Hydroxylic Solvents Research Articles

Influence of temperature on thermodynamics of protic ionic liquid 2-hydroxy diethylammonium lactate (2-HDEAL) + short hydroxylic solvents

In this work, we synthesized the protic ionic liquid 2-hydroxy diethylammonium lactate (2-HDEAL), the volumetric and acoustic behavior into different hydroxilic media (water, methanol and ethanol) at the range of temperature 288.15–323.15K and atmospheric pressure being studied. The corresponding apparent molar volume and apparent molar isentropic compressibility values have been evaluated from the experimental data and fitted to a temperature dependent Redlich–Mayer equation. Derived properties such as isobaric expansibility isothermal coefficient of pressure excess molar enthalpy and other acoustical parameters were computed due to their importance in the study of specific molecular interactions into this environment. The new experimental data were used to test the prediction capability of different models (Mchaweh–Nasrifar–Moshfeghian (MNM) model, the modified Heller temperature dependent equation (MHE) and the Collision Factor Theory (CFT)). The obtained results indicate that ionic liquid interactions in water are weaker than in the studied alcoholic solutions, in accordance with previous results. The excess molar volumes were negative throughout the composition range for all mixtures at any temperature condition. The observed inverse dependence on temperature for aqueous or alcoholic mixtures, points out the special trend of packing of this protic ionic liquid into hydroxilic solvents and its strong dependence on steric hindrance of aliphatic residues into anions and cations.

Photocyclization and Photoaddition Reactions of Arylphenols via Intermediate Quinone Methides.

A series of five benzannelated derivatives of 2-phenylphenol were prepared, and their photochemistry was investigated. Two of these (3-phenyl-2-naphthol, 10, and 1-phenyl-2-naphthol, 11) were photoinert. For 2-(1-naphthyl)phenol (12) and 1-(1-naphthyl)-2-naphthol (13), ESPT took place to either the 2'-position or the 7'-position of the naphthalene ring to give quinone methides (QMs) that underwent either reverse proton transfer (RPT) or electrocyclic ring closure to give dihydrobenzoxanthenes. The intermediate QMs for 12 and 13 were detected and characterized by laser flash photolysis. For 2-(9-phenanthryl)phenol (14), ESPT took place either to the 5'-position to give a QM that underwent quantitative electrocyclic ring closure to give the corresponding benzoxanthene or to the 10'-position to give a QM that underwent RPT. If the solution contained methanol, the QM produced on ESPT to the 10'-position in 14 could be trapped as the photoaddition product. The compounds studied in this work demonstrate three possible reactions of QMs produced following ESPT to aromatic carbon atoms: (1) reverse proton transfer (RPT) to regenerate starting material; (2) addition of hydroxylic solvents to give the photoaddition product; and (3) electrocyclic ring closure to give benzoxanthene derivatives.

Correlation of the Rates of Solvolysis of 2,1-Benzoxathiol-3-One-1, 1-dioxide (2-Sulfobenzoic Acid Cyclic Anhydride)

Solvolysis of acyclic mixed carboxylic–sulfonic anhydrides in hydroxylic solvents is known to involve displacement at the carbonyl carbon to produce a carboxylic acid (water as the nucleophile) and/or an ester (alcohol as the nucleophile) plus the anion of the sulfonic acid. Parallel solvolyses of the cyclic mixed anhydride 2-sulfobenzoic anhydride (structurally similar to phthalic anhydride but with one carbonyl group replaced by a sulfonyl group) involve expulsion from the carbonyl carbon of a sulfonate anion that remains attached as an ortho-substituent in the benzoic acid and/or benzoate ester produced. This complicates the choice of a solvent-ionising-power scale for use in an extended Grunwald–Winstein equation treatment. The YOTs scale, previously recommended as a good general purpose scale, is chosen and used in conjunction with the NT solvent nucleophilicity scale. An acceptable correlation is obtained, which is improved when the two solvents rich in the highly ionising 1,1,1,3,3,3-hexafluoro-2-propanol are excluded. As the solvent is varied, the sensitivities to the changes induced in the two scales are low, consistent with an early transition state, but their ratio has a value which is typical for a pathway involving addition–elimination, with addition rate-determining. Earlier reports, supporting aspects of the proposed mechanism, are reviewed.

