Conformation Control of Oligosilanes by Trimethylsilyl Groups: Dodecamethyl-, Undecamethyl-2-trimethylsilyl- and Decamethyl-2, 4-bis(trimethylsilyl)-n-pentasilane Studied by Raman Spectroscopy and Quantum Chemical Calculations

2,4-Bis(trimethylsilyl) substituted n-pentasilane Me₃SiSiMe(SiMe₃)SiMe₂SiMe(SiMe₃)SiMe₃ (1) has been prepared from Me₂SiCl₂ and (SiMe₃)₂SiMeK, and its solid state molecular structure has been determined by single crystal X-ray diffraction. By reaction of 1 with KO^tBu and subsequent treatment of the resulting silyl anion with (MeO)₂SO₂, the novel hexasilane Me₃SiSiMe(SiMe₃)SiMe₂SiMe₂SiMe₃ (2) has been synthesized. By again using the reaction sequence KO^tBu/(MeO)₂SO₂, known n-pentasilane Me₃SiSiMe₂SiMe₂SiMe₂SiMe₃ (3) has been prepared in a novel and very convenient way from 2. All silanes 1, 2, and 3 as well as the intermediate silyl anions obtained from 2 and 3 have been characterized by ²⁹Si and ¹H NMR spectroscopy, 1 and 2 by elemental analyses also. Raman spectra in the temperature range 210–370 K of the pure liquids 1, 2 and 3 as well as of solutions in toluene (1 and 2) or cyclopentane (3) reveal that all of the silanes exist as mixtures of conformers. The symmetric SiSi stretch observed in the range 341 to 363 cm^-1 and possessing by far the largest Raman intensity of all SiSi stretching vibrations splits into five bands for 3 and two bands for 1 and 3. Quantum chemical DFT B3LYP/6–311G(d) calculations located 15 conformational minima for 2 with relative energies up to 19.9 kJmol^-1, and five minima for 1 with relative energies up to 15.5 kJmol^-1. Calculated SiSiSiSi torsion angles vary between 26.2° (smallest value found) and 179.3°, demonstrating the flexibility of backbones composed of silicon.     

Synthesis and Redox Properties of an Electropolymerizable Amido Ferrocenyl Pyrrole-functionalized Dendrimer

A novel diaminobutane-based poly(propyleneamine) ferrocenyl dendrimer functionalized with electrochemically polymerizable pyrrole substituents, DAB-dend-[{η⁵-C₅H₄CONH}Fe{η⁵-C₅H₄C(O)NH(CH₂)₃NC₄H₄}]₄ (1), has been prepared and characterized. A secondary reaction product, the dipyrrole derivative [Fe{η⁵-C₅H₄C(O)NH(CH₂)₃NC₄H₄}₂] (2) has been also isolated and used as a model to facilitate the characterization of 1. The molecular structure of 2 has been determined by single crystal X-ray diffraction studies. Glassy carbon electrodes have been successfully modified by electropolymerization of the pyrrole-functionalized derivatives 1 and 2, in dichloromethane/acetonitrile solutions, resulting in visually detectable electroactive ferrocenyl polymer films persistently attached to the electrode surfaces. Osteryoung square wave voltammetry experiments (OSWV) showed that films of the electropolymerized amidoferrocenylpyrrole functionalized dendrimer 1 (poly-1) senses H₂PO₄⁻ in aqueous solution using Li[B(C₆F₅)₄] as supporting electrolyte. This paper is dedicated to Professor Didier Astruc in “recognition” of his outstanding contributions to so many fields of inorganic and organic chemistry. Furthermore, CMC and BA thank him for his counsel and friendship during and after their post doctoral stages in his lab.     

Ring-opening polymerization of various oxirane derivatives using organotin phosphate condensate; Selective synthesis of the polyether containing oxirane ring in the side chain

Ring-opening polymerization (ROP) of various oxirane derivatives of the type, 2,2-R¹,R²-CCH₂O [R¹ = H (1), CH₃ (2); R² = CH₃ (a), CH₂Cl (b), CH₂OCH₃ (c)], using organotin phosphate (Bu₂SnO-Bu₃PO₄) condensate has been explored. The ROP of monosubstituted oxiranes (1a-c) afforded ring-opened polymers in high yields (1a, 1c = 99% and 1b = 69%); the resultant polymers from monomers 1a and 1b possessed high molecular weights (M_n = 9.49 × 10⁴, 10.60 × 10⁴, respectively). In contrast, both polymer yields and molecular weights for resultant polymers in the polymerization of disubstituted oxiranes (2a-c) were considerably lower than those in the polymerization of monosubstituted monomers (1a-c). ROP of glycidyl 2-methylglycidyl ether (3) possessing two oxirane groups with different reactivity was thus conducted by organotin catalyst; the high molecular weight polyether (M_n = 9.17 × 10⁴) containing oxirane ring in the side chain has successfully been obtained in moderate yield.     

