Decomposition Path Research Articles

Thermolysis and UV-photolysis of perfluorinated iodo-alkanes and iodo-oxaalkanes: there is a preferred reaction channel

The thermal stability of perfluorinated iodides depends on their structure and decreases in the order of R FCF 2CF 2I>R FCF 2CF(CF 3)I>R FOCF(CF 3)I≈R FCF 2C(CF 3) 2I. The major decomposition path consists of the elimination of an unsaturated compound (CF 2CF 2, CF 2CFCF 3, OCFCF 3, CF 2C(CF 3) 2, respectively) with concomitant formation of R FI. The highest selectivities were found for tertiary iodides and 2-iodo- 3-oxaalkanes, whose decomposition is virtually irreversible. UV-photolysis of the iodo-compounds gave the same products as the thermolysis reactions.

Infrared laser induced decomposition of hexafluorobenzene and some monosubstituted derivatives. Intermediacy of the pentafluorophenyl radical

The infrared multiphoton laser induced reactions of hexafluorobenzene and related pentafluoro analogues (pentafluorobenzene, pentafluorochlorobenzene, pentafluorobromobenzene, and pentafluoroiodobenzene) have been investigated using a CO 2 TEA laser. The study was carried out in order to define the decomposition products and to attempt to clarify their mode of formation. Thus, the products (relative yield, %) of the irradiation of C 6F 6 (1027.3 cm −1; 0.73.J/cm 2; 10 pulses; 25% decomposition) were C 2F 4(64), C 6F 5CF 3(28), C 2F 6(7), CF 4(1) and that for C 6F 5H (949.4 cm −1; 0.80 J/cm 2; 10 pulses; 25% decomposition) was C 2F 4 and C 6F 5CF 3. Increasing the number of pulses in the reaction with C 6F 6 decreased the amount of C 2F 4 and increased the amount of C 6F 5CF 3 and C 2F 6 indicating secondary and tertiary reactions. Addition of halogen (X 2, X = Cl, Br) to these reactions caused different products to be formed. Thus, the irradiation of a C 6F 6/Cl 2 mixture (7.4/7 Torr; 1027.3 cm −1; 0.7 J/cm 2; 35 pulses; 35% reaction) afforded C 6F 5Cl(46); CF 3Cl(24) and CF 2Cl 2(30). Irradiation of C 6F 5H/X 2 mixtures afforded mainly C 6F 5X + HX. For example, C 6F 5H/Br 2 (10/40 Torr; 949.4 cm −1; 0.93 J/cm 2; 10 pulses; 10% reaction) gave C 6F 5Br and HBr exclusively. Irradiation of C 6F 5-X (X = Cl, Br, I) (977.2 cm −1; ca. 0.74 J/cm 2; 200 pulses, 39–74% reaction) gave C 6F 6 and a minor amount of decafluorobiphenyl [(C 6F 5) 2], a radical combination product of the pentafluorophenyl radical (C 5F 5·). Increasing the fluence in these reactions gave similar produts in most cases but in some instances increased the amount of C 2F 4 formed. The reactions and product distribution of the hydrogen substituted derivative (C 6F 5H) was examined in the presence of Br 2 as a function of laser fluence and halogen concentration. It was found that the threshold for C 6F 5H decomposition was higher for the reaction involving Br 2 (as compared with the reaction involving Cl 2 or neat C 6F 5H). The presence of Br 2 also decreased the amount of C 6F 5H that was decomposed, indicating a quenching process. The decomposition path with the lowest activation energy for these molecules is thought to be C 6F 5X→C 6F 5· + X· and was accessible using a laser pulse with a fluence as low as 0.7 J/cm 2. Using a higher laser fluence ( ca. 1.2 J/cm 2) diand triatomic radicals were defined by spectroscopic identification of the ·CF and :CF 2 species. These reactions are discussed in light of the formation of the C 6F 5· radical during a primary, larser induced, process. Subsequent decomposition to smaller fragments, combination with other radicals or scavenging by added reagents also takes place depending on the reaction conditions.

