Analytical applications of organic reagents in hydrophobic gel media-II Selective preconcentration of mercury(II) with dithizone or thiothenoyltrifluoroacetone gel

Mercury(II) at the sub-ppm level is selectively trapped on a column packed with cross-linked polystyrene gel beads soaked with zinc dithizonate or thiothenoyltrifluoroacetone. Mercury trapped on the beads can be back-extracted into the aqueous phase with a hydrogen halide solution. Mercury in sea water at ppm or ppM level has been successfully preconcentrated by this procedure.     

Analytical application of organic reagents in hydrophobic gel media-IV Selective preconcentration of Cobalt(II) with 1-nitroso-2-naphthol gel

Cobalt is selectively extracted from solution onto gel beads impregnated with 1-nitroso-2-naphthol. A concentration factor of 67 has been achieved by passing 2 litres of sea water containing 0.05 ppm of cobalt over the beads at a flow-rate of 40 ml/hr. The cobalt is eluted from the beads with methyl isobutyl ketone.     

Analytical complexation reactions of organic reagents with metal ions in a solidified gelatin gel

Solidified gelatin gel is an original medium for analytical complexation reactions between organic reagents and element ions. The chemical nature of this biopolymer enables the electrostatic immobilization of organic reagents bearing anionic groups, like Arsenazo III, by protonated amino groups of the macromolecule. It was shown that the exhaustive capacity of the matrix towards organic sulfonate reagents differing in the number of sulfonic groups and the geometrical size of molecules was related to the specific properties of matrices and the fractal properties of the gel surface. It was found that the conditions for the reactions of complex formation and decomposition of the reagents immobilized in the gel were identical to those for reactions in aqueous solutions. It was proved that the gel fixed on a transparent triacetylcellulose support could be used as a component of sensing elements of optical sensors and/or test systems. This was demonstrated by the examples of the determination of La(III), Th(IV), U(VI), Ca(II), and SO₄²⁻.     

亚磺化脱卤试剂在有机合成中的应用

本文综述了亚磺化脱卤试剂在有机合成中的应用。特别是氟烷基化反应中的应用。     

Simple semiquantitative determination of trace metal ions by use of reagent gel columns-II: determination of zinc with dithizone gel

Zinc(II) at the sub-ppm level was determined by using a column, packed with gel beads containing dithizone. The beads turned from green to pink when the sample solution containing zinc was passed through the column at pH 6.2. Various interfering cations were masked by the combined use of sodium thiosulphate, alpha'alpha-bipyridyl, hydroxylamine hydrochloride, N,N'-bis(beta-hydroxyethyl) dithiocarbamate and beta-dithiocarbaminopropionic acid. The length of the pink zone was proportional to the amount of zinc in the sample. With 0.01% dithizone gel, as little as 0.01 ppm of zinc could be determined in a 10-ml sample at a flow rate of 0.2 ml min .     

Simple semiquantitative determination of trace metal ions by use of reagent gel columns-I: determination of mercury with dithizone gel

Mercury(II) at the sub-ppm level was determined by using a column packed with gel beads containing dithizone stabilized as the zinc complex. The beads turned from pink to green when the acidified sample solution was passed through the column. If the solution contained mercury (II), the colour of the gel beads turned to orange owing to the formation of mercury dithizonate. The length of the coloured zone was proportional to the amount of mercury in the sample. With 0.01% dithizone gel, as little as 0.1 ppm of mercury(II) could be determined in a 20-ml sample at a flow-rate of 1 ml/min.     

Novel polymer-supported coupling/dehydrating reagents for use in organic synthesis

Two novel dehydrating reagents and, based on a phosphonium anhydride and an oxyphosphonium triflate respectively, were prepared by reaction of the corresponding polymer-supported phosphine oxides with triflic anhydride. Reagent, based on the novel phosphorus heterocycle 1,1,3,3-tetraphenyl-2-oxa-1,3-diphospholanium bis(trifluoromethanesulfonate), was found to be a useful reagent for ester and amide formation. A wide range of coupling/dehydration-type reactions, such as ester, amide, anhydride, peptide, ether and nitrile formation, were performed in high yield using the more readily prepared polymer-supported triphenylphosphine ditriflate, which was easily recovered and re-used several times without loss of efficiency. With primary alcohols, both reagents and provide an alternative to the Mitsunobu reaction, where the use of azodicarboxylates and chromatography to remove the phosphine oxide by-product can be avoided. The use of 4-dimethylaminopyridine allowed the esterification of secondary alcohols with to proceed in high yield but with retention of configuration.     

