Inert Atmosphere Conditions Research Articles

Cobalt(III) Werner Complexes with 1,2-Diphenylethylenediamine Ligands: Readily Available, Inexpensive, and Modular Chiral Hydrogen Bond Donor Catalysts for Enantioselective Organic Synthesis.

In the quest for new catalysts that can deliver single enantiomer pharmaceuticals and agricultural chemicals, chemists have extensively mined the “chiral pool”, with little in the way of inexpensive, readily available building blocks now remaining. It is found that Werner complexes based upon the D3 symmetric chiral trication [Co(en)3]3+ (en = 1,2-ethylenediamine), which features an earth abundant metal and cheap ligand type, and was among the first inorganic compounds resolved into enantiomers 103 years ago, catalyze a valuable carbon–carbon bond forming reaction, the Michael addition of malonate esters to nitroalkenes, in high enantioselectivities and without requiring inert atmosphere conditions. The title catalysts, [Co((S,S)-dpen)3]3+ ((S,S)-33+) 3X–, employ a commercially available chiral ligand, (S,S)-1,2-diphenylethylenediamine. The rates and ee values are functions of the configuration of the cobalt center (Λ/Δ) and the counteranions, which must be lipophilic to solubilize the trication in nonaqueous media. The highest enantioselectivities are obtained with Λ and 2Cl–BArf–, 2BF4–BArf–, or 3BF4– salts (BArf– = B(3,5-C6H3(CF3)2)4–). The substrates are not activated by metal coordination, but rather by second coordination sphere hydrogen bonding involving the ligating NH2 groups. Crystal structures and NMR data indicate enthalpically stronger interactions with the NH moieties related by the C3 symmetry axis, as opposed to those related by the C2 symmetry axes; rate trends and other observations suggest this to be the catalytically active site. Both Λ- and Δ-(S,S)-33+ 2Cl–BArf– are effective catalysts for additions of β-ketoesters to RO2CN=NCO2R species (99–86% yields, 81–76% ee), which provide carbon–nitrogen bonds and valuable precursors to α-amino acids.

Explosion behaviour of metallic nano powders

This paper describes experiences and results of experiments with several metallic dusts within the nanometer range. The nano dusts (aluminium, iron, zinc, titanium and copper) were tested in a modified experimental setup for the test apparatus 20 L-sphere (also known as 20-L Siwek Chamber), that enables the test samples to be kept under inert atmospheric conditions nearly until ignition. This setup was already introduced in earlier papers by the authors. It was designed to allow the determination of safety characteristics of nano powders under most critical circumstances (e.g. minimisation of the influence of oxidation before the test itself). Furthermore the influence of passivation on explosion behaviour is investigated and additional tests with deposited dust were carried out to describe the burning behaviour of all dusts. For a better characterisation all samples were tested with a simultaneous thermal analysis (STA). To minimise the influence of oxidation all samples were handled at inert conditions until shortly before ignition or start of the test respectively.

ChemInform Abstract: Iron‐Mediated Direct Arylation of Unactivated Arenes in Air.

AbstractIt is demonstrated that a preformed Fe/phen complex catalyzes the direct C‐H arylation with aryl iodides and bromides using excess KOtBu as the base without the use of an inert atmosphere and/or forcing conditions.

Size Controlled Synthesis of Germanium Nanocrystals: Effect of Ge Precursor and Hydride Reducing Agent

Germanium nanocrystals (Ge NCs) have attracted increasing attention as a promising alternative to II–VI and IV–VI semiconductor materials as they are cheap, “green,” electrochemically stable, and compatible with existing CMOS processing methods. Germanium is a particularly attractive material for optoelectronic applications as it combines a narrow band gap with high carrier mobilities and a large exciton Bohr radius. Solution‐phase synthesis and characterisation of size monodisperse alkyl‐terminated Ge NCs are demonstrated. Ge NCs were synthesised under inert atmospheric conditions via the reduction of Ge halide salts (GeX4) by hydride reducing agents within inverse micelles. Regulation of NC size is achieved by variation of germanium precursor and the strength of hydride reducing agents used. UV‐Visible absorbance and photoluminescence spectroscopy showed strong significant quantum confinement effects, with moderate absorption in the UV spectral range, and strong emission in the violet with a marked dependence on excitation wavelength.

