Thin-layer chromatographic separation and identification of some anions on copper sulphate impregnated silica gel layers

Summary Thin-layer chromatographic behaviour of thirteen anions on plain silica gel and silica gel impregnated with copper sulphate solution has been investigated in aqueous-organic solvents containing acetone, some of which have achieved reliable and reproducible separations. The effect of copper sulphate concentration on the mobility of anions has been examined. The results obtained on plain silica gel have been compared with those obtained on copper sulphate impregnated layers. The impregnated layers dramatically change the selectivity and permit separations not possible on untreated silica. Aqueous sodium chloride-acetone (9∶1) and ammonium hydroxide-acetone (9∶1) were the most effective solvent systems for differential migration of anions. Better results in terms of clarity of detection and compactness of spots were found with HCOOH-acetone as compared to HCl-acetone. The effect of anion loading on R_F values has been investigated and identification limits on impregnated layers determined.     

Controllable synthesis of highly crystallized mesoporous TiO_2/WO_3 heterojunctions for acetone gas sensing

Mesoporous semiconducting metal oxides(SMOs) heterojunctions are appealing sensors for gas detecting.However,due to the different hydrolysis and condensation mechanism of every metal precursor and the contradiction between high crystallinity and high surface area,the synthesis of mesoporous SMOs heterojunctions with highly o rdered mesostructures,highly crystallized frameworks,and high surface area remains a huge challenge.In this work,we develop a novel "acid-base pair"adjusted solvent evaporation induced self-assembly(EISA) strategy to prepare highly crystallized ordered mesoporous TiO_2/WO_3(OM-TiO_2/WO_3) heterojunctions.The WCl_6 and titanium isopropoxide(TIPO) are used as the precursors,respectively,which function as the "acid-base pair",enabling the coassembly with the structure directing agent(PEO-b-PS) into highly ordered meso structures.In addition,PEO-b-PS can be converted to rigid carbon which can protect the meso structures from collapse during the crystallization process.The resultant OM-TiO_2/WO_3 heterojunctions possess primitive cubic mesostructures,large pore size(～21.1 nm),highly crystalline frameworks and surface area(～98 m~2/g).As a sensor for acetone,the obtained OM-TiO_2/WO_3 show excellent re sponse/recovery perfo rmance(3 s/5 s),good linear dependence,repeatability,selectivity,and long-term stability(35 days).     

Synthesis,spectroscopic and structural characterization of diphenyltin(IV) complexes of acetone Schiff bases of S-alkyldithiocarbazates

New diphenyltin(IV) complexes of empirical formula, [Sn(C₆H₅)₂(NS)Cl] (NS = anionic forms of the acetone Schiff bases of S-methyl or S-benzyldithiocarbazate) have been prepared and characterized by IR, NMR and Mössbauer spectroscopic techniques. The crystal and molecular structures of the acetone Schiff bases of S-methyldithiocarbazate (Hacsme) and S-benzyldithiocarbazate (Hacsbz) and their tin(IV) complexes have been determined by X-ray diffraction. In the solid state, both the Schiff bases exist in their thioketo tautomeric forms with the azomethine nitrogen atom trans to the thione sulfur atom but in the tin(IV) complexes they are present in their deprotonated ene-thiolate forms being coordinated to the tin atom as bidentate chelating agents via the azomethine nitrogen and thiolate sulfur atoms. The tin atom adopts a five-coordinate, approximately trigonal bipyramidal geometry, with the thiolate sulfur atom of the Schiff base and the two phenyl groups occupying the equatorial positions. The azomethine nitrogen atom and the chlorine ligand occupy axial positions. The distortion from a regular trigonal bipyramidal or a square-pyramidal geometry is attributed to the restricted bite sizes of the five-membered chelate rings.     

Adsorbents for acetone in cyclohexane effuent employed in Ziegler-Natta catalyst process

Adsorption of acetone from cyclohexane on silica, alumina, coal, natural and leached chrysotile was investigated. Adsorption phenomenon was investigated by non-linear fitting, considering the Langmuir or Freundlich models. According to non-linear regression, coal present the highest K _L (12.07) and K _F (9.115) parameters. Silica and leached chrysotile exhibited similar behavior in terms of both K _L and K _F parameters. Alumina presented the highest adsorption capacity according to both Langmuir (q _m =58.689) and Freundlich (1/n=0.844) models. Non-supported Ziegler-Natta catalyst systems were shown to be more sensitive to acetone contamination. For the polymerization reactions carried on with contaminated solvent after the percolation through the adsorbents, good results were observed in the case of silica and alumina. Coal was not suitable for use in this catalyst system, probably due to leaching of organic components by the solvent (cyclohexane).     