Development of Abraham model expressions for predicting the enthalpies of solvation of solutes dissolved in acetic acid

ABSTRACTExperimental data have been compiled from the published chemical and engineering literature on the enthalpies of solvation for 92 different inorganic gases and organic vapours in acetic acid. The compiled data are used to derive mathematical correlations based on the Abraham solvation parameter model. The derived expressions describe the experimental solvation enthalpies in acetic acid to within a standard deviation (SD) of 2.2 kJ mol−1. Principal Component Analysis (PCA) on the five equation coefficients from a derived Abraham model correlation shows that acetic acid does not resemble hydroxylic solvents in terms of enthalpic interactions, but is more akin to moderately polar solvents such as ethyl acetate or acetone.

Comparison of lipid membrane–water partitioning with various organic solvent–water partitions of neutral species and ionic species: Uniqueness of cerasome as a model for the stratum corneum in partition processes

Lipid membrane–water partitions (e.g., immobilized artificial membrane systems where the lipid membrane is a neutral phospholipid monolayer bound to gel beads) were compared to various organic solvent–water partitions using linear free energy relationships. To this end, we also measured the retention factors of 36 compounds (including neutral and ionic species) from water to liposomes made up of 3-sn-phosphatidylcholine and 3-sn-phosphatidyl-l-serine (80:20, mol/mol), employing liposome electrokinetic chromatography in this work. The results show that lipid membranes exhibit a considerably different chemical environment from those of organic solvents. For both neutral species and ionic species, partitions into the more polar hydroxylic solvents are chemically closer to partition into the lipid membrane as compared to partitions into the less polar hydroxylic solvents and into aprotic solvents. This means that solutes partition into the polar parts of lipid membranes, regardless of whether they are charged or not. In addition, cerasome (i.e., liposome composed mainly of stratum corneum lipids) was compared with regular phospholipid liposomes as a possible model for human stratum corneum in partitions. It was found that the cerasome–water partition exhibits a better chemical similarity to skin permeation. This is probably due to the unique structures of ceramides that occur in cerasome and in the stratum corneum lipid domain. We further show that membranes in membrane–water partitions exhibit very different properties.

The solvatochromism of phenolate betaines: comparing different cavities of a polarized continuum model.

Two variations of the polarized continuum model employing default ("PCM model") and SMD radii ("SMD model") were compared for the reproduction of the solvatochromic behavior of Reichardt's betaine dye, and of eight other phenolate betaines that exhibit a negative, positive or an inverted solvatochromic behavior. Molecules were optimized at the CAM B3LYP/6-31+G(d,p) level of theory, and transition energies were calculated with the TD-DFT method. The PCM model failed to reproduce the negative and the inverted solvachromism of these dyes in protic solvents. The SMD model, though not entirely accounting for hydrogen-bond effects in small, polar hydroxylic solvents, should be recommended as a better alternative for the theoretical simulation of the solvatochromism of phenolate betaines in medium to highly polar solvents. Graphical Abstract A comparison of two polarized continuum models ("default PCM" and "PCM/SMD") for reproducing the solvatochromism of phenolate betaines, with nine examples of negative, positive, and inverted behavior.

Tuning organic carbon dioxide absorbents for carbonation and decarbonation.

The reaction of carbon dioxide with a mixture of a superbase and alcohol affords a superbase alkylcarbonate salt via a process that can be reversed at elevated temperatures. To utilize the unique chemistry of superbases for carbon capture technology, it is essential to facilitate carbonation and decarbonation at desired temperatures in an easily controllable manner. Here, we demonstrate that the thermal stabilities of the alkylcarbonate salts of superbases in organic solutions can be tuned by adjusting the compositions of hydroxylic solvent and polar aprotic solvent mixtures, thereby enabling the best possible performances to be obtained from the various carbon dioxide capture agents based on these materials. The findings provides valuable insights into the design and optimization of organic carbon dioxide absorbents.

Statistical Methods for the Investigation of Solvolysis Mechanisms Illustrated by the Chlorides of the Carbomethoxy Protecting Groups NVOC and FMOC.

The solvolysis of 4,5-dimethoxy-2-nitrobenzyl chloroformate (NVOC-Cl, 1) is followed at 25.0°C in twenty hydroxylic solvents. A comparison with previously published rates for benzyl chloroformate and p-nitrobenzyl chloroformate indicates that the inductive effect of the nitro and the two methoxy groups strongly influences the rate of reaction. For 1, the specific rates of solvolysis are correlated using an extended Grunwald-Winstein (G-W) treatment. A direct comparison with the data for phenyl chloroformate (PhOCOCl) in identical solvents strongly suggests that the addition step within an addition-elimination mechanism is rate-determining for both substrates. A reevaluation of the kinetic data for 9-fluorenylmethyl chloroformate (FMOC-Cl, 2) involves a correlation of log⁡(k/k o)2 versus log⁡(k/k o)PhOCOCl. In this plot, deviations were observed in solvents rich in a hydrogen-bonding fluoroalcohol component. Omitting the aqueous fluoroalcohol rate measurements for 2 in an analysis using the extended G-W equation suggested the occurrence of dual pathways differing in the dependences upon the ionizing power and nucleophilicity of the solvent. In addition, the fluorenyl ring is rotated out of the plane containing the ether oxygen and, as a result, PhOCOCl is found to solvolyze 20 times faster than 2 in ethanol and methanol.

