Concurrent Decomposition Research Articles

The Palladium‐Catalyzed Cross‐Coupling Reactions of 3‐Chloro‐4‐halogeno‐1,2,5‐thiadiazoles.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Palladium-catalyzed Cross-Coupling Reactions of 3-Chloro-4-halogeno-1,2,5-thiadiazoles

3,4-Dichloro- and 3-chloro-4-halogeno-1,2,5-thiadiazoles (halogeno-: bromo- and iodo-) are involved in Pd-catalyzed cross-coupling reactions under Stille and Suzuki conditions. As a result, by using the commercially available 3,4-dichloro-1,2,5-thiadiazole as substrate, several 3-alkyl-, 3-alkenyl-, 3-alkynyl-and 3-aryl-4-chloro-1,2,5-thiadiazoles can easily be prepared. However, these reactions through direct desymmetrization of the 3,4-dichloro-1,2,5-thiadiazole always occur with side-reactions resulting from the concurrent decomposition of the heterocyclic ring of the starting material. These problems are resolved by involving, in these Pd-catalyzed cross-coupling reactions, the more reactive and selective 3-bromo-4-chloro- and 3-chloro-4-iodo-1,2,5-thiadiazole. These new dihalogeno-1,2,5-thiadiazoles can easily be prepared, via diazotization reaction followed by halogen substitution, from the 3-amino-4-chloro-1,2,5-thiadiazole.

Electric arc generated (Bredig) palladium nanoparticles: Surface analysis by X-ray photoelectron spectroscopy for samples prepared at different pH

Nanoparticle (sol, colloid) science attracts increased interest these days due to the special optical and magnetic properties possessed by the particles. The current research activity is supplementing the older body of research work in this area from the early 20th century with more sophisticated and detailed characterizations of sol particles. For example, vaporization-condensation methods were popular early preparative routes to many metal sols [1]. One method involved striking an unprotected DC arc between 2 metal poles in a liquid, most frequently water (the “Bredig Method”). “Bredig” sols were judged to be impure due to impurities from the concurrent electrolytic decomposition of the electrolyte and oxidized material [2] thought to form during arcing. Such results, however, were not proven directly till later times when modern (surface analytical) XPS techniques became available [3]. In this study, modern XPS techniques are used to investigate the surface speciation of Bredig palladium sols as a function of pH of the aqueous medium in which the palladium arcs are struck. The production of nanoscale Pd materials is of obvious interest for catalytic purposes in the motor vehicle industry where Pd is used widely in catalytic convertors. The electric circuit diagram for the power supply used for generating the Bredig palladium sols is illustrated in Fig. 1. A three-phase AC electric power supply rectified to 200 V DC (with a resistive ballast of 40 ohms to control the current level) was used. Positive and negative pole sockets were incorporated into the unit to allow switching of electrodes so that different metals could be arced. The unit also incorporated a keylock and interlock system for safety purposes. An electrical fan on an independent 230 V mains AC circuit cooled the unit during operation. The pole electrodes were BNC plugins with insulating retractable shrouds. The entire electrode save for the (active) pole at the end was encased in heat shrunk insulation with a silicone seal plug at the end to prevent fluid seepage into the interior of the glass tubing housing the wiring. Short lengths of BDHL.R. grade Pd wire of 0.91 mm diameter and of 99.97% purity that were soldered onto the copper wire within the glass sleeving of each electrode was used for the palladium poles. The arcing vessel was a custom designed three-necked flask which had two of its necks arranged (see Fig. 1b) to allow the two

Modeling of aerosol-assisted chemical vapor co-deposition of NiO and carbon nanotubes

High yield catalytic growth of carbon nanotubes (NT's) at extremely low temperatures (<600 K) could be achieved by co-depositing carbon precursors along with Ni(2+) in aqueous solutions using Aerosol-Assisted CVD. Deposition experiments were carried out by using both concurrent decomposition of Ni-based chemicals and Ni colloids. Raman spectroscopy was used to quantify the relative amount of NT's grown over graphite-like carbon. Microscopy was also employed to confirm the deposition of NT's as well to provide further information on the growth mechanism. Modeling of NT nucleation will also be presented, leading to the understanding of the microscopic mechanism of NT embryo formation.

