Limonene in Arizona liquid systems used in countercurrent chromatography. I Physicochemical properties

Limonene is a biorenewable cycloterpene solvent derived from orange peel waste. Its potential as a “green” solvent to replace heptane was recently evaluated. Countercurrent chromatography (CCC) is a preparative separation technique using biphasic liquid systems. One liquid phase is the mobile phase; the other liquid phase is the stationary phase held in place by centrifugal fields. A particular range of special proportions of the heptane/ethyl acetate/methanol/water system is called the Arizona (AZ) liquid system when the heptane/ethyl acetate ratio is exactly the same as the methanol/water ratio. A continuous polarity decrease is obtained between the most polar A composition (ethyl acetate/water or 0/1/0/1 v/v) and the least polar Z composition (heptane/methanol or 1/0/1/0 v/v), replacing heptane by limonene and methanol by ethanol produce biphasic liquid systems much more environmentallyfriendly than the original AZ compositions. The chemical compositions of the two liquid phases of 12 AZ limonene/ethyl acetate/ethanol/water proportions were fully determined by Karl-Fisher titration of water and by gas chromatography for the organic solvents. The results were compared with the compositions of the corresponding AZ mixtures containing heptane and methanol. Significant differences in ethyl acetate and ethanol distribution between phases of the two systems with identical volume proportions were established. The ratio of the upper phase over the lower phase volumes and the phase density difference are important in CCC, there are also significant differences between the classic and “green” AZ systems that are discussed.     

Solvent dependent swelling behaviour of poly(<Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam) and poly(<Emphasis Type="Italic">N</Emphasis>-vinylcaprolactam-<Emphasis Type="Italic">co</Emphasis>-itaconic acid) gels and determination of solubility parameters

Swelling behaviour of poly(N-vinylcaprolactam) (PVC) and poly(N-vinylcaprolactam-co-itaconic acid) (P(VC-co-IA)) gels was investigated in different solvents (water, ethanol, methanol, isopropyl alcohol (IPA), chloroform, toluene, acetone) and in binary solvent mixtures (ethanol/chloroform, ethanol/methanol, IPA/chloroform, ethanol/water, IPA/water). Gels were synthesised in ethanol by the free radical cross-linking polymerisation method at 60°C for 24 h in the presence of azo-bis(isobutyronitrile) and allyl methacrylate as the initiator and cross-linker, respectively. And also, ethanol/distilled water mixture (?_r = 4:1) was used as the synthesis medium to determine its effect on the swelling of gels. It was found that the presence of water in the synthesis medium significantly affected the equilibrium swelling value (ESV) and the swelling tendency of gels both in solvents and in solvent mixtures. All gels synthesised in ethanol showed the highest swelling in chloroform. The gels synthesised in the ethanol/water mixture displayed different swelling behaviour. In this case, while chloroform was still valid for maximum swelling of PVC, P(VC-co-IA) had the highest swelling in methanol. Solubility parameters of gels were predicted by the van Krevelen-Hoftyzer (VKH) and Hoy methods (group contribution methods) and theoretical calculations verified the experimental swelling order.     

A thermodynamic study of complexation process between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-dipyridoxylidene(1,4-butanediamine) and Cd<Superscript>2+</Superscript> in some binary mixed solvents using conductometry

Complexation of the Cd²⁺ ion with N,N′-dipyridoxylidene(1,4-butanediamine) Schiff base was studied in pure solvents including acetonitrile (AN), ethanol (EtOH), methanol (MeOH), tetrahydrofuran (THF), dimethylformamide (DMF), water (H₂O), and various binary solvent mixtures of acetonitrile–ethanol (AN–EtOH), acetonitrile–methanol (AN–MeOH), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dimethylformamide (AN–DMF), and acetonitrile–water (AN–H₂O) systems at different temperatures using the conductometric method. The conductance data show that the stoichiometry of complex is 1: 1 [ML] in all solvent systems. A non-linear behavior was observed for changes of log K_f of [Cd(N,N′-dipyridoxylidene(1,4-butanediamine)] complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions. The results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents.     

