Thermal isomerization and decomposition of 1,2-butadiene in shock waves

1,2-Butadiene diluted with Ar was heated behind reflected shock waves over the temperature and the total density range of 1100–1600 K and 1.36 × 10^?5 ? 1.75 × 10^?5 mol/cm³. The major products were 1,3-butadiene, 1-butyne, 2-butyne, vinylacetylene, diacetylene, allene, propyne, C₂H₆, C₂H₄, CH₄, and benzene, which were analyzed by gas chromatography. The UV kinetic absorption spectroscopy at 230 nm showed that 1,2-butadiene rapidly isomerizes to 1,3-butadiene from the initial stage of the reaction above 1200 K. In order to interpret the formation of 1,3-butadiene, 1-butyne, and 2-butyne, it was necessary to include the parallel isomerizations of 1,2-butadiene to these isomers. The present data were successfuly modeled with a 82 reaction mechanism. From the modeling, rate constant expressions were derived for the isomerization 1,2-butadiene = 1,3-butadiene to be k₃ = 2.5 × 10¹³ exp(?63 kcal/RT) s^?1 and for the decomposition 1,2-butadiene = C₃H₃ + CH₃ to be k₆ = 2.0 × 10¹⁵ exp(?75 kcal/RT) s^?1, where the activation energies, 63 kcal/mol and 75 kcal/mol, were assumed. These rate constants are only applicable under the present experimental conditions, 1100–1600 K and 1.23–2.30 atm. © 1995 John Wiley & Sons, Inc.     

Thermal decomposition of 1-butyne in shock waves

1-Butyne diluted with Ar was heated behind reflected shock waves over the temperature range of 1100–1600 K and the total density range of 1.36 × 10^?5?1.75 × 10^?5 mol/cm³. Reaction products were analyzed by gas-chromatography. The progress of the reaction was followed by IR laser kinetic absorption spectroscopy. The products were CH₄, C₂H₂, C₂H₄, C₂H₆, allene, propyne, C₄H₂, vinylacetyiene, 1,2- butadiene, 1,3-butadiene, and benzene. The present data were successfully modeled with a 80 reaction mechanism. 1-Butyne was found to isomerize to 1,2-butadiene. The initial decomposition was dominated by 1-butyne → C₃H₃ + CH₃ under these conditions. Rate constant expressions were derived for the decomposition to be k₇ = 3.0 × 10¹⁵ exp(?75800 cal/RT) s^?1 and for the isomerization to be k₄ = 2.5 × 10¹³ exp(?65000 cal/RT) s^?1. The activation energy 75.8 kcal/mol was cited from literature value and the activation energy 65 kcal/mol was assumed. These rate constant expressions are applicable under the present experimental conditions, 1100–1600 K and 1.23–2.30 atm. © 1995 John Wiley & Sons, Inc.     

Quenching of I(2P½) by R-OH compounds. Influence of the alkyl group on the quenching efficiency

The deactivation of I(²P_½) by R-OH compounds (R = H, C_nH_2n+1) was studied using time-resolved atomic absorption at 206.2 nm. The second-order quenching rate constants determined for H₂O, CH₃OH, C₂H₅OH, n-C₃H₇OH, i-C₃H₇OH, n-C₄H₉OH, i-C₄H₉OH, s-C₄H₉OH, t-C₄H₉OH, are respectively, 2.4 ± 0.3 × 10⁻¹², 5.5 ± 0.8 × 10⁻¹², 8 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 10 ± 1 × 10⁻¹², 11.1 ± 0.9 × 10⁻¹², 9.8 ± 0.9 × 10⁻¹², 7.1 ± 0.7 × 10⁻¹², and 4.1 ± 0.4× 10⁻¹² cm³ molec⁻¹ s⁻¹ at room temperature. It is believed that a quasi-resonant electronic to vibrational energy transfer mechanism accounts for most of the features of the quenching process. The influence of the alkyl group and its role in the total quenching rate is also discussed. © 1997 John Wiley & Sons, Inc.     

Syntheses and Structures of 5-Membered Heterocycles Featuring 1,2-Diphospha-1,3-Butadiene and Its Radical Anion

LGa(P₂OC)cAAC 2 features a 1,2-diphospha-1,3-butadiene unit with a delocalized π-type HOMO and a π*-type LUMO according to DFT calculations. [LGa(P₂OC)cAAC][K(DB-18-c-6)] 3 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene radical anion 3 ⋅ ⁻ was isolated from the reaction of 2 with KC₈ and dibenzo-18-crown-6. 3 reacted with [Fc][B(C₆F₅)₄] (Fc=ferrocenium) to 2 and with TEMPO to [L^−HGa(P₂OC)cAAC][K(DB-18-c-6)] 4 [K(DB-18-c-6] containing the 1,2-diphospha-1,3-butadiene anion 4⁻ . The solid state structures of 2 , 3 K(DB-18-c-6], and 4 [K(DB-18-c-6] were determined by single crystal X-ray diffraction (sc-XRD).     

