Decomposition Of Iodide Research Articles

A high temperature study of the reaction SiH4+H ⇋ SiH3+H2

AbstractThe reaction of silane with H atomsmagnified imagewas studied behind reflected shock waves at temperatures between 998 K and 1273 K and pressures around 1.5 bar. The thermal decomposition of a few ppm ethyl iodide (C2H5I) was used as a well known H‐atom source. The atomic resonance absorption spectroscopy (ARAS) was applied for time resolved and simultaneous measurements of H‐ and Si‐atom concentrations. The presence of an excess of SiH4 causes a fast consumption of H atoms according to reaction (R 5). The signals obtained were kinetically evaluated by computer simulations based on a simplified reaction mechanism. The rate coefficient for reaction (R 5) was found to be:

Optimization of microwave digestion for determination of selenium in human urine by flow injection-hydride generation-atomic absorption spectrometry

A microwave digestion program, which completely decomposes and oxidizes selenium compounds in urine to selenate, was developed by monitoring the pressure and the temperature during microwave digestion. The efficient decomposition and quantitative recovery of trimethylselenonium iodide spiked into urine was achieved in 18 min using the optimized microwave program reaching 200 °C and 8 bar. The selenate in the digest was reduced to selenite by hydrochloric acid with the aid of microwave energy. Urea was found useful to eliminate NOx fumes, which might be absorbed in the digest and interfere in the determination of selenium by flow injection-hydride generation-atomic absorption spectrometry (FI-HG-AAS). The recovery of trimethylselenonium iodide, selenomethionine, and selenoethionine added to urine was 96.5–105%. The whole procedure, FI-HG-AAS determination following microwave digestion of urine sample and microwave reduction of selenate in the digests into selenite, was checked with two Standard Reference Materials 2670 (toxic metals in human urine). The results showed good agreement with the certified values (normal level 30 ± 8 µg Se l–1 and elevated level 460 ± 30 µg Se l–1. The detection limit of the whole procedure was 3 µg Se l–1 urine. Selenomethionine and selenoethionine were found unstable during the microwave heating used to reduce selenate to selenite. Such a microwave reduction procedure should be cautioulsy used to distinguish selenate from selenite in the matrices which might contain organic selenium compounds.

Shock Tube Study of the Reaction of H Atoms with TiCl4

The reaction of H atoms with TiCl4 was studied behind reflected shock waves at temperatures between 1190 and 1500 K and pressures around 1.5 bar by applying atomic resonance absorption spectrometry for time-resolved measurements of H atoms at the Lα line. The thermal decomposition of ethyl iodide (C2H5I) served as the H atom source. By using a high excess of TiCl4, the consumption of H could be modeled by pseudo first-order kinetics. For the reaction TiCl4 + H → TiCl3 + HCl a temperature-independent rate coefficient of k1 = 3.5 ± 0.9 × 1013 cm3 mol-1 s-1 was found for the temperature range of the present experiments.

Adsorption and Decomposition of Methyl Iodide on Low Index Planes of NiAl

Surface chemistry of CD3I (CH3I) on the (111), (100), and (110) planes of NiAl has been investigated with X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). On the basis of XPS, adsorption of CD3I on the (110) and (111) planes is primarily associative at 120 K. In contrast, adsorption of the majority of the reactant on the NiAl(100) plane at 120 K is dissociative. This enhanced dissociation on NiAl(100) is attributed to its Al terminated surface. In addition to molecular CD3I desorption, TPD shows that CD4 and D2 are reaction products that desorb from the NiAl planes during the reaction of CD3I. TPD also suggests that methyl radical, CD3, may result during the thermal decomposition of CD3I on all three NiAl surfaces. Some C−C bond formation leading to the desorption of CD2CD2 is experimentally observed to occur on the (111) plane that exposes both Ni and Al atoms in the outermost surface.

Studies and Preparation of Hafnium Metal

This paper discusses in detail the results of investigations on the preparation of hafnium metal either by calciothermic reduction of HfO 2 or by fused salt electrolysis of HfCl 4 . The metal so produced has been purified by the iodide decomposition process. The results obtained from the purification studies indicate that a metal meeting the AEC specifications can be obtained from these feeds.

The surface chemistry of methylene iodide adsorbed on clean and oxygen-covered Mo(100): formation and chemistry of carbenes

Carbene species are grafted onto Mo(100) by the thermal decomposition of methylene iodide, where the decomposition is followed using ultraviolet photoelectron spectroscopy. Carbenes hydrogenate to methane by reaction with surface hydrogen via a second-order reaction with an activation energy of 21 ± 2 kJ mol −1. Experiments with deuterium show that there appears to be no hydrogen-deuterium exchange between the carbene and surface hydrogen. The carbene decomposition temperature increases with the addition of oxygen to the surface, and this effect is ascribed to the effect of site blocking rather than a chemical modification of the adsorbed carbene by coadsorbed oxygen. Similarly, although the methane desorption temperature increases with increasing oxygen coverage, this effect is found to be due to a change in the surface coverage of carbene and hydrogen rather than a chemical modification of the carbene itself. Finally, no ethylene or ethane are found to desorb from the surface.

