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The kinetics of hydrogen storage in magnesium can be accelerated by nanocarbon additives. In this study, we show that loading magnesium by graphene nanoplatelets (GNP) enhances the kinetics by more than an order of magnitude. The GNP presence reduces the Mg agglomeration, induced by de/hydriding, and accelerates the kinetics by connecting between Mg particles. The GNP were prepared by top-down graphite ball-milling in the presence of various organic protective agents. We found that both the molecular structure of the protective agent and the milling energy dictated the GNP properties, namely, size, thickness, defect density and specific surface area. We demonstrated how manipulation of the GNP size has a major effect on the hydrogen storage kinetics in magnesium-GNP composites.

Mg-nanocarbon composites demonstrate fast reversible hydriding kinetics. The kinetics is strongly correlated with the structure of the added nanocarbon allotrope. We conducted a systematic exploration of the reversible hydriding kinetics of Mg upon addition of nanocarbons with different dimensionalities, namely, 1D carbon nanotubes, 2D graphene nanoplatelets and 3D activated carbon. Our findings showed that the Mg (de)hydriding rate could be tuned by the dimensionality and defect density of the nanocarbon. The resulting kinetic enhancement was explained in terms of the hydrogen spillover mechanism. The use of nanocarbons offers an alternative to the utilization of high concentrations of expensive transition-metal catalysts for hydrogen storage.

We explored the hydrogen storage kinetics of Pd-Mg composites upon addition of different carbonaceous spillover agents (activated carbon and a wide spectrum of carbon nanotube types). We found that the hydrogen (loading or release) kinetics is strongly dependent on the nanocarbon morphology and configuration (e.g., length, diameter and Pd distribution). We therefore define a figure of merit quantifying the de/hydriding performance of previously reported systems and the system investigated in the present study. It demonstrates that the fastest kinetics is obtained for our Pd-decorated carbon nanotubes having the largest diameter. We found a clear structure-function relation between the spillover agent properties and the Mg de/hydriding rates, which could be applied in replacing the heavy and expensive transition metal catalyst by lightweight nanocarbon additive.

Solid-phase hydrogenation kinetics can be substantially increased by utilizing hydrogen spillover phenomenon. Carbonaceous allotropes are considered as promising spillover agents (SOAs) for improved hydrogen transport rate. We studied the effect of carbon-based SOA properties on irreversible hydrogenation. We divided the reaction into two major stages, near- and far-field hydrogenation (with respect to a catalyst), and determined their rate-limiting steps. The hydrogenation kinetics was analyzed for hydrogen originating from either catalyst on activated carbon or catalyst-decorated carbon nanotubes. The far-field hydrogenation is investigated for three types of loaded nanocarbons: 1D (nanotubes), 2D (graphene), and 3D (activated carbon). We found that the kinetics acceleration is strongly correlated with the nanocarbon dimension, 1D > 2D > 3D, and could reach almost 2 orders of magnitude. These findings are useful for the study of reversible hydrogen storage applications.

The adsorption kinetics of hydrogen on solid support is accelerated by three orders of magnitude upon adding carbon nanotubes (CNT) to the support. The gas–solid catalytic hydrogenation is studied at ambient temperature and sub atmospheric pressure while the support consists of a mixture of nano Pd-on-carbon with unsaturated hydrocarbon H-acceptor. The addition of a small amount of pristine CNT minimizes the required Pd concentration. A similar effect is demonstrated by addition of different oxides to the composite, but at much higher additive concentrations. The addition of the spillover agent improves the transport of the hydrogen atoms in the composite to remote sites with low Pd concentration via a spillover mechanism. Therefore, it is possible to overcome the decelerating effect of inhomogeneity in the support. The irreversible gas–solid hydrogenation could serve as a simplified platform to study the slower step of hydrogen spillover, which operates also in hydrogen storage processes.

The rush to develop graphene applications mandates mass production of graphene sheets. However, the currently available complex and expensive production technologies are limiting the graphene commercialization. The addition of a protective diluent to graphite during ball-milling is demonstrated to result in a game-changer yield (>90%) of defect-free graphene, whose size is controlled by the milling energy and the diluent type.

International audience; The binding of block copolymer Pluronic F-127 in aqueous dispersions of single- (SWCNT) and multiwalled (MWCNT) carbon nanotubes has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that a major fraction of polymers exist as a free species while a minor fraction is bound to the carbon nanotubes (CNT). The polymers exchange between these two states with residence times on the nanotube surface of 24 ± 5 ms for SWCNT and of 54 ± 11 ms for MWCNT. The CNT concentration in the solution was determined by improved thermal gravimetric analysis (TGA) indicating that the concentration of SWCNT dispersed by F-127 was significantly higher than that for MWCNT. For SWCNT, the area per adsorbed Pluronic F-127 molecule is estimated to be about 40 nm2.

