Recurrent relations for the approximation of the physicochemical constants of homologues

In addition to the earlier revealed physicochemical constants of homologues whose changes in arbitrary series obey the simplest linear recurrent relations A (n + k) = aA(n) + b, such equations are shown to be applicable to the approximation of the solubility of organic compounds in water (k = 1), temperature dependences of the solubility of organic and inorganic compounds in water (k = ΔT), and nematic-isotropic phase transition temperatures for liquid crystals (k = 2). The a and b coefficients of linear recurrent relations are only determined by the nature of the homologous difference, and, if the homologous difference is the same, they are close for different series. This enables various properties of virtually arbitrary organic compounds to be described by unified recurrent equations, which is equivalent to the existence of a general method for their calculation. For continuous properties (for the example of the temperature dependence of solubility), a method for solving recurrent equations with nonintegral or nonequidistant argument values is suggested.     

Prediction of infinite dilution activity coefficients for systems including water based on the group contribution model with mixture-type groups: II. Extension and application

Group contribution models such as ASOG or UNIFAC were known to be inaccurate in the prediction of infinite dilution activity coefficients (γ^∞) for most of the systems containing water. To overcome the weakness inherent with the UNIFAC models, Zhang et al. (Fluid Phase Equil. 149 (1998) 27) have recently proposed a group-contribution-based model with mixture-type groups, where the mixture-type group is a hypothetical concept for taking into account the particular hydrophobic effects in aqueous organic systems. The proposed methodology has been proven to be applicable to alkane/water and alcohol/water mixtures in our previous study. In this work, the proposed method was further extended to the other classes of compounds, e.g. aromatics, ketones, acids, aldehydes, esters, ethers, nitriles and halogenated compounds. Compared to the conventional UNIFAC models, the proposed method demonstrates significant improvements in accuracy for various organic compounds in water mixtures.     

The effect of organic sorbates on water associated with environmentally important sorbents: estimating and the LFER analysis

The effect of organic sorbates on the water associated with naturally occurring sorbents is of significant interest since it probes the hydration of a sorbate-specific microenvironment and its role in a compound partitioning between various environmental compartments. This effect was described in a thermodynamically strict way by converting the sorption isotherms of organic vapors on variously hydrated sorbents into the derivatives relating the change in the amount of water associated with a sorbent to the change in the amount of an organic sorbate. Further, these derivatives were analyzed by means of the Linear Free Energy Relationship (LFER). The analysis included the sorption data for various organic vapors on such environmentally important sorbents as quartz, metal oxides, calcite, clay minerals and humic acid. From the LFER analysis it followed that (i) organic sorbate polarizability contributions from n- and π-electrons resulted in driving water into the sorbent phase; (ii) the increasing volume of the organic compounds involved expelling water molecules; (iii) the increasing hydrogen-bond acidity and basicity of organic sorbates resulted in expelling water from inorganic surfaces but in enhancing hydration of the humic phase. In contrast to inorganic surfaces, when sorbed on strongly hydrated humic acid, the majority of organic sorbates containing oxygen, nitrogen or sulfur atoms drive water into the sorbent phase. Several molecules of water may need to be cosorbed by a humic sorbent for each sorbed molecule of an organic compound thus supporting the possibility of the concomitant participation of a number of water molecules in organic sorbate–humic matter interactions.     

Recovery of metals from raw materials of industrial origin

Interaction of d elements and their compounds (oxides, sulfides, carbonates, and other compounds poorly soluble in water) with organic ligands in aprotic solvents was studied. Methods for recovery of metals from nonaqueous solutions of the resulting complex compounds are suggested.     

Asymmetric synthesis of warfarin and its analogues on water

The asymmetric Michael addition of 4-hydroxycoumarin to α,β-unsaturated ketones on water without organic co-solvents is reported to be catalysed by organic primary amines. The application of enantiomerically pure (S,S)-diphenylethylenediamine affords a series of important pharmaceutically active compounds in good to excellent yields (73–98%) and with good enantioselectivities (up to 76% ee) via reactions accelerated by ultrasound. In particular, our developments led to an efficient protocol for the ‘solids on water’ formation of the anticoagulant warfarin in both enantiomeric forms. The presented scalable and environmentally friendly organocatalytic approach affords the target drug in enantiomerically pure form.     