Nitrate Reduction by Redox-Modified Smectites Exchanged with Chitosan

AbstractThe presence of nitrate and other redox-active anionic contaminants in terrestrial ecosystems poses a significant risk to humans and other forms of life on Earth. The purpose of the present study was to test a potential in situ system, using poly-(D) glucosamine (chitosan) adsorbed to mineral surfaces under redox-active conditions in order to degrade nitrate to lower oxidation states. Chitosan is a linear polysaccharide derived from the chitin found in the shells of shrimp and other shellfish. Five different loadings of chitosan (0, 0.075, 0.25, 0.50, and 1.0 g/L; labeled C0, C1, C2, C3, and C4, respectively) were adsorbed to ferruginous smectite (SWa-1) to form chitosan-SWa-1 composites (CSC) in the pH range 5.8–4. The CSC was then reduced by Na2S2O4 in a citrate-bicarbonate buffered dispersion and washed free of excess salts under inert-atmosphere conditions. Upon addition of the nitrate, the solution pH remained slightly acidic, ranging from 5.5 to 4.7. Samples were analyzed for Fe(II) content, reacted with a NaNO3 solution, and then re-analyzed for structural Fe(II) content. Supernatant solutions were analyzed for nitrate, nitrite, and ammonium. In samples C1 to C4, extensive concentrations of nitrite were observed in the supernatants with a corresponding increase in the reoxidation of structural Fe(II), proving that a coupled redox reaction had occurred between the nitrate and the structural Fe in the clay mineral. The most efficient loading, defined as the largest percentage of adsorbed nitrate reduced to nitrite, occurred in sample C1. The total amount of nitrate reduced and Fe(II) reoxidized followed the trend 0 = C0 < C2 < C3 < C4 ≈ C1. Chitosan showed the potential to reverse the surface charge of constituent clay minerals, thereby enabling the CSC to remove nitrate anions from aqueous mineral systems via redox reactions with structural Fe(II) in clay minerals.

Novel single pot synthesis of metal (Pb, Cu, Co) sulfide nanomaterials -Towards a quest for paintable electrode materials that supersedes Pt electrode

Novel single pot selective stoichiometric synthesis of cobalt, copper and lead sulfide nanomaterials has been carried out in an energy and time efficient manner by using combustion synthesis for the first time without using surfactants, capping agents and inert atmospheric conditions. X-ray diffraction and transmission electron microscope revealed the formation of respective nanocrystalline metal sulfides with different stoichiometry, whereas, electrochemical impedance analyses confirmed the low charge transfer resistance of all metal sulfide counter electrodes when compared to the Pt counter electrode, indicating their potential to be used as electrode materials. The efficiency of metal sulfide counter electrodes was tested in quantum dot sensitized solar cells (QDSSC) by applying the metal sulfide paint on fluorine doped tin oxide (FTO) plates. Current-voltage characteristics ratified the solar conversion efficiencies of 0.85, 1.3, 0.91 and 0.25, respectively for PbS (2), CuS (3), CoS (2) and Pt counter electrodes with CdS/TiO2 (1:1) working electrode and Na2S electrolyte. Thus the present study furnishes a novel method for the synthesis of metal sulfides as efficient paintable counter electrodes that can overcome Pt as counter electrode in QDSSC.