Primary, secondary and tertiary benzylamines were oxidized to aromatic aldehydes and ketones when their HX (X = Br, I) salts were heated, under anhydrous conditions, in excess of alkyl sulphoxide. Quaternary benzylammonium salts also react, to give lower yields of carbonyl compounds. Benzylamine is being oxidized in the presence of anhydrous HX formed in situ by the reaction of alkyl halide and hydrosiloxane, but not in the presence of aqueous HX.

Palladium-catalyzed, mechanochemical hydrodechlorination (HDC) of solid hexachlorobenzene (HCB) with various solid hydrogen donors was carried out at ambient temperature in a planetary ball-mill to give benzene and a mixture of partially chlorinated benzenes. The mechanochemical hydrogen transfer dechlorination is effected in the presence of Pd on carbon, or palladium(II) acetate, and in the absence of a solvent, while no such reaction took place in the absence of Pd. The presence of a base (NaOH) and mmol amounts of water (introduced in the form of sodium phosphate heptahydrate) were needed to improve HDC efficiency. Of the H-donors studied: sodium hypophosphite, sodium borohydride and calcium hydride, the last one was the most efficient, realizing complete loss of HCB over 20 h. The chemoselectivity of the HDC depends on the hydrogen donor, e.g., sodium hypophosphite (SHP) gives 1,2-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,3,4-tetrachlorobenzene and pentachlorobenzene as the major intermediates in the dechlorination process. A chemoselectivity similar to that determined in mechanochemical HDC was found in a liquid phase hydrogen transfer HDC using a Pd/C catalyst and SHP in aqueous acetonitrile.

The rapid increase in graphene-based applications has been accompanied by novel top-down manufacturing methods for graphene and its derivatives (e.g., graphene nanoplatelets (GnPs)). The characterization of the bulk properties of these materials by imaging and surface techniques (e.g., electron microscopy and Raman spectroscopy) is only possible through laborious and time-consuming statistical analysis, which precludes simple and efficient quality control during GnP production. We report that thermogravimetry (TG) may be utilized, beyond its conventional applications (e.g., quantification of impurities or surfactants, or labile functional groups) to characterize bulk GnP properties. We characterize the structural parameters of GnP (i.e., defect density, mean lateral dimension, and polydispersity) by imaging and surface techniques, on one hand, and by a systematic TG, on the other. The combined data demonstrate that the combustion temperature of commercially available and laboratory-prepared GnPs is correlated with their mean lateral dimension and defect density, while the combustion temperature range is proportional to their polydispersity index. Mapping all these parameters allows one to evaluate the GnPs' structure following a simple thermogravimetric experiment (without necessitating further statistical analysis). Finally, TG is also used to detect and quantify different GnP constituents in powder and to conduct rapid quality-control tests during GnP production.

A palladium-catalyzed, low pressure hydrogenation of phenylalkynyl derivatives in a gas–solid reaction in the absence of a solvent was studied. The distinctive initiation step was found to be related to the catalyst activation stage and was directly affected by the treatment of the metallic catalyst: deoxygenating of the catalyst helped to diminish the initiation step, while partial poisoning of the catalyst resulted in extending the slower initial step. In the following propagation step, triple bonds are being hydrogenated to give initially a phenylalkenyl and phenylalkanyl products mixture. The chemoselectivity of the hydrogenation depends both on hydrogen pressure and on the mode of preparation of the reacting phenylalkynyl/catalyst powder. A mechanism, which is based on hydrogen mobility in the phenylalkynyl lattice, is suggested and a direct measurement of hydrogen mobility in the lattice was demonstrated.

Solid phase catalytic hydrogenation of phenylalkynyl and of azobenzene derivatives was studied with accordance to a mechanism proposing a supramolecular selective hydrogenation of assemblies of the unsaturated substrates on a metallic catalyst matrix. The kinetics of the solid phase reaction is shown to be affected by a combination of three factors: intermolecular distances, intact of alignment of molecules and the rigidity of the molecular stacks. A stepwise stereospecific hydrogenation of diphenylacetylene (DPA) via the cis -isomer intermediate was found, while a one-step hydrogenation to saturated bibenzyl derivative took place in the case of diphenylethynylbenzene (PEB). Solid phase hydrogenation of azobenzene derivatives resulted in a fast reaction giving aniline derivatives as the final product. The hydrogenation kinetics of substituted azobenzene with hydroxy- or amino-group could be significantly increased as a result of better alignment, or drastically decreased due to the increase in the rigidity of the molecular assembly. A secondary small hydrogen–deuterium isotopic effect k h / k d =1.45 was measured, indicating a weakening of the carbon–hydrogen bond as the rate determining step of the reacting molecule. The presence of traces of impurities such as water or peroxides, during the process of the construction of the molecular stacks on the metallic catalyst, results in a major reduction of the hydrogenation rate as an outcome of interference in the self-assembly process.

