Calorimetric investigation of the complex formation reaction of 18-crown-6 ether with d,l-alanine in water–ethanol mixtures

The standard thermodynamic parameters (Δ r G °, Δ r H °, and T Δ r S °) of the reaction of molecular complex formation of 18-crown-6 ether (18C6) with d , l -alanine (Ala), [Ala18C6], have been obtained from calorimetric titration experiments carried out using the microcalorimetric system TAM III (TA Instruments, USA) at T = 298.15 K in water–ethanol (H 2 O–EtOH) solvents at X EtOH = 0 ÷ 0.6 mol fractions. Results show that the increase of the EtOH concentration in solvent brings about an increase of the [Ala18C6] complex stability and of the exothermicity of the reaction of complex formation. The solvation contributions of 18C6, Ala, [Ala18C6] to Δ r G ° and Δ r H ° at various X EtOH values are also analyzed.