Strong Hydrogen-bond Basicity Research Articles

Catalytic performance of ionic liquid for dehydrochlorination reaction: Excellent activity and unparalled stability

Gas phase catalytic process with the advantages of simply product separation and maximized atom economy, which was a green path used in industrial production. At present, heterogeneous dehydrochlorination catalysts are facing challenge of rapid deactivation caused by released HCl and carbon deposit. In this paper, a series of supported ionic liquid catalysts (SILCs) was synthesized by wet impregnation method and applied to 1, 1, 2-trichloroethane (TCE) dehydrochlorination to produce 1, 1-dichloroethylene (VDC). Tetraarylphosphonium chlorine was the active component with the unique acid resistance and the ability to dissolve coke, which determined the activity and stability of the catalyst. For 6%Tetraphenylphosphonium chloride (TPPC)/SiO2(260 °C, WHSV = 0.19 h−1), the conversion of 1, 1, 2-TCE was ＞99.5%, selectivity of VDC was 86%, and the catalytic activity remained stable within 1100 h. Herein, highly activity for dehydrochlorination was attributed to the strong hydrogen-bond basicity of Cl-, which was decided largely by the interaction between anion and cation of ionic liquid. The reaction mechanism was investigated using FTIR, XPS, TGA-MS, XRF, DFT calculation and two step elimination model induced by alkaline active center is proposed. Such catalysts provide a viable industrial solution to gas dehydrochlorination reaction and design of heterogeneous basic catalysts.

Supported ionic liquid membranes with high carrier efficiency via strong hydrogen-bond basicity for the sustainable and effective olefin/paraffin separation

Supported ionic liquid membranes (SILMs) constitute a radical advance in olefin/paraffin separation membranes. Unfortunately, the applications of SILMs are vastly hindered by low carrier efficiency. Herein, SILMs with high carrier efficiency via strong hydrogen-bond basicity were designed to carry out efficient ethylene/ethane separation. The strong hydrogen-bond basicity of ILs not only endowed the membranes with high carrier concentration, but also effectively favored for the good disassociation of carrier to form solvated free ions through coordinative interactions between IL and carrier, which greatly increased the number of carrier and enhanced the carrier efficiency. Benefiting from the high carrier efficiency, both ethylene permeability and ethylene/ethane selectivity were significantly elevated, which could reach up to 100 Barrers and 40, respectively, surpassing most of results reported in the open literature. Meanwhile, the ethylene and ethane solubility data in the carrier/ILs were measured in a pressure range from 0 to 3.5 bar at 298.15 K, a first-order equilibrium model based on the formation carrier-ethylene complex species has been developed to describe the physical and chemical dissolving behaviors of ethylene and the equilibrium constants were obtained accordingly. Moreover, the membrane separation process was optimized, confirming that ethylene permeability and ethylene/ethane selectivity increased with the increase of carrier concentration due to the combined effects of gas solubility and diffusion. It was notable that the selectivity of as-prepared SILMs was more effective at lower transmembrane pressures and operating temperatures, which contributed to designing the energy-efficient and sustainable membrane processes. This study opens a new route for the utilization of the IL properties to manipulate the carrier efficiency for developing high performance SILMs.

Nanostructured Branched-Chain Carboxylate Ionic Liquids: Synthesis, Characterization, and Extraordinary Solubility for Bioactive Molecules

The design of multifunctional ionic liquids (ILs) that integrate different attractive characteristics, such as strong hydrogen-bonding interactions, good lipophilicity, significant nanoscale organization, and low viscosity, in a molecular structure is of great importance for the application of ILs in extraction, biomass conversion, and catalysis but remains challenging. Here, we synthesized a family of novel phosphonium ILs featuring branched chain carboxylate anions with carbon number up to 18 and systematically characterized the physicochemical properties of prepared ILs. The branched chain carboxylate ILs (BCC-ILs) exhibit very strong hydrogen-bond basicity (β = 1.49–1.72, 30 °C) and excellent lipophilicity (π* = 0.73–0.95, 30 °C), and have obvious nanoscale segregation and moderate viscosity (η = 91.8–200.5 mPa, 40 °C). The d value of BCC-ILs ranged from 10.5 to 15.6 A when the length of alkyl chain in anions or cation rose. These nanostructured solvents can undergo self-assembly processes with typica...