New Insights into the Effects of Tetrahydrofuran and Dioxane on the Selectivity of Ternary Eluent Compositions in RP-HPLC Systems

The present paper discusses the tendencies in the retention changes of a diverse set of organic model compounds on HPLC C18 stationary phases in aqueous ternary eluent mixtures containing tetrahydrofuran or 1,4-dioxane, and one short chain aliphatic alcohol (ethanol, n-propanol or isopropanol). The set of compounds consisted of steroid and non-steroid molecules with different hydrogen bond donor and/or acceptor abilities. Every eluent mixture contained 75 V/V% water and 25 V/V% organic solvent(s). The composition of the mixture was changed in 5 V/V% steps, starting with the binary alcohol–water mixtures and finishing with the binary ether–water mixtures. The results show clearly the dependency of retention times on the eluent composition, the size of the molecules, and the occurence of the hydrogen bond donor/acceptor groups. The isopropanol–tetrahydrofurane–water mixtures resulted in selective changes in the retention times of the compounds with acidic groups or with other non-acidic OH or NH protons in the neighborhood of electron-withdrawing groups. Every compound has shown elevated retention times in the isopropanol–dioxane–water, n-propanol–tetrahydrofuran–water, or n-propanol–dioxane–water mixtures. Clear trends could not be observed in the eluents with ethanol. The probable reason for the retention enhancement is the adsorption of the organic components of the mobile phase on the surface of the stationary phase. The different effects of the alcohols may originate from the interaction of their varying aliphatic alkyl chains with the C18 chains. This phenomenon may result in different availability of the C18 chains for dioxane, tetrahydrofuran and the model compounds.     

Austauscher mit cyclischen Polyethern als Ankergruppen—II: Anwendungen

Exchangers with cyclic polyethers as anchor groups have a large range of applications such as separations of cations with a common anion, of anions with a common cation, and of neutral organic compounds, and the determination of water by elution chromatography. Some crown ether monomers, especially 4- and 4,4′-alkyl-substituted benzo-derivatives are suitable for extractions and their adducts with heteropoly acids are used as liquid ion-exchangers. The exchangers are also applied in thin-layer chromatography and thin-layer electrophoresis. Furthermore the exchangers are successfully used in preparative chemistry, e.g., in salt conversions in order to isolate salts which are difficult to prepare by other means, in isolation and purification of organic compounds, and for anion activation in organic reactions.     

Removal of volatile organic components (VOCs) from water by pervaporation: separation improvement by Dean vortices

Dense polydimethylsiloxane (PDMS) hollow-fibre membrane modules built in straight and coiled configurations were studied in pervaporation for volatile organic compounds (VOCs) removal. Two different aqueous organic mixtures, n-butanol–water and chloroform–water, were investigated to determine how the permeate fluxes are affected by the module geometry. Data with chloroform–water mixtures of 0.1 and 0.05 wt% chloroform revealed that, in the laminar regime, coiled modules show improved chloroform mass transfer compared to conventional modules where straight hollow-fibre membranes are aligned in parallel. The improvement factor increases with the Reynolds number to reach a value of 2.3 at N_Re=2000. In the conventional and helical designs, with a calculated diffusion coefficient, the results are lower than those given by the Lévêque equation and the mass transfer correlation previously found for water oxygenation respectively. With an apparent diffusion coefficient, these experimental values are consistent with these two equations.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow.     

Retention Behavior of Some Compounds Containing Polar Functional Groups on Perfluorophenyl Silica-Based Stationary Phase

A retention study on perfluorophenyl silica-based stationary phase was undertaken for some organic compounds containing different polar functionalities. The dependence of the retention factor on the content of organic modifier (acetonitrile, or methanol) in mobile phase was fitted by polynomial equations. The only exception was observed for adenine, which showed a sigmoidal dependence for the retention factor versus organic modifier content. The extrapolated values of retention factor for water as mobile phase (log k _w) from these dependences were well correlated with octanol–water partition constants (log K _ow), excepting the values for hexachlorocyclohexane isomers and adenine. Temperature dependences of the retention factor obeyed the van’t Hoff equation with thermodynamic parameters similar to those obtained in reversed phase on C8 or C18 stationary phases, excepting two statines whose dependences of ln k on the reciprocal value of absolute column temperature were nonlinear. Again, adenine had an atypical behavior with decrease in the retention factor with the increase in column temperature, due to possible tautomeric equilibria of this compound in presence of water, in accordance with theoretical models reported by literature. Charge modeling with MarvinSketch package program revealed charged centers from analyte molecule that could interact differently with charge centers from stationary phase.     

