Stoichiometric Amount Of Water Research Articles

Quantum chemical modeling of the structure formation and proton transfer in 2-hydroxybenzenesulfonic, 4-hydroxy-1,3-benzenedisulfonic, and 1,3-benzenedisulfonic acids

Hydrate clusters of 2-hydroxybenzenesulfonic and 1,3-benzenedisulfonic acids were calculated in terms of the density functional theory (DFT) by the B3LYP/6-31G** method. The process of water adsorption on the crystal surface of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate was simulated using the generalized gradient approximation (DFT/PBE) and periodic boundary conditions. For the model system (OHC6H4SO3 −)·H5O2 +, the activation barriers for the proton transfer were calculated depending on the distance between the O atoms and the deviation of the proton from the O...O bond line. The presence of one H2O molecule per SO3H group is energetically most favorable for the formation of clusters of 1,3-benzenedisulfonic acid containing a stoichiometric amount of water. The simulation of the hydration of 4-hydroxy-1,3-benzenedisulfonic acid dihydrate (OHC6H3(SO3H)2·2 H2O + n H2O, n = 1–3) showed that the superstoichiometric H2O molecule is adsorbed on the crystal surface of this dihydrate with energy release of 0.75–0.95 eV. The position of this water molecule is less favorable in the bulk than on the surface.

Synthesis and Characterization of Pd Complexes of a Carbazolyl/Bis(Imine) NNN Pincer Ligand

A serendipitously discovered construction of a carbazole nucleus by lithiation of N-methylated bis(4-methyl-2,6-dibromophenyl)amine is described. It was used to synthesize an NNN pincer-type ligand that combines a central carbazole site (N-methylated in the precursor ligand) with two flanking aldimine donors bearing mesityl substituents. The installation of this ligand on Pd was accomplished via an N-Me cleaving reaction with (COD)PdCl(2) producing MeCl and (NNN)PdCl (where NNN is an anionic carbazolyl/bis(imine) pincer ligand). Several (NNN)PdX complexes were characterized spectroscopically. (NNN)PdOTf ((-)OTf = triflate or (-)O(3)SCF(3)) readily reacted with stoichiometric amounts of water in benzene or dichloromethane to give a cationic water adduct [(NNN)Pd(OH(2))]OTf. An X-ray diffraction study on a single crystal of (NNN)PdCl revealed an almost perfectly square planar environment about Pd and an almost perfectly planar carbazole/bis(imine) conjugated system. Cyclic voltammetry of (NNN)PdCl showed quasi-reversible oxidation at E(1/2) = 0.72 V vs Fc/Fc(+) which is most likely ligand-based.

The Adsorption and Chemistry of Tripropyl phosphate (TPP) into Microporous and Mesoporous NaX Zeolites

ABSTRACTAdsorption and chemistry of tripropylphosphate (TPP) in mesoporous NaX zeolite, which was templated by cationic templated polymer (polydiallyldimethylammonium chloride, PDADMAC) with two different length chains, was investigated. The structural properties of the zeolites were characterized by X-ray diffraction (XRD) and nitrogen adsorption analysis. The chemical activities of different zeolites toward the decomposition of TPP were determined with solid state 31P NMR spectra. After exposure of zeolites to TPP was sufficient and equilibrium was reached, a stoichiometric amount of water was also adsorbed and hydrolysis was observed. The TPP decomposition yields in different NaX zeolites were compared.

Effects of the addition of an organic polymer on the hydrolysis of sodium tetrahydroborate in batch reactors