Influence of the compensating anions of Ni/Al and Ni/Mg/Al layered double hydroxides on their activation under oxidising and reducing atmospheres

The activities and selectivities in the hydrogenation of acetonitrile on catalysts obtained from Ni/Al and Ni/Mg/Al layered double hydroxides (LDHs) precursors depend on the nature of their compensating anions: CO 2− 3,NO − 3 or Cl −. The latter gives rise to sample with low activity and the less selective to primary amine. Studies by XRD, TG–DSC, mass spectrometry and TPR experiments show that the anion influences the thermal stability and the reducibility of the Ni-containing LDHs. The thermal decomposition of LDH into the mixed oxide form involves the dehydration, then the dehydroxylation of the layers with the concurrent decomposition of CO 2− 3 and NO − 3 which occurs at similar temperature in air or H 2 atmosphere. In TPR experiments the reduction of Ni 2+ to Ni 0 takes place at above 800 K. A specific behaviour is observed when Cl − is the compensating anion, with a better reducibility of Ni 2+ and the existence of Ni species reduced at low temperatures, not observed with CO 2− 3 and NO − 3 as anions. In addition, all the mixed oxides are poorly reconstructed in water, and a clear segregation of bayerite occurs on the chloride samples. This last phenomenon is enhanced in the Mg-containing compound. It is proposed that the presence of both Cl and Mg favours the extraction of aluminium and makes the accessibility to a significant amount of Ni 2+ cations easier, thus increasing their reducibility. In this case, Ni 0 particles with an average size around 65 nm are detected after reduction at 723 K, while the other samples, poorly reduced, still contain the mixed oxide structure.

Pyridines as bifunctional co-catalysts in the CrO 3-catalyzed oxygenation of olefins by t-butyl hydroperoxide

t-Butyl hydroperoxide (TBHP) oxidizes olefins to epoxides and allylic oxidation products in the presence of a Cr(VI) catalyst. A concurrent decomposition of the oxidant occurs. Pyridine-derived additives alter the behavior of this catalytic system: monodentate pyridines and trans-chelated bidentate bipyridines retard the decomposition of TBHP, and arrest the epoxidation reaction, shifting the product selectivity towards allylic oxidation. Adversely, cis-chelated bipyridines accelerate the decomposition of TBHP. Depending on ligand nature and concentration, the initial decomposition rate can be slowed down to 1/8th, or accelerated up to two orders of magnitude, (relative to CrO 3 catalysis). The allylic oxidation and the TBHP decomposition are free-radical reactions, but the epoxidation is evidently not. A reaction mechanism is proposed, where the diverse role of the pyridine ligands is attributed to specific complex formations.

The influence of microencapsulation using Eudragitr` RS100 on the hydrolysis kinetics of acetylsalicylic acid

Homogeneous Eudragit® RS100 matrix microspheres containing molecularly dispersed acetylsalicylic acid (ASA) were prepared in order to investigate the effect of encapsulation on the decomposition rate of a hydrolytically susceptible drug. ASA-loaded microspheres of this non-eroding polymer matrix were analysed at predetermined time points following immersion of the microspheres in temperature controlled buffer systems at pH 1.2 or pH 12.1 at 30, 40 or 50°C. The mass balance of the total amount of solutes (ASA and SA) initially located within the microsphere interior was equal to the sum of the amount of solutes remaining in the microsphere interior and the amount of solutes in the aqueous phase at any time during the course of the study. Each analysis involved the quantitation of four species; the drug and decomposition product, salicylic acid (SA), in both the microsphere phase and the external aqueous phase. A simple model system using first-order rate approximations for the concurrent Fickian diffusion and hydrolysis decomposition of the drug resulted in a multi-exponential expression which adequately described the time-course profile of the drug. SA-loaded microspheres were used as a control under similar conditions to determine the magnitude of the contribution of microsphere phase hydrolysis of ASA to the overall rate of drug loss from the microspheres. Results indicated that microsphere phase hydrolysis of ASA was minimal. Even after 900 h of immersion in pH 12.1 buffer some ASA remained within the micro-sphere. It is postulated that the matrix incorporated drug is essentially shielded from hydrolytic attack until it is liberated into the external aqueous environment. Electrostatic association of the drug with the charged quaternary residues in the polymer along with the limiting availability of water within the micro-sphere may be responsible for the observed stability of ASA in aqueous swollen ASA-loaded Eudragit® microspheres.