Surface chemistry of carbon-nitrogen bonds on rhodium(111). 1. Ethanedinitrile and methylamine

The adsorption and decomposition of C{sub 2}N{sub 2} and CH{sub 3}NH{sub 2} on Rh(111) have been studied by using temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). Both molecules adsorb readily on Rh(111) at 300 K and totally decompose. Adsorption of CH{sub 3}NH{sub 2} at 300 K produces H{sub 2} and N{sub 2} as major products at low coverages. CH{sub 3}NH{sub 2} is totally dehydrogenated by 500 K to leave surface CN which then follows the same decomposition path as C{sub 2}N{sub 2}. The chemistry of the C-N bonds in C{sub 2}N{sub 2} and CH{sub 3}NH{sub 2} is therefore similar in that 20% (in C{sub 2}N{sub 2}) and 39% (in CH{sub 3}NH{sub 2}) of the bond is cleaved to produce N{sub 2} and surface carbon residues while the rest desorbs intact as HCN and C{sub 2}N{sub 2}.

Thermal evolution of benzene adsorbate phases on a Os(0001) surface

The molecular structure and orientation of adsorbed benzene (C 6H 6) on Os(0001) has been investigated by angle resolved UV photoemission spectroscopy (ARUPS), low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS) in the temperature range 200 < T < 1000 K. A well ordered ( 7 × 7 )R 19.1° structure of intact benzene molecules was observed for 200 < T < 290 K. Dissociative desorption associated with successive dehydrogenation in five steps was recorded for T > 290 K at saturation coverages. Dehydrogenation occurs via C 6H 5 and C 6H 4 species which are expected to have an intact carbon ring system up to a temperature of T ≈ 500 K. Cracking of the carbon ring occurs at T > 500 K where C-H fragments are formed at the substrate surface. Increasing the temperature leads to a successive loss of H atoms. For T > 830 K H 2 desorption ends and an ordered (9 × 9) graphitic carbon structure was detected. The characterisation of the different adsorption phases was performed by calculating ARUPS spectra. A reaction and decomposition path for the system C 6H 6 + Os(0001) is proposed.

Thermal and structural relationships within the Cd-picoline-chloride family including the α, β and γ-types

Thermal and structural properties of complexes of CdCl2 with picolines were studies. The structures of tetra-γ- and tetra-β-picoline as well as di-γ- and di-β-picoline complexes were found to be identical and their thermal decomposition paths were analogous. New polynuclear complexes which could not be obtained from solution have been prepared through thermal decomposition. Their symmetry and cell dimensions were determined.

The effect of nitric oxide on the hydrogen-atom induced decomposition of monogermane

The effect of low concentrations of nitric oxide on the hydrogenatom initiated decompositton of monogermane at room temperature has been studied by a mass-spcctrometrtc technique. Initiation by hydrogen atoms, formed by mercury photosensitization of hydrogen-rich mixtures, insure the primayy decomposition path to be one forming germyl free radicals. The nitric oxide reacts efficienlly with germyl radicals thereby completely suppressing the normal formation of digermane until the nitric oxide concentration has been greatly reduced. The producss of the suppressonn reaction are digermylether (digermoxane), nitrous oxide, nitrogen and a solid containing germanium, hydrogen and oxygen. A mechanssm to account for these experimental facts is proposed and some of the rate constanss of the elementary chemical reactions have been estimaeed.

Synthesis of 14C-labeled cyclic peroxide, 4-ethoxy-2,3-benzodioxin-1-ol, and its decomposition.

Synthesis of 14C-labeled 4-ethoxy-2, 3-benzodioxin-1-ol (EtO-BD) from [1 (4, 5, 8) -14C] naphthalene and the decomposition behavior of the labeledEtO-BD are described. 14C-EtO-BD is stable over months as long as kept at . -40°C as a solid state, and over weeks in acetonitrile. The decomposition ofEtO-BD is facilitated by the presence of H2O giving rise to two major decomposition products, o-phthalaldehydie acid and its ethyl ester. Thus the generation ofOHradical is expected on its decomposition path and is enhanced as increasingH2O concentration.Fe (II) seems to facilitateEtO-BD decomposition through the electron transfer reaction.

