Solvation Of Reagents Research Articles

Predictive calculation of the stability constants of silver(I) ion with pyridine and 2,2′-bipyridyl in a solvent environment

In the present study, the stability constants of silver(I) coordination compounds with 2,2′-bipyridyl (bpy, L) in mixed methanol–acetonitrile solvents (MeOH-AN, χAN = 0.0 ÷ 1.0 mol fr.) were determined by the potentiometric method at 25.0 °C. The influence of reagents solvation on the change in stability of [Ag(bpy)]+ and [Ag(bpy)2]+ complexes upon changing the composition of the solvent MeOH→(MeOH-AN) was analyzed. It has been established that the determining factor in the shift of the complex formation equilibrium along the first and second steps of coordination with a change in the composition of the solvent is the contribution from the central ion resolvation. The obtained results and data on the thermodynamics of complex formation reactions of Ag+ with bpy and pyridine (py, L) in a few binary non-aqueous solvents were compared. The possibility of carrying out an estimated calculation of the stability constants of [Ag(L)]+ in non-aqueous solvents was confirmed.

Thermodynamics of reactions of stepwise complex formation of silver(I) ion with pyridine in binary solvents

In this study, the enthalpies of stepwise complexation reactions between silver(I) ions and pyridine in methanol–acetonitrile mixed solvents (MeOH-AN, with molar fractions of AN varying from 0 to 1) were determined by the calorimetric method at 298.15 K. The analysis of the solvation contributions of the reactants to the alterations in the thermodynamic characteristics associated with the formation of [AgPy]+ and [AgPy2]+ complexes as the solvent composition transitions, i.e. from methanol to its mixtures with acetonitrile (MeOH → χAN), from methanol to its mixtures with N,N-dimethylformamide (MeOH → χDMF) and from acetonitrile to its mixtures with dimethyl sulfoxide (AN → χDMSO) was carried out. The research methodology was based on the provisions of the solvation-thermodynamic approach, based on the relationship between changes in the thermodynamic characteristics of the reactions of complex formation and solvation of reagents with a change in the composition of the solvent.

The effect of reagents solvation on change in the stability of coordination compounds of silver(I) ion with pyridine in mixed methanol–acetonitrile solvents

In this study, potentiometric titration was used to determine the stability constants of mono- and bis(pyridine) complexes with silver(I) in mixed methanol–acetonitrile solvents. Gibbs free energies of transfer of pyridine from methanol to methanol–acetonitrile mixtures were determined by the method of distribution between two immiscible phases. The effect of solvent composition on change in the solvation state of pyridine was analyzed. The replacement of methanol by acetonitrile leads to the desolvation of pyridine. The resolvation of pyridine occurs predominantly due to the resolvation of the nitrogen atom at the concentration of acetonitrile >0.5 mol fr. The enthalpic contribution was shown to have a major contribution in ΔtrG0(Py)MeOH→(MeOH-AN). The effect of reagents solvation on the stability of [AgPy]+ and [AgPy2]+ complexes upon the change of the solvent composition was investigated. The resolvation of silver(I) was established to be a key factor controlling the stability of both complexes in MeOH-AN mixtures. The possibility of predictive calculation of the stability constants [AgPy]+ in individual and mixed non-aqueous solvents through the change in the Gibbs free energy of the solvation of the complexing ion was shown. Proper data are compared with data reported in the literature.

Complexation of Cyclodextrins with Benzoic Acid in Water-Organic Solvents: A Solvation-Thermodynamic Approach.

The aim of this research is to obtain new data about the complexation between β-cyclodextrin (β-CD) and benzoic acid (BA) as a model reaction of the complex formation of hydrophobic molecules with cyclodextrins (CDs) in various media. This research may help developing cyclodextrin-based pharmaceutical formulations through the choice of the appropriate solvent mixture that may be employed in the industrial application aiming to control the reactions/processes in liquid phase. In this paper, NMR results for the molecular complex formation between BA and β-CD ([BA⊂β-CD]) in D2O-DMSO-d6 and in D2O-EtOH have shown that the stability of the complex in the H2O-DMSO-d6 varies within the experimental error, while decreases in H2O-EtOH. Changes in the Gibbs energy of BA resolvation in water and water–dimethylsulfoxide mixtures have been obtained and have been used in the analysis of the reagent solvation contributions into the Gibbs energy changes of the [BA⊂β-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between β-CD and BA as well as the structure of the [BA⊂β-CD] complex and the energy of β-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BA⊂β-CD] complex in H2O-EtOH and H2O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BA⊂β-CD] molecular complexation as well as the reagent solvation contributions in H2O-EtOH and H2O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.