Delay-fault testability preservation of the concurrent decomposition and factorization transformations

Recently, a new, very efficient method of multilevel logic synthesis based on factorization and decomposition of Boolean expressions has been introduced. It has been shown that the transformations used by this method preserve the single stuck-at testability of two-level circuits. This paper shows that single-cube extraction, double-cube extraction, and dual-extraction of double-cubes/spl isin/D/sub 1,1,2/ and D/sub 2,2,2/ preserve testability with respect to a general robust path-delay-fault (RPDF) test set. However, the authors show that while dual-extraction of double-cubes/spl isin/D/sub 2,2,3/ preserves RPDF testability of paths through the extracted divisors with respect to a single-input-changing test set, it does not guarantee RPDF testability preservation of unmodified paths. Furthermore, the authors provide sufficient conditions for algebraic resubstitution with complement to preserve RPDF testability that cover a larger class of complementary expressions than was known previously. The testability preservation of these transformations is demonstrated on a set of RPDF testable Berkeley PLAs. >

Effects of the deposition temperature on the resistivity of copper films produced by low-pressure metal-organic chemical vapour deposition on a TiN barrier layer

Copper was deposited on to TiN by low-pressure metal-organic chemical vapour deposition, using hexafluoroacetylacetonate-Cu+1-trimethylvinylsilane (hfacCu(I)TMVS) and argon carrier gas. The resistivity of the deposited copper films was investigated by observing the effects of the deposition temperature on the composition, microstructure and surface morphology of the copper films. The resistivity of the copper films decreases as the deposition temperature decreases. The copper films deposited at high temperatures, tend to contain the pores and or/ channels as well as carbon and oxygen, which results in the increase of the resistivity of the deposited films. The pores and/or channels come from the island-like growth of the copper films, while carbon and oxygen are due to the concurrent thermal decomposition of hfac during the disproportionation reaction between hfacCu(I) molecules.

Adsorption and decomposition of CH 3NH 2 on Mo(100)-c(2 × 2)N

The adsorption and decomposition of CH 3NH 3 on a Mo(100)-c(2 × 2)N surface has been studied using temperature-programmed desorption and Auger electron spectroscopy. The initial sticking coefficient for CH 3NH 2, at 210 K, is estimated to be ~ 10 −1, with the absolute value expected to be within a factor of three, and the maximum adsorption capacity is 0.28 ML. Temperature-programmed desorption studies show that adsorbed CH 3NH 2 undergoes desorption and concurrent decomposition. The major decomposition products are H 2, NH 3, C s, and N s. In addition, C 2H 4 is a minor decomposition product. D 2/CH 3NH 2 coadsorption studies suggest that the decomposition of adsorbed CH 3NH 2 is initiated by intramolecular hydrogen transfer to form adsorbed CH 2 and NH 3. Most of the CH 2 species undergo dehydrogenation to form C and H 2. Some of the adsorbed NH 3 decomposes to form N and H 2, but most of the NH 3 desorbs into the gas phase.

Interactions of H 2 and NH 3 with Mo(100) and Mo(100)-c(2 × 2) N surfaces

The interactions of H 2 and NH 3 with Mo(100) and Mo(100)-c(2 × 2)N surfaces were studied using temperature programmed desorption and Auger electron spectroscopies. For a clean Mo(100) surface, the initial sticking coefficient is 1.0 and the maximum adsorption capacity is 2.0 ML. On the nitrided surface, the sticking coefficient decreases to 0.4 and the maximum capacity decreases to 0.5 ML. The initial sticking coefficient for NH 3 on Mo(100) is 0.36, and the saturation adsorption capacity is 0.6 ML. Nitriding the surface reduces the initial sticking coefficient to 0.24 and the saturation capacity to 0.35 ML. Temperature programmed desorption studies show that adsorbed NH 3 undergoes desorption and concurrent decomposition, the extent of decomposition being much less significant on the Mo(100)-c(2 × 2)N than on the Mo(100) surface. D 2/NH 3 coadsorption studies reveal that NH 3 decomposition proceeds via a stepwise dehydrogenation process.

