Hydrogen Bond Donor Acidity Research Articles

Solvatochromic parameters for binary mixtures of an ionic liquid with various protic molecular solvents

Solvatochromic parameters (E N , normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results. Predicted values of solvatochromic parameters (SP) (E N , normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.

Investigation of retention behavior of drug molecules in supercritical fluid chromatography using linear solvation energy relationships

In this study, the retention behaviors of pharmaceutical and drug-like compounds in supercritical fluid chromatography (SFC) with polar stationary phases were evaluated using linear solvation energy relationships (LSERs). We used more than 200 compounds, including mono-, di-substituted benzenes, and other marketed drugs with a wide range of solvation descriptors. The dominant contribution to positive retention was the hydrogen bond donor acidity of the solutes, particularly for pyridine and amino columns. That factor is determined by the difference in basicity between the mobile and stationary phases. Another significant contributor to retention behavior was the hydrogen bond acceptor basicity of the solutes made particularly for diol and amino columns. The hydrogen bond donating ability is small for cyano and pyridine stationary phases (or should be zero) since those two phases lack hydrogen bond donor groups. The LSER results showed that the SFC retention behavior of compounds using carbon dioxide–methanol with polar stationary phases was close to that reported for normal phase LC using hexane–methanol. As expected, mobile phases containing high percentages of modifier resulted in decreased retention times for most compounds. A greater knowledge of the nature of solute/stationary phase and solute/mobile phase allows a more rapid and efficient choice in high-throughput screening of compound libraries.

Hydrolysis of dimethylphenyltin(IV) and triphenyltin(IV) chlorides in different aqueous ethanol solutions

The hydrolysis of [(Me)2(Ph)Sn(IV)]+ and [(Ph)3Sn(IV)]+ has been investigated at 25 °C and different aqueous solutions of ethanol, using a combination of spectrophotometric and potentiometric techniques. The species formed together with their formation constants have been determined using the computer program Squad over a wide pH range of 1 to 11. The hydrolysis constants in different media were analyzed in terms of Kamlet and Taft parameters. Single-parameter correlation of the formation constants, K11 and K12, versus α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), and π* (dipolarity/polarizability) for both cases are relatively poor in all solutions, but multiparameter correlation represents significant improvement with regard to the single-parameter models. In this work, we have also used the normalized polarity parameter, ETN, alone and in combination with the Kamlet–Taft parameter to find a better correlation of the formation constants in different aqueous ethanol solutions.Key words: dimethylphenyltin(IV) chloride, triphenyltin(IV) chloride, hydrolysis constant, aqueous ethanol solutions, solvent effect.

Solvent Effects on Protonation and Complexation of Glutamic and Aspartic Acids with Molybdenum(VI) in Different Aqueous Solutions of Methanol

The formation constants of the species formed in the systems H+ + Mo(VI) + aspartic and glutamic acids and H+ + aspartic and glutamic acids have been determined in different aqueous solutions of methanol [(0 to 40) % v/v] at 25 °C and constant ionic strength (0.1 mol·dm−3 sodium perchlorate), using a combination of spectrophotometric and potentiometric techniques. The composition of the complexes was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with the amino acids of the type MoO3L2− at pH 5.8. The protonation and formation constants in various media were analyzed in terms of Kamlet and Taft’s parameters. Single-parameter correlations of the formation constant, KS, versus α (hydrogen-bond donor acidity), β (hydrogen-bond accepter basicity), and π* (dipolarity/polarizability) are poor in all solutions, but multiparameter correlations represent significant improvements with regard to the single-parameter models. Linear correlation is obser...

Unusual Solvatochromism within 1-Butyl-3-methylimidazolium Hexafluorophosphate + Poly(ethylene glycol) Mixtures