Effect of cyclodextrin types and reagents solvation on the stability of complexes between B-cyclodextrins and rutin in water-ethanol solvents

In this work, the solubility of rutin was first obtained in the water-ethanol solvents with small composition of co-solvent in the mixture at 25 °C. The results showed that the solubility of rutin improved with increasing ethanol content in the studied range 0–0.1 mol. fr. Solvation of hydroxypropyl-β-cyclodextrin in binary solvents was first studied by the method of interfacial distribution of the substance between two immiscible phases. It was found that when moving hydroxypropyl-β-cyclodextrin from water to the water-ethanol solvent, a decrease in the solvation of hydroxypropyl-β-cyclodextrin was observed. Complexation between rutin and β-cyclodextrin or hydroxypropyl-β-cyclodextrin was also studied in water and in the water-ethanol solvents. In the aqueous solution containing hydroxypropyl-β-cyclodextrin, the solubility of rutin was improved significantly and better than in the solution containing β-cyclodextrin. The stability of (rutin-hydroxypropyl-β-cyclodextrin) complex decreased with increasing the ethanol content and was determined by the sum of solvation of rutin (ΔtrGRuT) and hydroxypropyl-β-cyclodextrin (ΔtrGHPβCD). This effect was also observed for the complexation reaction between quercetin and hydroxypropyl-β-cyclodextrin in our previous study.

Reaction acceleration at air‐solution interfaces: Anisotropic rate constants for Katritzky transamination

To disentangle the factors controlling the rates of accelerated reactions in droplets, we used mass spectrometry to study the Katritzky transamination in levitated Leidenfrost droplets of different yet constant volumes over a range of concentrations while holding concentration constant by adding back the evaporated solvent. The set of concentration and droplet volume data indicates that the reaction rate in the surface region is much higher than that in the interior. These same effects of concentration and volume were also seen in bulk solutions. Three pyrylium reagents with different surface activity showed differences in transamination reactivity. The conclusion is drawn that reactions with surface-active reactants are subject to greater acceleration, as seen particularly at lower concentrations in systems of higher surface-to-volume ratios. These results highlight the key role that air-solution interfaces play in Katritzky reaction acceleration. They are also consistent with the view that reaction-increased rate constant is at least in part due to limited solvation of reagents at the interface.

Кинетика и механизм реакций ацильного переноса. Часть 15. Квантово-химическое моделирование механизмов реакций сульфонилирования N-этиланилина

The RHF/6-31G(d) quantum chemical simulation of the mechanism of the interaction of the secondary fatty aromatic amine N-ethylaniline with benzenesulfonyl chloride under conditions of non-specific water solvation, using the continuum model of the solvent, as well as of sulfonylation reactions of N-ethylaniline solvation complexes containing one water molecule, modeled specific solvation of N-ethylaniline with water, and one molecule of water and one of dioxane, which simulate the solvation of the amine with aqueous dioxane. Three-dimensional potential energy surface of these processes is calculated. It is shown that in the case of a reaction proceeding under conditions of non-specific solvation of reagents, the route with axial attack of the N-ethylaniline molecule to the sulfonyl reaction center is realized, in the two other cases the reactions proceed along a single route, starting as an axial attack of the nucleophile, which goes further with decreasing of the attack angle as reagent molecules approach each other. It was established that all the simulated reactions proceed in accordance with bimolecular coordinated mechanism of nucleophilic substitution SN2, which implies the formation of a single transition state in the reaction path. It was found that geometrical configuration of the reaction center in the transition state of N-ethylaniline reaction with benzenesulfonyl chloride under non-specific solvation by water is close to trigonal-bipyramidal, which is determined by the axial direction of the nucleophilic attack, in the two other cases it is medium between the trigonal-bipyramidal and tetragonal-pyramidal, which is associated with the change in the angle of N-ethylaniline attack as the reactant molecules approach each other. In a reaction involving N-ethylaniline monohydrate, a water molecule forms a 6-membered cyclic structure with reagent molecules in the transition state, in which the transfer of a proton from N-ethylaniline amino group to a hydrogen chloride molecule occurs via a relay mechanism involving the water molecule. The activation energy values of the studied processes were calculated; it is shown that both specific and universal solvation significantly lower the energy barrier of the reaction compared to the reaction occurring in gas phase, which is consistent with the data obtained earlier for related processes.