Laser assisted chemical vapour deposition of hydrogen containing amorphous carbon at room temperature

Hydrogen containing amorphous carbon films were deposited by photolytic decomposition of methylene iodide, CH2I2, at room temperature. An excimer laser operated at 193 nm was used as the excitation source. Smooth and adherent films were produced on Si(100) substrates. The influence of the CH2I2 partial pressure and the laser beam to substrate distance on the growth process was investigated. The films were characterized by Raman spectroscopy, atomic force microscopy, energy dispersive X-ray spectroscopy. and X-ray photoelectron spectroscopy. The iodine and oxygen contents in the carbon films were less than 1% and the hydrogen content was approximately 50%.

Photoassisted catalytic oxidation of alcohols and halogenated hydrocarbons with amorphous manganese oxides

This manuscript discusses the synthesis of Amorphous Manganese Oxide (AMO) materials that are used for efficient photoassisted catalytic oxidation of alcohols and halogenated hydrocarbons. Characterization studies suggest that oxygen is lost from AMO very readily under illumination, creating oxygen vacancies that may be important in photooxidation reactions. Alcohols are converted to ketones such as acetone from isopropanol with 100% selectivity at room temperature. These AMO systems have turnover numbers that are over one order of magnitude greater than TiO 2 systems for isopropanol oxidation and over an order of magnitude greater than for TiO 2 systems in decomposition of halogenated hydrocarbons. In addition the TiO 2 systems are poisoned much faster than the AMO materials, especially in degradation of halogenated hydrocarbons. The same high activity and selectivity occur for the total oxidation of halogenated hydrocarbons such as methyl bromide which is converted into CO 2, H 2O and Br 2. The synthesis, characterization, and photoactivity of these materials will be discussed. AMO photocatalysts are also active in the decomposition of methyl choride and methyl iodide.

A shock tube study of the reaction of H atoms with SiCl4

The reaction of H atoms with SiCl4 was studied behind reflected shock waves at temperatures between 1530 K and 1730 K and pressures around 1.5 bar by applying atomic resonance absorption spectroscopy (ARAS) for time resolved measurements of H atoms at the Lα-line. The thermal decomposition of a few ppm ethyl iodide (C2H5l) was used as a H-atom source. In the presence of a high excess of the molecular reactant SiCl4 a slow consumption of H was observed, which follows a pseudo-first-order rate law. Rate coefficient for the consumption of H by the reaction: was determined to be: © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 469–472, 1997.

Toward Hexaphenylethane: Structure and Decomposition of Crystalline Triphenylmethyl Iodide

Triphenylmethyl iodide (C19H15I) crystallizes in the monoclinic system: a = 15.919(6) Å, b = 10.826(6) Å, c = 19.397(11) Å, β = 114.86(4)°, space group C2/c, Z = 8. In the structure, heterochiral propeller molecules are interdigitated. This arrangement, coupled with earlier reports of the thermal instability of triphenylmethyl iodide, suggested a convenient, topochemically controlled, solid-state synthesis of the elusive hydrocarbon hexaphenylethane. Crystals of the 13Cmethyl-labeled triphenylmethyl iodide were heated to 100 °C in a rotor spinning at the magic angle within an NMR spectrometer. Spectral changes and accompanying analyses by plasma desorption mass spectrometry, calorimetry, and ESR spectroscopy reveal that the major product in the decomposition is triphenylmethane, produced by hydrogen atom abstractions from neighboring triphenylmethyl radicals, that subsequently oligomerize. These data provide a new view of the thermal stability of triphenylmethyl iodide in the solid state and an old view of the accessibility of hexaphenylethane.

