is retained in the non-aqueous mixtures. • The partial molar excess enthalpy $x_{\mathrm{AcOH}}{H}_{\mathrm{AcOH}}^E$ dominates $H^E$. • AcOH reacts with [AcO]⁻ anionsto form diacetatohydrogenate(I) anions, [H(OAc )₂]⁻. Isothermal titration calorimetry (ITC) experiments were performed for investigation of binary mixtures comprised of the Brønsted superbase DBN with hydrogen ethanoate (AcOH). The heat of mixing ($H^E$) profile was recorded at (343.15 ± 0.1) K and fitted with a 5-parameter Redlich-Kister (RK) polynomial. RK fit parameters were subsequently used to quantify partial molar heats of mixing, $x_i{H}_i^E$, for each component i. ITC-based complexometric titration data for the binary mixtures were recorded separately in methyl isobutyl ketone (mibk) and dodecane, to investigate the energetics of non-random clustering phenomena. Variable temperature ¹H-NMR in combination with ATR-FTIR spectroscopic analyses were employed in parallel for elucidation and verification of liquid state ion speciation. These investigations reveal a strongly non-ideal system, and indicate "superbase" character of DBN is preserved for specific compositions where stoichiometric ionic liquids (ILs) form. Available ion speciation has been found to include [DBN-H]⁺, [AcO]⁻ as well as μ₂-hydrogen-bridged, hydrogen-bonded homoassociate anions, of the type [H(OAc)₂]⁻, with double liquid salt formation characterising various compositions based on spectroscopic determinations.