Specific interactions in hydroxyl ternary solutions of three carbanion monosubstituted 4′-tolyl-1,2,4 triazol-1-ium-4-R-phenacylids studied by visible electronic absorption spectra

The visible absorption band of triazolium ylids is relatively sensitive to the solvent nature and can be used to characterize the intermolecular interactions in liquid solutions. Ternary solutions of the types: methanol (1)+benzene (2)+ylid and water (1)+methanol (2)+ylid were studied by means of the visible absorption spectra.Three carbanion monosubstituted 4′-tolyl-1,2,4-triazol-1-ium-4-R-phenacylids with variable R substituent were used to evidence the specific interactions between OH group of hydroxyl solvents and the ylid carbanion. The differences between the intermolecular potential energies in pairs of the types: methanol–ylid, benzene–ylid and water–ylid were estimated in the limits of statistic cell model of ternary solutions.The average statistic weights of the two solvents in the first solvation shell of ylids (estimated on the basis of the statistic cell model of ternary solutions) were compared with the corresponding molar fractions in the bulk solution, in order to obtain information about the ternary solution homogeneity.

Moderately Strong Photoacid Dissociates in Alcohols with High Transient Concentration of the Proton-Transfer Contact Pair.

Proton transfer from strong photoacids to hydroxylic solvents is much under debate. Experimentally, the main issue stems from relaxation and diffusion processes that are concomitant with ultrafast proton transfer and blur population dynamics. To overcome this, we propose a fast photodissociation reaction that, however, proceeds slower than solvent relaxation. Fluorescence spectroscopy of the cationic photoacid 2-(1'-hydroxy-2'-naphtyl)benzimidazolium reveals a two-stage mechanism: (a) reversible elementary proton transfer inside the solvent shell and (b) irreversible contact-pair splitting. The time evolution of the fluorescence signal is complex, yet this is explained quantitatively by simultaneous, spectrally overlapping emission of the acid, the conjugate base, and the contact proton-transfer pair. The latter attains high transient concentration in linear alcohols. Microscopic rate constants of dissociation are determined.

Thermal and solvent effects on the triplet formation in cinnoline

Cinnoline (1,2-diazanaphthalene) is of particular interest among the diazanaphthalenes. Its triplet quantum yield upon photoexcitation depends strongly on the temperature and the solvent environment. At the beginning of this study, the properties of the lowest triplet electronic state were not understood either. To elucidate the photophysics of cinnoline, we implemented algorithms based on the time-dependent approach for calculating intersystem crossing rates and one-photon spectra of thermally equilibrated vibronic levels. Our quantum chemical investigations reveal that the triplet formation in hydrocarbon solutions at low temperatures is an El-Sayed forbidden process. At higher temperatures and in hydroxylic solutions an additional El-Sayed allowed channel opens up, increasing the intersystem crossing rate substantially. Furthermore, we have solved the old puzzle concerning the character of the lowest triplet state of cinnoline. In the gas phase the electronic structure has mainly nπ* character with additional contributions from ππ* configurations since the nuclear arrangement in the pyridazine ring is not planar. In hydroxylic solvents, the electronic structure of the T1 state is altered. The simulation of the triplet emission shows that the experimentally observed phosphorescence of cinnoline in ethanol most certainly stems from the (3)(ππ*) emission.

Extent of Nucleophilic Participation in the Solvolyses of an Aryl Chloromethyl Ether, α,p-Dichloroanisole

The specific rates of solvolysis of α, p-dichloroanisole (chloromethyl p-chlorophenyl ether, 1) have been measured conductimetrically in a variety of hydroxylic solvents. In three typical solvents, at 25.0 °C, the rate is 20–45 times greater than for the corresponding sulfide. In a comparison with the solvolysis of a substrate with an alkyl group replacing the aryl group, chloromethyl ethyl ether (2), at −10.0 °C in four typical solvents, 1 reacted considerably more slowly than 2, by a little over four orders of magnitude. An extended Grunwald–Winstein equation treatment of the specific rates of solvolyses in 24 solvents at 25.0 °C leads to an l value of 0.68 ± 0.04 and an m value of 0.59 ± 0.03 ( l/ m = 1.15). Appreciable nucleophilic assistance in the progress to the transition state is indicated and either nucleophilic solvation to an ionisation process or a loose SN2 transition state with extensive bond-breaking accompanied by a smaller degree of bond-making lead to an appropriate transition state.