An experimental study is presented both on the generation and storage of molecular hydrogen (H 2) by small additions of an organic polymer – carboxymethyl cellulose (CMC) – to sodium borohydride (NaBH 4) through the alkaline hydrolysis, in the presence of a powdered nickel–ruthenium based catalyst reused from 274 to 282 times. The experiments were performed at 45 °C in two batch reactors with internal volumes of 0.229 L and 0.369 L, made of stainless-steel with bottom conical shape, positioned vertically. The results showed that working at moderate pressures, up to 2.7 MPa, increases slightly the H 2 dissolution in the liquid phase, enhanced by the changing of the polarity of the remained solution inside the reactor: a value of 0.182 for dimensionless H 2 solubility in the liquid phase with 0.25 wt% CMC was found, at 45 °C, based on Henry’s law. As a consequence, sodium tetrahydroxoborate, NaB(OH) 4 by-product was produced in the presence of CMC additive, showing the absence of crystalline water in its crystal structure (NaB(OH) 4 presents structural water, with boron atoms linked to four hydroxyl groups). This new finding never reported to form at < 50 °C, has a positive impact in recyclability costs of NaBO 2 back to NaBH 4 due to the elimination of two energy consuming steps in the metaborate dehydration kinetics. In fact our system of compressed hydrogen, shows that both H 2 generation rates and yields and hydrogen storage capacities can be augmented, the latter to reach ≈ 6 wt%, by adding small amounts of an organic polymer (CMC) to the classic NaBH 4 hydrolysis, performed with stoichiometric amount of water. The eventual success of this new route will depend upon developing a advantageous method of converting borates into tetrahydroborate and also finding materials (chemicals) which enhance the solubility of H 2, promoting its reversible storage in the liquid phase. We therefore attempted to show that a less Polar Organic Polymeric Solution ( lPOPS) of NaBH 4 is a suitable hydrogen carrier for portable and/or niche applications.

Loading silica with metals (palladium or platinum) under mild conditions by using well-defined molecular precursors

The loading of pre-treated amorphous silica with platinum or palladium was carried out by using the molecular precursors Pt2(micro-Cl)2Cl2(CO)2, or Pd2(micro-Cl)2Cl2(CO)2, respectively, which contain the required amount of coordinated CO to carry out the formation of the metal particles upon contact with moisture. The reactivity of the well-soluble mononuclear platinum complex cis-PtCl2(CO)2 with stoichiometric amounts of water was investigated either under N2 or CO. The metal nanoparticles produced on the silica matrix have been characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The catalytic performance of the silica-supported metals thus produced was evaluated in the hydrogenation of cyclohexene.

Synthesis and reactivity of silylated tetrathiafulvalenes

Novel organosilylated tetrathiafulvalenes (TTFs) possessing Si-H or Si-Si bonds have been synthesised. The crystal structures of several derivatives have been determined by X-ray diffraction, including that of dimeric (Si2Me4)(TTF)2 (11) incorporating a diatomic SiMe2-SiMe2 linker. Cyclic voltammetry measurements in all cases show two oxidation waves. DFT calculations were performed to rationalize the absence of an electronic communication between the two TTF moieties of 11 through the disilanyl spacer. The reactivity of the Si-H bond has been exploited to prepare the dinuclear complex [{Ru(CO)4}2{mu-(Me2Si)4TTF}] (14), starting from Ru3(CO)12 and TTF(SiMe2H)4 (1). Treatment of 14 with 2 equiv. of PPh3 or dppm results in selective substitution of a CO ligand trans to a SiMe2 group to afford mer-[{Ru(PPh3)(CO)3}2{mu-(Me2Si)4TTF}] (13) and mer-[{Ru(CO)3}2(eta1-dppm){mu-(Me2Si)4TTF}] (16). Attempts to transform the Si-H bonds of some TTF(SiMe2H)n (n = 1, 2) into Si-O functions using stoichiometric amounts of water in the presence of tris(dibenzylideneacetone)dipalladium(0) were unsuccessful. Quantitative cleavage of the C(TTF)-Si bond was observed instead of formation of TTF-based-siloxanes. Essays of catalytic bis-silylation of phenylacetylene with 11 and TTF(SiMe2-SiMe3) (9) in the presence of Pd(OAc)2/1,1,3,3-tetramethylbutylisocyanide failed. Again, cleavage of the C(TTF)-Si bond was noticed.

Hydrolysis of a (2‐Propanol)yttrium Triiodide Complex in the Presence of Glymes: Synthesis and X‐ray Structures of Hydroxo‐Bridged Dinuclear Yttrium Complexes and Their Applications in Materials Science