Kinetic study of the oxidation reaction of 4-methylphenyl radical

A kinetic study of the reaction of the 4-methylphenyl radical (4-C₆H₄CH₃) with the oxygen molecule was conducted using experimental and theoretical approaches. The absorption spectrum for the λ = 266 nm photolysis of the 4-C₆H₄CH₃X (X = Cl, Br)/N₂/O₂ mixture was measured in the wavelength range of λ = 503-512 nm using N₂ as the buffer gas at a total pressure of 40 Torr using a cavity ring-down spectroscopy apparatus coupled with a pulsed laser photolysis system. Based on the absorbance of the product of the 4-C₆H₄CH₃ + O₂ reaction at λ = 504 nm, the reaction rate coefficient for the 4-C₆H₄CH₃ + O₂ reaction was determined to be k = (1.21 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k = (1.18 ± 0.21) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using 4-C₆H₄CH₃Cl and 4-C₆H₄CH₃Br, respectively, as the radical precursor. And there was no pressure dependence in the total pressure range of 10-90 Torr varying partial pressure of N₂ buffer gas at T = 296 ± 5 K. The geometries, vibration frequencies, and potential energy surfaces of the reactants, major products, and transition states in the 4-C₆H₄CH₃ + O₂ reaction were determined using the CBS-QB3 method. The k value at the high-pressure limit was calculated to be 1.26 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ using the variational transition-state theory. The calculated value of k was consistent with the experimental value, which indicated that the 4-C₆H₄CH₃ + O₂ reaction reaches the high-pressure limit at 10 Torr. Therefore, the oxidation of the 4-C₆H₄CH₃ radical is almost 10 times faster than that of the benzyl radical, which has the same chemical formula, at the high-pressure limit.     

Kinetics and products of propargyl (C3H3) radical self‐reactions and propargyl‐methyl cross‐combination reactions

Propargyl (HCC CH₂) and methyl radicals were produced through the 193‐nm excimer laser photolysis of mixtures of C₃H₃Cl/He and CH₃N₂CH₃/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self‐reactions and propargyl‐methyl cross‐combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C₆H₆ isomers with 1,5‐hexadiyne(CHC CH₂ CH₂ CCH, about 60%); 1,2‐hexadiene‐5yne (CH₂CC CH₂ CCH, about 25%); and a third isomer of C₆H₆ (∼15%), which has not yet been, with certainty, identified as being the major products. The rate constant determination in the propargyl‐methyl mixed radical system yielded a value of (4.0 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for propargyl radical combination reactions and a rate constant of (1.5 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ for propargyl‐methyl cross‐combination reactions. The products of the methyl‐propargyl cross‐combination reactions were two isomers of C₄H₆, 1‐butyne (about 60%) and 1,2‐butadiene (about 40%). © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 118–124, 2000     

Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane

The photolysis of azomethane in the near UV has been studied at room temperature and pressures from 10 mtorr to 10 torr. The main products, C₂H₆ and N₂, accounted for more than 99% of the reaction. Minor hydrocarbon products observed were (with quantum yields) C₃H₈ (3.5 × 10^?3), C₂H₄ (3.2 × 10^?4), CH₄ (3 × 10^?3), and n-C₄H₁₀ (trace). Quantum yields of H₂ of 4 × 10^?5 and 2 × 10^?5 were measured at azomethane pressures of 0.1 and 1.0 torr, respectively. The minor hydrocarbon products can be accounted for by reactions of CH₃ and C₂H₅ radicals following hydrogen abstraction from azomethane by CH₃. The H₂ product observed represents an upper limit for the H₂ elimination from vibrationally excited C₂H₆ formed by CH₃ combination in the system, corresponding to a rate of elimination ca. 5 × 10^?5 times the competing rate of dissociation to 2CH₃. Assuming a frequency factor of 10¹³ s^?1 for the H₂ elimination, a lower limit of about 90 kcal mol^?1 was estimated for the energy barrier.     