Kinetics of thermal, non-catalytic decomposition of hydrogen sulphide

The reaction kinetics of the thermal, non-catalytic decomposition of H 2S in a non-isothermal flow reactor was studied at pressures of 1.3–3.0 atm, temperatures of 600–800°C, and specific flow rates of 3.4 × 10 −4−3.6 × 10 −3 mol/(cm 2s). The effects of the temperature, pressure and space velocity on the conversion and reaction rates were investigated. The overall kinetics of the process are considered as the difference of the rates of the forward reaction of H 2S decomposition and the reverse reaction of H 2S synthesis from hydrogen and sulphur. Activation energies of 46.8 and 25.1 kcal/mol were yielded for the decomposition and synthesis of H 2S, respectively. A free-radical mechanism has been suggested to explain the decomposition paths, on the basis of the results of this study.

Decomposition of methanol over oxidized and reduced copper surfaces studied by double modulation Fourier transform infrared reflection absorption spectroscopy

Adsorption and decomposition of methanol over oxidized and reduced copper surfaces with or without vapor phase were observed by double modulation Fourier transform infrared reflection adsorption spectroscopy (DM FT-IRAS). Over the oxidized copper surface, methanol is adsorbed to form a formate ion and decomposes to CO 2 and H 2O at 423 K. Over the reduced copper surface, adsorbed species of methanol were physically adsorbed methanol, methoxide, and polyoxymethylene after the reaction at 473 K and measured at 300 K with the vapor phase. The decomposition products of methanol at 473 K are CO, H 2 and methylformate. The decomposition path of methanol over the oxidized and reduced Cu surfaces are discussed.

Epitaxial metastable (GaSb) 1- x(Ge( 2- y)Sn 2y) x quarternary alloys on GaAs(100): 1085 Crystal growth, structure, and raman scattering

Epitaxial metastable (GaSb) 1- x )(Ge 2(1- y) Sn 2y x quaternary alloys have been grown with 0 ≤ x ≤ 1 and 1085 y ≤ 0.27 by RF multitarget sputter deposition on GaAs(100) substrates. Films, ≈1 μm thick, deposited under the same growth conditions on Corning 7059 glass substrates were polycrystalline with a very strong (220) preferred orientation. A growth phase map, plotted as a function of x, y, and deposition temperature T s, showed that the maximum growth temperature decreased rapidly with increasing Sn concentration, ranging from ≥ 500°C for 0 ≤ x ≤ 1 with y = 0 to ⩾ 150°C for x = 0.6 with y = 0.27. The lattice parameter a 0 of the alloys decreased linearly with increasing x for a given y and increased linearly with y for a given value of x. a 0 ranged from 0.6094 nm for GaSb to 0.5775 nm for (GaSb) 0.2(Ge 1.86Sn 0.14) 0.8. Form an analysis of fundamental and superstructure diffraction peak intensities, the zincblende-to-diamond structural phase transition was found to occur near x ≈ 0.3. Raman scattering results showed a two-peak behavior over the composition range investigated. The GaSb-like longitudinal-optical peak near 234 cm -1 softened and broadened with increasing x for all y values. A weak “Ge-like” mode increased in frequency from 265 cm -1 at x = 0.05 with y = 0.07−0.27 to 280 cm -1 at x = 0.6 and y = 0.07. The reaction path for phase decomposition in these alloys was found using hot-stage transmission electron microscopy to proceed through a series of intermediate metastable phases. Alloys with low Sn concentrations were stable for 2 h anneals at temperatures ⩾ 475°C. However, thermal stability decreased with increasing Sn concentrations to ⩾ 225°C for a 2 h anneal of alloys with low x and high y values.