Hybrid "green" solvent systems composed of room-temperature ionic liquids (ILs) and poly(ethylene glycols) (PEGs) may have enormous future potential. Solvatochromic absorbance probe behavior is used to assess the physicochemical properties of the mixture composed of IL 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)]) and PEG (average molecular weights of 200, 400, 600, and 1500) at ambient conditions. Lowest energy intramolecular charge-transfer absorbance maxima of a betaine dye, i.e., E(T)(N), indicates the dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity of the [bmim][PF 6] + PEG mixtures to be even higher than that of neat [bmim][PF(6)], the solution component with higher dipolarity/polarizability and/or HBD acidity. Dipolarity/polarizability (pi*) obtained separately from the electronic absorbance response of probe N, N-diethyl-4-nitroaniline shows a trend similar to E(T)(N ) thus confirming the unusually high dipolarity/polarizability of the [bmim][PF(6)] + PEG mixtures. Similar to E(T)(N ) and pi*, the HBD acidity (alpha) of [bmim][PF(6)] + PEG mixtures is also observed to be anomalously high. Contrary to what is observed for E(T)(N ), pi*, and alpha, the hydrogen-bond accepting (HBA) basicity (beta) of the [bmim][PF(6)] + PEG mixtures is observed to be lower than that predicted from ideal additive behavior indicating diminished HBA basicity of the mixture as compared to its neat components. A four-parameter simplified combined nearly ideal binary solvent/Redlich-Kister (CNIBS/R-K) equation is shown to satisfactorily predict the solvatochromic parameters within [bmim][PF(6)] + PEG mixtures. It is demonstrated that [bmim][PF(6)] + PEG mixtures possess physicochemical properties that are superior to those of either the neat IL or the neat PEG.

Kinetic study of heterogeneous catalytic hydrogenation of cyclohexene to cyclohexane in ionic liquid–alcohols mixtures

Abstract Heterogeneous catalytic hydrogenation of cyclohexene, catalyzed by Pt/Al2O3, was carried out in solutions of 2-hydroxyethylammonium formate (a room temperature ionic liquid, RTIL) mixed with methanol, ethanol and propan-2-ol at 25 °C. The rate constants of the reaction in ionic liquid alcohol mixtures were higher than alcohol alone. First-order rate constant of the reaction in the RTIL relative to propan-2-ol is approximately 28. Furthermore, the rate constant of the reaction increases with the mole fraction of the ionic liquid. Single-parameter correlations of log k vs. normalized polarity parameter ( E T N ), hydrogen-bond acceptor basicity (β) and hydrogen-bond donor acidity (α) do not give acceptable results in the solutions. In addition, log k does not show an acceptable dual-parameter correlation with π* (dipolarity/polarizibility, one of the Kamlet–Taft parameters for solvent that shows the dipolarity of the solvent) and α, π* and β and E T N and β. However single-parameter correlation of log k vs. π* gives reasonable results. The increase of the reaction rate with π* is attributed to the non-polar nature of the reactants.

Solvent effects on kinetics of the reaction between 2‐chloro‐3,5‐dinitropyridine and aniline in aqueous and alcoholic solutions of [bmim]BF4

AbstractRate constants, kA, for the aromatic nucleophilic substitution reaction of 2‐chloro‐3,5‐dinitropyridine with aniline were determined in different compositions of 1‐(1‐butyl)‐3‐methylimidazolium terafluoroborate ([bmim]BF4) mixed with water, methanol, and ethanol at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: water > methanol > ethanol > [bmim]BF4. In these solutions, rate constants of the reaction decrease with the mole fraction of the ionic liquid. Single‐parameter correlations of log kA versus normalized polarity parameter (E), hydrogen bond acceptor basicity (β), hydrogen bond donor acidity (α), and dipolarity/polarizability (π*) do not give acceptable results in all solutions. Dual‐parameter correlations of log kA versus E and β also α and β gave reasonable results (e.g., in solutions of water with [bmim]BF4, the correlation coefficients are 0.994 and 0.996, respectively). The proposed dual‐parameter models demonstrate that the reaction rate constant increases with E, β, and α. The increase in the rate constant is attributed to hydrogen‐bonding interactions (donor and acceptor) of the media with an activated complex of the reaction that has the zwitterionic character. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 681–687, 2007