CO2 laser-induced photolysis of spirohexane: Time resolved observation of vibrationally excited 1,3-butadiene

Vibrationally excited spirohexane (SHX) generated in CO₂ laser irradiation undergoes photolysis producing ethylene, 1,3-butadiene and a C₄ compound as major products. Collisional energy pooling plays a major role in the multiphoton excitation process. Time-resolved formation of 1,3-butadiene is monitored by UV absorption from which the unimolecular rate constant for SHX dissociation is found to be 5.6 × 10⁵ s⁻¹. A red shift of 4O nm observed in the transient UV absorption spectrum has been assigned to nascent 1,3-butadiene, which suggests that vibrationally hot 1,3-butadiene molecules are formed. The effects of laser energy fluence and pressure of SF₆ as a sensitizer on dissociation yield are also investigated.     

Temperature-dependent kinetics studies of the reactions of C2H5O2 and n-C3H7O2 radicals with NO

The rate coefficients for the gas-phase reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO have been measured over the temperature range of (201–403) K using chemical ionization mass spectrometric detection of the peroxy radical. The alkyl peroxy radicals were generated by reacting alkyl radicals with O₂, where the alkyl radicals were produced through the pyrolysis of a larger alkyl nitrite. In some cases C₂H₅ radicals were generated through the dissociation of iodoethane in a low-power radio frequency discharge. The discharge source was also tested for the i-C₃H₇O₂ + NO reaction, yielding k_{298 K} = (9.1 ± 1.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, in excellent agreement with our previous determination. The temperature dependent rate coefficients were found to be k(T) = (2.6 ± 0.4) × 10⁻¹² exp{(380 ± 70)/T} cm³ molecule⁻¹ s⁻¹ and k(T) = (2.9 ± 0.5) × 10⁻¹² exp{(350 ± 60)/T} cm³ molecule⁻¹ s⁻¹ for the reactions of C₂H₅O₂ and n-C₃H₇O₂ radicals with NO, respectively. The rate coefficients at 298 K derived from these Arrhenius expressions are k = (9.3 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for C₂H₅O₂ radicals and k = (9.4 ± 1.6) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ for n-C₃H₇O₂ radicals. © 1996 John Wiley & Sons, Inc.     

A shock tube study of methyl-methyl reactions between 1200 and 2400 K

The methyl-methyl reaction was studied in a shock tube using uv narrowline laser absorption to measure time-varying concentration profiles of CH₃. Methyl radicals were rapidly formed initially by pyrolysis of various precursors, azomethane, ethane, or methyl iodide, dilute in argon. The contributions of the various product channels, C₂H₆, C₂H₅ + H, C₂H₄ + H₂, and CH₂ + CH₄, were examined by varying reactant mixtures and temperature. The measured rate coefficients for recombination to C₂H₆ between 1200 and 1800 K are accurately fit using the unimolecular rate coefficients reported by Wagner and Wardlaw (1988). The rate coefficient for the C₂H₅ + H channel was found to be 2.4 (±0.5) × 10¹³ exp(?6480/T) [cm³/mol-s] between 1570 and 1780 K, and is in agreement with the value reported by Frank and Braun-Unkhoff (1988). No evidence of a contribution by the C₂H₄ + H₂ channel was found in ethane/methane/argon mixtures, although methyl profiles in these mixtures should be particularly sensitive to this channel. An upper limit of approximately 10¹¹ [cm³/mol-s] over the range 1700 to 2200 K was inferred for the rate coefficient of the C₂H₄ + H₂ channel. Between 1800 and 2200 K, methyl radicals are also rapidly removed by CH₃ + H ? ¹CH₂ + H₂. In this temperature range, the reverse reaction was found to have a rate coefficient of 1.3 (±0.3) × 10¹⁴ [cm³/mol-s], which is 1.8 times the room-temperature value. © 1995 John Wiley & Sons, Inc.     

Gas-Phase Synthesis of 3-Vinylcyclopropene via the Crossed Beam Reaction of the Methylidyne Radical (CH; X2Π) with 1,3-Butadiene (CH2CHCHCH2; X1Ag)

The crossed molecular beam reactions of the methylidyne radical (CH; X²Π) with 1,3-butadiene (CH₂CHCHCH₂; X¹A_g) along with their (partially) deuterated counterparts were performed at collision energies of 20.8 kJ mol⁻¹ under single collision conditions. Combining our laboratory data with ab initio calculations, we reveal that the methylidyne radical may add barrierlessly to the terminal carbon atom and/or carbon−carbon double bond of 1,3-butadiene, leading to doublet C₅H₇ intermediates with life times longer than the rotation periods. These collision complexes undergo non-statistical unimolecular decomposition through hydrogen atom emission yielding the cyclic cis- and trans-3-vinyl-cyclopropene products with reaction exoergicities of 119±42 kJ mol⁻¹. Since this reaction is barrierless, exoergic, and all transition states are located below the energy of the separated reactants, these cyclic C₅H₆ products are predicted to be accessed even in low-temperature environments, such as in hydrocarbon-rich atmospheres of planets and cold molecular clouds such as TMC-1.     