Cu(II) 2-quinoxalinol salen catalyzed oxidation of propargylic,benzylic, and allylic alcohols using tert-butyl hydroperoxide in aqueous solutions

The synthesis of carbonyl compounds by oxidation of alcohols is a key reaction in organic synthesis. Such oxidations are typically conducted using catalysts featuring toxic metals and hazardous organic solvents. Considering green and sustainable chemistry, a copper(II) complex of sulfonated 2-quinoxalinol salen (sulfosalqu) has been characterized as an efficient catalyst for the selective oxidation of propargylic, benzylic, and allylic alcohols to the corresponding carbonyl compounds in water when in combination with the oxidant tert-butyl hydroperoxide. The reactions proceed under mild conditions (70 °C in water) to produce yields up to 99% with only 1 mol % of catalyst loading. This reaction constitutes of a rare example of propargylic alcohol oxidation in water, and it makes this process greener by eliminating the use of hazardous organic solvents. Excellent selectivity was achieved with this catalytic protocol for the oxidation of propargylic, benzylic, and allylic alcohols over aliphatic alcohols. The alcohol oxidation is thought to go through a radical pathway.     

Computational simulation of the molecular structure and properties of heterocyclic organic compounds with possible corrosion inhibition properties

The damages by corrosion generate not only high costs for inspection, repairing and replacement, but in addition these constitute a public risk. Thus the necessity of developing novel substances that behave like corrosion inhibitors. In general, the organic compounds have demonstrated a great effectiveness in inhibiting the watery corrosion of many metals and alloys. It has been demonstrated that the compounds that have nitrogen and sulfur in their structure provide a greater inhibition than those than only contain one of the atoms at a time, being this property attributable to its molecular structure. The objective of this work is to provide information about the electronic and molecular structure of several heterocyclic organic compounds: 1,3,4-thiadiazole and its derivatives, with different nucleophilic and electrophilic alkyl substituents (R1 and R2), obtained through quantum-chemistry calculations conducted by means of the gaussian 03W set of programs. It is an attempt to find the correlation between the molecular structure of these compounds and their possible behavior like corrosion inhibitors. It is important to take into account the effect of films formed by products of corrosion. Thus, the incorporation of metallic atoms in the calculations provides greater information about the relation between the reactivity of compounds and the metallic surface, in addition to the formation of stable complexes. The behavior of these organic substances in the presence of several solvents, among them water, facilitates the understanding of the processes of inhibition of the corrosion.     

Salt addition effect on partition coefficient of some phenolic compounds constituents of olive mill wastewater in 1-octanol-water system at 298.15 K

The 1-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. For biological systems, electrolytes play an important role in thermodynamic properties. The salt addition effect on the distribution of phenolic compounds between water and 1-octanol at 298.15 K has been studied. The phenolic compounds used were vanillic acid, protocatechuic acid, vanillin, tyrosol, cathecol, caffeic acid and syringic acid, and the considered salts were potassium chloride, sodium chloride and lithium chloride. The influence of both the concentration and size of the added salt on the partition coefficient (K _ow) have been considered. This study shows a salting in with the following decreasing order: LiCl > NaCl > KCl. The Gibbs energies of transfer of phenolic compounds (168–1) form chloride solutions to organic phase have been calculated using experimental 1-octanol-water partition coefficients.     

Adsorption and photoelectrocatalytic characteristics of organics on TiO2 nanotube arrays

The adsorption and photoelectrocatalytic characteristics of four different kinds of organic compounds (d-fructose, glutamic acid, fumaric acid, and nicotinic acid) on TiO₂ nanotube arrays (TNAs) were investigated using a thin-layer cell, wherein the compounds were rapidly and exhaustively oxidized. The photogenerated current–time (I _ph–t) profiles were found to be related to the adsorption, the degradation rate, and the reaction mechanism. The relationship between the initial organic compounds concentrations and photocurrent peaks (I _0ph) fit the Langmuir type adsorption model well, thereby confirming that the adsorption of organic compounds on TNAs was via monolayer adsorption. The adsorption equilibrium constant was obtained from the Langmuir equation. The results indicate that the adsorption performance of the organic compounds on TNAs were in the following order: nicotinic acid < d-fructose < glutamic acid < fumaric acid. The degradation of organic compounds on TNAs was classified as either easy or difficult based on the time of complete mineralization (t _end) of the organic samples under an equal holes consumption; the degree of degradation were as follows: fumaric acid < d-fructose < glutamic acid < nicotinic acid. The photoelectrocatalytic characteristics of the organic compounds on TNAs were also discussed by analyzing the changes in the I _ph –t profiles.