Tetrahydrofuran-Water System

It was also highly desirable to learn how to better control the salting-out effect in water-tetrahydrofuran systems so that extractions in this pair of mixed solvents could be performed. This present study of the phase relationships in some of the solvent systems used in aminosugar research includes the determination of the phase diagrams of the systems potassium acetate-water-dioxane, potassium acetate-water-tetrahydro-furan, and potassium chloride-water-tetrahydrofuran, and an attempt to provide a theoretical explanation for the experimental results. 

Gel permeation chromatography was performed in tetrahydrofuran using a Waters pump system and a Model 410 differential refractive index detector for the eluant. Five Ultrastyragel columns with nominal porosities ranging from 500 to 105 angstroms were used for all the samples and the polystyrene standards. 

The Group VI metal carbonyls demonstrate good activity in the WGSR, but differ significantly from ruthenium carbonyl in several ways. Tables IV and V summarize some WGSR experiments with chromium and tungsten carbonyls in a tetrahydrofuran-water solvent system. 

The compound [(i7s-CsHs)Cr(NO)2] 2 was first prepared in low yields (<5%) by the reduction of (i75-CsHs)Cr(NO)2Cl with sodium tetrahydroborate in a two-phase water-benzene system.6 Recently, this complex was isolated in 75% yield from the zinc amalgam reduction of (i7s-C5Hs)Cr(NO)2Cl in tetrahydrofuran over a period of 21 hours.2 However, [07s-CsH5)Cr(NO)2]2 is synthesized most conveniently by the reduction of the above-mentioned chloro complex with sodium amalgam in benzene as outlined below. 

The use of nonpolar chemically bonded stationary phases with a polar mobile phase is referred to as reverse-phase HPLG This technique separates sample components according to hydrophobicity. It is widely used for the separation of all types of biomolecules, including peptides, nucleotides, carbohydrates, and derivatives of amino acids. Typical solvent systems are water-methanol, water-acetonitrile, and water-tetrahydrofuran mixtures. Figure 3.15 shows the results of protein separation on a silica-based reverse-phase column. 

When HPLC is used as part of the analysis, the mobile phase is typically a mixture of methanol and methyl-tert-butyl ether (i.e., 50 50, v/v), although other HPLC solvents for LC/MS using APCI (e.g., water, tetrahydrofuran) can be used. It is important to note that if combustible nonaqueous solvent systems are used, water or a halogenated solvent such as methylene chloride or chloroform should be added to the mobile phase postcolumn to suppress ignition in the ion source. In addition, the APCI source must be vented outside the laboratory and should not allow air into the ionization chamber. A scan range of m/z 300 to 1000 will include the known carotenoids and their most common esters. 

Lower-sulfonated subsidiary colors of sunset yellow, among them 5-(phenylazo)-6-hydroxy-naphthalene-2-sulfonic acid (ANSC) and 4-[(2-hydroxynaphthalene-l-yl)azo]benzenesulfonic acid (BNSC), were determined by reverse-phase HPLC using Novapak Cl 8 and gradient elution with a water-tetrahydrofuran solvent system buffered with ammonium acetate (192). 

More recently, this method has been successfully extended by us18 to form the inverse systems, i.e. water core/polymer shell particles dispersed, initially in oil, but then transferred to an aqueous continuous phase. Clearly, whether one needs an oil or a water core depends on the nature of the active material to be released. Now one starts with a water/oil emulsion, rather than an oil/water emulsion, but the basic principles are very similar. A variety of shell polymer systems were prepared, including PMMA and poly(tetrahydrofuran) [PTHF]. The high vapor pressure liquid used in this case was in general, acetone. It turned out, however, that these water core systems are intrinsically more difficult to make than the equivalent oil core systems, because large amounts of acetone were required to dissolve the polymers initially in the water-acetone mixtures. An oil was then required which did not mix too well with acetone. In general, mineral oil worked reasonably well. In order to transfer the water core capsules into an aqueous continuous phase, the particles were centrifuged in... 

Table II. Solubility Curve and Tie-Line Data for the System Potassium Acetate—Water-Tetrahydrofuran in Weight Percentage...

Fig. 11. Dependence of the exchange current of the Zn(II)/Zn(Hg) system on the mole fraction (jCj) of organic solvents in their mixtures with water. Curve 1, water-diox-ane curve 2, water-ethanol curve 3, water-acetonitrile curve 4, water-tetrahydrofuran curve 5, water-acetone.

Figure 3.7 Phase diagram for methanol-acetonitrile tetrahydrofuran-water solvents systems in reversed-phase liquid chromatography, showing the isoelutropic plane, A-B-C, and the positions of the isoelutropic mobile phases D and E described in Table 3.5.