Descriptors for the α,ω-dicarboxylic acids from oxalic acid to sebacic acid

We use literature data on solubilities in water and solvents, water-solvent partition coefficients and vapor pressures at 298 K to obtain Abraham (Absolv) descriptors for the neutral, unionized, forms of oxalic acid, malonic acid, glutaric acid, succinic acid, pimelic acid, suberic acid, azaleic acid and sebacic acid. With a knowledge of equations for partition coefficients for numerous water-wet solvents, water to dry solvents and water to ionic liquid systems, we can then predict partition coefficients of the various acids in a huge number of systems. We set out the solubility of the acids in water and these, together with estimated partition coefficients yield solubilities of the acids into the corresponding solvents. The descriptors themselves show that the acids are dipolar, are strong hydrogen bond acids and reasonably strong hydrogen bond bases, although their hydrogen bond acidity is less than expected for compounds containing two (independent) carboxylic acid groups.

Recovery of methacrylic acid from dilute aqueous solutions by ionic liquids though hydrogen bonding interaction

Abstract The recovery of carboxylic acids from dilute aqueous solution is necessary but difficult in chemical industry. Methacrylic acid (MAA) is an important chemical widely used in polymer industry. In this work, the recovery of carboxylic acid from diluted aqueous solution by liquid-liquid extraction using ionic liquids (ILs) as extractants was studied. MAA was employed as model carboxylic acid. The partition coefficients of MAA in biphasic system and the extraction efficiencies of MAA were determined for imidazolium-based ILs and quaternary ammonium salt ILs with different structure of cation and anion. The extraction conditions such as extraction time, extraction temperature, mass ratio of ILs to MAA aqueous solution, initial concentrations of MAA, and water content were evaluated. An internal mechanism of the MAA extract by ILs was revealed by combining solvatochromic study, FT-IR and quantum chemical calculations. The results show that the strong hydrogen bond basicity (β) of ILs results in the high partition coefficient of MAA, which provides guidance to molecular design of ILs for the high efficient extractive separation of MAA from diluted aqueous solution. Based on this, IL with strong hydrogen bond basicity ([N8881]Cl) was used to extract MAA from dilute aqueous solution. Compared with hexane which is conventional solvent used in MAA extractive separation, [N8881]Cl can get 49 times higher of partition coefficient value and the extraction efficiency reach 94.57% for the single-stage extraction.

Confining Noble Metal (Pd, Au, Pt) Nanoparticles in Surfactant Ionic Liquids: Active Non-Mercury Catalysts for Hydrochlorination of Acetylene

Metal catalysts often encounter the dilemma of rapid deactivation due to reduction or particle aggregation/growth during the reaction. Here we reported an active and stable metal nanoparticles (NPs)/surfactant ionic liquid (IL) system for the catalytic hydrochlorination of acetylene. The NPs of Pd, Au, and Pt with a narrow size distribution and well-defined lattice fringes experienced in situ generation in the reaction medium of anionic surfactant carboxylate ILs (ASC-ILs). Benefiting from the high reactivity of NPs and the self-assembly property of ASC-ILs, an effective redox cycle between Pd0 and PdII was established to reduce the deactivation of metal catalysts. The Pd NPs/surfactant IL systems showed excellent catalytic activity toward acetylene hydrochlorination. An acetylene conversion of 93% and a selectivity of 99.5% were achieved with no discernible deterioration over a reaction time of 55 h. Furthermore, ASC-ILs were endowed with a unique property of the strong hydrogen-bond basicity, which was ...

Long-Chain Fatty Acid-Based Phosphonium Ionic Liquids with Strong Hydrogen-Bond Basicity and Good Lipophilicity: Synthesis, Characterization, and Application in Extraction

The development of ionic liquids (ILs) with strong hydrogen-bond basicity is of great importance for the application of ILs in liquid–liquid extractions, but a long-standing problem is that the increase in hydrogen-bond basicity of ILs usually comes along with undesired changes in other properties such as reduced lipophilicity, raised melting point, and difficulty of forming biphasic systems with water. Herein, we provided a promising solution to this problem by synthesizing a class of functional phosphonium ILs with the use of biocompatible saturated/unsaturated long-chain fatty acids (carbon number up to 20) as anion precursors, and we also carried out systematic investigations on their physicochemical properties. These long-chain fatty acid ILs (LCFA-ILs) featured very strong hydrogen-bond basicity, up to the top level of all reported solvents, along with good lipophilicity and a wide liquid range. Moreover, the viscosity of LCFA-ILs exhibited only a slight increase with increasing chain length, and th...