AbstractThe reactions of (2‐propanol)yttrium triiodide, Y(iPrOH)4I3, with stoichiometric amounts of water in the presence of di‐, tri‐, and tetraglyme yield a facile synthetic route to hydroxo‐bridged, centrosymmetric dimeric yttrium complexes. These ionic derivatives, [Y2L2(μ‐OH)2(H2O)x(ROH)y]I4 [1: L = triglyme, x = 2, y = 2, R = iPr; 2: L = tetraglyme, x = 2, y = 0; 3·2EtOH: L = diglyme, x = 2, y = 4, R = Et; 4·2EtOH: L = triglyme, x = 4, y = 0; 5: L = tetraglyme, x = 2, y = 2, R = Et] have been characterized by elemental analysis, IR and 1H NMR spectroscopy, as well as by single‐crystal X‐ray diffraction for 3, 4, and 5. Preliminary results on the utility of these ionic derivatives as potential sources of yttrium oxide in high Tc superconductors are also presented.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Selenium‐Catalyzed Iodohydrin Formation from Alkenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Mesoporous alumina (I): Comparison of synthesis schemes using anionic, cationic, and non-ionic surfactants

A series of mesoporous alumina was prepared using a selected group of anionic, non-ionic, and cationic surfactants with Al-tri- sec-butoxide or Al 3+ in organic solvent with stoichiometric amount of water, and in aqueous solution with different hydrolyzing agents, or with complexing agent at room temperature to 100 °C. A comparison of the physicochemical properties of the materials prepared was made with respect to surface area, thermal stability, and porosity. Anionic surfactants in aqueous solution produced thermally unstable materials but in organic solvent resulted in a moderately stable alumina phase. Both cationic and non-ionic surfactants produced thermally stable mesoporous alumina after removal of the surfactant upon calcination at 500 °C when the materials were synthesized in organic solvents. Overall, mesoporous alumina prepared with cationic cetyltrimethylammonium bromide in sec-butanol in the optimized substrate composition of Al:surfactant:H 2O:solvent = 1.0:0.3:2.0:15 exhibited the best textural property among the various synthesis systems investigated.

From Monomers to Solids: Controlled Hydrolysis To Form Novel, Heteroleptic Hydroxide-Containing Complexes

Four novel alkaline earth metal tetranuclear aryloxide/pyrazolate hydroxides of the general formula M4(ligand)6(OH)2(donor)n have been prepared by either adding stoichiometric quantities of water to preformed alkaline earth metal aryloxides or in a direct metalation regime combining metal, ligand (alcohol, pyrazole), and donor with stoichiometric amounts of water. The compounds are considered as potential intermediates in the sol-gel process. A nonhydrolyzable magnesium aryloxide has also been obtained using the same reaction scheme. Unexpectedly, a dimeric strontium complex with further association of a second dimer via hydrogen bonding from the solvent of crystallization, ethylenediamine, has been isolated by the treatment of strontium metal with a mixture of alcohol and water. All compounds were characterized using X-ray crystallography, 1H and 13C NMR, and IR spectroscopy.

Selenium-catalyzed iodohydrin formation from alkenes

A new simple method for catalyzed iodohydroxylation of alkenes using stoichiometric amounts of water is described. The iodohydrins were prepared in good yields from the corresponding alkenes using N-iodosuccinimide, 2 equiv of H 2O, and catalytic amounts of diphenyl diselenide in MeCN.

Structural ordering of self-assembled alkylene-bridged silsesquioxanes probed by X-ray diffraction experiments

Powder X-ray diffraction experiments have been performed to analyse the structural order in alkylene bridged silsesquioxanes. These organic–inorganic hybrids were obtained by the hydrolysis–condensation of a series of six α,ω-bis[triethoxysilyl(propyl)ureido]alkylenes associating hydrophobic alkylene units with various chain length and H-bonding urea groups. The sol–gel hydrolysis in ethanol with a stoichiometric amount of water and using fluoride anion as catalyst only afforded amorphous bridged silsesquioxanes. Conversely, the hydrolysis with a large excess of water under acidic catalysis produced materials as layered sheets. A lamellar periodicity on the molecular scale level was observed for longer alkylene chain (Cn C8–C12). Under similar reaction conditions, the hydrolysis of the short alkylene chain precursor (C6) led to an amorphous solid. The medium to long range arrangement of the organic fragment in the solids is attributable to a combination of the hydrogen bonding interactions between the urea groups and of the van der Waals interactions between the long alkylene chains. In excess water, the hydrophobic nature of the long alkylene chains prevails and favours the formation of the intermolecular H-bonds between the urea groups leading to ordered assemblies of the organic substructures in the silsesquioxane network.