Mass spectrometry of some fluorinated alcohols

AbstractThe 70 eV electron impact mass spectrometric behaviour of some fluorinated alcohols, i.e. 2‐fluoroethanol, 2,2,2,‐trifluoroethanol, 2,2,3,3‐tetrafluoropropan‐1‐ol and 1.3‐difluoropropan‐2‐ol, was studied in detail by means of mass‐analysed ion kinetic energy Spectrometry, deuterium‐labelling experiments and comparison with unfluorinated analogues. Composite metastable peaks related to HF losses were rationalized by invoking the presence of two concurrent decomposition pathways, the first consisting in a 1,2‐elimination and the second requiring the implication of hydroxyl hydrogen. This last process and other decomposition routes suggest the presence of H. bridging between the hydroxyl oxygen atom and fluorine.

Structures and reactivity of some fluorine-containing gaseous ions

The 70 eV Electron Impact mass spectrometric behaviour of some fluorinated alcohols, i.e. 2-fluoroethan-1-ol, 2,2,2-trifluoroethan-1-ol, 2,3,3,3-tetrafluoropropan -1-ol and 1,3-difluoropropan-2-ol, has been studied in detail by means of mass-analyzed ion kinetic energy spectroscopy, deuterium labelling experiments and comparison with nonfluorinated analogues. Composite metastable peaks related to HF loss have been rationalized by invoking the presence of two concurrent decomposition pathways, the first consisting of a 1–2 elimination and the second requiring the implication of hydroxyl hydrogen. This last process and other decomposition routes suggest the presence of H bridging the hydroxyl oxygen and fluorine.

The testability-preserving concurrent decomposition and factorization of Boolean expressions

The authors present a concurrent method for the decomposition and factorization of Boolean expressions. The method uses only two-literal single-cube divisors and double-cube divisors considered concurrently with their complements. The authors demonstrate that these objects, despite their simplicity, provide a very good framework on which to reason about common algebraic divisors and the duality relations between expressions. The simplicity of these objects makes it possible to compute the cost function associated with them accurately and dynamically. Hence, the method is entirely greedy, and in each iteration it extracts the best expression along with its complement. The decomposition is based on testability-preserving transformations, and the synthesized multilevel network is fully tested by a complete test derived for the original circuit. The algorithm has been implemented and excellent results on several benchmark circuits illustrate its efficiency and effectiveness.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Retrosynthesis vs ketene loss in electron-ionization-induced decompositions of 1,5-benzodiocapine, 1,5-benzodiazepine, 1,5-benzodithiepine, 1,5-benzoxazepine and 1,5-benzoxathiepine

The 70 eV electron ionization mass spectrometry of the title compounds has shown the presence of two concurrent primary decomposition pathway, corresponding to the retrosynthetic process and to CH2CO loss. The yields of the two pathways can be related tothe XCO bond strengths: as the XCO bond becomes weaker, [MCH2CO]+˙ ion formation is favoured.

The reaction of geminal bromonitroalkanes with nucleophiles. Part 1. The decomposition of 2-bromo-2-nitropropane-1,3-diol (‘Bronopol’) in aqueous base

2-Bromo-2-nitropropane-1,3-diol decomposes in aqueous base to give tris(hydroxymethyl)-nitromethane, glycolic acid, formic acid, methanol and 2,2-dinitroethanol. It also releases NO2– and Br– ions but not BrO–. These products are shown to form via four concurrent decomposition pathways, three of which involve 2-bromo-2-nitroethanol as a reactive intermediate.

Photochemical synthesis of disilane from silane with infrared laser radiation

The authors report the clean and efficient conversion of silane to disilane by CO{sub 2} laser irradiation. The direct irradiation of pure silane at high pressures (from 75 to 1,700 Torr) converts silane to disilane with high selectivity and with efficient use of the absorbed laser radiation. Hydrogen is the only other major volatile product, and the production of solid products is minimal. The proposed mechanism of the photochemical reaction includes (1) collisionally enhanced absorption of the laser radiation by silane, (2) collisional deexcitation of the vibrationally excited silane, (3) concurrent decomposition to SiH{sub 2} and H{sub 2}, (4) production of vibrationally excited disilane by SiH{sub 2} insertion into a silane Si-H bond, (5) collisional quenching of the excited disilane, and (6) rapid cooling of the irradiated gas by thermal expansion. They support the proposed mechanism by additional experiments and model calculations.