Adsorption from ternary liquid mixtures on silica gel and aluminium oxide

Formation of mixed adsorbed layers was tested for ternary liquid mixtures containing methanol or acetone and the binary solvent benzene+n — heptane. The specific excess adsorption isotherms from the liquid phase were measured on silica gel, silanized silica gel and aluminium oxide. The experimental adsorption data are discussed on the basis of the changes in the mixed solvent composition.     

Phase behavior of polylactides in solvent–nonsolvent mixtures

Isothermal phase diagrams for the semicrystalline poly-L-lactide (PLLA) and the amorphous poly-DL-lactide (PDLLA) in combination with several solvent–nonsolvent combinations (dioxane/water, dioxane/methanol, chloroform/methanol, and NMP/water) have been determined. The locations of the liquid–liquid miscibility gap, the solid–liquid miscibility gap and the vitrification boundary in the isothermal phase diagrams at 25°C were identified. The liquid–liquid miscibility gap for the systems with PLLA was located in the same composition range as the corresponding systems with PDLLA. For the systems containing PLLA solid–liquid demixing was thermodynamically preferred over liquid–liquid demixing. Attempts were made to correlate the experimental findings with predictions on the basis of the Flory-Huggins theory for ternary solutions using interaction parameters derived from independent experiments. Qualitative agreement was found between the theoretical predictions and the experimentally obtained liquid–liquid miscibility gap. No good agreement was found for the solid–liquid miscibility gap. © 1996 John Wiley & Sons, Inc.     

Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator

Low concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free-radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems.     

Controlled crystallization of poly(vinylidene fluoride) chains from mixed solvents composed of its good solvent and nonsolvent

Poly(vinylidene fluoride) (PVDF) chains with the same expanded state were obtained by dissolving PVDF resin in good solvent. Then, the crystallization of PVDF chains from mixed solvents composed of its good solvent and nonsolvent was investigated. N,N‐dimethylformamide (DMF) and ethanol were used as good solvent and nonsolvent of PVDF, respectively. The crystalline phases of PVDF were characterized by Fourier transform infrared (FTIR) spectroscopy and wide angle X‐ray diffraction (WAXD). For the crystallization of PVDF chains from mixed solvents, low ethanol content favored the formation of β phase, while high ethanol content resulted predominantly in the α phase. Different crystallization morphology was observed from the scanning electron microscopy (SEM) images. The obvious spherulite morphology disappeared with the increase in ethanol content in mixed solvent. According to thermal analyses, the crystallized PVDF from mixed solvents with high ethanol content had lower onset melting temperatures than that from low ethanol content. Smaller lamellar thickness calculated from WAXD data reasoned the low onset melting temperatures. The above results indicated that the crystallization of PVDF chains from mixed solvent was a “controlled” process by ethanol content. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 575–581, 2010     

Liquid trapping after supercritical fluid extraction with modified carbon dioxide

A polarity test mix consisting of acetophenone, N,N-dimethylaniline, naphthalene, 2-naphthol, and n-tetracosane was spiked onto sand and extracted with carbon dioxide modified with acetonitrile, methanol, or toluene. The extracts were collected in chloroform, hexane, methanol, or a mixed collection solvent consisting of equal parts chloroform-hexane-methanol. The mixed collection solvent which showed excellent recoveries for pure CO₂, had the worst recoveries of all the collection solvents with modified CO₂. Overall hexane was the best collection solvent studied for these analytes under these extraction conditions.     

Anion-exchange behaviour of several elements in hydrobromic acid-organic solvent media

The anion-exchange behaviour of 19 elements in hydrobromic acid-organic solvent media has been investigated. The batch distribution coefficients of the metal ions were determined in these systems employing the strongly basic anion-exchange resin Dowex 1, x 8. Organic solvents used were methanol, ethanol, n-propanol, isopropanol, methyl glycol, acetone, tetrahydrofuran and acetic acid. The most suitable conditions for some quantitative separations based on these equilibrium studies are indicated and discussed.     