Germanium Nanocrystals As Anode Materials for Lithium Ion Batteries

For the last two decades rechargeable Li-ion batteries (LIBs) have been widely used in portable electronic devices owing to their peculiar characteristics such as high gravimetric and volumetric energy. In fact, LIBs are considered the most suitable candidates for hybrid (HEV) and electric vehicles (EV) [1-3]. However, towards the employment of Li-ion batteries into HEV/EV, a substantial improvement in energy and power density of the electrode materials is needed. In particular, at the anode side, the present Li-ion battery technology is mostly based on graphite anodes, providing a 372 mAh/g lithium storage capacity.In this regard, both Silicon and Germanium are excellent candidates as active anodes for LIBs owing to their high lithium storage capability, that is 4200 and 1620 mAh g-1, respectively [1,4]. Although Ge, owing to the drawback of its expensiveness, was in the recent past attracting considerably less attention than Si, it is now undergoing an increase in popularity because of its desirable advantages such as high intrinsic electrical conductivity (104 times higher than silicon) and higher capacity than graphite anodes. Furthermore, it has been reported that the lithium diffusion into Ge is 15 and 400 times faster than in Si at 360o C and at room temperature, respectively [1,5]. This ensures higher rate capability and more efficient charge transport than in silicon and graphite as well, fundamental properties in advanced high power density applications such as hybrid electric vehicles. However, similarly to silicon, the lithiation of Ge anode during cycling undergoes dramatic volume changes (~ 300%), which leads to pulverization and capacity fading in bulk. One of the most successful techniques to overcome the aforementioned problem and to improve the performance of LIBs, is the reduction of Ge size to the nanoscale.Here, we report about a novel synthesis method to produce Ge nanocrystals through solvothermal approach (200-300 oC), with size in 5-10nm range, used as anode in lithium ion batteries. The novelty lies in the simplicity of the proposed approach in fact, differently from standard processes [6], non-hazardous reducing agents were used and, at the same time, there is no longer need of maintaining inert atmosphere conditions. In particular, our approach starts from Germanium halogen GeX (X= Cl2, I2) salts. The Ge nanocrystals have been characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning (SEM) and transmission (TEM) electron microscopies. Figure 1 shows the X-ray diffraction pattern of Ge nanocrystals with JCPDS card No. 03-065-0333 together with the TEM image of Ge nanocrystals. The latter demonstrates a good uniformity in the nanocrystals dimensions, falling in the range between 5nm and 10nm. Finally, the electrochemical investigation of lithium insertion/de-insertion of these nanocrystals have been studied with cyclic voltammetry, A.C impedance and galvanostatic charge-discharge measurements.

Stereospecific synthesis of highly substituted novel carbasugar as carbonic anhydrase inhibitors: decahydronaphthalene-1,2,3,4,5,6,7-heptol

Decahydronaphthalene-1,2,3,4,5,6,7-heptol, a new polycyclitol, was synthesized starting from p-benzoquinone. An endo selective Diels-Alder cycloaddition between p-benzoquinone and 1-acetoxybutadiene followed by stereoselective reduction with NaBH4/CeCl3·7H2O led to the formation of an allylic cis-diol. The formed diol was converted into its acetate with Ac2O/pyridine, in a transformation that required inert atmosphere conditions to suppress a competing aromatization. Controlled oxidation by OsO4 of two olefinic bonds followed by acetylation yielded the heptaacetate whose structure was established unequivocally via application of X-ray crystallographic methods. Removal of the acetate groups by NH3 provided the target heptol. In addition, the carbonic anhydrase inhibitory potency of the title compound was investigated and it was shown to be a potent inhibitor compared to the standard CA inhibitors.

Peculiarities of thermochemical transformations of polyacrylonitrile synthesized by anionic polymerization

Abstract The behavior of polyacrylonitrile synthesized by anionic polymerization (A-PAN) was studied during heating up to 550 °C in dynamic conditions in inert atmosphere and in air. Endo- and exothermic effects without mass losses were revealed within the 400–550 °C. The data of differential scanning calorimetry (DSC), differential thermal analysis (DTA) and X-ray analysis confirm the formation of mesogenic structures determined by the conformation of initial A-PAN samples. Changes in quantitative characteristics of phase states were explained by reorganization of the formed structures resulting from thermotropic mesophase transition from cyclic macromolecules to nuclei of turbostratic carbon structure.