High temperature pyrolysis of methane in shock waves. Rates for dissociative recombination reactions of methyl radicals and for propyne formation reaction

The pyrolysis of 2% CH₄ and 5% CH₄ diluted with Ar was studied using both a single–pulse and time–resolved spectroscopic methods over the temperature range 1400–2200 K and pressure range 2.3–3.7 atm. The rate constant expressions for dissociative recombination reactions of methyl radicals, CH₃ + CH₃ → C₂H₅ + H and CH₃ + CH₃ → C₂H₄ + H₂, and for C₃H₄ formation reaction were investigated. The simulation results required considerably lower value than that reported for CH₃ + CH₃ → C₂H₄ + H₂. Propyne formation was interpreted well by reaction C₂H₂ + CH₃ → P-C₃H₄ + H with ?? = 6.2 × ¹⁰12 exp(?17 kcal/RT) ^cm3 mol^?1 s^?1.     

Thermal decomposition of propane in shock waves

The thermal decomposition of propane was studied behind reflected shock waves over the temperature range 1100–1450 K and the pressure range 1.5–2.6 atm, by both monitoring the time variations of absorption at 3.39 μm and analyzing the concentrations of the reacted gas mixtures. The rate constants of the elementary reactions were discussed from the results. The rate constant expressions, k₁ = 1.1 × 10¹⁶ exp (?84 kcal/RT) s^?1 and k₄ = 9.3 × 10¹³ exp(?8 kcal/RT) cm³ mol^?1 s^?1, of reactions C₃H₈ → CH₃ + C₂H₅ and C₃H₈ + H → n-C₃H₇ + H₂ were evaluated, respectively.     

The synthesis and reactions of cationic rhodium and iridium complexes; evidence for hydrogen-transfer processes

Reactions of rhodium(I) and iridium(I) chlorocomplexes of cyclohexa-1,3-diene, cyclohepta-1,3-diene, and cylo-octa-1,3,5-triene with AgBF₄/CH₂Cl₂ afford respectively the cations [M(C₆H₆)(1,3-C₆H₈)]⁺, [M(η⁵-C₇H₇)(η⁵C₇H₉)]⁺ and [M(η⁶-C₈H₁₀)(η⁴-C₈H₁₀)]⁺; the latter complex is a hydrogenation catalyst for olefins.     

Novel Copolymers of Styrene. 3. Some Ring-Substituted Butyl 2-Cyano-3-Phenyl-2-Propenoates

Novel trisubstituted ethylenes, ring-substituted butyl 2-cyano-3-phenyl-2-propenoates, RPhCH=C(CN)CO₂C₄H₉ (where R is 2-C₆H₅CH₂O, 3-C₆H₅CH₂O, 4-C₆H₅CH₂O, 4-CH₃COO, 3-CH₃CO, 4-CH₃CO, 4-CH₃CONH, 2-CN, 3-CN, 4-CN, 4-(CH₃)₂N, 4-(C₂H₅)₂N) were prepared and copolymerized with styrene. The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring-substituted benzaldehydes and butyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C-NMR. All the ethylenes were copolymerized with styrene (M₁) in solution with radical initiation (ABCN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C-NMR. The order of relative reactivity (1/r₁) for the monomers is 4-C₆H₅CH₂O (6.39) > 2-C₆H₅CH₂O (2.06) > 3-CH₃CO (1.86) > 3-C₆H₅CH₂O (1.78) > 4-CH₃COO (1.58) > 3-CN (1.47) > 4-CN (1.21) > 4-(C₂H₅)₂N (1.19) > 4-(CH₃)₂N (1.18) > 2-CN (1.04) > 4-CH₃CO (0.71) > 4-CH₃CONH (0.63). Decomposition of the copolymers in nitrogen occurred in two steps, first in the 200–500°C range with residue (3.6–9.5% wt), which then decomposed in the 500–800°C range.     

β-Tricarbonyl compounds. I. 2,4-Disubstituted 1,3-cyclopentanediones

Summary Stable enolic isomers of 2-aroyl-4-aracyl-1,3-cyclopentanediones such as3 and4 were prepared by condensation of aryl methyl ketones and diethyl maleate using an excess of sodium ethoxide (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br and 4-C₆H₄Cl).