Linear Solvation Energy Parameters for Model Tropospheric Aerosol Surfaces

Excited-state absorption spectra for several coumarin derivatives adsorbed to aerosol particles provide linear solvation energy (LSE) relationships for the aerosol surfaces. This study focuses on NaCl and (NH4)2SO(4) particles as models for tropospheric aerosol. We investigate several others, including NH(4)Cl, NaBr, KI, Na(2)SO(4), NaNO(3), Al(2)O3, and CaCO(3), to establish trends and understand the factors that control polarity for surfaces. The Kamlet-Taft dipolarity/polarizability parameter, pi*, for these particles ranges from 0.73 to 1.69. The values are high compared to most homogeneous molecular solvents and are attributable to ion-dipole forces, especially at defect sites. We also find that the smaller values of pi* (1.01 for (NH4)2SO(4) and 0.73 for NH(4)Cl) correlate with appreciable hydrogen bond donor acidity in the surface (alpha = 0.23 and 1.06, respectively). Strong hydrogen bonds with the surface lead to a drop in overall polarity either by making interaction with very polar defect sites less likely or orienting the probe molecule away from the surface. Adsorbed water layers mainly alter the alpha value of the surface, but can have indirect effects on pi* by changing the interaction of the adsorbed molecule with the surface.

Solute–solvent interactions within aqueous poly(ethylene glycol): solvatochromic probes for empirical determination and preferential solvation

Due to their vast industrial importance, poly(ethylene glycols) [PEGs] have become substances of major investigations. The hypothesis that aqueous PEG rather than pure PEG may provide substantially improved physicochemical properties for many industrial applications is addressed. Solvatochromic electronic absorbance probes are utilized to gather important information about these systems. Response from a water-soluble betaine dye suggests a decrease in dipolarity/polarizability and/or hydrogen-bond donating (HBD) acidity as the PEG is added to water. This is further confirmed by the response of N,N-diethyl-4-nitroaniline, which shows a decrease in dipolarity/polarizability and, in concert with the response from the betaine dye, a decrease in HBD acidity as the amount of PEG is increased. Response from 4-nitroaniline combined with dipolarity/polarizability is used to show that hydrogen-bond accepting (HBA) basicity increases with the addition of PEG to water. The extent of change in these important physicochemical properties depends on the PEG molecular mass. A simple mole-fraction weighted solvation model suggests significant preferential solvation of the betaine dye by PEG molecules in aqueous PEG solutions.

Solvation Effects on Imidazolium Salts That Contain Alkyl Side Chains

Solvation effects of imidazolium salts that contain alkyl side chains in the 1 and 3 positions have been analyzed using multi-linear regression equations. The major contribution for the solvation of these compounds comes from the solvents' hydrogen bond acceptor basicity contribution, in which there is an interaction between the solvent and H2 hydrogen of the imidazolium cation. Another solvation effect, which is minimal, comes from the solvents' hydrogen bond donor acidity contribution, which serves to solvate the anions. The nature of the anion plays a role in the solvation of the anions. Salts with hard anions are solvated to a lesser extent via the solvents' hydrogen bond acceptor basicity; whereas, salts with softer anions are solvated to a larger extent via this mode. There is not much discrimination in the solvation of imidazolium salts that contain the same anion and different alkyl groups in positions 1 and 3.

Solvatochromic Absorbance Probe Behavior and Preferential Solvation in Aqueous 1-Butyl-3-methylimidazolium Tetrafluoroborate

The hypothesis that aqueous, rather than pure, ionic liquids provide substantially altered physicochemical properties and versatile/increased solute solvation is addressed. Solvatochromic absorbance probes are utilized to gather information on aqueous solutions of a completely water-miscible ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4). A simplistic solvation model suggests possible preferential solvation of a water-soluble betaine dye by bmimBF4. The lowest-energy electronic absorption band of this dye is further used to interpret dipolarity/polarizability and hydrogen-bond donating (HBD) acidity of aqueous bmimBF4. On the basis of the responses of two other probes, N,N-diethyl-4-nitroaniline and 4-nitroaniline, dipolarity/polarizability, HBD acidity, and hydrogen-bond accepting basicity are separately assessed.

Molecular Descriptors of N‐Arylhydroxamic Acids: A Tool in Drug Design

The partition coefficient in the 1-octanol/water system, log P(O/W), is a measure of lipophilicity. It is used as a predictor of solute-membrane partitioning. The objective of this study was to measure the log P(O/W) of five hydroxamic acids. Other molecular descriptors of these solutes, namely molar volume, molar refraction, parachor, polarizability (pi*), hydrogen-bond donor acidity (epsilon alpha) and hydrogen-bond acceptor basicity (epsilon beta), have also been discussed. These properties represent the combined effects of a number of intermolecular forces between a solute and its environment.