On the Structure-Function Relationship of Cobalt and Manganese Oxides as Oxygen Evolving Catalysts for Light-Driven Water Electrolysis: An In-Line Synchrotron Radiation Photoelectron Spectroscopy Study

The oxygen evolution reaction (OER) represents a bottle neck in the development of sustainable light-driven production of hydrogen from water using cheap and abundant electro-catalysts. Even though metal oxide catalysts have been used for decades, the mechanism of the OER has not been fully understood yet. We investigated Cobalt and Manganese Oxide thin films in their behavior during OER using photoelectron spectroscopy (PES) and synchrotron radiation. In an in-line system we could perform cyclic voltammetry as well as potentiostatic measurements in the anodic range under well-defined inert atmospheric conditions and afterwards transfer the samples into the UHV system for PES studies, without breaking the atmosphere. The electrochemical experiments have been interrupted at several potentials by removing the electrolyte drop and XPS as well as UPS spectra have been recorded successively. Despite the fact that the cyclic voltammetry curves (CV) of amorphous CoOx layers - deposited potentiostatically on FTO glass – and crystalline α-Mn2O3 – prepared by reactive sputtering and galvanostatic deposition – differ significantly in the low potential range before the onset of the OER, the differences in the PES spectra are little. Nevertheless, we could find some shifts in the peaks that have been interpreted as a change in the oxidation state of the metal ions at the surface depending on the potential applied and associated with the appearance of new oxo-bondings.

The Pyrolysis Behavior of Evolved Species from Date Palm Seeds

The pyrolytic behavior of evolved gases from date palm seeds (DPSs) were measured to gain insight into the mechanism of DPSs pyrolysis. Six different cultivars were used in this study, namely Deglet nour, Piarom, Suffry, Safawi, Mabroom and Aliya. A thermo-gravimetric analyzer (TGA) and a real-time gas analyzer (GA) were used to calculate the mass losses and the mole fraction of evolved gases, respectively. DPSs samples were pyrolyzed in an inert atmosphere condition using argon with a purge rate of 100 mL/minute. The samples were subjected to non-isothermal operation. An independent single model and parallel reaction model were adopted to interpret the empirical data collected from TGA and GA, respectively. The results reveled that there are three types of pyrolysis zones depending on the main constituents of every cultivars. Moreover, the potentialty of the zones in controlling the pyrolysis behavior was noticeable. The dominant hydrocarbon species in DPSs were CO and CH4 (40 to 50% higher than the rest of species). The mole fraction of CO was 2 to 4 times higher than the mole fraction of CO2. The activation energy and frequency factor of DPSs evolved species showed that Mabroom has the highest activation energy regarding H2 (63.21kJ/mol) and CO (74.32 kJ/mol).

Systematic Study to Convert Polyvinyl Chloride Waste into Commercial Chemicals

Polyvinyl chloride (PVC) waste is considered one of the environmentally hazardous plastic materials accumulating in huge quantities in landfills. This work was conducted for the purpose of using green chemistry techniques to convert the PVC waste into other chemicals that could be used for commercial purposes. Pyrolysis process of the PVC waste was carried out under inert atmospheric condition. The effect of grain size, temperature and heating time on the amount of evolved hydrogen chloride gas (HCl) was investigated. More than 95% of theoretical calculated amount of HCl was evolved before any emission of any other organic fumes. The evolved HCl was trapped and converted into concentrated hydrochloric acid (11.22 M) and then to a highly pure sodium chloride salt. The residual black material was heated further to remove and trap oily organic fumes. About 14% of initial PVC weight was found to be as heavy metals free oil and may be used as fuel. Finally, 27.74% of the degraded PVC remained as carbon black. The carbon black was grounded and acid digested to remove and determine heavy metal ions content.

