Thermal dehydration kinetics of disaccharides

The vacuum decomposition of sucrose and cellobiose has been observed in the 150–250°C temperature range. The predominant decomposition product of both sugars is H₂O with less than 5% CO, CO₂, CH₂O, CH₃CHO, CH₃OH, and C₂H₅OH formed. The detailed rates and temperature dependences suggest that with the possible exception of C₂H₅OH, the minor products are formed in secondary reactions of the dehydration products. Further it is shown that the so-called “melting with decomposition” of a sugar is in reality a high-temperature dissolution of the disaccharide in the eliminated water.     

The decomposition of ethanol vapour by infrared radiation from a pulsed HF-laser

The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be:C₂H₅OH → H₂ + CH₃CHO,C₂H₅OH → C₂H₄ + H₂O,C₂H₅OH → CH₃ + CH₂OHin a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C₂H₄ and H₂O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S0 State

This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S₀ state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, CH₂O + CH₃CHO, HCOH + CH₃CHO, C₂H₆ + CO₂, and H₂ + CH₂CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, and CH₂O + CH₃CHO.     

Hydrocarbon Effects on the Promotion of Non-Thermal Plasma NO–NO2 Conversion

Kinetic modeling of non-thermal plasma chemistry is conducted to investigate hydrocarbon (CH₄, C₂H₄, C₃H₆, and C₃H₈) effects on the promotion of NO–NO₂ conversion. A reduced plasma chemistry model, in which radical reactions are selectively involved, is validated with experimental data. The higher reactivity of hydrocarbon additive with O radicals, which produces initial radicals, is requisite to initiate hydrocarbon decomposition, thus providing NO–NO₂ conversion. Initial radicals by plasma discharge induce continual hydrocarbon decomposition and this self-preserved reaction mechanism greatly contributes to the promotion of energy efficient NO–NO₂ conversion. Increase in the conversion extent by ethylene and propylene additives is substantial because of their stronger affinity with O radical. The primary routes of NO–NO₂ conversion process differed by hydrocarbon additives are presented and discussed with the assistance of sensitivity analysis.     

Thermal decomposition of 1,2 butadiene

The thermal decomposition of 1,2 butadiene has been studied behind reflected shock waves over the temperature and total pressure ranges of 1300–2000 K and 0.20–0.55 atm using mixtures of 3% and 4.3% 1,2 butadiene in Ne. The major products of the pyrolysis are C₂H₂, C₄H₂, C₂H₄, CH₄ and C₆H₆. Toluene was observed as a minor product in a narrow temperature range of 1500–1700 K. In order to model successfully the product profiles which were obtained by time-of-flight mass spectrometry, it was necessary to include the isomerization reaction of 1,2 to 1,3 butadiene. A reaction mechanism consisting of 74 reaction steps and 28 species was formulated to model the time and temperature dependence of major products obtained during the course of decomposition. The importance of C₃H₃ in the formation of benzene is demonstrated.     

Organische Phosphorverbindungen. XXVII Die direkte Synthese von Tetramethylphosphoniumhalogeniden

The reaction of methyl chloride and methyl bromide with white phosphorus is studied under a variety of conditions, and the conditions giving a high yield of tetramethylphosphonium chloride and bromide are established. Thermal decomposition of [(CH₃)₄P]+Cl^? gives (CH₃)₃P and CH₃Cl, and alkaline decomposition of [(C₄H₉)₃(C₁₂H₂₅)P]+Cl? gives C₄H₁₀ and (C₄H₉)₂(C₁₂H₂₅)P?O.     