The Number of Water-Water Hydrogen Bonds in Water-Tetrahydrofuran and Water-Acetone Binary Mixtures Determined by Means of X-Ray Scattering

The liquid structures of water-tetrahydrofuran (THF) and water-acetone binary mixtures were investigated by the X-ray scattering method. Comparison of the X-ray scattering data revealed that only one kind of intermolecular water-organic molecule interaction is commonly involved throughout all mole fractions of these liquid mixtures, in addition to the intermolecular water-water and organic molecule-organic molecule interactions, which are present in neat water and organic liquids, respectively. On the basis of this finding, we proposed a new analytical method for studying liquid mixtures. By this method the structural information on the intermolecular water-organic molecule interaction as well as the concentrations of the intermolecular water-water, water-organic molecules, and organic molecule-organic molecule interactions were obtained. Combining the concentrations of the intermolecular water-water interaction with the concentrations of water in the liquid mixtures, the number of water-water hydrogen bonds at various mole fractions was experimentally determined for the first time. From the dependence of the number of water-water hydrogen bonds on the composition of the liquid mixtures, the change of the size of the self-associated water-water clusters was deduced.     

Acetone promoted 1,4-migration of an alkoxycarbonyl group on a syn-1,2-diamine

A 2-protected cis-amino mitosene undergoes an irreversible acetone promoted isomerization and converts to the 1-isomer. Kinetic studies and DFT calculations of the reaction are reported. An organocatalytic mechanism is proposed, involving a covalent intermediate formed by reaction of the mitosene and acetone.     

Bifunctional thiophosphinamide catalyzed highly enantioselective Michael addition of acetone to (E)-2-azido β-nitrostyrenes and the subsequent reductive cyclization

We have proven that primary amine/thiophosphinamide incorporating (1R,2R)-1,2-diphenylethane-1,2-diamine is an efficient catalyst for the asymmetric Michael addition of acetone to (E)-2-azido β-nitrostyrenes. Under the optimal reaction conditions, the corresponding Michael addition products were obtained in excellent yields with almost perfect stereocontrol. Upon treatment with Et₃SiH/InCl₃, the Michael addition products could be successfully converted to the related 2-methyltetrahydroquinolines in acceptable yields with moderate to excellent diastereoselectivity and without appreciable loss in optical purity. This process provides a highly enantioselective pathway for the synthesis of biologically important 2-methyltetrahydroquinoline derivatives.     

Facile Amberlyst A-21 catalyzed access of β-hydroxynitriles via epoxide opening in water

β-Hydroxynitriles are essential intermediates in the synthesis of diverse bioactive compounds and clinical drugs. One of the precursor reactions to these intermediates is the opening of an epoxide ring with a cyanide nucleophile. In the present study, we report a milder and safer route to β-hydroxynitriles employing recyclable, Amberlyst A-21 resin in the ring-opening of epoxides with acetone cyanohydrin in water. A diverse range of substrates (fifteen), including aromatic epoxides, phenoxy epoxides, non-terminal, and terminal aliphatic epoxides, are investigated under the optimized conditions to afford the desired β-hydroxynitriles in good to excellent yield. In addition to this, the recyclability of the Amberlyst A-21 resin is also successfully demonstrated. This relatively safer methodology has the potential to be explored in other organic transformations.     

Gram-scale preparation of dialkylideneacetones through Ca(OH)2-catalyzed Claisen-Schmidt condensation in dilute aqueous EtOH

A practical synthetic method of dialkylideneacetones has been developed. Compared with known protocols, the method employed catalytic Ca(OH)₂ as the cheap, mild base catalyst and dilute aqueous EtOH (20%, v/v) as the green and safe solvent. The products could be synthesized in gram-scale and isolated by a simple filtration.     

The complexation of alkaline cations by crown ethers and cryptands in acetone

Stability constants and thermodynamic values for the complex formation of alkali ions by crown ethers, diaza crown ethers and cryptands have been measured by means of potentiometric and calorimetric titrations in acetone as solvent. The interactions between the ligands and solvent molecules play an important role for the complex formation. Cryptands form the most stable complexes with alkali ions if inclusion complexes are formed. Even in the case that the salts are not completely dissociated in acetone the presence of ion pairs does not influence the calculated values of the stability constants.