Search

A simple dual impedance tester has been designed for determining the water content in organic solvents. The detection cells are formed by a pair of semi-cylindrical electrodes of aluminium foil, located opposite one another around the outer surface of a glass tube with the tested solution. Thus, the electrodes are not in contact with the analysed solution. The detection cells are connected as a capacity determining the frequency of the integrated multivibrator. The analytical signal is the difference between the frequency of the multivibrator with the measuring cell filled with the analysed solution and the multivibrator with the cell filled with pure anhydrous solvent. Solvents with various permittivities and water contents to 50% v/v were tested, with a detection limit from 0.2% (dioxane) to 1.4% (acetonitrile). The method can also be used for determining the relative permittivity of solvents with various water contents. The detector can even be used outside the laboratory because it can be powered by a standard 9-V battery. [ABSTRACT FROM AUTHOR]

Abstract: Tri-n-butyl phosphate (TBP) is a common solvent used for extracting metal ions from acidic solutions. In this work, the extraction of water and acid by TBP was modelled up to 16molal HCl, which is considerably above the range of existing work. The solubility parameter and thermodynamic equilibrium constant for the formation of each extracted species were determined using both experimental and literature data. The resulting model was able to successfully predict both the water and hydrochloric acid extraction by undiluted TBP or TBP diluted in aliphatic solvent within this concentration range. Water was shown to be extracted as the mono-hydrate at lower water activities and the di-hydrate as activity further increased. HCl was extracted as the tri-solvate at low acid concentrations, with the di-solvate , and mono-solvate forming as acid concentration increased. The present results show that at high acid concentrations, water is rejected from the organic phase as the acid is extracted, with the species formed having a typical composition of . The speciation also depends upon the extent of the dilution of TBP within the organic phase. Thus, tri-solvates are not present in undiluted TBP below 2mol/L HCl, but are present in TBP diluted in aliphatic solvent. [Copyright &y& Elsevier]

Abstract: To develop an efficient green extraction approach for recovery of bioactive compounds from natural plants, we examined the potential of pressurized liquid extraction (PLE) of ginger (Zingiber officinale Roscoe) with bioethanol/water as solvents. The advantages of PLE over other extraction approaches, in addition to reduced time/solvent cost, the extract of PLE showed a distinct constituent profile from that of Soxhlet extraction, with significantly improved recovery of diarylheptanoids, etc. Among the pure solvents tested for PLE, bioethanol yield the highest efficiency for recovering most constituents of gingerol-related compounds; while for a broad concentration spectrum of ethanol aqueous solutions, 70% ethanol gave the best performance in terms of yield of total extract, complete constituent profile and recovery of most gingerol-related components. PLE with 70% bioethanol operated at 1500psi and 100°C for 20min (static extraction time: 5min) is recommended as optimized extraction conditions, achieving 106.8%, 109.3% and 108.0% yield of [6]-, [8]- and [10]-gingerol relative to the yield of corresponding constituent obtained by 8h Soxhlet extraction (absolute ethanol as extraction solvent). [Copyright &y& Elsevier]

Abstract: Clegg–Pitzer–Brimblecombe ion-interaction semi-empirical approach was rarely exploited for modeling electrolyte, particularly, in mixed solvent systems. Indeed, a review of the literature shows that the use of an exact and complete form of this model (PSC) was only limited to the works of two research groups for the investigation of electrolyte in mixed solvent systems. In this work, we have used both Pitzer and PSC ion-interaction theoretical approaches for modeling the non-ideal behavior of HCl in the ternary HCl+methanol+water electrolyte system. The modeling purposes were achieved based on the experimental determination of the mean molal activity coefficients for HCl in this ternary system by using the potentiometric data of a galvanic cell containing a pH glass membrane and Ag/AgCl electrodes. The measurements were performed over the electrolyte molality ranging from 0.01 up to 5.75mol/kg in mixed methanol (x%)+water (100− x%) solvent, with solvent mass fraction percents: x%=10, 20, 30, 40 and 50%, at 298.15±0.05K. [Copyright &y& Elsevier]

Abstract: A LFE (Linear Free Energy) analysis of kinetic data for different organic reactions in various organic aqueous solutions was carried out. The rate constants of these reactions were compared with those for the solvolysis of tert-butyl chloride in the same solvents in terms of the LFE Relationships, and linear plots were observed in a wide range of the co-solvent content. This similarity points to a common nature of the solvent effect in these reactions in variety of water–organic mixtures, regardless of largely different reaction mechanisms. We explain these results by the prevalence of hydrophobic stabilization of the initial state of these reactions in water-rich solvent mixtures. Recently the same conclusion was also made on the basis of investigations into sonication effects in kinetics of organic reactions. A considerable contribution of hydrophobic effects to the Y scale by Grunwald and Winstein was deduced. [Copyright &y& Elsevier]

Abstract: Cationic corn starch derivatives with a high degree of substitution are prepared in alkaline solution or in mixed media of organic solvent and water with different levels of the cationic reagent, 2,3-epoxypropyltrimethylammonium chloride. The starch cationization yield is investigated, and the results indicate that the degree of substitution (DS) of the samples depends on the reaction conditions and reaction media. The maximum DS values are up to 1.37 in 1,4-dioxane alkaline–aqueous solution. Meanwhile, the structures of the cationic starch derivatives are characterized by elemental analyses, FTIR spectroscopy, X-ray diffraction, and 13C NMR spectroscopy, as well as by SEM techniques. [Copyright &y& Elsevier]

Abstract: An efficient method for the conjugate addition of unactivated alkyl iodides to α,β-unsaturated carbonyl compounds using indium/copper in water is described. The reactions proceed more efficiently in water than in organic solvents. In, CuI, and InCl3 are all essential for efficient reaction. Formation of a symmetrical vic-diarylalkane is observed when an aryl-substituted alkene is used as substrate. [Copyright &y& Elsevier]

Abstract: The asymmetric transfer hydrogenation of nonfunctionalized aromatic ketones catalyzed by Ru-TsDPEN was performed successfully in a mixture of poly(ethylene glycol) (PEG) and water. High activity and enantioselectivity were obtained, which were better than or comparable to those obtained in conventional organic solvents. The unmodified catalyst could be easily recovered after extraction of the reduced product with a less polar solvent such as hexane, and was reused at least 14 times without obvious loss in enantioselectivity. These results indicate that the inexpensive and non-toxic aqueous PEG can serve as a new means for the immobilization of Ru-TsDPEN catalyst and related variants without calling for catalyst modification. [Copyright &y& Elsevier]