Sonichemical Synthesis of a New Ethylene Diamine Lead(II) Coordination Polymer as Precursor for Preparation of PbO Nano-Structure

A new nano-coordination polymer of lead(II) nitrate with the ethylenediamine (en) ligand, [Pb(en)(NO₃)₂] _n (1), has been synthesized by a sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. The structure of 1 has been characterized by single crystal X-ray diffraction. In 1, Pb(II) ions are bridged by nitrate ligands forming linear chains, which are also further coordinated by neutral en ligands. This polymeric precursor has been used to prepare Pb(II)O nano-particles using two different methods. The prepared Pb(II)O nano-structure was characterized by scanning electron microscopy and X-ray powder diffraction.     

Synthesis and Properties of N-Organosililmethyllactams

Abstract

The heterofunctional condensation of lactams with chloromethyl derivatives of organosilanes in the presence of catalyst-acceptor of anhydrous K₂CO₃ or Na²CO₃ has been investigated. The hydrolytic stability of N-dialkyl(aryl)silylmethyllactams in neutral, acid and alkaline media has been studied. The biological activity of synthesized silicon-containing lactams has been investigated. The hydrolytic poly-condensation of N-(methyldimethoxysilylmethyl) lactams in the presence of a catalytic quantity of concentrated hydrochloric acid at room temperature has been conducted.     

Efficient Synthesis of the Very-Long-Chain n-3 Fatty Acids,Tetracosahexaenoic Acid (C<Subscript>24</Subscript>:6n-3) and Tricosahexaenoic Acid (C<Subscript>23</Subscript>:6n-3)

Tetracosahexaenoic acid (C₂₄:6n-3, THA, 3) is an essential biosynthetic precursor in mammals of docosahexaenoic acid (C₂₂:6n-3, DHA, 1), the end-product of the metabolism of n-3 fatty acids. THA 3 is present in commercially valuable fishes, such as flathead flounder. Tricosahexaenoic acid (C₂₃:6n-3, TrHA, 2), an odd-numbered-chain fatty acid, has been identified from marine organisms such as the dinoflagellate, Amphidinium carterae. To date, few studies have examined THA 3 and TrHA 2 due to difficulties in detecting and identifying these compounds, so their chemical and biological properties remain poorly characterized. Only one methodology for the chemical synthesis of THA 3 has been presented, and no method for the synthesis of TrHA 2 has been reported. We report here the efficient synthesis of THA 3 in four steps in 56% overall yield, and the synthesis of TrHA 2 in six steps in 48% overall yield. We also present the synthesis of Δ²-THA 4, an intermediate of β-oxidation of THA 3 to DHA 1, in three steps in 73% overall yield.     

Synthesis of soluble oligsiloxane-end-capped hyperbranched polyazomethine and their application to CO2/N2 separation membranes

Three soluble hyperbranched polyazomethines containing oligosiloxane end group HBP-PAZ-SiO_n were successfully synthesized. HBP-PAZ-SiO_ns were used as modifiers of ethyl cellulose (EC) and polysulfone (PS) membranes. Blend membranes, HBP-PAZ-SiO_n/EC and HBP-PAZ-SiO_n/PS were prepared by blending the THF solution of HBP-PAZ-SiO_n with ethanol solution of EC and dichloromethane solution of PS, respectively. Surprisingly, the permeabilities for CO₂ of the blend membranes were more than 15–16 times higher than those of pure EC and PS membranes without any drop of pemselectivity to N₂. This unusual improvement has been achieved by both enhancement of diffusivity for carbon dioxide and nitrogen by the oligosiloxane groups and enhancement of affinity of the amino groups with carbon dioxide at the end groups of HBP-PAZ-SiO_n.     