Evaluation of Triethylamine as a Counter Solvent in Totally Organic Biphasic Liquid–Liquid Partition Systems

Partition coefficients for varied compounds were determined for the triethylamine–organic solvent biphasic partition systems where the organic solvent is dimethyl sulfoxide, ethanolamine or formamide. These partition coefficient databases are analyzed using the solvation parameter model facilitating a quantitative comparison of the triethylamine-based partition system with other totally organic partition systems. By comparison with the system constants for the biphasic systems formed between n-heptane and dimethyl sulfoxide, ethanolamine and formamide, triethylamine is a weakly cohesive solvent (slightly stronger than n-heptane), weakly dipolar/polarizable (only slightly larger than n-heptane), and non-hydrogen-bond acidic. Triethylamine is moderately hydrogen-bond basic, but much less so than ethanolamine, formamide and dimethyl sulfoxide, which are strong hydrogen-bond bases. The separation properties of triethylamine–dimethyl sulfoxide are more similar to the isopentyl ether-propylene carbonate biphasic system; the triethylamine-formamide system octan-1-ol-formamide biphaic system; and triethylamine–ethanolamine the 1,2-dichloroethane–formamide and 1,2-dichloroethane–ethylene glycol systems. None of these pairs of biphasic systems are selectivity equivalent. In the first case, the significant difference in cohesive properties favors the distribution of larger solutes to the triethylamine layer and the greater hydrogen-bond basicity of dimethyl sulfoxide the selective extraction of hydrogen-bond acids. For the triethylamine–formamide system larger molecules have a slight preference for transfer to the triethylamine layer compared with octan-1-ol, and hydrogen-bond bases will be selectively extracted to the formamide layer, since triethylamine is not competitive with octan-1-ol as a hydrogen-bond acid. There are few totally organic biphasic systems suitable for the determination of solute hydrogen-bond basicity (B descriptor) and the triethylamine–formamide biphasic system can be used to supplement these.

The transfer of neutral molecules, ions and ionic species from water to benzonitrile; comparison with nitrobenzene

Equations have been constructed for the transfer of 64 neutral solutes from water and from the gas phase to the solvent benzonitrile. The equations contain five descriptors and can be used to predict further values of the water–benzonitrile and gas–benzonitrile partition coefficients for a wide range of solutes. The water–benzonitrile equation has been extended to include ions and ionic species derived from acids by loss of a proton and bases by acceptance of a proton. Only two further descriptors are needed, one for anions and one for cations. A previous equation for transfer of neutral solutes from water to nitrobenzene has also been extended to include ions and ionic species. Comparison of the equations for transfer to benzonitrile and to nitrobenzene shows that the two solvents behave quite similarly, although benzonitrile as a solvent is a stronger hydrogen bond base.

Hydrogen bond descriptors and other properties of ion pairs

Descriptors, including those for hydrogen bond acidity and hydrogen bond basicity, have been obtained for some 80 ion pairs, including those for the alkali halide series, sodium carboxylates, and protonated base chlorides. These descriptors are on the same scales as those for ions and neutral molecules, so that equations can be constructed that include all these species together. It is shown that ion pairs are both strong hydrogen bond acids and strong hydrogen bond bases. The descriptors for the ion pairs can be used to predict ion pair partition coefficients from water to a number of solvents, there being good agreement with experiment. It is also shown that for partition into polar phases or into the polar parts of phases such as liposomes and membranes, it is likely that ions and not ion pairs are involved. Only for partition into rather nonpolar membranes will ion pairs be partitioned preferentially over the corresponding ions. The diffusion coefficient in water for an ionic species is about the same as for the neutral species, and diffusion coefficients for a pair of ions are calculated to be slightly greater than for the ion pair.

Models for the sorption of volatile organic compounds by diesel soot and atmospheric aerosols

The solvation parameter model is used to characterize interactions responsible for the sorption of varied organic compounds by diesel soot and atmospheric aerosols at 15 degrees C and 50% relative humidity. Individual models are obtained for eight aerosol samples characterized as urban, suburban, rural and coastal. Combining the individual aerosol models resulted in a general aerosol model with only a minor loss of modeling power for alkanecarboxylic acids and low-molecular weight alcohols compared with the individual models. A second group of compounds identified as weak nitrogen-containing bases were consistent outliers to all models most likely due to participation in ion-exchange interactions not considered by the models. The diesel soot and atmospheric aerosols exhibit similar characteristics with respect to their sorption interactions although differences in relative magnitude allow the two particle types to be easily distinguished. Sorption interactions are favored by strong dispersion interactions for both particle types. Of note is the strong hydrogen-bond basicity and relatively weak hydrogen-bond acidity of these materials. The particles are quite dipolar/polarizable and slightly electron lone pair repulsive. The sorption properties of the atmospheric aerosols are influenced by the relative humidity, in particular, the aerosols become significantly more hydrogen-bond acidic at high relative humidity most likely due to incorporation of increasing amounts of condensed or film water in the aerosol phase. Dividing the data into training and test sets suggests that the proposed models are capable of estimating distribution constants (log K) to about 0.20 log units for diesel soot (n = 84) and 0.14 log units for the general atmospheric aerosol model (n = 385) where n indicates the number of compounds included in the model.