How Ionic Are Room-Temperature Ionic Liquids? An Indicator of the Physicochemical Properties

Room-temperature ionic liquids (RTILs) are liquids consisting entirely of ions, and their important properties, e.g., negligible vapor pressure, are considered to result from the ionic nature. However, we do not know how ionic the RTILs are. The ionic nature of the RTILs is defined in this study as the molar conductivity ratio (Lambda(imp)/Lambda(NMR)), calculated from the molar conductivity measured by the electrochemical impedance method (Lambda(imp)) and that estimated by use of pulse-field-gradient spin-echo NMR ionic self-diffusion coefficients and the Nernst-Einstein relation (Lambda(NMR)). This ratio is compared with solvatochromic polarity scales: anionic donor ability (Lewis basicity), E(T)(30), hydrogen bond donor acidity (alpha), and dipolarity/polarizability (pi), as well as NMR chemical shifts. The Lambda(imp)/Lambda(NMR) well illustrates the degree of cation-anion aggregation in the RTILs at equilibrium, which can be explained by the effects of anionic donor and cationic acceptor abilities for the RTILs having different anionic and cationic backbone structures with fixed counterparts, and by the inductive and dispersive forces for the various alkyl chain lengths in the cations. As a measure of the electrostatic interaction of the RTILs, the effective ionic concentration (C(eff)), which is a dominant parameter for the electrostatic forces of the RTILs, was introduced as the product of Lambda(imp)/Lambda(NMR) and the molar concentration and was compared with some physical properties, such as reported normal boiling points and distillation rates, glass transition temperature, and viscosity. A decrease in C(eff) of the RTILs is well correlated with the normal boiling point and distillation rate, whereas the liquid-state dynamics is controlled by a subtle balance between the electrostatic and other intermolecular forces.

Solvent Parameters Effects on the Second-Order Rate Constants of the Reaction of 2-Chloro-3,5-Dinitropyridine with Aniline in Aqueous Solutions of Alcohols

Aromatic nucleophilic substitution reaction kinetics of 2-chloro-3,5-dinitropyridine with aniline was studied in aqueous solutions of methanol, ethanol, and 2-propanol at room temperature. The obtained results for aqueous solutions indicate that the second-order rate constants are in order of 2-propano > ethano > methanol with a maximum at water mole fraction of 0.9. The influence of solvent parameters including normalized polarity (ETN), dipolarity/polarisability (π*), and hydrogen bond donor acidity (α) on the second-order rate constants were investigated and multiple regressions gave much better results with regard to single parameter regressions. Dipolarity/polarisability and hydrogen bond donor acidity of media demonstrate opposite effects on the reaction rate. The dipolarity/polarisability of media has a positive effect regarding to zwitterionic character of the reaction intermediate and the hydrogen bond donor acidity shows a negative effect because of hydrogen-bonding interactions between aniline and solvent molecules.

Intermolecular interactions on multiwalled carbon nanotubes in reversed-phase liquid chromatography

Retention on multiwalled carbon nanotubes (MWCNTs) in RPLC has been correlated with solute descriptors of dispersion, polarizability, dipolarity, hydrogen bond donor acidity, and hydrogen bond acceptor basicity through the use of the linear solvation energy relationship. Intermolecular interactions influencing solute retention on MWCNTs were compared with those on a graphitic carbon-deposited zirconia and a common RPLC stationary phase, octylsilane-bonded silica.

Solvatochromic Parameters for Binary Mixtures of 1-(1-Butyl)-3-methylimidazolium Tetrafluoroborate with Some Protic Molecular Solvents

The solvatochromic parameters (ET(N), normalized polarity parameter; pi*, dipolarity/polarizability; beta, hydrogen-bond acceptor basicity; alpha, hydrogen-bond donor acidity) were determined for binary solvent mixtures of 1-(1-butyl)-3-methylimidazolium tetrafluoroborate ([bmim]BF4) with water, methanol, and ethanol at 25 degrees C over the whole range of mole fractions. In nonaqueous solutions, the value of the mixture increases with mole the fraction of [bmim]BF4 and then decreases gradually to the value of pure [bmim]BF4. Positive deviation from ideal behavior was observed for the solvent parameters ET(N), pi*, and alpha, whereas the deviation of the beta parameter is negative. The applicability of the combined nearly ideal binary solvent/Redlich-Kister equation for the correlation of various solvatochromic parameters with solvent composition was proved too for the first time. This equation provides a simple computational model to correlate and/or predict various solvatochromic parameters for many binary solvent systems. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute-solvent and solvent-solvent interactions have been applied for interpretation of the results.