Experimental evidence for the gaseous HSO 3• radical. The key intermediate in the oxidation of SO 2 in the atmosphere

The HSO 3 • radical has been generated and characterized by neutralization/reionization mass spectrometry. The HSO 3 • radical exhibits a minimum lifetime of 0.7 σs when isolated in the gas phase. The principal unimolecular decomposition paths of HSO 3 were found to be loss of •OH and O, respectively.

Preparation and characterization of supported mixed metal oxides: Thermal decomposition of heteropoly metal complexes immobilized on silica

Supported mixed metal oxides were prepared by the temperature-programmed decomposition of a highly characterized system of silica-immobilized heteropoly complexes containing Cu(II) and M(III) ( M(III) = Al, Cr, Fe). The investigation focused on two main aspects of the thermal degradation: a study of the decomposition path and characterization of the resultant samples. The decomposition process, monitored in situ by thermogravimetric analysis, infrared spectroscopy, and mass spectrometry, appeared to lead to the formation of mixed oxides with a stoichiometry of MCu 6O 7.5. Electron microscopy showed sintering of the oxides into particles which contain Cu and M. The population of these particles increased with increasing temperature. Selective chemisorptions of NH 3, CO, and NO indicated that temperature of decomposition affects active site densities. In particular, it was observed that conditions for the decomposition could be selected to maximize the activation of metal oxide sites by complex decomposition yet minimize the deactivation by sintering of supported oxide particles.

ChemInform Abstract: Reaction Ergodography for the Hydrolysis of Urea

Abstract An ab initio molecular orbital (MO) calculation was carried out for the reaction path of the interaction between a urea and a water molecule. The potential energy surface for the urea—water super-molecule reveals that the hydrolysis of urea is a much more energetically favoured decomposition mechanism than unimolecular decomposition of urea. The RHF/4-31G energy barrier for the hydrolysis agrees with the experimental values and the analysis for the reaction path of unimolecular decomposition explains the geometrical change through the reaction process.

ChemInform Abstract: Photoacoustic Study of 280 nm Band of Acetone Vapor.

Relaxation of the energy absorbed by acetone vapor (200 Torr) on excitation with UV (230–340 nm) was investigated by the photoacoustic technique. The presence of two relaxation paths was found by their difference in heat production rates: The faster path is S0→S1→T1→S0 and the slower path is S0→radicals→recombination products. The PA spectra corresponding to these paths were determined separately. The spectrum for the T1 path has a peak around 295 nm and extends to longer wavelengths beyond 310 nm. The spectrum for the decomposition path has a peak around 275 nm and overlaps with the spectrum for the T1 path in the region of λ<310 nm. The study of frequency dependences of PA signals showed the presence of faster and slower heat releasing steps in each path. In the T1 path, the faster and the slower steps are due to vibrational deactivation of hot T1 formed from S1 and of hot S0 formed from T1 respectively. In the radical path, the faster and slower steps are the deactivation of the hot radicals and the re...

Thermal decomposition of iron(II) sulphate heptahydrate in air in the presence of calcium, strontium and barium carbonates

The thermal decomposition in air of iron(II) sulphate heptahydrate in the presence of calcium, strontium and barium carbonates has been carried out. The decomposition path varies from carbonate to carbonate. Also, these decompositions are different from those of basic beryllium carbonate and basic magnesium carbonate. The results obtained for the kinetics of thermal decomposition have also been presented.

Reaction ergodography for the hydrolysis of urea

An ab initio molecular orbital (MO) calculation was carried out for the reaction path of the interaction between a urea and a water molecule. The potential energy surface for the urea—water super-molecule reveals that the hydrolysis of urea is a much more energetically favoured decomposition mechanism than unimolecular decomposition of urea. The RHF/4-31G energy barrier for the hydrolysis agrees with the experimental values and the analysis for the reaction path of unimolecular decomposition explains the geometrical change through the reaction process.