Pyrolysis of methyl chloride,a pathway in the chlorine-catalyzed polymerization of methane

The reaction of CH₄ + Cl₂ produces predominantly CH₃Cl + HCl, which above 1200 K goes to olefins, aromatics, and HCl. Results obtained in laboratory experiments and detailed modeling of the chlorine-catalyzed polymerization of methane at 1260 and 1310 K are presented. The reaction can be separated into two stages, the chlorination of methane and pyrolysis of methylchloride. The pyrolysis of CH₃Cl formed C₂H₄ and C₂H₂ in increasing yields as the degree of conversion decreased and the excess of methane increased. Changes of temperature, pressure, or additions of HCl had little effect. In the absence of CH₄ C₂H₄ and C₂H₂ are formed by the recombination of ?H₃ and ?H₂Cl radicals. With added CH₄ recombination of ?H₃ forms C₂H₆, which dehydrogenates to C₂H₄ + H₂. C₂H₄ in turn dehydrogenates to C₂H₂ + H₂. While HCl, C, CH₄, and H₂ are the ultimate stable products, C₂H₄, C₂H₂, and C₆H₆ are produced as intermediates and appear to approach stationary concentrations in the system. Their secondary reactions can be described by radical reactions, which can lead to soot formation. ?H₃ - initiated polymerization of ethylene is negligible relative to the ?₂H₃ formation through H abstraction by Cl. The fastest reaction of ?₂H₃ is its decomposition to C₂H₂. About 20% of the consumption of C₂H₂ can be accounted for by the addition of ?₂H₃ to it with formation of the butadienyl radical. The addition of the latter to C₂H₂ is slow relative to its decomposition to vinylacetylene. Successive H abstraction by Cl from C₄H₄ leading to diacetylene has rates compatible with the experimental values. About 10% of ?₄H₅ abstracts H from HCl and forms butadiene. Successive additions of ?₂H₃ to butadiene and the products of addition can account for the formation of benzene, styrene, naphthalene, and higher polyaromatics. The following rate parameters have been derived on the basis of the experimentally measured reaction rates, the estimated frequency factors, and the currently available heat of formation of the ?₂H₃ radical (69 kcal/mol):      

Comparative Study of Methane Activation Process by Different Plasma Sources

In this paper, we compare the characteristics of methane activation by diverse plasma sources. The test conditions of reactant flow rate and composition are fixed for each plasma source to eliminate any possible misleading effects from varying test conditions. Among the diverse characteristics of each plasma source, we focus on the electron energy and degree of thermal activation in evaluating the cost-effectiveness of methane decomposition. The reaction is evaluated based on the selectivity of specific products, including H₂, C₂H₆, and C₂H₂. Among the tested plasma sources, those that provide a somewhat thermal environment have a rather high degree of warmness, resulting in higher methane conversion and lower operational costs. As the non-thermal characteristics of the plasma sources become stronger, the selectivity of C₂H₆ increases. This reflects C₂H₆ formation from the direct collision of CH₄ with high-energy electrons. On the other hand, as the degree of warmness increases, the selectivity of H₂ and C₂H₂ increase. The results give an insight into possible tools for process control or selectivity control by varying the degree of warmness in the plasma source. The process optimization and cost reduction of methane activation should be based on this concept of selectivity control.     

Reforming of CO<Subscript>2</Subscript>-Containing Natural Gas Using an AC Gliding Arc System: Effect of Gas Components in Natural Gas

The objective of the present work was to study the reforming of simulated natural gas via the nonthermal plasma process with the focus on the production of hydrogen and higher hydrocarbons. The reforming of simulated natural gas was conducted in an alternating current (AC) gliding arc reactor under ambient conditions. The feed composition of the simulated natural gas contained a CH₄:C₂H₆:C₃H₈:CO₂ molar ratio of 70:5:5:20. To investigate the effects of all gaseous hydrocarbons and CO₂ present in the natural gas, the plasma reactor was operated with different feed compositions: pure CH₄, CH₄/He, CH₄/C₂H₆/He, CH₄/C₂H₆/C₃H₈/He and CH₄/C₂H₆/C₃H₈/CO₂. The results showed that the addition of gas components to the feed strongly influenced the reaction performance and the plasma stability. In comparisons among all the studied feed systems, both hydrogen and C₂ hydrocarbon yields were found to depend on the feed gas composition in the following order: CH₄/C₂H₆/C₃H₈/CO₂ > CH₄/C₂H₆/C₃H₈/He > CH₄/C₂H₆/He > CH₄/He > CH₄. The maximum yields of hydrogen and C₂ products of approximately 35% and 42%, respectively, were achieved in the CH₄/C₂H₆/C₃H₈/CO₂ feed system. In terms of energy consumption for producing hydrogen, the feed system of the CH₄/C₂H₆/C₃H₈/CO₂ mixture required the lowest input energy, in the range of 3.58 × 10⁻¹⁸–4.14 × 10⁻¹⁸ W s (22.35–25.82 eV) per molecule of produced hydrogen.     