Isolation and characterization of chlorophylls and xanthophylls in grass by high-speed countercurrent chromatography

To isolate chlorophyll from grass extract by means of high-speed countercurrent chromatography, a solvent system composed of n-hexane–dichloromethane–ethanol–water 4:2:6:2 (v/v/v/v) was applied. The isolation of chlorophylls a, b, and pheophytins a, b was successfully performed from grass when dichloromethane was part of the solvent system. Comparatively, when chloroform is part of the stationary phase instead of dichloromethane, the xanthophyll separation showed better resolution compared to chlorophylls. Through the solvent system, we could demonstrate the meaningful difference of polarity between dichloromethane, a polar aprotic solvent, and chloroform, a non-polar solvent. Therefore, n-hexane–dichloromethane–ethanol–water 4:2:6:2 (v/v/v/v) is adequate for chlorophylls separation because it changes the system to yield more polarity. This hypothesis supports the fact that the elution mode length was 10?hr and the extrusion mode 2?hr, whereas with chloroform the elution mode length was 7?hr and the extrusion mode 4?hr. Online high-performance liquid chromatography in conjunction with atmospheric pressure chemical ionization mass spectrometry (HPLC/APCI-MS) was suitable to identify xanthophylls and chlorophylls fractions by means of mass spectra in positive (+) mode. Structure elucidation of chlorophylls and pheophytins was done by nuclear magnetic resonance (NMR) 1D/2D-NMR experiments.     

Enthalpy Characteristics and State of N,N-Disubstituted Amides of Formic and Acetic Acids in Water-Formamide Mixtures

The enthalpies of solution of N,N-disubstituted amides of formic and acetic acids at 298.15 K throughout the entire range of compositions of the water-formamide mixed solvent were measured. The enthalpies of solvation and transfer of the amides from water into the mixed solvent were calculated. The effects of the structure and properties of the solutes and also of the composition of the mixed solvent on their thermochemical characteristics were considered. The monotonous weakening of solvation of the alkylamides throughout the entire range of mixture compositions results from reduced exothermicity of their nonspecific and specific solvation. Analysis of the deviations of the enthalpies of transfer from additivity in composition showed that the hydrocarbon radicals of the amides are slightly more solvated by formamide, while the polar functional groups, by water.     

Preferential Solvation in Aqueous–Organic Mixed Solvents Using Solvatochromic Indicators

Solvatochromism of the twisted intramolecular charge-transfer (TICT) fluorescence of 4-(N,N-dimethylamino)benzonitrile (DMABN) in pure water, methanol, ethanol, 1-propanol, 2-propanol, acetone, acetonitrile, and in the corresponding aqueous–organic binary mixed solvents was systematically studied and an empirical solvent polarity scale (F _B) based on the DMABN solvatochromism was defined. The F _B parameters of the explored binary mixed solvents as a function of solvent composition were analyzed by a stepwise solvent-exchange (SSE) model to clarify the preferential solvation (PS) of the probe dye in these binary mixed solvents. Solvation diagrams toward DMABN in the mixed solvents, i.e., the local solvent composition in the solvation shell of DMABN molecules was depicted as a function of bulk solvent composition to visualize the PS in these mixed solvents. For comparison, a similar PS analysis was applied to the solvatochromism of 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1- yl)phenolate (ET-30) and pyrene (Py) in these mixed solvents; the responsive PS pattern of the mixed solvents toward the specific indicator dye of DMABN, ET-30, and Py was then discussed in terms of the chemical properties of the probe dye, the properties of the mixed solvents, and the solute–solvent and solvent–solvent interactions.     