Synthesis of nanostructured γ-alumina with a cationic surfactant and controlled amounts of water

Nanostructured crystalline γ-alumina was synthesized by a simpler and improved method proposed here from aluminum alkoxide precursor in the presence of a cationic surfactant and controlled amounts of water under hydrothermal conditions without any extra additives such as hydrolysis controlling agents. The material synthesized with a stoichiometric amount of water (H 2O/Al = 2) was a mesoporous molecular sieve with a ‘wormhole-like’ pore structure. With increasing amounts of water (H 2O/Al = 10 or 20), bundles of γ-alumina nanofibers were formed, and with H 2O/Al > 20, materials with no definite morphology were formed, probably due to too fast hydrolysis of the precursor. The nanostructured materials had high surface areas and a good thermal stability.

Lamellar Organo-Bridged Silicones

The acid-hydrolysis of an organo-bridged bisdiethoxysilylated molecular precursor bearing urea groups, (EtO)2MeSi(CH2)3NHCONH(CH2)12NHCONH(CH2)3SiMe(OEt)2, has been performed in pure aqueous medium. Scanning electron microscopy (SEM) analysis of the resulting insoluble solid revealed plate-like forms with a lamellar structure as determined by powder X-ray diffraction (PXRD) studies with a sharp peak at 28.5 A. The solid state 29Si MAS-NMR spectrum of this bridged siloxane hybrid is consistent with a moderately condensed material with complete preservation of the Si–C bonds throughout the hybrid network. In comparison, the classical sol–gel hydrolysis-condensation of the molecular precursor in ethanol with stoichiometric amount of water and fluoride anion as catalyst produced an amorphous featureless solid.

Hydrogen generation by hydrolysis reaction of lithium borohydride

The hydrolysis reaction of LiBH 4 with a stoichiometric amount of water had 5 times the H 2 yield in comparison with that of using water exceeding the stoichiometric amount. The gravimetric and the volumetric hydrogen densities increased with increasing water added (H 2 O/LiBH 4 ) followed by a decrease. Those densities had maximum values at H 2 O/LiBH 4 =1.3: gravimetric hydrogen density per unit weight of LiBH 4 and H 2 O is 7.4 wt %, volumetric hydrogen density per unit weight of NaBH 4 and H 2 O is 60 kgH 2 / m 3 . It can be used for a fuel cell uninterrupted power supply.

Hydrogen generation by hydrolysis reaction of lithium borohydride

The hydrolysis reaction of LiBH 4 with a stoichiometric amount of water had 5 times the H 2 yield in comparison with that of using water exceeding the stoichiometric amount. The gravimetric and the volumetric hydrogen densities increased with increasing water added (H 2O/LiBH 4) followed by a decrease. Those densities had maximum values at H 2O/LiBH 4=1.3: gravimetric hydrogen density per unit weight of LiBH 4 and H 2O is 7.4 wt %, volumetric hydrogen density per unit weight of NaBH 4 and H 2O is 60 kgH 2/ m 3 . It can be used for a fuel cell uninterrupted power supply.

Pyrolysis study of sol-gel derived TiO2powders

An amorphous TiO2 gel was obtained by hydrolysing titanium(IV) isopropoxide with a stoichiometric amount of water using SnCl2 as catalyst. In these operative conditions, a TiO2 gel matrix containing a lower fraction of organic residual was obtained with respect to samples prepared by previously modifying the titanium alkoxide precursor with chelating ligands. Dried gel powders were characterized by N2 adsorption analyses, FT-IR and XRD measurements. Thermogravimetric (TG) and differential thermal analysis (DTA) coupled with mass spectrometric (MS) and gas chromatographic (GC) measurements were performed in order to identify the organic products released from TiO2 gel pyrolysis. The Tg-MS semiquantitative analysis of the main evolved species allowed to describe both the chemical composition of the initial TiO2 gel and the chemical rearrangements occurring in the matrix during heating up to its crystallisation to anatase form at 420°C.