Solvolysis of 4-Halogeno-4-Alkyl-2,6-di-tert-butylcyclohexa-2,5-dienones Induced by Positive Halogen Donors as Electrophiles

Positive halogen donors such as N-iodosuccinimide (NIS) induce solvolysis of dienones 1, as model 4-halogenocyclohexa-2,5-dienones, in different hydroxylic solvents (ROH), yielding the 4-RO-cyclohexa-2,5-dienones (2). The rate of the solvolysis with NIS is highly dependent on the structure of ROH. The problem of such dependency is overcome by running the reaction in ROH diluted with MeCN, a polar aprotic solvent, in place of pure ROH; the rate of the reaction in the ROH-MeCN solvent mixture is almost independent of the structure (or the polarity) of ROH, and the reaction is completed faster or markedly faster than in neat ROH. The results suggest that the solvolysis rate is controlled by the polarity of the solvent system, although the hydrogen-bond acceptability of MeCN for dilution also accelerates the reaction. A mechanism for the solvolysis is proposed, involving electrophilic attack of a positive halogen donor at the halogen atom of 1, generating the 4-oxocyclohexa-2,5-dienyl cation intermediates (8) via the rate-limiting polar transition states.

Rate and Product Studies of 1-Adamantylmethyl Haloformates Under Solvolytic Conditions

Reactions of 1-adamantylmethyl chloroformate (, 1) and 1-adamantylmethyl fluoroformate (, 2) in hydroxylic solvents have been studied. Application of the extended Grunwald-Winstein (G-W) equation to solvolyses of 1 in a variety of pure and binary solvents indicates an addition-elimination pathway in the majority of the solvents except an ionization pathway in the solvents of relatively low nucleophilcity and high ionizing power. The solvolyses of 2 show an addition-elimination pathway in all of the mixed solvents. The leaving group effects (), the kinetic solvent isotope effects (KSIEs, ), and the enthalpy and entropy of activation for the solvolyses of 1 and 2 were also calculated. The selectivity values (S) for each solvent composition are reported and discussed. These observations are compared with those previously reported for other alkyl haloformate esters.

CCVJ Is Not a Simple Rotor Probe

The photochemistry of the rotor probe 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ) was studied to elucidate a curious effect of fluid flow previously reported. The apparent sensitivity to fluid motion observed in CCVJ but not in the closely related molecule 9-(dicyanovinyl)julolidine (DCVJ) is found to be an indirect effect of a photoisomerization reaction. The results presented here demonstrate that it is this isomerization, rather than the commonly assumed TICT process, that confers viscosity-sensing ability on these fluorophores. In micromolar solutions in hydroxylic solvents CCVJ exists primarily in the carboxylate form. Only the E isomer of this anion is initially present in solutions prepared from the solid, but in room light such solutions rapidly achieve a photostationary state in which the E isomer and an essentially nonfluorescent Z isomer exist in comparable concentrations. The Z isomer is metastable in S(0) such that in the absence of light the solution reverts slowly to pure E. Unlike DCVJ where only a single isomer is possible, the production of long-lived photoproducts in CCVJ and other asymmetrically substituted styryenyl probes complicates their fluorescence response. Considerable care is needed when such fluorphores are used as steady-state sensors of environmental fluidity are used.

Kinetics of hydrogen peroxide decomposition by catalase: hydroxylic solvent effects

The effect of water-alcohol (methanol, ethanol, propan-1-ol, propan-2-ol, ethane-1,2-diol and propane-1,2,3-triol) binary mixtures on the kinetics of hydrogen peroxide decomposition in the presence of bovine liver catalase is investigated. In all solvents, the activity of catalase is smaller than in water. The results are discussed on the basis of a simple kinetic model. The kinetic constants for product formation through enzyme-substrate complex decomposition and for inactivation of catalase are estimated. The organic solvents are characterized by several physical properties: dielectric constant (D), hydrophobicity (log P), concentration of hydroxyl groups ([OH]), polarizability (α), Kamlet-Taft parameter (β) and Kosower parameter (Z). The relationships between the initial rate, kinetic constants and medium properties are analyzed by linear and multiple linear regression.

