Complexation of Phenol and Thiophenol by Amine N‐Oxides: Isothermal Titration Calorimetry and ab Initio Calculations

Abstract

To develop a new solvent-impregnated resin (SIR) system for removal of phenols from water, the complex formation of dimethyldodecylamine N-oxide (DMDAO), trioctylamine N-oxide (TOAO), and tris(2-ethylhexyl)amine N-oxide (TEHAO) with phenol (PhOH) and thiophenol (PhSH) is studied. To this end we use isothermal titration calorimetry (ITC) and quantum chemical modeling (on B3LYP/6-311G(d,p)-optimized geometries: B3LYP/6-311+G(d,p), B3LYP/6-311++G(2d,2p), MP2/6-311+G(d,p), and spin component scaled (SCS) MP2/6-311+G(d,p); M06-2X/6-311+G(d,p)//M06-2X/6-311G(d,p), MP2 with an extrapolation to the complete basis set limit (MP2/CBS), as well as CBS-Q). The complexes are analyzed in terms of structural (e.g., bond lengths) and electronic elements (e.g., charges). Furthermore, complexation and solvent effects (in benzene, toluene, and mesitylene) are investigated by ITC measurements, yielding binding constants K, enthalpies ΔH(0), Gibbs fre energies ΔG(0), and entropies ΔS(0) of complex formation, and stoichiometry N. The ITC measurements revealed strong 1:1 complex formation between both DMDAO-PhOH and TOAO-PhOH. The binding constant (K=1.7-5.7×10(4) M(-1)) drops markedly when water-saturated toluene was used (K=5.8×10(3) M(-1)), and π-π interaction with the solvent is shown to be relevant. Quantum mechanical modeling confirms formation of stable 1:1 complexes with linear hydrogen bonds that weaken on attachment of electron-withdrawing groups to the amine N-oxide moiety. Modeling also showed that complexes with PhSH are much weaker than those with PhOH, and in fact too weak for ITC determination. CBS-Q incorrectly predicts equal or even higher binding enthalpies for PhSH than for PhOH, which invalidates it as a benchmark for other calculations. Data from the straightforward SCS-MP2 method without counterpoise correction show very good agreement with the MP2/CBS values.

Predicting solvent effects on relative volatility behavior in extractive distillation using isothermal titration calorimetry (ITC) and molecular modeling (MM)

“…Thermodynamics of interactions can be studied experimentally with ITC. It is widely applied in the fields of biomolecular chemistry and ligand-protein interactions (Falconer, 2016), and also for the study of solvent-solute interactions in separation processes (Cuypers et al, 2010a;Cuypers et al, 2010b;Sprakel and Schuur, 2018a). Examples of isotherms and an accuracy analysis of the thermodynamic data obtained with ITC for extraction processes were published in previous work (Sprakel and Schuur, 2018a, b;.…”

Thermal Activity in Affinity Separation Techniques Such as Liquid–Liquid Extraction Analyzed by Isothermal Titration Calorimetry and Accuracy Analysis of the Technique in the Molar Concentration Domain

“…ITC analysis for higher concentration domains was shown by Cuypers et al, , who studied interactions of phenols and thiophenols with phosphine oxide and phosphate extractants, and N -oxides . The concentrations applied by Cuypers et al , were approximately 1 mM for the phenols and 10 mM for the phosphine oxides, and no sensitivity or accuracy analysis was performed.…”

“…ITC analysis for higher concentration domains was shown by Cuypers et al, , who studied interactions of phenols and thiophenols with phosphine oxide and phosphate extractants, and N -oxides . The concentrations applied by Cuypers et al , were approximately 1 mM for the phenols and 10 mM for the phosphine oxides, and no sensitivity or accuracy analysis was performed. The use of ITC in this field enabled direct analysis of the interactions, whereas interactions between extractants and solutes otherwise are typically indirectly derived, and model parameters are fitted on measurements in heterogeneous systems.…”

Computational Study of Bond Dissociation Enthalpies for Substituted β‐O‐4 Lignin Model Compounds

“…[40][41][42] The M06-2X functional has been developed to improve the description of medium-range correlation, [43][44][45] which is important to compute hydrogen bonding. Hydrogen bonding has been accurately described by M06-2X in several systems, [43,[46][47][48][49][50][51] and the addition of dispersion changes the M06-2X results by less than 1.6 kcal mol À1 , [47][48][49] making it unnecessary to include dispersion in this work. The functional has been parameterized to an extensive database and shows excellent performance for main-group thermochemistry and kinetics.…”