New and efficient synthesis of solid-supported organotin reagents and their use in organic synthesis

Novel resin-bound organotin reagents have been prepared, including for the first time resin-bound dimethyl tin reagents. Mild methodology has also been developed for the very efficient synthesis of resin-bound distannanes. The resin-bound tin chloride reagents have been used in a catalytic Stille coupling cycle and the resin-bound distannanes have been used in atom transfer cyclisations and proved to be much more effective than previously described resin-bound distannanes. As expected the use of resin-bound tin reagents facilitated their easy removal at the end of the reaction, and consequently residual tin levels in the organic products were low or negligible. The resin-bound distannanes could not, however, be successfully used for the palladium catalysed stannylation of a simple aryl iodide, which would have provided a useful approach to radiolabeling of aromatic substrates. The reasons for the failure in the stannylation process is unclear but crystal structure evidence indicates that there is a hypervalent interaction between the resin-bound tin atom and an adjacent ether oxygen which may effect the reactivity of the tin intermediates in the stannylation sequence.     

Analytical treatment of electrokinetic microfluidics in hydrophobic microchannels

Microfluidics in microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) devices is complex due to the large surface area to volume ratio. Thus, surface properties play an important role in flow behavior. In this paper, we summarize the effects of electric double layer and surface hydrophobicity of rectangular microchannels on time-dependent electrokinetic flow. Theoretically, we have shown that flow resistance can, in principal, be significantly reduced so that a larger flow rate can be obtained for pressure-driven flow or electric-field-driven flow. This relies on the ability to change surface charges and surface hydrophobicity independently. Our theoretical results provide guidelines for the design and operation of microfluidic flow in rectangular microchannels. Because of liquid slippage, zeta potential determination by traditional method could be overestimated. Taking into account the effect of hydrophobicity, a modified method is proposed to determine the zeta potential and slip coefficient for parallel-plate microchannels with hydrophobic surfaces.     

Studies with dithizone : Part 26. The interaction of thallium(III) with solutions of dithizone in organic solvents

The strong oxidising capacity of thallium(III) dominates its reaction with solutions of dithizone (H₂Dz) in organic solvents. When carbon tetrachloride is used as solvent, the unstable thallium(III) complex Tl(HDz)³ is found in the organic phase but it very quickly disproportionates to the thallium(I) complex [Tl(HDz)], and bis-1,5-diphenylformazan-3-yl-disulphide. This reaction is notably faster in chloroform, in which thallium(I) dithizonate is the first identifiable product. In contact with an acidic aqueous phase, thallium(I) dithizonate is reverted to regenerate dithizone in the organic phase and Tl⁺ ions appear in the aqueous phase. Organic solutions of the disulphide disproportionate spontaneously by first-order kinetics to give an equimolar mixture of dithizone and the mesoionic compound, 2,3-diphenyl-2,3-dihydrotetrazolium-5-thiolate: this change is much slower in carbon tetrachloride than in the more polar chloroform and is catalysed by both Tl⁺ and Tl³⁺. If thallium(III) is present in excess, the mesoionic compound is the principal oxidation product of the dithizone although a dication may also be formed. The mesoionic compound does not react with thallium(I) but forms a water-soluble 2:1 complex with thallium(III); partition of this complex into the organic phase is uninfluenced by chloride ions. Because of the large number of competing reactions, the composition of the reaction mixture at any stage of the reaction between thallium(III) and dithizone depends on the relative concentrations of the components, the order in which they are brought together, the time elapsed after mixing, the pH of the aqueous phase, and the nature of the organic solvent.     