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-Tricarbonyl Verbindungen. I. 2,4-Disubstituierte 1,3-Cyclopentandione

Zusammenfassung Stabile Enol-Isomere von 2-Aroyl-4-aracyl-1,3-cyclopentandionen wie3 und4 wurden durch Kondensation von Arylmethylketonen und Diethylmaleat mit einem Überschuß von Natriumethoxid dargestellt (Aryl=C₆H₅, 4-C₆H₄CH₃, 4-C₆H₄Br und 4-C₆H₄Cl).

     

The mechanism of ethylene pyrolysis at small conversions

Kinetic modelling is used in conjunction with measurements of product yields to develop a mechanism for the pyrolysis of ethylene at 896K and ethylene pressures ranging from approximately 3 to 78 kPa. An induction period was observed for all products except H₂, and was followed by a steady rate, which was of second-order for all products except 1,3-C₄H₆, the most abundant product. The mechanism quantitatively accounts for the yields of H₂, CH₄, C₂H₆, C₃H₆, 1-C₄H₈ and 1,3-C₄H₆. The reaction is initiated by disproportionation of C₂H₄ and the product 1,3-C₄H₆ results from decomposition of the C₄H₇ radical, formed by addition of C₂H₃ to C₂H₄. The other organic products that were measured are formed as a result of reactions involving the C₂H₅ radical. The hydrogen is produced by abstraction from C₂H₄ by atomic hydrogen and its rate is controlled by the reaction C₂H₅ → C₂H₄ + H which is nearly equilibrated. The main termination reaction is recombination of C₂H₅. The auto-acceleration which is evident particularly in the yields of H₂, CH₄, C₂ H₆, and C₃H₆ is accounted for by the decomposition of 1-C₄H₈. © 1996 John Wiley & Sons Inc.     

π-Olefin-iridium-komplexe : IV. Umsetzungen von chloro-dien-iridium-verbindungen mit lithiumorganylen

The complexes [(1,3-C₆H₈)₂IrR] and [(1,3-C₇H₁₀)₂IrR] (R = CH₃, C₆H₅) are obtained by reaction of the corresponding chloro compounds with RLi. Interaction of [Ir(COD)Cl]₂ (COD = 1,5-cyclooctadiene) with CH₃Li in the presence of 1,3-cyclohexadiene or isoprene yields [(COD)(1,3-C₆H₈IrCH₃] and [(COD)(C₅H₈IrCH₃], respectively. The products of the reaction of chlorodicyclodieneiridium with n-C₄H₉Li depend on the ring size of the cyclodiene ligands; with 1,3-cyclohexadiene [(1,3-C₆H₈)₂IrH] is formed while with 1,3-cycloheptadiene [(1,3-C₇H₁₀)(C₇H₉)Ir] is obtained together with [(1,3-C₇H₁₀)₃Ir₂(μ-H)₂]. Chemical and spectroscopic properties of the new compounds are discussed.     

Rate constants and vibrational distributions for water-forming reactions of OH and OD radicals with thioacetic acid, 1,2-ethanedithiol and tert-butanethiol

Reactions of OH and OD radicals with CH₃C(O)SH, HSCH₂CH₂SH, and (CH₃)₃CSH were studied at 298 K in a fast-flow reactor by infrared emission spectroscopy of the water product molecules. The rate constants (1.3 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + CH₃C(O)SH reaction and (3.8 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for the OD + HSCH₂CH₂SH reaction were determined by comparing the HOD emission intensity to that from the OD reaction with H₂S, and this is the first measurement of these rate constants. In the same manner, using the OD + (C₂H₅)₂S reference reaction, the rate constant for the OD + (CH₃)₃CSH reaction was estimated to be (3.6 ± 0.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Vibrational distributions of the H₂O and HOD molecules from the title reactions are typical for H-atom abstraction reactions by OH radicals with release of about 50% of the available energy as vibrational energy to the water molecule in a 2:1 ratio of stretch and bend modes.     

Shock tube and modeling study of propene pyrolysis

The thermal decomposition of propene behind reflected shock waves with 1200 < T₅ < 1800 K and 1.6 × 10^?5 < ρ₅ < 2.7 × 10^?5 mol/cm³ was studied by IR laser kinetic absorption spectroscopy and gas-chromatographic analysis of reaction products. The present data together with earlier shock tube data were satisfactorily modeled with a 51-reaction mechanism. As the initial step of the reaction, three channels, C₃H₆ = CH₃ + C₂H₃ (1), C₃H₆ = H + AC₃H₅ (2), and C₃H₆ = CH₄ + C₂H₂ (3), were necessary to interpret all the experimental data. © John Wiley & Sons, Inc.