Reactivity Variation of Tetracyanoethylene and 4-Phenyl-1,2,4-Triazoline-3,5-Dione in Cycloaddition Reactions in Solutions

The reasons for the very high reactivity and variability of reactivity of two dienophiles, tetracyanoethylene (1) and 4-phenyl-1,2,4-triazoline-3,5-dione (2), in the Diels–Alder reactions were considered. The data on the rate of reactions with anthracene (3), benzanthracene (4) and dibenzanthracene (5) in 14 solvents over a range of temperatures and high pressures, data on the change in the enthalpy of solvation of reagents, transition state, and adducts in the forward and backward reactions, and the enthalpies of these reactions in solution were obtained. Strong π-acceptor dienophile 1 has sharply reduced reactivity in reactions in π-donor aromatic solvents. It was observed that the π-acceptor properties of dienophile 1 disappear upon passage to the transition state and adduct. Large solvent effects on the reaction rate can be predicted for all types of reactions involving tetracyanoethylene. Very high reactivity of dienophiles 1 and, especially, 2 can be useful to catch such carcinogenic impurities such as 3–5 and neutralize them by transformation into less dangerous adducts.

Molecular complexes and solvation interactions in the reaction of quinone imines with thiols

This study aims to investigate the role of complexation between reagents and the role of solvation of reagents by solvents in the kinetics of chain reactions of quinone imines with thiols. The thermodynamic characteristics of the complexation of quinone imines with thiophenol in CCl4, chlorobenzene, and ethanol, as well as of the complexation of quinone imines and thiophenol with these solvents were calculated by quantum chemical methods (DFT calculations at the PBE/cc-pVDZ level of theory) and in terms of the additive-multiplicative model. Both approaches give consistent results. The formation of molecular complexes in quinone imine–thiphenol systems is accompanied by a 10–30 kJ mol–1 decrease in enthalpy and has only a slight effect on the reaction mechanism.

Influence of reagents solvation on [Ag18C6]+ complex formation in methanol‒acetonitrile mixed solvents

The influence of the composition of the methanol—acetonitrile (MeOH—AN) solvent on the solvation of 18-crown-6 ether (18C6) has been studied. Increasing fraction of AN in the binary solvent stabilizes the 18C6 solvation complex by increasing the exothermicity of 18C6 solvation. Analysis of the solvation contributions of the reagents to the enthalpies of complex formation of silver(I) ion with 18C6 in MeOH—AN mixtures has been performed to establish that the decrease in the exothermicity of complex formation in going from MeOH to AN is mostly associated with the solvation contribution of Ag(I).

Influence of aqueous dimethyl sulfoxide on pyridoxine protonation and tautomerization

The constants of pyridoxine (vitamin B6) protolytic and tautomeric equilibria were determined by means of potentiometry and spectrophotometry respectively in wide range of binary solvent (aqueous dimethyl sulfoxide) compositions. The free Gibbs energies of pyridoxine molecular and zwitterionic species transfer from water to aqueous DMSO were obtained using method of partition between immiscible phases. These results were employed for discussing the transmembrane transport capability of B6 vitamin. The influence of mixed solvent composition on pyridoxine protonation was analyzed taking into account the reagents solvation data.

Protolytic and tautomeric equilibria of pyridoxine in aqueous ethanol

The present work reports the constants of pyridoxine (vitamin B6) protolytic and tautomeric equilibria determined by means of potentiometry and spectrophotometry respectively in wide range of binary solvent (aqueous ethanol) compositions. The Gibbs energies of pyridoxine molecular and zwitterionic forms transfer from water to aqueous ethanol were obtained using method of partition between immiscible phases. The dependences of equilibrium processes constants on mixed solvent composition were analyzed taking into account the reagents solvation data. The transmembrane transport capability of B6 vitamin was discussed. The effect of binary solvent composition on pyridoxine reactivity towards nucleophilic substitution reactions including phosphorylation reaction was estimated by quantum chemical calculations.

Thermodynamics of nickel(II) and iron(III) complexation with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide

The complexation of Ni(II) and Fe(III) with nicotinamide in aqueous ethanol and aqueous dimethyl sulfoxide was directly studied by calorimetry at T=298.15K and ionic strength value 0.25 (NaClO4). The results of thermochemical study were discussed using solvation-thermodynamic approach basing on the accounting of reagents solvation. The absence of contact ion pairing between Ni2+ and ClO4- was observed by IR-spectroscopy at ionic strength value 0.25. Nicotinamide was found to replace the water molecule within cation coordination sphere by means of UV–Vis spectroscopy.

Higher enantioselectivities in thiourea-catalyzed Michael additions under solvent-free conditions

Enantioselective Michael additions catalyzed by hydrogen-bonding catalysts produce many important compounds. Solvent-free reaction conditions in a ball mill can provide an improved enantioselectivity over the reaction in solution, due to lack of disruptive solvation of reagents. A range of 15 structurally different hydrogen-bonding organocatalysts were tested in two Michael additions to β-nitrostyrene under solvent-free conditions and compared with corresponding experiments in solution. With several thiourea catalysts, these Michael additions proceeded with higher enantioselectivities under solvent-free conditions than in solution.