Thermischer zerfall von β-phenyl- und β,β-diphenyl- nitroalkanen

Elimination of nitrous acid is the exclusive reaction path for the thermal decomposition of the nitroalkanes 1, 2 and 5. Homolytic CC-cleavage cannot compete. A concerted β-elimination is the favoured mechanism.

In situ mass spectroscopy studies of the decomposition of organometallic arsenic compounds in the presence of Ga(CH3)3 and Ga(C2H5)3

The gas phase decomposition and reaction mechanisms of As(CH3)3 (TMAs), As(C2H5)3 (TEAs), and H2AsC4H9 (tBAs) in the presence of Ga(CH3)3 (TMG) and Ga(C2H5)3 (TEG) are studied by molecular beam mass spectroscopy sampling in an organometallic chemical vapor deposition (OMCVD) reactor. Experiments are reported for H2, D2, and He carrier gases. The 50% decomposition temperature of TMAs, TEAs, and tBAs are determined to be 765, 690, 560 K, respectively. TMAs decomposes via a unimolecular reaction involving the loss of methyl groups. TEAs pyrolizes with C2H4 as the main hydrocarbon product regardless of the carrier gas used. When TEG and TMAs or TMG and TEAs are mixed, decreases in the decomposition temperature of the methyl compounds are observed. This effect is attributed to an exchange process between the methyl and the ethyl groups through the formation of an adduct. The primary decomposition path of tBAs is proposed to be via the loss of tert-butyl radicals and AsH2 resulting in production of AsH3 starting at 500 K with isobutene and isobutane as the main hydrocarbon products. Mass spectra of mixtures of TMG and tBAs show new peaks corresponding to methylarsenic fragments indicating the formation of an adduct.

Photoacoustic Study of 280 nm Band of Acetone Vapor

Abstract Relaxation of the energy absorbed by acetone vapor (200 Torr) on excitation with UV (230–340 nm) was investigated by the photoacoustic technique. The presence of two relaxation paths was found by their difference in heat production rates: The faster path is S0→S1→T1→S0 and the slower path is S0→radicals→recombination products. The PA spectra corresponding to these paths were determined separately. The spectrum for the T1 path has a peak around 295 nm and extends to longer wavelengths beyond 310 nm. The spectrum for the decomposition path has a peak around 275 nm and overlaps with the spectrum for the T1 path in the region of λ&amp;lt;310 nm. The study of frequency dependences of PA signals showed the presence of faster and slower heat releasing steps in each path. In the T1 path, the faster and the slower steps are due to vibrational deactivation of hot T1 formed from S1 and of hot S0 formed from T1 respectively. In the radical path, the faster and slower steps are the deactivation of the hot radicals and the recombination of the thermalized radicals respectively. The addition of O2 to the system accelerated the heat release process via the relaxed T1 and also converted the slow heat release process of recombination into a fast process of addition reactions of O2 to the radicals.

An ab initio study of the reaction pathways for OH + C2H4 .fwdarw. HOCH2CH2 .fwdarw. products

The energetically favorable reaction paths for the unimolecular decomposition of the primary addition product of OH + C/sub 2/H/sub 4/ have been studied with ab initio techniques. Equilibrium geometries and transition structures were fully optimized with 3-21G and 6-31G* basis sets at the Hartree-Fock level. Heats of reaction and barrier heights have been computed with Moeller-Plesset perturbation theory up to fourth order, with and without annihilation of spin contamination. At the MP4 level barrier heights are lowered by 2-7 kcal/mol when the largest spin contaminant is removed. After the addition of OH + C/sub 2/H/sub 4/ to form the 2-hydroxyethyl radical, the most favorable reaction path (other than decomposition to reactants) is the (1,3)-hydrogen shift to form ethoxy radical followed by a dissociation into CH/sub 3/ + CH/sub 2/O. Other slightly higher energy paths include dissociation of ethoxy into H + CH/sub 3/CHO and decomposition of the 2-hydroxyethyl radical into H + HOCHCH/sub 2/.