New piperazine‐based polymerizable monoquaternary cationic surfactants: Synthesis,polymerization, and swelling characteristics of gels

Monoquaternary cationic polymerizable surfactants of type N‐acryloyl‐N′‐methyl‐N′‐alkyl piperazinium bromide based on piperazine heterocycle was synthesized by reacting N‐acryloyl‐N′methyl piperazine with the corresponding n‐alkyl bromide (decyl, dodecyl, tetradecyl, and hexadecyl) in anhydrous acetone at room temperature. The resulting surfactants were deliquescent to display any sharp melting points. The surface activity was studied by surface tension measurements. Due to the complex head group geometry of these surfactants, the critical micelle concentration value was high in comparison to the analogous alkyltrimethyl ammonium bromides of similar alkyl chain length. The surfactants were polymerized by micellar (in water) and isotropic (in benzene) conditions and the resulting polymers were characterized by solubility and viscosity studies. The polymers prepared in water showed higher viscosity than the ones prepared in benzene as a result of micellar aggregation in water. The reduced viscosity of the polymers in polar solvents such as methanol and dimethyl formamide (DMF) showed polyelectrolyte‐like behavior, whereas nonelectrolyte behavior was observed in chloroform. pH‐responsive hydrogels were prepared by polymerizing the surfactants in the bicontinuous phase of a microemulsion. The resulting polymers did not exhibit any definite micro/nanostructure due to cross‐polymerization of the hydrophilic oil in the bicontinuous network structure. The gels were highly responsive to changes in pH of the medium and showed high‐swelling degree in acidic media owing to the protonation of the tertiary nitrogen of the piperazine ring. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2059–2072, 2009     

Water-methanol-benzene ternary system. Thermochemical experiment and computer simulation

Solution heats have been measured for benzene dissolved in mixtures of water with methanol at 25°C. The resulting values are compared with data for water-methanol-aniline, water-acetonitrile-benzene, and water-acetonitrile-aniline systems. Computer simulations have been performed for binary mixtures of water with methanol and dilute solutions of benzene in these mixtures. Thermodynamic and structural characteristics of solutions were obtained by calculations. The enthalpy of benzene transfer from water into a mixed solvent correlates with the relative deviation of the local composition from the mean composition of the mixture.     

Preferential sorption and permeation of binary liquid mixtures in poly (vinyl chloride) membrane by pervaporation

Preferential sorptions and pervaporation selectivities in poly (vinyl chloride) (PVC) membrane for various binary liquid mixtures were investigated. Methanol/n-propanol, benzene/n-hexane, and ethanol/water mixtures were selected as the binary liquid mixture. In the methanol/n-propanol mixture, methanol was preferentially sorbed in the PVC membrane and predominantly permeated. In the benzene/n-hexane mixture, benzene was incorporated and permeated preferentially. In the ethanol/water mixture, ethanol was preferentially sorbed in the PVC membrane and water was preferentially permeated. The preferential sorptions were analyzed according to Mulder's model derived from Flory-Huggins thermodynamics. The pervaporation selectivity in these systems were discussed using a sorption selectivity and diffusion selectivity. © 1995 John Wiley & Sons, Inc.     

Dilute solution properties of tactic poly(2-hydroxyethyl methacrylate)

Isotactic and syndiotactic poly(2-hydroxyethyl methacrylate) (PHEMA) have been prepared. Intrinsic viscosity–molecular weight relationships were established for the isotactic and syndiotactic PHEMA in N,N-dimethylformamide (DMF) at 25°C by solution viscometry and light scattering. The unperturbed dimensions and interaction parameters were examined in DMF, water, methanol, ethanol, and water–methanol (1:7 by volume) mixture for isotactic PHEMA and in DMF, methanol, and water–methanol (1:7 by volume) mixture for syndiotactic PHEMA using the Stockmayer–Fixman representation. The results suggest that the compact random coil structure for isotactic PHEMA occurs in water solvent and the isotactic PHEMA is more highly extended in polar solvents.     