Directed Gas‐Phase Synthesis of Triafulvene under Single‐Collision Conditions

The triafulvene molecule (c‐C₄H₄)—the simplest representative of the fulvene family—has been synthesized for the first time in the gas phase through the reaction of the methylidyne radical (CH) with methylacetylene (CH₃CCH) and allene (H₂CCCH₂) under single‐collision conditions. The experimental and computational data suggest triafulvene is formed by the barrierless cycloaddition of the methylidyne radical to the π‐electron density of either C₃H₄ isomer followed by unimolecular decomposition through elimination of atomic hydrogen from the CH₃ or CH₂ groups of the reactants. The dipole moment of triafulvene of 1.90 D suggests that this molecule could represent a critical tracer of microwave‐inactive allene in cold molecular clouds, thus defining constraints on the largely elusive hydrocarbon chemistry in low‐temperature interstellar environments, such as that of the Taurus Molecular Cloud 1 (TMC‐1).     

Thermal decomposition of organo-bielemental vanadium compounds Cp2V(ER3) (ER3 - GeEt3, SnEt3, CH2SiMe3 SeGeEt3)

The thermal decompositon of a number of organo-bielemental vanadium compounds with the general formula Cp₂V(ER₃) (ER₃ - GeEt₃, SnEt₃, CH₂SiMe₃, SeGeEt₃) has been investigated in solids and in solution. The main decomposition products of Cp₂V(SnEt₃) are vanadocene and hexaethyldistannane. Et₃GeH, Et₃GeCp, Cp₂V and CpV(C₅H₄GeEt₃) are formed from Cp₂V (GeET₃) decomposition. Isolated CpV(C₅H₄GeEt₃) is characterized by IR and mass spectra. The decomposition of Cp₂V(CH₂SiMe₃) is accompanied by Me₄Si, Cp₂V and CpV-(C₅H₄CH₂SiMe₃) formation, the latter is identified from the mass spectrum. Triethylgermane, vanadocene, and a diselenide of vanadium are isolated on decomposition of Cp₂V(SeGeEt₃). Based upon the experimental data, mechanisms for the decompositon are proposed.     

Structure and fragmentation mechanism of [C3H7S]+ ions

From a comparison of the metastable ion bundance ratios for loss of C₂H₄ and H₂S from [C₃H₇S]⁺ ions in a series of alkyl thio ethers and thiols it was concluded that in most compunds these ion s isomerize to a common structure prior to decomposition in the first field free region. The mechanism for C₂H₄ loss from the [C₃H₇S]⁺ ion gen erated from CH₃SCH₂CH₃ was investigated in detail using ¹³C and ²H labelling. A rearrangement with formation of a cyclic intermediate prior to the decompistion reaction is proposed. The fragmentation is preceded by extensive hydrogen scrabling. The carbon atoms of the expelled C₂H₄ molecule are those of the CH₂?CH₃ moiety.     