Solvent effects on complexation of molybdenum(VI) with nitrilotriacetic acid in different aqueous solutions of methanol

The formation constants of the species formed in the systems H + + Mo(VI) + nitrilotriacetic acid and H + + nitrilotriacetic acid have been determined in different aqueous solutions of methanol at 25 °C and constant ionic strength 0.1 mol dm − 3 sodium perchlorate, using spectrophotometric and potentiometric techniques. The composition of the complex was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with nitrilotriacetic acid of the type MoO 3L − 3 at − log[H +] = 5.8. The formation constant in various media was analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlations of the formation constant, K S, versus α (hydrogen-bond donor acidity) and π* (dipolarity/polarizability) are poor in all solutions, except for β (hydrogen-bond acceptor basicity), but multi-parameter correlations represent significant improvement with regard to the single-parameter models. Linear relationship is observed when the experimental log K S is plotted versus the calculated ones, while all the Kamlet and Taft's parameters are considered. Finally, the results are discussed in terms of the effect of solvent on complexation.

Complexation of Thallium(I) with Adenosine 5′-Monophosphate in Aqueous Methanol Solutions

The formation constants of the species formed in the systems H+ + thallium(I) + AMP and H+ + AMP have been determined in aqueous solutions of methanol at 25 degrees C and constant ionic strength 0.1 mol dm(-3) sodium perchlorate, using spectrophotometric and potentiometric techniques. Thallium(I) forms two mononuclear 1:1 complexes with AMP of the type TlHL and TlL- in the pH range of study (1-11), where L2- represents the fully dissociated ligand. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, beta111, and beta101, versus alpha (hydrogen-bond donor acidity), beta (hydrogen-bond accepter basicity), and for pi* (dipolarity/polarizability) are relatively poor in all solutions, but multi-parameter correlation represents significant improvement with regard to the single-parameter models. Finally, the results are discussed in terms of the effect of the solvent on complexation.

Solvent Effects on Complexation of Dioxovanadium(V) with Penicillamine in Methanol−Water Mixtures

The formation constants of the species formed in the systems H+ + dioxovanadium(V) + penicillamine and H+ + penicillamine have been determined in aqueous solutions of methanol at 25 °C and constant ionic strength, using spectrophotometric and potentiometric techniques. It was shown that dioxovanadium(V) forms two mononuclear 1:1 and 1:2 complexes with penicillamine. The formation constants in various media were analyzed in terms of Kamlet and Taft's parameters. Single-parameter correlation of the formation constants, β121 and β142, versus α (hydrogen-bond donor acidity) and β (hydrogen-bond acceptor basicity) is poor in all solutions, except for π* (dipolarity/polarizability), but multiparameter correlation represents significant improvement with regard to the single-parameter models. Linear relationships are observed when log β121 and log β142 are plotted versus π*. Finally, the results are discussed in terms of the effect of the solvent on complexation.

Solute–solvent interaction effects on second‐order rate constants of reaction between 1‐chloro‐2,4‐dinitrobenzene and aniline in alcohol–water mixtures

AbstractThe second‐order rate coefficients for aromatic nucleophilic substitution reaction between 1‐chloro‐2,4‐dinitrobenzene and aniline have been measured in aqueous solutions of ethanol and methanol at 25°C. The plots of rate constants versus mole fraction of water show a maximum in all‐aqueous solutions. The effect of four empirical solvent parameters including hydrogen bond donor acidity (α) dipolarity/polarizability (π*) normalized polarity (ENT) and solvophobicity (Sp) has been investigated. This investigation has been carried out by means of simple and multiple regression models. A dual‐parameter equation of log k2 versus Sp and α was obtained in all‐aqueous solutions (n = 41, r = 0.962, s = 0.053, p = 0.0000). This equation shows that solvophobicity and hydrogen bond donor acidity are important factors in the occurrence of the reaction and they have opposite effects on reaction rate. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 90–97, 2005