Adsorption of Uranium from Dilute Aqueous Solution on Inorganic Adsorbents

Abstract

The adsorption of uranium from a dilute aqueous solution by a large number of inorganic adsorbents has been investigated. A mixture of aluminum hydroxide, ferric hydroxide, and activated carbon in the weight ratio 1:3:4 has shown a high adsorbability for uranium. The separation of uranium from a dilute aqueous solution by this mixed adsorbent under various temperatures and pH values has been studied. The adsorbability was found to exhibit a maximum at pH 4.0 to 5.5 and to decrease with increasing temperature. A number of eluting solutions for the desorption of uranium from the mixed adsorbent were also tested; 1 N (NH₄)₂ CO ₃ was found to be the most suitable eluting solution (93% recovery of uranium).     

Production and EDM of Si3 N4–TiB2 ceramic composites

Abstract

Ceramic matrix composites containing TiB₂ as a particulate phase have been produced by hot pressing. The problems of the reactivity of TiB₂ with the Si₃ N₄ matrix and with the sintering environment have been successfully addressed. A novel dual atmosphere sintering profile combined with low temperature hot pressing has been used to successfully produce fully dense materials. The effect of TiB₂ addition on mechanical properties has been investigated. Composites containing TiB₂ show significant improvements in hardness and fracture toughness. The addition of TiB₂ at a level of 40 vol.-% raises the conductivity of the composite to a level where electro-discharge machining (EDM) is possible. A comprehensive study of the application of EDM has been carried out and the optimum machining conditions have been identified. Under these conditions Si₃ N₄–TiB₂ composites have been shaped with relative ease and proved to be ‘robust’ materials under EDM.     

The Absorption Spectrum of UOCl2 in Molten Chloride Salts

Abstract

The absorption spectrum of UOCl₂ in molten KCl-MgCl₂ salts has been measured and compared with that of the related UCl₄ spectrum at temperatures up to 932°C and melt compositions of 60–40, 34–66, and 0–100 mol %, respectively, KCl-MgCl₂. The species UOCl₂ is an important intermediate in the conversion of UO₂ to UCl₄ and its spectrum provides a means of monitoring the reaction, and other similar reactions, in situ. The solubility of UOCl₂ has been determined from absorption spectra and has been found to be 10 to 25 times higher than reported earlier with mole fractions as high as 0.0019 in pure MgCl₂ at 932°C.     

Aerosol Retention in the Vicinity of a Breach in a Tube Bundle: An Experimental Investigation

This article summarizes the main results of a bench-scale program focused on experimentally assessing the aerosol retention near the tube breach in a tube bundle. The major variables investigated were particle nature (polydispersed TiO ₂ agglomerates vs. solid, monodisperse SiO ₂ spheres) and Re _D (0.8?2.7· 10 ⁵ ). In addition, comparisons to other data sets provided insights into the particle aerodynamic size effect on retention efficiency. Results showed that particle nature substantially affects aerosol retention in the tube bundle: mass retention efficiency was low for TiO ₂ agglomerates (less than 30%) whereas it was much higher for SiO ₂ particles (around 85%). Retention efficiency is also affected by Re _D : its sensitivity was found to follow a log-normal behavior with a maximum retention attained at Re _D near 1· 10 ⁵ . This evolution with Re _D was similar for both types of compounds. Particle size also influences retention efficiency: the bigger the TiO₂ agglomerates the lower retention efficiency (no data were available for SiO ₂ ). Among all these variables, particle nature was noted to have a prime importance for in-bundle retention, whereas Re _D and particle aerodynamic size, although also affect retention efficiency, did not play such a key role. In light of the results, the presence of retention-inhibiting mechanisms such as fragmentation, resuspension or bouncing has been discussed. The data recorded will enhance the overall understanding of the governing mechanisms involved and will serve as a database against which compare model predictions. Nevertheless, further experimental data would be desirable to set up a sound database.     

The Measurement of Ambient Bioaerosol Exposure

Monitoring of ambient bioaerosol concentrations through the characterization of outdoor particulate matter (PM) has only been performed on a limited basis in North Carolina (NC) and was the goal of this research. Ambient samples of PM _2.5 (fine) and PM _10?2.5 (coarse) were collected for a six-month period and analyzed for mold, endotoxins and protein. PM _2.5 and PM _10?2.5 concentrations of these bioaerosols were reported as a function of PM mass, as well as volume of air sampled. The mass of PM _2.5 was almost twice that of the PM _10?2.5 ; however, the protein and endotoxin masses were greater in the coarse than the fine PM indicating an enrichment in the coarse PM. The protein and mold results demonstrated a seasonal pattern, both being higher in the summer than in the winter. Except for an occasional excursion, the endotoxin data remained fairly constant throughout the six months of the study.     