Mass spectrometric studies on the decomposition of trialkylgallium on gaas surfaces

The thermal decomposition of trimethylgallium [(CH₃)₃Ga] and triethylgallium [(C₂H₅)₃Ga] on gallium arsenide (GaAs) surfaces was studied under an ultra-high vacuum using mass spectrometry. It was observed that the decomposition process of (CH₃)₃Ga and (C₂H₅)₃Ga depends on the arsenic coverage of the substrate surface. On a (100)-oriented surface, increasing the arsenic coverage basically enhances the decomposition of (CH₃)₃Ga and (C₂H₅)₃Ga to gallium atoms above 350 and 300°C, respectively. The decomposition of (CH₃)₃Ga proceeds by emitting CH₃ radicals. On a surface with low arsenic coverage, the decomposition of (CH₃)₃Ga is imperfect and fewer than three methyl groups of alkylgallium are desorbed. On a (111)B-oriented surface, however, an increase in the surface arsenic coverage suppresses the decomposition of alkylgallium, which is different from the case for a (100) surface.     

An experimental and modeling study of ethanol oxidation kinetics in an atmospheric pressure flow reactor

Experimental profiles of stable species concentrations and temperature are reported for the flow reactor oxidation of ethanol at atmospheric pressure, initial temperatures near 1100 K and equivalence ratios of 0.61–1.24. Acetaldehyde, ethene, and methane appear in roughly equal concentrations as major intermediate species under these conditions. A detailed chemical mechanism is validated by comparison with the experimental species profiles. The importance of including all three isomeric forms of the C₂H₅O radical in such a mechanism is demonstrated. The primary source of ethene in ethanol oxidation is verified to be the decomposition of the C₂H₄OH radical. The agreement between the model and experiment at 1100 K is optimized when the branching ratio of the reactions of C₂H₅OH with OH and H is defined by (30% C₂H₄OH + 50% CH₃CHOH + 20% CH₃CH₂O) + XH. As in methanol oxidation, HO₂ chemistry is very important, while the H + O₂ chain branching reaction plays only a minor role until late in fuel decay, even at temperatures above 1100 K.     

THE REACTION OF METHYLENE WITH METHYL CHLORIDE THE EFFECT OF EXCESS ENERGY IN METHYLENE

Abstract This paper reports studies of the reaction between methyl chloride and methylene produced by the photolysis of ketene in the two spectral regions Λ? 2600 Å to 3200 Å and Λ? 3220 Å. The course of reactin is best described by an abstraction process CH₂+ CH₂CI—Ch₂CI + CH₃ followed by recombination of the CH₃ and CH₂ Cl radicals to yield C₂H₅, C₂H₅Cl, C₂H₄Cl₂. The recombination processes are highly exothermic, and excitation of the product molecules occurs, which in the case of C₂H₅Cl and C₂H₄Cl₂ leads to some unimolecular decomposition. It is shown that the rate constant for the decomposition of ethyl chloride depends upon the wavelength of the radiation used to photolyse the ketene, and it is suggested that the excess energy with which the methylene is born is handed on to the alkyl radicals. A simplified kinetic analysis of the system is given, and it is shown that the relative reactivity of methylene towards ketene and methyl chloride increases with an increase in the energy of the methylene. The rates of product formation predicted on the basis of the kinetic scheme agree satisfactorily with the measured values. “Insertion” of methylene into C-H and C-CI bonds has been postulated by other workers. The present results are inconsisistent with an insertion mechanism, since such a mechanism does not account for all the observed products. The effect of wavelength of photolysis and of total pressure predicted on the basis of an insertion process is the reverse of that observed experimentally.     