Carbon nanofibres coated with Ni decorated MoS2 nanosheets as catalyst for vacuum residue hydroprocessing

Catalysts based on functionalised carbon nanofibers (FCNF) coated with Ni-decorated MoS2 nanosheets were obtained by direct decomposition of ammonium thiomolybdate and nickel nitrate impregnated on the FCNF under controlled temperature conditions in inert atmosphere. The catalysts were characterised by X-ray diffraction (XRD), N2 adsorption, Raman spectroscopy, temperature programmed reduction of sulfur species (TPR-S), NH3 temperature programmed desorption (NH3-TPD) and transmission electron microscopy (TEM). Decomposition temperature was found to have a paramount importance in the formation of uniform MoS2 slabs, as revealed by the TEM study: at 600°C, non-uniform covering of the carbon nanofiber (CNF) was observed together with the presence of small round-shaped metal particles (ca. 20nm). On the other hand, at 450°C CNF appeared homogeneously covered by amorphous MoS2 slabs decorated with Ni, resulting in higher amount of coordinated unsaturated sites (CUS), as determined by TPR-S. Catalysts were tested in the hydroprocessing of a vacuum residue and the results were compared against a benchmark alumina-supported NiMo catalyst. Higher asphaltene conversions were obtained for the CNF-supported catalysts prepared at 450°C, which overperformed the Al2O3-supported benchmark catalyst. However, the catalytic performance in hydrodesulfurisation and hydrodemetallisation of the CNF-based catalysts was slightly lower than that of the benchmark catalyst.

A facile synthetic pathway of monodisperse Fe3O4 nanocrystals

A facile approach was used for synthesize size-controlled monodisperse magnetite (Fe3O4) nanoparticles. In this method, precursors were obtained only using iron (III) chloride though a simple non-alkoxide sol–gel method. Meanwhile, this operation is without the need for inert gas atmosphere and refluxing conditions and without the strict control of high temperature and pressure. The phase structures, morphologies, particle sizes and magnetic properties of Fe3O4 nanoparticles were characterized by X-ray diffraction, transmission electron diffraction, fourier-transform infrared spectroscopy, near-edge X-ray absorption fine structure and vibrating sample magnetometer. Although this approach is a small modification to other methods, the synthetic pathway includes the advantages of several other methods. In addition, this method may offer a feasible strategy for those reaction which need more moderate reaction conditions.

Synthesis of a Fluorescent Conjugated Polymer in the Undergraduate Organic Teaching Laboratory

Fluorescent organic polymers are used in a wide range of applications, including explosive sensing, clean energy technologies, and biological detection schemes. However, such polymers are rarely synthesized in an undergraduate organic teaching laboratory due to their air and moisture sensitivity. The synthesis of a fluorescent organic polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), is described for the upper-division undergraduate organic laboratory. This polymerization is accomplished using straightforward procedures to exclude air and moisture, without requiring the use of a glovebox or strict inert-atmosphere conditions. Once synthesized, the polymer is used for two applications, the fabrication of fluorescent thin films and the formation of organic conjugated nanoparticles, and leads to a number of pedagogical opportunities about polymerization, organic fluorescence, solid-state properties, and hydrophobic nanoparticle formation.

Modified Setup of 20-L-Sphere for the Determination of Safety Characteristics of Nano Powders

This paper describes a modified experimental setup for the test apparatus 20-L-Sphere (also known as 20-L Siwek Chamber), that enables the test samples to be kept under inert atmospheric conditions nearly until ignition. This setup was designed to allow the determination of safety characteristics of nanopowders under most critical circumstances (e.g. minimisation of the influence of oxidation before the test itself). The aim of this modification was to determine, whether or not the current setup and procedures underestimate the explosion violence and ignitability of nanopowders. The work includes experimental results of micrometer dusts to validate the modified setup. Moreover first results of nanometer iron and aluminium dusts are presented, which were kept at inert conditions until shortly before the ignition. The tested nano iron was found to react pyrophoric, as soon as it gets in contact with air, while the tested nano aluminium did not generally show such behaviour.