Solvation of reagents in a silver(I)-nicotinamide coordination equilibrium in water-ethanol solutions, according to NMR data

The solvation state of nicotinamide in water-ethanol solvent is investigated by means of 1H and 13C NMR spectroscopy. It is found that the nitrogen heteroatom is resolvated at x EtOH = 0.05–0.25. The resolvation boundary of the silver(I) ion is determined by nuclear magnetic relaxation. The relationship between the structural and thermodynamic characteristics of the solvation of nicotinamide and the silver(I) ion is demonstrated.

Experimental and theoretical studies on polar Diels–Alder reactions of 1-nitronaphathalene developed in ionic liquids

The reactions between 1-nitronaphthalene 1 and two nucleophilic dienes, Danishefskýs diene 2 and 1-trimethylsilyloxy-1,3-butadiene 3, to yield phenanthrenols 7 and 8 developed in protic and aprotic ionic liquids (ILs) with an imidazolium cation base permit to conclude that the reactions occur in better experimental conditions than in molecular solvents. The yields obtained with protic ILs are better than those observed with aprotic ILs. In this sense, the higher yields obtained with aprotic ILs, (working at 60 °C, 48 h) are comparable with the lower yields observed in protic ILs (60 °C, 24 h). DFT calculations for the reaction of 1-nitronaphthalene 1 with diene 3, in the absence and in the presence of tetrafluoroborate of 1-metilimidazolium [HMIM][BF4] as protic ILs, indicate that this reaction is a domino process that comprises two consecutive processes: i) a polar Diels–Alder (P-DA) reaction between 1 and 3, and ii) an elimination of nitroso acid 5 to yield dihydrophenanthrene 11. Thermodynamic calculations indicate that while the first reaction is the rate-determining step of this domino process, the nitroso acid elimination is the driving force responsible for the formation of dihydrophenanthrene 11. Implicit and explicit solvent effects indicate that while the hydrogen bond formation between HMIM and one oxygen atom of the nitro groups favour the two reactions, implicit solvent effects modelled by PCM decelerate the P-DA reaction by a large solvation of reagents. Finally, DFT analysis of reagents offers an explanation of the catalytic role of protic ILs in these P-DA reactions.

Thermochemical characteristics of nicotinamide protolytic equilibria in water-dimethylsulfoxide mixtures

The heat effects of nicotinamide protonation in water-dimethylsulfoxide (DMSO) solutions over the concentration range 0–0.75 DMSO mole fractions were determined calorimetrically at 25.00 ± 0.01°C and ionic strength 0.25 (NaClO4). Changes in the enthalpy of protonation as the content of DMSO increased were found to be described by an S-shaped curve. This curve shape was caused by the dynamics of reagent solvation contributions as the concentration of DMSO grew with the predominance of the nicotinamide solvation contribution.

Calculating the solvation contributions from reagents to the change in enthalpy of silver(I) complexation with 18-crown-6 ether in binary methanol-acetonitrile solvents

The enthalpies of the transfer of silver(I) ions from methanol to mixed methanol-acetonitrile solvents are calculated using the literature data. An estimative calculation of the enthalpies of transfer of the reaction of formation of [Ag18C6]+ upon a change in the solvent composition MeOH → AN is performed on the basis of previously found laws of change in the thermodynamic characteristics of complexation and solvation of reagents. It is shown that the governing factor in the change in the energy of the reaction is the enhancement of the solvation of the central ion.

The influence of reagents solvation on enthalpy change of glycine-ion protonation and silver(I) glycine-ion complexation in aqueous-dimethylsulfoxide solutions

The calorimetric method was used to determine the heats of glycine-ion (Gly−) protonation and silver(I) glycine-ion complexation at the ionic strength 0.3 (NaClO4) and 298 K in the range of mixed solvent composition of 0.0 < χ < 0.3 and 0.0 < χ <0.4 molar fraction of dimethylsulfoxide, respectively. Anomalous ratio of enthalpies change of step formation of mono-glycinate and bis-glycinate complexes in water was revealed. The exothermicity of second ligand joining is almost twice the coordination effect of the first one. It was shown the decrease of glycine-ion solvation is the main reason of enthalpies change in case of glycine-ion protonation and silver(I) glycine-ion complexation in aqueous-dimethylsulfoxide solutions.

The influence of solvation on the formation of Ag+ complexes with 18-crown-6 ether in water-dimethyl sulfoxide solvents

The Gibbs energies of transfer of 18-crown-6 ether from water into water-dimethyl sulfoxide (DMSO) solvents (χDMSO = 0.0–0.97 mole fractions) at 298.15 K were determined by the interphase distribution method. Changes in the composition of the aqueous-organic solvent did not cause noticeable changes in the stability of 18-crown-6 ether solvato complexes. Reagent solvation contributions to shifts of complex formation equilibrium between silver(I) and 18-crown-6 ether when water was replaced with dimethyl sulfoxide were analyzed.