Preparation and characterization of TADDOLs immobilized on hydrophobic controlled-pore-glass silica gel and their use in enantioselective heterogeneous catalysis

Highly porous silica gel (controlled-pore glass, CPG, ca. 300 m2 g(-1)) with covalently attached TADDOLs (loading 0.3-0.4 mmol g(-1)) and Me3Si-hydrophobized surface has been prepared: First, mercaptopropyl groups were attached to the silica gel by treatment with (mercaptopropyl)trimethoxysilane; then the SH groups were trityl-protected, and the remaining accessible SiOH groups hydrophobized by silylation (heating with Me3Si-imidazole); after deprotection, the SH groups were used as nucleophiles for benzylation with TADDOLs carrying a 4-bromomethyl-phenyl group in the 2-position of their dioxolane rings; alternatively, the SH groups have been benzylated with the 4-bromomethyl-benzaldehyde acetal of diethyltartrate, and the diarylmethanol moieties of the TADDOLs created on the solid support by addition of excess phenyl, or 1- or 2-naphthyl magnesium bromide. Each step of the immobilizing procedure was carefully monitored and analyzed (Ellman's test, methyl-red test), and resulting materials characterized by electron microscopy, DRIFT spectroscopy (IR), 13C- and 29Si NMR solid-state NMR spectroscopy, and elemental analysis. The immobilized TADDOLs were titanated to give (iPrO)2Ti-, Cl2Ti-, or (TosO)2Ti-TADDOLates which were used for catalyzing the additions of Et2Zn or Bu2Zn to PhCHO and of diphenyl nitrone to 3-crotonoyl-oxazolidinone. The following findings are remarkable: i) The enantioselectivities and conversions of the reactions mediated by the CPG-immobilized Ti-TADDOLates match those observed under standard homogeneous conditions. ii) If and when the rates and/or the enantioselectivities of reactions have dropped after several applications of the same catalyst batch, washing with aqueous HCl/acetone and reloading with titanate leads to full restoration of its performance. iii) There is no detectable loss of the hydrophobizing Me3Si groups after nine acidic washes! iv) There is a seasoning of the catalyst material in the Cl2Ti-TADDOLate-mediated [3+2] cycloaddition of diphenylnitrone: Initially it is necessary to use 0.5 equivalents of the immobilized catalyst to match the performance of the homogeneous catalyst; after three runs the reaction rate, enantio- and diastereoselectivity have dropped considerably; acidic washing after each subsequent run completely restores the performance; after a total of seven runs the amount of catalyst can be reduced to 0.4, 0.3, 0.2, and 0.1 equivalents in the following runs, with identical good results!     

锰试剂在有机合成中的应用

主要综述了近年来有机锰化合物及单质锰直接参与的有机反应有机合成中的应用。     

铟试剂在有机合成中的应用

综述了近十年来铟试剂在有机合成中的应用。重点讨论了铟试剂参与的有关碳-碳键形成的反应,如羰基化合物的烯丙基化、Reformatsky反应、成环以及三氯化铟作为Lewis酸的催化反应以及铟试剂的水相反应化学。铟试剂的这些反应,尤其是水相反应具有其它金属有机试剂在化学选择性和立体选择性方面具有独特的优势。     

Application of samarium reagents in organic synthesis

Application of samarium diiodide, samarium triiodide, Sm0/auxiliary system and organosamarium reagents in organic synthesis was reviewed.     

Use of organic reagents in inorganic analysis

Summary Paper chromatography of cobalt, palladium, uranium, thorium, and zirconium/1-nitroso-2-hydroxy-3-naphtholates which are quantitatively precipitated, has been studied. As most of the complexes were not soluble in organic solvents, their hydrochloric acid solutions and solution of the cobalt, palladium, and uranium complexes in ammonium hydroxide were used for spotting. A large number of developing solvents were tried both on plain and salt-impregnated papers. A solvent mixture containing 60% acetone, 38% isobutyl alcohol and 2% 12N HCl, by volume was found suitable for the resolution of a mixture of complexes of cobalt, palladium, and uranium on plain paper. Thorium and zirconium complexes, however, did not move appreciably with any of the solvent mixtures tried. The paper impregnated with salt solutions did not show any improvement in the separation. The effect of HCl in the above solvent mixture on the separation of cobalt, palladium, and uranium, was also studied. It was observed that a small amount of HCl was necessary in this developing solvent for the migration of the metals, a large excess of this acid, increases their R_f values and these are brought so close that the separation of the metals becomes difficult. The colour of the cobalt, palladium, and uranium spots on the developed chromatograms indicated that the metals migrated as their complexes. Similar experiments were done with free metals ions, which gave different R_f values and this confirmed the fact that it was the metal complexes that moved and these complexes were stable under the conditions of the experiment. Precipitation of Co, Pd and U with 1-nitroso-2-hydroxy-3-naphthoic acid is quantitative and the paper chromatographic experiment affords a convenient method of concentrating the metal ions.Part IV: See Z. anal. Chem. 155, 241 (1957).