New Pt(II)(dithiolate) Compounds Possessing an Energetically Accessible Diphosphine-Based LUMO: Syntheses,Redox Properties,and Solid-State Structures of PtCl<Subscript>2</Subscript>(pbpcd), Pt(tdt)(pbpcd), and Pt(tdt)(bpcd)

Abstract  

The new ligand 2-(pyren-1-ylidene)-4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (pbpcd) has been synthesized from the Knoevenagel condensation using 1-pyrenecarboxaldehyde with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd). Displacement of the cod ligand in PtCl₂(cod) by pbpcd furnishes PtCl₂(pbpcd) (2) in near quantitative yield. Treatment of 2 with the dipotassium salt of toluene-3,4-dithiol (K₂tdt) affords the dithiolate compound Pt(tdt)(pbpcd) (3) as a 1:1 mixture of diastereomers. An alternative synthesis of 3 from Pt(tdt)(bpcd) (5) and 1-pyrenecarboxaldehyde also affords 3 in 23% yield. The pbpcd ligand and all new diphosphine-substituted compounds have been isolated and fully characterized in solution by IR and NMR spectroscopies, and the solid-state structures of 2·CH₂Cl₂, 3·toluene, and 5·CH₂Cl₂ established by X-ray diffraction analyses. The solid-state structure of each product exhibits a square-planar architecture at the metal center. The redox properties of the pbpcd ligand and the tdt-substituted compound 3 have been explored by cyclic and differential-pulse voltammetry, and these data are discussed with respect to extended Hückel MO calculations and the nature of the HOMO and LUMO levels in each compound.     

Synthesis, characterization, and platinum-catalyzed hydrosilation cross-linking of copoly(methylsilylene/1,4-phenylene/methylvinylsilylene): Properties of aromatic carbosilane thermosets

Low molecular weight copoly(methylsilylene/1,4-phenylene/methylvinylsilylene) (I) has been prepared by the reaction of a mixture of methyldichlorosilane and methylvinyldichlorosilane with the di-Grignard reagent prepared fromp-dibromobenzene.I has been characterized by¹H,¹³C, and²⁹Si NMR as well as FT-IR spectroscopy. Its molecular weight distribution has been determined by gel permeation chromatography (GPC), its thermal stability in nitrogen evaluated by thermogravimetric analysis (TGA), and its glass transition temperature (T _g) measured by differential scanning calorimetry (DSC). Platinum-catalyzed hydrosilation cross-linking ofI yields a thermoset material. The bending modulus (logE), tan·, andT _g of these cross-linked materials have been measured by dynamic mechanical thermal analysis (DMTA). Carbon fabric treated with catalytic amounts of platinum has been coated withI. Multilayers of coated carbon fabric have been consolidated (cured) to yield aromatic carbosilane/carbon composite materials. The interlaminar shear strength of these materials has been determined by short beam shear. Flexure strength and modulus of elasticity of these composite samples have been measured. The ultimate compressive strength and compression modulus as well as the tensile strength and elastic modulus of these have been determined.Presented at the XXVIth Silicon Symposium, Indiana University-Purdue University of Indianapolis, March 26–27, 1993.     

New 2-pyridinealdehyde N 4-hydroxyethyl thiosemicarbazone and their Cd(II) and Cu(II) complexes: synthesis,spectral, in vitro antibacterial activity and molecular and supramolecular structure study

N ⁴-hydroxyethyl-pyridinealdehyde thiosemicarbazone (HL, 1) as a tridentate Schiff base has been synthesized by 1:1 reaction of S-methyl-3-((pyridyl)methyl) dithiocarbazate and 2-aminoethanol. Complexes [Cd(HL)₂](NO₃)₂ (2), [Cd(HL)I₂] (3), [Cd(HL)Cl₂] (4), [Cu(HL)₂](NO₃)₂ (5) and [Cu(HL)Cl₂] (6) have been obtained and characterized by elemental analyses, molar conductivities, and spectroscopic studies. The ligand molecule binds the metal ion using pyridyl nitrogen, azomethine nitrogen and the sulfur atoms. The crystal structure analysis of 3 has been determined and showed to be a distorted square pyramidal geometry complex. The inter- and intramolecular interactions give rise to a supramolecular network. Compounds 2, 3, 5 and 6 were assayed for their bioactivities against selected pathogens. Copper(II) complexes 5 and 6 showed antimicrobial activities against Gram-positive (Bacillus anthracis) and Gram-negative (Pseudomonas aeruginosa and Yersinia pseudotuberculosis) bacteria, complexes 2–4 showed antimicrobial activities against Bacillus atrophaeus, while the ligand itself showed antimicrobial activities against Escherichia coli and Y. pseudotuberculosis.     