An easy one-pot desilylation/copper-free Sonogashira cross-coupling reaction assisted by tetra-butylammonium fluoride (TBAF): synthesis of highly π-conjugated porphyrins

Sonogashira cross-coupling is a key reaction for the synthesis of highly conjugated oligomers. However, its application has well known drawbacks; it requires drastic inert atmosphere conditions, generates homocoupling by-product of the terminal alkyne and others. In this paper, we describe a new and easy procedure using PdCl2(PPh3)2 as catalyst assisted by TBAF in a one-pot desilylation/copper-free Sonogashira reaction for the synthesis of highly conjugated porphyrin oligomers.

Pd2dba3/Bippyphos: A Robust Catalyst System for the Hydroxylation of Aryl Halides with Broad Substrate Scope

AbstractA mixture of tris(dibenzylideneacetone)dipalladium(0) (Pd2dba3) and 5‐(di‐tert‐butylphosphino)‐1′,3′,5′‐triphenyl‐1′H‐[1,4′]bipyrazole (Bippyphos) is shown to be a robust and efficient catalyst system for the hydroxylation of structurally diverse (hetero)aryl halides under mild conditions and with broad substrate scope. Included in this reactivity survey is the successful synthesis of substituted benzofurans and related heteroatomic derivatives, which are formed via the hydroxylation of 2‐haloalkynylarenes. Notably, a significant number of the reactions reported herein proceed at room temperature, and we have demonstrated that it is possible to conduct reactions on the benchtop under air using unpurified solvents with negligible loss in reactivity versus related transformations conducted under inert atmosphere conditions. We also report herein the first crystallographically characterized (Bippyphos)Pd(II) complex, which confirms the ability of this synthetically useful ligand to adopt a bidentate binding motif in a manner similar to Buchwald’s biarylphosphine ligand class.

Modeling of Wheat Straw Torrefaction as a Preliminary Tool for Process Design

Torrefaction is considered as a kind of mild pyrolysis that is carried out under inert atmosphere (usually nitrogen) conditions. During this process, the moisture of the initial fuel and a portion of its volatiles are removed from the biomass particles towards the inert atmosphere. The resulted torrefied solid biomass has high energy density, durability and less hydrophilic character. The most beneficial result of torrefaction process is that biomass feedstock logistics cost can be reduced, as less tones of biomass are required for a given amount of energy input. The development of a process model examining basic parameters as reaction temperature and residence time can provide useful information, which can be used for the more efficient design of a torrefaction reactor. This study presents such a process model for a straw torrefaction pilot plant. This model is based on the thermodynamic calculation of a single and/or a two batch reactor, built on the commercial software ASPEN Plus. The calculation of required flow rates of inert gas, cooling medium for a specific biomass feedstock value, is based on relevant results found in literature.

The characterization of scintillator performance at temperatures up to 400 degrees centigrade

The logging and characterization of geothermal wells requires improved scintillator systems that are capable of operation at temperatures significantly above those commonly encountered in the logging of most conventional oil and gas wells (e.g., temperatures nominally in the range of up to 150°C). Unfortunately, most of the existing data on the performance of scintillators for radiation detection at elevated temperatures is fragmentary, uncorrelated, and generally limited to relatively low temperatures—in most cases to temperatures well below 200°C. We have designed a system for characterizing scintillator performance at temperatures extending up to 400°C under inert atmospheric conditions, and this system is applied here to the determination of scintillator performance at elevated temperatures for a wide range of scintillators including, among others: bismuth germanate, cadmium tungstate, cesium iodide, cesium iodide (Tl), cesium iodide (Na), sodium iodide, sodium iodide (Tl), lutetium oxy-orthosilicate (Ce), zinc tungstate, yttrium aluminum perovskite (Ce), yttrium aluminum garnet (Ce), lutetium aluminum perovskite (Ce), and barium fluoride, strontium iodide (Eu). Most of the scintillator samples exhibited severe degradation in light yield at elevated temperatures. Measurements were terminated at temperatures at which the measured light yield no longer appeared useful. The results of these high-temperature scintillator performance tests are described in detail here. Comparisons of the relative elevated-temperature properties of the various scintillator materials have resulted in the identification of promising scintillator candidates for high-temperature use in geothermal and fossil-fuel well environments.