An unusual catalyzed hydrogenation reaction of solid pheylalkynyl derivatives in the absence of a solvent is studied. The unique solid state catalytic reaction of a pheylalkynyl substrate precoated on a supported metallic catalyst is being explained in terms of supramolecular chemistry. The formation of molecular aggregates of the alkyne substrate in a close proximity to the transition metal enables a fast catalytic process in the solid phase. Catalytic sites are created via molecular recognition and self-assembly mechanisms. The accessibility of the metallic catalyst to the molecular stacks of the substrate enables a fast catalytic reaction in the absence of a solvent. The kinetics of the hydrogenation reaction is interpreted and explained via self-assembled stacks that are constructed as a result of the well-known π – π interaction between pheylalkynyl molecules. XRD and TGA characteristics of the supported substrate also indicate the formation of substrate-catalyst sites, which have different characteristics from the pure substrate. The dependence of the hydrogenation kinetics on the type of catalyst support, size of the molecular stack, and catalyst concentration is studied.

The synthesis of six useful auxins labelled with tritium is described. The following compounds were prepared: 3-indoleacetic acid-5-3H (28.9 Ci-1.07 TBq/mmol), 3-indolebutyric acid-5-3H (7.3 Ci-270 GBq/mmol), 1-naphthylacetic acid-4-3H (27.6 Ci-1.02 TBq/mmol), 2,4-dichlorophenoxyacetic acid-5-3H (18.5 Ci-685 GBq/mmol), 2(2,4-dichlorophenoxy-5-3H)-propionic acid (20.7 Ci-766 GBq/mmol), 2(2,4-dichlorophenoxy)-propionic acid-3-3H (0.39 Ci-14.4 GBq/mmol), and 4-chlorophenoxyacetic acid-2-3H (13.3 Ci-492 GBq/mmol).

A radioimmunoassay for clenbuterol detection in cattle has been validated and used to monitor treated cattle. The tracer used was 4-amino-3,5-dichloro-alpha(tert-butylamino-methyl) benzyl alcohol (benzyl-3H)(clenbuterol) prepared by catalytic tritiation with tritium gas of 4-amino-3,5-dibromo-alpha-(tert-butylamino)-acetophenone, followed by chlorination at positions 3 and 5 in the aromatic ring. The rabbit antiserum was raised against a diazotized clenbuterol/human serum albumin conjugate. The assay described was sensitive (7.8 pg/tube) and reproducible. The intra- and inter-assay variability, which was assessed by measuring known quantities of clenbuterol in plasma, urine and faeces, was satisfactory for RIA. When this assay was used to monitor treated cattle the concentrations of clenbuterol in plasma, urine and faeces were directly related to the administered dose. The absorption and elimination of clenbuterol in cattle was rapid. Data obtained were consistent with results obtained in other species where a rapid clearance rate was also demonstrated.

Tritiated clenbuterol was prepared starting from 4-aminoacetophenone (I) which was selectively brominated to 4-amino-3,5-dibromoacetopheno ne (II), then to 4-amino-α,3,5-tribromoacetophenone (III) and reacted with tert.butylamine to 4-amino-3,5-dibromo-α-tert.butylaminoacetoph-none(IV). (IV) was dehalogenated and reduced with tritium gas to give 2-(tert.butylamino)-1-(4-amino-[3,5-3H]-phenyl)-[1-3H]-ethanol (V). This tritiated compound underwent selective aromatic chlorination to give the desired 2-(tert.butylamino)-1-(4-amino-3,5-dichlorophenyl)-[1-3H]-ethanol, [ethanol-1-3H]clenbuterol, with specific activity of 13.4 Ci/mmol (496 GBq/mmol).

Iodine is an effective promoter for the carbonylation of primary and secondary amines to ureas using palladium acetate as the catalyst and a base (e.g. K2CO3) in acetonitrile (3 h at 95 °C and 2.7 atm). Oxamides are formed in excellent yields when secondary amines are carbonylated in the presence of iodide ion and oxygen, while primary amines give ureas as the principal product at 95 °C, and oxamide at room temperature. Keywords: oxamides, ureas, double carbonylation, amines.