Separation of Ions Using Countercurrent Electrolysis in a Thin,Porous Membrane

Abstract

Separation of ions in a thin, porous membrane using countercurrent electrolysis has been studied both theoretically and experimentally. A set of differential equations which describes the separation process is presented. These equations are solved numerically. The separation has been verified in the ternary systems NaCl-HCl-H₂O and NaBr-KBr-H₂O.     

Use of Strong Base Organic Anion Exchangers for the Removal of Suspended Alumina Particles in Light Water/Heavy Water Systems

Abstract

A method for the removal of suspended alumina particles from H₂O/D₂O systems has been developed. It is based on the modification of surface charge of the suspended hydrated alumina particles by the addition of sulfate ions and adsorbing them on conventional strong base anion exchanger. 48 ppm of added sulfate has been found to be the required concentration for treating 30 ppm Al₂O_{3 3}D₂O suspensions.     

A glutamic acid-based polymer keeping intact the integrity of all the three original functionalities of the amino acid

Dimethyl glutamate, on treatment with allyl bromide, afforded dimethyl N,N-diallylglutamate which upon alkaline ester hydrolysis followed by acidification with aqueous HCl gave N,N-diallylglutamic acid hydrochloride [(CH₂=CH–CH₂)₂NH⁺CH(CO₂H)(CH₂)₂CO₂H Cl^?] I. Using Butler’s cyclopolymerization protocol, new monomer I underwent ammonium persulfate-initiated polymerization to give pyrrolidine ring-embedded linear cyclopolymer II i.e. ?[?CH₂(C₄H₆)NH⁺{CH(CO₂H)(CH₂)₂CO₂H Cl^?}CH₂?]?_n retaining the integrity of all the three functionalities of glutamic acid. Under the influence of pH, the repeating units of triprotic acid (+) in II were equilibrated to those of water-insoluble diprotic polyzwitterionic acid (±) III, water-soluble monoprotic poly(zwitterion-anion) (±?) IV, and its conjugate base polydianion (=) V. The critical salt concentration required to promote water solubility of (±) III has been determined to be 0.548 M NaCl, 0.271 M NaBr, 0.133 M NaI. The basicity constants of the carboxyl groups and trivalent nitrogen in (=) V have been determined. A 5 ppm and 20 ppm concentrations of III are effective in inhibiting the precipitation of CaSO₄ from its supersaturated solution with a ≈100% scale inhibition efficiency at 40 °C for a duration of over 3 and 16 h, respectively.     

Single and Multicomponent Sorption of CO2, CH4 and N2 in a Microporous Metal-Organic Framework

Abstract

Single and multicomponent fixed-bed adsorption of CO₂, N₂, and CH₄ on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO₂ and the loadings of CH₄ and N₂ are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO₂ is one order of magnitude faster than for CH₄ and N₂.     

Extraction of Furfural with Carbon Dioxide

Abstract

A new approach to separate furfural from aqueous waste has been investigated. Recovery of furfural and acetic acid from aqueous effluents of a paper mill has successfully been applied on an industrial scale since 1981.

The process is based on the extraction of furfural and acetic acid by the solvent trooctylphosphineoxide (TOPO). Common extraction of both substances may cause the formation of resin residues. Improvement was expected by selective extraction of furfural with chlorinated hydrocarbons, but ecological reasons stopped further development of this project.

The current investigation is centered in the evaluation of extraction of furfural by supercritical carbon dioxide. The influence of temperature and pressure on the extraction properties has been worked out. The investigation has considered the multi-component system furfural-acetic acid-water-carbon dioxide. Solubility of furfural in liquid and supercritical carbon dioxide has been measured, and equilibrium data for the ternary system furfural-water-CO₂ as well as for the quaternary system furfuralacetic acid-water-CO₂ have been determined. A high-pressure extraction column has been used for evaluation of mass transfer rates.