Mass and momentum transfer in polymers. III. Effects of liquid penetrants on tensile stress relaxation of amorphous polymers

Sorption, diffusion, swelling, and tensile stress relaxation measurements were made at room temperature (23°C) for the systems poly(n-butyl methacrylate) (PBMA) with liquid methanol and ethanol, and poly(methyl acrylate) (PMA) with liquid water. Stress relaxation curves for the fully swollen polymers could be superimposed approximately with those for the dry polymers by appropriate shifting along the long axes. For PMA–water the measured curve for stress relaxation with concurrent sorption could be predicted accurately by using a moving boundary theory with data measurements of stress relaxation of the unswollen and swollen polymer combined with sorption data. The modified moving boundary theory is generalized to include the effects of dimension changes through swelling and the larger effects of plasticization associated with sorption of liquids. This improved theory accurately predicts measured curves of stress relaxation with concurrent sorption for the PBMA–alcohol systems from individual stress relaxation, sorption, diffusion and swelling data. The general approach should be applicable to other amorphous polymer–liquid swelling agent systems. The anisotropic nature of swelling of polymer films and its effect on calculated diffusion coefficients are discussed briefly.     

Bubble temperature measurements on the binary mixtures formed by chlorobenzene with methanol,ethanol, n-propanol and sec-butanol at 94.6 kPa

Bubble temperatures at 94.6?kPa, over the entire composition range have been measured for the binary mixtures formed by chlorobenzene with methanol, ethanol, n-propanol and sec-butanol using a Swietoslawski type ebulliometer. The liquid phase composition versus temperature data are found to be well represented by the Wilson model.     

Preparation of a monolithic column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction for capillary liquid chromatography

A monolithic capillary column with a mixed‐mode stationary phase of reversed‐phase/hydrophilic interaction chromatography was prepared for capillary liquid chromatography. The monolith was created by an in‐situ copolymerization of a homemade monomer N,N‐dimethyl‐N‐acryloxyundecyl‐N‐(3‐sulfopropyl) ammonium betaine and a crosslinker pentaerythritol triacrylate in a binary porogen agent consisting of methanol and isopropanol. The functional monomer was designed to have a highly polar zwitterionic sulfobetaine terminal group and a hydrophobic long alkyl chain moiety. The composition of the polymerization solution was systematically optimized to permit the best column performance. The columns were evaluated by using acidic, basic, polar neutral analytes, as well as a set of alkylbenzenes and Triton X100. Very good separations were obtained on the column with the mixed‐mode stationary phase. It was demonstrated that the mixed‐mode stationary phase displayed typic dual retention mechanisms of reversed‐phase/hydrophilic interaction liquid chromatography depending on the content of acetonitrile in the mobile phase. The method for column preparation is reproducible.     

Specific swelling behaviors of alkali‐metal poly(styrene sulfonate) gels in aqueous solvent mixtures

Counterion‐ and solvent‐specific swelling behaviors were investigated for alkali‐metal poly(styrene sulfonate) (PSSM) gels having different degrees of sulfonation in aqueous organic solvent mixtures [water plus methanol, ethanol, 2‐propyl alcohol, t‐butyl alcohol, dimethyl sulfoxide (DMSO), acetone, acetonitrile, tetrahydrofuran, or dioxane]. With an increasing organic solvent concentration, most gel systems, except for DMSO, showed a volume phase transition. The transition abruptly occurred without significant deswelling in the lower solvent concentration region. Such swelling behavior contrasted with that of other common charged gel systems, including alkali‐metal polyacrylate (PAAM) gels, which showed gel collapse after gradual deswelling with an increasing organic solvent concentration. The dielectric constant at the critical transition point (D_cr) for most mixed solvent systems decreased in the order of PSSK ≥ PSSCs ≥ PSSNa > PSSLi; that is, larger counterion systems were favorable for the transition. The counterion specificity also contrasted with our previous results for PAAM gels: PAANa > PAAK > PAALi ～ PAACs. On the other hand, the solvent specificity for the PSSM gels was similar to that for the PAAM gels; the higher the dielectric constant was of the organic solvent, the higher the D_cr value was at which the transition occurred. These specificities were examined on the basis of the solvation properties of the counterions and polymer charged groups and the solvent properties such as the Gutmann–Mayer donor number and acceptor number. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1166–1175, 2007