Functional group interaction in the fragmentation of protonated 2,7-octanedione

The fragmentation of 2,7-octanedione, induced by chemical ionization with methane as a reagent gas (CI (CH₄)), is shown to be extensively governed by the interaction of the two carbonyl groups. Tandem mass spectrometry reveals that a sequential loss of H₂O and C₂H₄O from the [M + H]⁺ ion competes with sequential loss of H₂O and C₆H₁₀, and that both processes occur via the same [MH - H₂O]⁺ intermediate. This intermediate is likely to be formed via intramolecular gas-phase aldol condensation and subsequent dehydration. The resulting C(1) protonated 1-acetyl-2-methylcyclopentene structure readily accounts for the observed further decomposition to CH₃C?O⁺ and 1-methylcyclopentene (C₆H₁₀) or, alternatively, to [C₆H₉]⁺ (e. g. 1-methylcyclopentenylium) ions and acetaldehyde (C₂H₄O). Support for this mechanistic rationale is derived from deuterium isotope labelling and low-energy collision-induced dissociation (CID) of the [MH - H₂O]⁺ ion. The common intermediate shows a CID behaviour indistinguishable by these techniques from that of reference ions, which are produced by gas-phase protonation of the authentic cyclic aldol or by gas-phase addition of an acetyl cation to 1-methylcyclopentene in a CI (CH₃COOCH₃) experiment.     

Study of the ethane oxidation reaction by the kinetic tracer method

The kinetics of ethane oxidation was studied at 320, 340, 353 and 380°C, mixture composition 2 C₂H₆ + 1 O₂, and total pressure 609 torr. It was found that at 320°C CH₂O and CH₃CHO were branching agents. A series of experiments was conducted on 2C₂H₆ + O₂ oxidation in the presence of 0.7% ¹⁴C-labeled ethylene. The ethylene oxide was found to form only from C₂H₄, formaldehyde formed from C₂H₄ and C₂H₆; and CH₃CHO, C₂H₅OH, and CH₃OH formed only from ethane. The formation rates of C₂H₄, C₂H₄O, and CH₂O were calculated by the kinetic tracer method. At 320°C the fraction of oxygen-containing products formed from C₂H₄ was 16–18%, and at 353 and 380°C it was 30–40%.     

Thermal decomposition of ethane in shock waves

The thermal decomposition of ethane was studied behind reflected shock waves over the temperature range 1200–1700 K and over the pressure range 1.7?2.5 atm, by both tracing the time variation of absorption at 3.39 μm and analyzing the concentration of the reacted gas mixtures. The mechanism to interpret well not only the earlier stage of C₂H₆ decomposition, but also the later stage was determined. The rate constant of reactions, C₂H₆ → CH₃ + CH₃, C₂H₆ + C₂H₃ → C₂H₅ + C₂H₄, C₂H₅ → C₂H₄ + H were calculated. The rate constants of the other reactions were also discussed.     

Effect of the cation structure on the thermal stability of ionic liquids,quaternary ammonium tetrachloroferrates(III)

New ionic liquids, tetrachloroferrates(III) of quaternary ammonium salts [(CH₃)₂NR₁R₂]FeCl₄ [R₁ = CH₃; C₄H₉; (CH₂)₃CN. R₂ = C₁₀H₂₁; C₁₆H₃₃; CH₂CH₂OH; CH₂C₆H₅], were synthesized and their thermal stability was investigated in air in the range 25–600°С. The mechanism of thermal decomposition of the investigated ionic liquids is suggested in agreement with Hofmann’s rule as β-E2-elimination.     

Bildung und Charakterisierung von Oberflächenverbindungen in den Systemen (C6H5CH2)4M/γ-Al2O3 (M = Ti,Zr)

Formation and Characterization of Surface Compounds in the Systems (C₆H₅CH₂)₄M/γ-Al₂O₅ (M = Ti, Zr) By O-bridges anchored surface-compounds are formed by protolytic splitting off of benzyl groups if tetrabenzyltitanium and -zirconium are added to γ-alumina. These compounds contain the metal in different oxidation states in dependence on the carrier/substrate ratio and the density of OH groups on the alumina surface. The different kinds of surface compounds are discussed. Furthermore, the products formed by thermal decomposition and hydrogenolysis of the surface compounds were analysed. With regard to catalytic conversion reactions of hydrocarbons systems of the type (C₆H₅CH₂)₄M/Pt/γ-Al₂O₃were involved in the investigations.