A Shock Tube Study of the Reactions of H Atoms with COS, CS2, and H2S

AbstractReactions of H atoms with COS, CS2, and H2S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time‐resolved measurements of H atoms at Lα. The thermal decomposition of a few ppm ethyl iodide (C2H5I) was used as a H‐atom source. In the presence of a large excess of the molecular reactant COS, CS2, or H2S, a consumption of H was observed which follows a pseudo first‐order rate law. Rate coefficients for the reactions:magnified imagewere determined to be:k1 = 2.4 × 1014exp(–3415 K/T) cm3mol−1s−1k2 = 1.4 × 1015exp(–9250 K/T) cm3mol−1s−1k3 = 2.5 × 1014exp(–2890 K/T) cm3mol−1s−1

Synthesis and Decomposition of Zinc Iodide: Model Reactions for Investigating Chemical Change in the Introductory Laboratory

The purpose of this article is to discuss two colorful reactions not widely used by chemical educators in high schools or college chemistry laboratories: The synthesis of zinc iodide from its elements, zinc and iodine, and the subsequent decomposition of zinc iodide back into its elements. These reactions are important for chemistry teachers to know about because they can be performed by introductory students to understand different aspects of chemical change such as the concepts of reaction, compound, bonding, excess and limiting reactants, an empirical formula, balanced chemical equation, the conservation of matter and energy, the Law of the Conservation of Mass, and the Law of Constant Composition. These concepts, in turn, are important because they are fundamental to chemistry, are widely taught by chemistry teachers, and are deceptively difficult for introductory chemistry students to understand.The synthesis of zinc iodide has many scientific advantages over current syntheses of binary compounds fro...

Preparation of vanadium nitride and its subsequent metallization by thermal decomposition

The preparation of high purity (greater than 99.8%) ductile grade vanadium is extremely difficult owing to its exceptionally high affinity towards carbon, nitrogen and oxygen. The removal of these interstitial impurities by conventional melt-refining routes is rather difficult. Specialized techniques such as pyrovacuum treatment, iodide decomposition and fused salt electrorefinement are normally adopted to prepare ultrapure vanadium. In the present investigation a new technique which involves the preparation and subsequent thermal decomposition of vanadium nitride (VN) has been attempted to obtain vanadium metal. The vanadium nitride in this study was prepared by carbonitrothermic reduction of vanadium pentoxide (V 2O 5) at a temperature of 1500 °C. The VN thus formed was thermally decomposed at 1750 °C under reduced pressure (3 × 10 −2 Pa) to metallic vanadium. Consolidation of the product metal sponge (by arc melting) under a low pressure, high purity argon atmosphere yielded vanadium of purity better than 97%. The arc-melted metal can be further refined by fused salt electrolysis, leading to a purity better than 99.5%.

Solvent Effects on the Rate of Heterolysis of t-Butyl Chloride, Bromide, Iodide, and 2,4-Dinitrophenolate

Abstract Rates of heterolytic decompositions of t-butyl chloride, bromide, iodide, and 2,4-dinitrophenolate have been measured by an NMR method in eight deuterated or undeuterated polar solvents; methanol-d4, ethanol-d6, dimethyl-d6 sulfoxide, N,N-dimethylformamide-d7, acetonitrile-d3, pyridine, nitrobenzene, and acetone-d6. The observed solvent effect is discussed on the basis of cation and anion solvation. With t-butyl halides, the anion solvation due to hydrogen bonding by protic solvents drastically decreases on increasing the radius of halide ions, and thus the differential solvation transferred from anion-solvating methanol to cation-solvating dimethyl sulfoxide is dramatically reversed on going from the chloride to the iodide (kMe2SO–d6/kmethanol–d4 at 60 °C: t-BuCl, 5 × 10−2; t-BuBr, 6 × 10−1; t-BuI, 7). The 2,4-dinitrophenolate behaves like the iodide. Complicated products are obtained in the decomposition of t-butyl bromide in dimethyl sulfoxide; however, a mechanism involving a bimolecular decomposition process of the bromide is ruled out. During the decomposition of t-butyl iodide in dimethyl sulfoxide, an intermediate salt t-butoxydimethylsulfonium iodide has been detected. The salt decomposes to isobutene, but the process is much slower than the heterolytic decomposition of t-butyl iodide itself at ambient temperature.

The Effect of Hydrogen Coadsorption on the Thermal Chemistry of Methyl Iodide on Ni(100) Surfaces

A detailed investigation of the surface chemistry of methyl iodide with preadsorbed hydrogen on Ni( 100) is reported here. TPD data indicate that, in general, the presence of hydrogen on the surface induces a yield increase in methane formation and a reduction of the extent to which methyl species decompose as compared with the case where the methyl iodide is adsorbed by itself on a clean surface. Furthermore, two very different methane desorption regimes are observed at 150 and 220 K. By using both isotopically labelled methyl iodide and deuterium (D2 + CH3I and H2 + CD3I) it was determined that while the high-temperature methane is formed via the reductive elimination of surface methyl species produced by decomposition of methyl iodide with coadsorbed hydrogen atoms, the lower temperature methane TPD peak may be the result of a direct attack of the surface hydrogen on adsorbed methyl iodide molecules in a concerted fashion instead. The TPD data also indicate that neither methylene nor methylidyne intermediates form during the decomposition of methyl iodide on nickel below 200 K, and experiments with CH2I2 clearly show that methylene species can be easily hydrogenated to methane in the presence of D2 coadsorption at quite low temperatures. Finally, no H-D exchange between methyl species and coadsorbed hydrogen (H2) was observed.