Upon dispersant-assisted exfoliation, pristine carbon nanotubes (CNTs) are divided between the supernatant and precipitate, which makes the determination of dispersant concentration a challenging task. We have developed a thermogravimetric-spectroscopy-based approach to accurately determine the dispersant-assisted CNT (or nanoparticles, in general) concentration in dispersion. A thermogravimetric analysis of the filtered and washed precipitate, that is usually discarded after centrifugation, is used here to accurately calculate the CNT mass in the precipitate and (through mass-balance) its mass in the supernatant. Once the true CNT concentration has been determined, a conventional spectroscopy-based concentration calibration plot is constructed for simple and swift use in further concentration measurements. Such true concentration analysis is crucial for studying the concentration-property relationship.

Catalytic condensation of amines and isonitriles can be accomplished efficiently at 100 °C using a palladium complex catalyst, oxygen, and iodine to give N,N-dialkylcarbodiimides.

A continuous three-step micro-synthesis of 1,2-dibromo-3-chloropropane, labelled with tritium in position 1 and 2, is described. A specific activity of 10.8 Ci/mmol is obtained. The yield observed in the uninterrupted overall synthesis is appreciably lower than that in the controlled step-by-step synthesis.

1-Methyl-[2-13C]ethylene oxide (I) is prepared in a four-step synthesis, starting from [1-13C]propionic acid. A method for an efficient α-chlorination of low carboxylic acids is developed, 2-chloropropionyl chloride being esterified without separation to give 72% of phenyl-2-chloro-[1-13C]propionate. The ester is hydrogenated with LiAlH4 to give 95% yield of 2-chloro-[1-13C]propan-1-ol which is then subjected to alkaline dehydrochlorination, giving 35% yield of the isolated product (I). This micro-scale method is also suitable for syntheses of 14C-labelled epoxides of low molecular weight.

The ion pair formed from rhodium trichloride and methyltrioctyl-ammonium chloride (Aliquat ® -336) was shown to catalyze, under mild conditions, hydrogen transfer from polymethylhydrosiloxane (PMHS) to substituted acetylenes, olefins, aroyl chlorides, α,β-unsaturated aldehydes ketones and esters and saturated carboxyl compounds, respectively. Addition of aqueous sodium perchlorate to the reaction mixtures at low to medium conversions allowed facile recovery of the catalyst as aqueous NaRhCl 4 which, with fresh Aliquat-336, could be re-extracted into a new reagent-containing organic solution.

Methods for tritiation of sulpiride, sultopride and metoclopramide were developed and optimized. 3H-sulpiride (7.1 Ci/mmol), 3H-sultopride (2.1 Ci/mmol) and 3H-metoclopramide (18.0 Ci/mmol) were obtained by hydrodebromination of the related bromo derivatives. The bromo derivatives were prepared, in turn, by appropriate procedures specified for each case.

Ethenol, 2-hydroxypropene and 2-hydroxybutene-1 were prepared by low-pressure pyrolysis of cyclobutanol, 1-methylcyclobutanol and 1-ethylcyclobutanol, respectively. Mass spectra, ionization energies, appearance energies of metastable ions and kinetic energy releases were determined on a reverse Nier-Johnson double-focusing mass spectrometer. Mercury and CH3 radicals from the pyrolysis of dimethylmercury were employed for calibration of the energy scale. The ionization energy of 2-hydroxybutene-1 is 8.55 ± 0.1 eV and the appearance energies of [C2H5CO]+ and [CH3CO]+ from that molecule are 10.25 ± 0.1 and 10.40 ± 0.1 eV, respectively. Changes observed in metastable peak shapes for certain fragmentation reactions upon pyrolysis are discussed.

Hydrogenolyse de bromo-2acetophenone, β-bromo- et bromo-4 styrene, (iodo nitro) benzene a l'aide du polymethylhydrosiloxane ou des formiates (donneurs protons)

La reaction se fait a partir de formiates de metaux alcalins ou alcalino-terreux; elle est catalysee par Pd(0)

The homogeneous and heterogeneous dehydrogenation, dehydration, reductive coupling and disproportionation of diaryl carbinols by group VIII metal catalysts were investigated. Conditions under which each of these catalyses take place independently have been defined using benzhydrol as substrate and RuCl2(PPh3)3 as catalyst. Kinetic measurements revealed that the various transformations of the carbinols are part of the same catalytic cycle. In aromatic hydrocarbon solvent, the active catalyst proved to be solvated RuCl2(PPh3)2 while in DMSO it is RuCl2(PPh3)(DMSO)2. The key intermediates are ruthenium alkoxides and ruthenium hydrides, Steric factors play a crucial part in catalyses by triphenylphosphine containing complexes but are of less significance in phosphine free heterogeneous systems.

La reaction se fait a partir de formiates de metaux alcalins ou alcalino-terreux; elle est catalysee par Pd(0)