Nucleophilic Participation in the Solvolyses of (Arylthio)methyl Chlorides and Derivatives: Application of Simple and Extended Forms of the Grunwald-Winstein Equations

The specific rates of solvolysis of chloromethyl phenyl sulfide [(phenylthio)methyl chloride] and its p-chloro-derivative have been determined at 0.0 °C in a wide range of hydroxylic solvents, including several containing a fluroalcohol. Treatment in terms of a two-term Grunwald-Winstein equation, incorporating terms based on solvent ionizing power (Y(Cl)) and solvent nucleophilicity (N(T)) suggest a mechanism similar to that for the solvolyses of tert-butyl chloride, involving in the rate-determining step a nucleophilic solvation of the incipient carbocation in an ionization process. A previous suggestion, that a third-term governed by the aromatic ring parameter (I) is required, is shown both for the new and for the previously studied related substrates to be an artifact, resulting from an appreciable degree of multicollinearity between I values and a linear combination of N(T) and Y(Cl) values.

Semiempirical Hamiltonian for Simulation of Azobenzene Photochemistry

We present a semiempirical Hamiltonian that provides an accurate description of the first singlet and triplet potential energy surfaces of azobenzene for use in direct simulations of the excited-state dynamics. The parameterization made use of spectroscopic and thermochemical data and the best ab initio results available to date. Two-dimensional potential energy surfaces based on constrained geometry optimizations are presented for the states that are most relevant for the photochemistry of azobenzene, namely, S(0), S(1), and S(2). In order to run simulations of the photodynamics of azobenzene in hydrocarbons or hydroxylic solvents, we determined the interactions of methane and methanol with the azo group by ab initio calculations and fitted the interactions with a QM/MM interaction Hamiltonian.

Effect of temperature and composition on the density, viscosity, surface tension, and thermodynamic properties of binary mixtures of N-octylisoquinolinium bis{(trifluoromethyl)sulfonyl}imide with alcohols

Density and viscosity were determined for the binary mixtures containing the ionic liquid N-octylisoquinolinium bis{(trifluoromethyl)sulfonyl}imide ([C8iQuin][NTf2]) and 1-alcohol (1-butanol, 1-hexanol, and 2-phenylethanol) at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15)K and ambient pressure. The density and viscosity correlations for these systems were tested by an empirical second-order polynomial and by the Vogel–Fucher–Tammann equation. Excess molar volumes were described by the Redlich–Kister polynomial expansion. The density and viscosity variations with compositions were described by polynomials. Viscosity deviations were calculated and correlated by the Redlich–Kister polynomial expansions. The surface tensions of pure ionic liquid and binary mixtures of [C8iQuin][NTf2] with 1-hexanol were measured at atmospheric pressure at three temperatures (298.15, 308.15, and 318.15) K. The surface tension deviations were calculated and correlated by the Redlich–Kister polynomial expansion. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values. The critical temperature, parachor, and speed of sound for pure ionic liquid were described. A qualitative analysis on these quantities in terms of molecular interactions is reported. The obtained results indicate that ionic liquid interactions with alcohols are strong dependent on the special trend of packing effects and hydrogen bonding of this ionic liquid with hydroxylic solvents. As previously observed, an increase by a 1-alcohol carbon chain length leads to lower interactions on mixing.

Solvatochromism and Preferential Solvation of 4-Pentacyanoferrate 4′-Aryl Substituted Bipyridinium Complexes in Binary Mixtures of Hydroxylic and Non-hydroxylic Solvents

The intense solvatochromic behavior of several pentacyanoferrate complexes with aryl substituted 4,4′-bipyridines acting as ligands, was investigated in six hydroxylic and non hydroxylic solvents using UV-Visible spectroscopy. The metal-to-ligand-charge-transfer bands of the visible spectra of these compounds proved to be markedly affected by solvent polarity. In order to quantify the extent of the observed solvatochromism and reveal the dominant interactions which take place in the cybotactic region, resulting in solvatochromism, the Kamlet-Taft equation was used. This is a multiparametric linear-solvation-energy-relationship (LSER) widely used for the study of solvent effects on various physicochemical properties. Through this analysis it was proved that both specific and non specific interactions contribute to the observed solvatochromism. Furthermore, the preferential solvation of the complex salts was studied in binary solvent mixtures. Solvatochromism was used as the key approach to rationalize solvent-solute and solvent-solvent interactions in the binary solvent mixtures studied.