Sections 9.4 and 10.3 have already provided the basis for optimization by attempting to work with three different solvent mixtures hexane-ether, hexane-dichloromethane and hexane-ethyl acatate for adsorption chromatography and water-methanol, water-acetonitrile, water-tetrahydrofuran for reversed-phase systems. However, this concept is not restricted to binary mixtures but a third or even a fourth component may be added in an attempt to improve the separation. An arrangement of seven different mixtures (Figure 18.11) provides the best basis for systematic evaluation. An example is outlined below. 

Reagent grade water was prepared from distilled water using a Millipore Milli-Q2 water purification system. Distilled-in-glass, UV grade tetrahydrofuran (THF) and acetonitrile (CH.CN) was used as received from Burdick Jackson Labs. Solutions were prepared in volumetric flasks and were filtered through 0.2UM Millipore membrane filters. 

Fig. 11.3-3 Pressure swing distillation of the azeotropic system water/tetrahydrofuran...

MAG Maghsoud, Z., Famili, M.H.M., and Madaeni, S.S., Phase diagram calculations of water/tetrahydrofuran ly(viityl chloride) ternary system based on a compressible regular solution model, Iran. Polym. J., 19, 581,2010. 

The two-pressure system is also used for the separation of acetonitrile-water, tetrahydrofuran-water, methanol-MEK, and methanol-acetone tFrank. 19971. In the latter application the second column is at 200 torr. Realize that these applications are rare. For most azeotropic systems the shift in the azeotrope with pressure is small, and use of the system shown in Figure 8-6 will involve a very large recycle stream This causes the first column to be rather large, and costs become excessive. 

Polythiophene is readily produced by inserting a working electrode, counterelectrode, and reference electrode into a nonaqueous electrolyte in which 0.1 to 1.0 M thiophene is dissolved and then increasing the cell potential to greater than 1.6 V (versus SCE). Salts such as lithium or tetrabutylammonium perchlorate, hexafluo-rophosphate, or trifluoromethylsulfonate are typical electrolytes. Acetonitrile, ben-zonitrile, dichloromethane, and tetrahydrofuran are suitable solvents. As previously discussed for polypyrrole, polythiophene has been prepared in aqueous solutions [247]. A conductive, electroactive poly thiophene film was polymerized from a phosphoric acid-water-thiophene system using mild electrochemical polymerization conditions. 

Alkyl ether sulphates can be analysed on a 2.5 cm x 2 mm i.d. column of CIS reverse phase material with a water/tetrahydrofuran gradient system [20]. In this example the detector was the evaporative light scattering detector, as a gradient system was being used with a molecule with no strong chromophore. Alternatively, to obtain more detailed distributions, the molecule could be desulphated and analysed as described for alcohol ethoxylates. 

There are many important industrial applications of azeotropic separations, which employ a variety of methods. In this book we discuss several of these chemical systems and demonstrate the application of alternative methods of separation. The methods presented include pressure-swing distillation, azeotropic distillation with a light entrainer, extractive distillation with a heavy entrainer (solvent), and pervaporation. The chemical systems used in the numerical case studies included ethanol-water tetrahydrofuran (THF)-water, isopropanol-water, acetone-methanol, isopentane-methanol, n-butanol-water, acetone-chloroform, and acetic acid-water. Economic and dynamic comparisons between alternative methods are presented for some of the chemical systems, for example azeotropic distillation versus extractive distillation for the isopropanol-water system. 

DBC complexes with metal salts in the water-benzene system are the products of the interfacial reaction [119]. The measured work of adsorption (15.9 kJ/mol) can be taken as a sum of the free energy of complex formation and work of adsorption of DBC at the water-benzene interface. The dissolution of complexes in bulk phases was neglected. The interfacial constants of complex formation (Table 3) calculated from the work of adsorption are close to the constants determined in the mixed solvent - water-tetrahydrofuran [114]. The only exceptions are the complexes of DBC with Ba " and La salts. Apparently this is due to stronger Coulomb repulsion of ions in DBC-salt complexes at the interface as compared to the bulk phases. (At the interface, the anions... 

While the monomer is soluble in virtually all common solvents, the polymer is soluble in water and in many water-solvent systems. Suitable solvents for the polymer are alcohols, ketones, tetrahydrofuran, chlorinated hydrocarbons, pyridine, and lactones. Aromatic solvents and esters swell the polymer, and ether and aliphatic hydrocarbons are nonsolvents. 

Ramkumar, D. H. S. Odak, S. V. Kudchadker, A. P. Mixture properties of the water +. gamma.-butyr-olactone + tetrahydrofuran system. 3. Isobaric vapor-liquid equilibrium of water -1-. gamma.butyrolactone and tetrahydrofuran -1-.gamma.-butyrolactone at 1.013 bar. J. Chem. Eng. Data 1989, 34, 466-467. 

Johnson et al. (34) eoupled SEC in the non-aqueous mode (Mieropak TSK gel eluted with tetrahydrofuran) to a gradient RP LC system using aeetonitrile/water for the determination of malathion in tomato plants and lemonin in grapefruit peel. 

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