Kinetics of hydrolysis of tetrahydrofurfuryl butyrate in a three phase system containing immobilized lipase from Candida antarctica

Hydrolysis of tetrahydrofurfuryl butyrate (THFB) in heptane was carried out at 30 °C in a triphasic system by using stoichiometric amounts of water and immobilized Candida antarctica lipase (Novozym 435) as catalyst. The three phase system has several advantages in hydrolysis reaction due to the very high solubility of the hydrophobic substrate in the organic medium and suppression of enzyme inhibition by the products alcohol and acid, which are partitioned into the bulk organic phase. The effects of various parameters such as speed of agitation, concentration of the ester, quantity of water, temperature, catalyst loading, and reusability of the enzyme were systematically studied in detail. The catalyst reusability studies showed that the deactivation was reversible. The reaction was free from external mass transfer and intra-particle diffusion limitations. Based on the initial rates and concentration profiles, the hydrolysis reaction was found to obey the ping-pong bi-bi mechanism with inhibition by the reactant water. This also demonstrates the significance of the three phase hydrolysis by enzyme catalysis. It indicates that by taking stoichiometric amounts of reagents, inhibition due to reactants can be reduced in a three phase system and the reusability of the catalyst also can be improved.

Oxidative dehydrogenation of isobutane over V 2O 5-based catalysts prepared by grafting vanadyl alkoxides on TiO 2SiO 2 supports

Following four different procedures many vanadium-based catalysts have been prepared by using the grafting technique and have been tested on the oxidative dehydrogenation of isobutane. The best results of selectivity have been obtained with catalysts prepared by grafting bimetallic vanadium–titanium alkoxides directly on silica. The alkoxide precursors have been obtained by partially hydrolysing titanium alkoxide, dissolved in isopropanol, with a stoichiometric amount of water and reacting then with vanadyl tri-isopropoxide, or alternatively by mixing the two mentioned alkoxides in isopropanol and submitting both to controlled partial hydrolysis. The bimetallic alkoxide grafted on silica show a prevalence of isolated VOTi bonds with respect to polyvanadylic VOV bonds that are prevalent, on the contrary, when vanadyl tri-isopropoxide dissolved in n-hexane is grafted on a TiO 2SiO 2 support. Catalysts characterised by the prevalence of VOTi bonds are slightly less active but two times more selective than catalysts in which VOV bonds prevail. The preparation of vanadium-based catalysts with a favourable TiO 2 environment has been largely simplified by avoiding the use of a TiO 2SiO 2 support obtaining, in the meantime, a remarkable improvement in the selectivity.

Reaction of (mu-oxo)diiron(III) core with CO2 in N-methylimidazole: formation of mono(mu-carboxylato)(mu-oxo)diiron(III) complexes with N-methylimidazole as ligands.

Several iron(III) complexes with N-methylimidazole (N-MeIm) as the ligand have been synthesized by using N-MeIm as the solvent. Under anaerobic conditions, [Fe(N-MeIm)(6)](ClO(4))(3) (1) reacts with stoichiometric amounts of water in N-MeIm to afford the (mu-oxo)diiron(III) complex, [Fe(2)(mu-O)(N-MeIm)(10)](ClO(4))(4) (3). Exposure of a solution of 3 in N-MeIm to stoichiometric and excess CO(2) gives rise to the (mu-oxo)(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-HCO(2))(N-MeIm)(8)](ClO(4))(3) (4) and the methyl carbonate complex [Fe(2)(mu-O)(mu-CH(3)OCO(2))(N-MeIm)(8)](ClO(4))(3) (5), respectively. Formation of the formato-bridged complex 4 upon fixation of CO(2) by 3 in N-MeIm is unprecedentated. Methyl transfer from N-MeIm to a bicarbonato-bridged (mu-oxo)diiron(III) intermediate appears to give rise to 5. Complex 3 is a good starting material for the synthesis of (mu-oxo)mono(mu-carboxylato)diiron(III) species [Fe(2)(mu-O)(mu-RCO(2))(N-MeIm)(8)](ClO(4))(3) (where R = H (4), CH(3) (6), or C(6)H(5) (7)); addition of the respective carboxylate ligand in stoichiometric amount to a solution of 3 in N-MeIm affords these complexes in high yields. Attempts to add a third bridge to complexes 4, 6, and 7 to form the (mu-oxo)bis(mu-carboxylato)diiron(III) species result in the isolation of the previously known triiron(III) mu-eta(3)-oxo clusters [[Fe(mu-RCO(2))(2)(N-MeIm)](3)O](ClO(4)) (8). The structures of 3, 4, 6, and 7 allow one, for the first time, to inspect the various features of the [Fe(2)(mu-O)(mu-RCO(2))](3+) moiety with no strain from the ligand framework.