Degradation of 2-deoxyaldoses by alkaline hydrogen peroxide

Reaction of 2-deoxy- D- arabino-hexose, 2-deoxy- D- lyxo-hexose, and 2-deoxy- D- erythro-pentose with alkaline hydrogen peroxide in the presence of magnesium hydroxide afforded the corresponding 2-deoxyaldonic acid, the 1,4-lactone, and the 1- O-formyl derivative of the next lower alditol. The 2-deoxyaldonic acids were separated in 60–80% yields, as new, crystalline lithium salts. The 1,4-lactones were obtained under conditions that precluded intermidiate formation of the free acids: presumably, the reaction proceeded by way of an intermediate, furanosyl hydroperoxide, which was converted into the lactone by elimination of water. With an excess of alkaline hydrogen peroxide, in the absence of magnesium hydroxide, the substrates were degraded to formic acid, with concurrent decomposition of hydrogen peroxide. It is shown that decomposition of hydrogen peroxide is catalyzed by hydroperoxide anion, and that it takes place by both a chain, and a non-chain, process. The decomposition reactions afford an abundant source of hydroxyl radical capable of oxidizing a wide variety of compounds.

Melting and decomposition of RDX&2sbndHMX mixtures by dta

The melting and decomposition behavior of various RDX&2sbndHMX mixtures was studied by DTA (the HMX apparently existed in the δ-polymorphic form during the physical and chemical changes which occurred). Non-cyclic heating programs (thermodynamically unstable states existed) and cyclic heating and cooling programs (H/C/H) (thermodynamically stable states existed) were employed. Data from those programs indicated that solid solutions of RDX&2sbndHMX occurred in the composition range of ca.55–83 wt % RDX. Thus, below this lower limit, HMX separated from the mixture while above the upper limit, RDX separated. From the van’t Hoff freezing point relation for eutectic equilibria, the heat of fusion of RDX ▪ was estimated as ca.33 g −1 p]When a cyclic run was carried out for a mixture containing less than 55 wt % RDX, a single endotherm resulted (presumably, melting of a 55 wt % solid solution) followed by two strong exotherms. The first exotherm was attributed to decomposition of the 55 wt % solid solution while the second to HMX decomposition. Upon subjecting an RDX&2sbndHMX mixture containing more than 83 wt % RDX to a H/C/H program, two endotherms appeared followed by a single strong exotherm. The endotherms were ascribed to melting of an 83 wt % solid solution and of RDX, respectively. The strong exotherm was attributed to concurrent decomposition of RDX and the 83 wt % solid solution (no HMX exotherm could be detected). When mixtures containing ca.55–83 wt % RDX underwent cyclical programs, only one endotherm and only one exotherm could be observed. The endotherm resulted presumably from melting of a solid solution whereas, the exotherm from decomposition of the solid solution. p]From the data obtained, approximate phase diagrams were constructed for the melting and decomposition of RDX&2sbnd;HMX mixtures based upon cyclic and non-cyclic programs.

Acid-catalysed oxygen-18 exchange, racemisation, and aquation studies with the trisoxalatocobaltate(III) anion in aqueous solution

Kinetic data on the acid-catalysed exchange of oxygen between the trisoxalatocobaltate(III) anion and solvent water, obtained by use of oxygen-18, are reported. At 25°C, in the presence of 1M-HCl, the carbonyl oxygen exchanges ca. 50 times faster than the bridging oxygen. Owing to the concurrent decomposition the bridging oxygen exchange could be followed for only 0·1 t½ for exchange. Kinetic data for inversion and decomposition have been obtained under the same experimental conditions as used for studying the oxygen exchange. The data exclude the possibility that the mechanism of inversion involves ‘one-ended dissociation’. A twist mechanism is favoured.