Determination of descriptors for organosilicon compounds by gas chromatography and non-aqueous liquid–liquid partitioning

Measurements of retention factors by gas chromatography on up to 10 complementary stationary phases at up to 5 temperatures for each stationary phase and liquid–liquid partition coefficients in three biphasic organic solvent systems ( n-hexane-acetonitrile, n-heptane- N, N-dimethylformamide and n-heptane-2,2,2-trifluoroethanol) were used to estimate solute descriptors for 54 organosilicon compounds for use in the solvation parameter model. Many of the E descriptor values (electron lone pair interactions) are negative for simple siloxanes and silanes indicating that these compound bind electron lone pairs more tightly than n-alkanes. Silanes and siloxanes with alkyl groups have near zero dipolarity/polarizability ( S descriptor). The S descriptor is only modest for simple phenylsilanes, silazanes, silanols, orthosilicates, and alkoxides. All organosilicon compounds with silicon-oxygen bonds are reasonably strong hydrogen-bond bases ( B descriptor) but only the silanol group is a reasonably strong hydrogen-bond acid ( A descriptor). Silanes (Si H) and silazanes (Si NH Si) are weak hydrogen-bond acids. Cavity formation and dispersion interactions ( V or L descriptor) are often the main component of solvation models for siloxanes and silanes that have simple alkyl and aromatic substituents. A number of physicochemical properties (vapor pressure, aqueous solubility, biphasic partition coefficients, sorption coefficients, etc.) for linear and cyclic dimethylsiloxanes can be reliably predicted from their descriptors in established models for organic compounds.

Comparison of the Separation Characteristics of the Organic–Inorganic Hybrid Octadecyl Stationary Phases XTerra MS C18 and XBridge C18 and Shield RP18 in RPLC

Differences in the system constants of the solvation parameter model, discontinuities in retention factor plots (log k against volume fraction of organic solvent) and retention factor correlation plots are used to study the retention mechanism on XTerra MS C18, XBridge C18 and XBridge Shield RP18 stationary phases with acetonitrile–water and methanol–water mobile phases containing from 10 to 70% (v/v) organic solvent. Wetting of XBridge C18 at 10 and 20% (v/v) acetonitrile is incomplete and is responsible for small changes in the retention mechanism. The intermolecular interactions responsible for retention on XTerra MS C18 and XBridge C18 are similar with minor differences in cavity formation and hydrogen-bonding interactions responsible for small selectivity differences. On the other hand, for bulky solutes there are large changes in retention at low volume fractions of organic solvent (<40% v/v) associated with steric repulsion on the XTerra MS C18 stationary phases that is absent for XBridge C18. Selectivity differences are more apparent for XBridge C18 and XBridge Shield RP18. For acetonitrile-water mobile phases cavity formation in the solvated XBridge Shield RP18 is slightly more difficult and hydrogen-bond acid and base interactions are more important than for XBridge C18. With methanol–water mobile phases it becomes slightly easier to form a cavity in the solvated XBridge RP18 compared with XBridge C18. In addition, the methanol-water solvated XBridge RP18 is a stronger hydrogen-bond base and more dipolar/polarizable than XBridge C18. These variations in selectivity justify the use of XBridge C18 and XBridge Shield RP18 as complementary stationary phases for method development.

Determination of Solvation Descriptors for Ionic Species: Hydrogen Bond Acidity and Basicity

Literature values of Gibbs energies of transfer of ions from water to other solvents have been used in conjunction with our solvation equation to obtain descriptors for univalent ions. It is suggested that descriptors used for nonelectrolytes are not adequate to describe transfers of single ions, and that two specific ionic descriptors (J(+) and J(-)) for cations and anions, respectively, are required. The ions studied include the alkali metal and tetraalkylammonium cations, halide and other anions, and the tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions. It is shown that simple cations such as Na(+) act as very strong hydrogen bond acids and that the R(4)N(+) ions are only weak hydrogen bond acids. The halide anions are very strong hydrogen bond bases, as is also the acetate anion. Other anions, such as azide, cyanide, and nitrate, are again very strong hydrogen bond bases. The tetraphenylarsonium, tetraphenylphosphonium, and tetraphenylborate ions have no hydrogen bond acidity but are quite strong hydrogen bond bases. It is suggested that this is due to the basic properties of the phenyl groups.