Structural characteristics of silver-chromate glasses and performance of silver-chromate electrochemical cells

Silver-chromate glasses xAgl-yAg2O-zCrO3 (x= 64, 67 and 70 mol% and y/z= 1) were prepared by rapid quenching of the melt. The microstructure of the as-quenched samples showed different surface agglomerates which led to non-uniformity in chemical distribution throughout the sample. The presence of potassium, detected by energy dispersive analysis of X-rays EDAX, was due to contamination of potassium nitrate produced during the preparation of Agl via the double decomposition of silver nitrate and potassium iodide. The battery fabricated from the glass with 70 mol % Agl contaminated with potassium showed an unstable discharge compared to the battery fabricated from glass with 70 mol % Agl of AR grade. This was attributed not only to the formation of low-conducting silver iodide but also to low-conducting potassium compounds which increased the internal resistance of the battery leading to a quick drop in cell voltage.

Two mechanisms for formation of methyl radicals during the thermal decomposition of methyl iodide on a copper surface

When submonolayer quantities of iodomethane (CH 3 I) are condensed on a Cu(111) surface and the surface is heated, methyl radicals are evolved at 140 and 470 K. These methyl radicals have been identified by mass spectrometry. The 140 K pathway for methyl radicals correlates with the temperature for carbon-iodine bond dissociation in CH 3 I, and thermally-activated, dissociative electron transfer is shown to be a viable mechanism for reaction. The 470 K radical pathway results from homolysis of the Cu-CH 3 bond for surface-bound methyl groups and corresponds to a Cu-CH 3 bond strength of ∼29 kcal/mol. A competing reaction pathway at 470 K is methyl decomposition to produce methane, ethylene, and propylene

A RAIRS study on the surface chemistry of ethyl iodide on Pt(111)

The chemisorption and thermal decomposition of ethyl iodide on Pt(111) have been studied by reflection-absorption infrared spectroscopy (RAIRS). At 100 K the chemisorption is molecular, and a change in adsorption geometry occurs from a flat to an upright orientation as the surface coverage is increased. Ethyl, ethylene and ethylidyne were identified at higher temperatures by IR spectrometry as decomposition products. As a consequence of the coverage-dependent orientation of the ethyl iodide molecules on the surface, different reaction mechanisms are operative at low and high coverages. At low coverages, ethyl iodide decomposes quantitatively between 150 and 200 K through a C-I bond breaking step followed by immediate dehydrogenation to ethylene. At saturation coverages, some ethylene formation competes with molecular desorption around 200 K (analogous to the low coverage decomposition), but additional ethylene is produced between 200 and 240 K in a slower, reversible reaction which involves the formation of ethyl species as stable intermediates. Ethylene further decomposes around 300 K to form ethylidyne.

Alkyl iodide decomposition on copper surfaces: .alpha.-elimination and .beta.-hydride elimination from adsorbed alkyls

Alkyl iodide decomposition on copper surfaces: .alpha.-elimination and .beta.-hydride elimination from adsorbed alkyls

Mechanism for the catalytic exchange of methane with deuterium on Pt(111) surfaces

The reaction of methane with deuterium on Pt(111) single crystals was studied using thermal programmed desorption (TPD) under ultra-high vacuum conditions. Methyl groups, believed to result from the dissociative adsorption of methane under catalytic conditions, were deposited directly by thermal decomposition of methyl iodide. TPD experiments after coadsorption with deuterium show that methane formation occurs in very high yields. Furthermore, the desorbing molecules display a bimodal distribution very similar to that obtained under atmospheric pressures, with maxima for CH3D and CD4. This distribution can be explained by a competition between two surface reactions, namely, direct incorporation of hydrogen in methyl groups and methylene formation followed by rapid interconversion to methylidyne before final hydrogenation to methane. We found that the rates for both reactions depend linearly on the coverage of methyl groups, but while the hydrogenation rate is also proportional to the coverage of deuterium, in the case of multiple H-D exchange an almost zero order dependence at low temperatures slowly becomes first order as the reaction temperature is increased. The activation energies for CH3D and CD4 formation were estimated to be 17.0 and 6.5 kcal/mol respectively even though the reaction rates displayed comparable values because of a compensation effect in the preexponential factors. Finally, the relative yields for CH2D2, CHD3 and CD4 are close to the equilibrium values, a result that is consistent with the proposed methylene-methylidyne interconversion step in our mechanism.