Hydrogen bond and other descriptors for thalidomide and its N-alkyl analogs; prediction of physicochemical and biological properties.

Descriptors for thalidomide and its N-alkyl derivatives have been obtained from solubilities reported by Goosen et al. It I shown that thalidomide and the three N-alkylthalidomides are reasonably strong hydrogen bond bases, and that thalidomide is a hydrogen bond acid. From the obtained descriptors, a large number of physicochemical and biochemical properties of the four thalidomides were predicted, including several water-solvent partition coefficients. Predictions of skin permeation of the four thalidomides are in excellent agreement with experiment. Thalidomide is predicted to be only moderately to poorly distributed to the brain, but N-pentylthalidomide, is predicted to be very well distributed to the brain. All four thalidomides have very high predicted % human intestinal absorption.

The lipophilicity of Sudan I and its tautomeric forms

Partition coefficients from water to wet octanol and to 24 dry solvents have been obtained for Sudan I from the ratio of solubilities in water and the solvents. From these (global) partition coefficients for Sudan I and the equilibrium constants for the azo (Z) ⇌ quinone (Q) tautomeric equilibrium, partition coefficients for the Z and Q tautomers have been calculated. The three sets of partition coefficients have been analyzed using the solvation equation of Abraham to yield descriptors for Sudan I, the Z and the Q forms. It is shown that the water–wet octanol partition coefficient, as log Poct, for Sudan I is 5.60, that is almost 5 log units more than the recorded literature value. The Z and Q tautomers have very small hydrogen bond acidities, suggesting that they form strong intramolecular hydrogen bonds. The Q tautomer is a stronger hydrogen bond base than the Z tautomer, and consequently partition coefficients are smaller for the Q tautomer; values of log Poct are 5.30 and 5.94 respectively. It is suggested that the literature value of 0.64, obtained by the shake flask method, is wrong because the very low aqueous solubility of Sudan I, that we have determined to be 5.1 × 10−8 mol dm−3, precludes any accurate shake flask determination.

Hydrogen bond basicity of the chlorogroup; hexachlorocyclohexanes as strong hydrogen bond bases.

A simple chloroalkane or chlorocycloalkane has a very small hydrogen bond basicity, B = 0.1 units. Since B is often an additive function, it is possible that polychloro-alkanes or -cycloalkanes could have quite large hydrogen bond basicities. Literature data on the 1,2,3,4,5,6-hexachlorocyclohexanes (HCHs) have been analyzed by Abraham's linear free energy relationships to obtain solvation descriptors. These are not extraordinary except for the hydrogen bond basicity, B, which is indeed very large. Values of B for the HCHs are larger than many functionally substituted aliphatic compounds and as large as that of aliphatic amines. We find that B is 0.62-0.72 for the HCHs compared to 0.45 for propanone and 0.70 for ethylamine, the first time that such large hydrogen bond basicities have been identified in compounds with no functional groups. Hydrogen bond basicities are analyzed in order to examine what types of polychlorocompounds give rise to these elevated B values.

Chemometric evaluation of the solvent properties of liquid organic salts

Abraham's solvation parameter model was used to characterize the solvent properties of 38 liquid organic salts at a reference temperature of 121.4 °C. These salts are strong hydrogen-bond bases with a significant capacity for dipole–dipole and dipole-induced dipole interactions. The primary characteristics that dominate their solvent properties are the extent of charge localization on the anion and the extent of association between solvent molecules resulting from intermolecular hydrogen bonding. Their solvent properties cannot be duplicated by common non-ionic solvents used as stationary phases in gas chromatography.

Partition between phases of a solute that exists as two interconverting species

The partition between water and other solvents of a solute that exists as two rapidly interconverting species is discussed with specific reference to acetylacetone. Partition coefficients for the keto form and the enol form have been obtained from the global observed partition coefficient and the equilibrium constant for the ketoenol equilibrium in the various solvents. It is shown that global descriptors can be assigned to acetylacetone that reproduce the observed partition coefficients to 0.125 log units, and which can be used to predict further such coefficients in other solvents. In a similar way, descriptors can be assigned to the separate keto and enol forms that can be used to predict the individual partition coefficients. It is further shown that the keto form is more dipolar/polarizable than the enol form, and is a stronger hydrogen-bond base as well. Neither the keto nor the enol form have any significant hydrogen-bond acidity, which indicates that the enol must form a very strong intramolecular hydrogen-bond that remains intact in all the solvents studied; this conclusion is in accord with previous findings of Emsley and Freeman.