The kinetics of the reactions of C2F5 radicals with Br2 and HBr

A mixture of Br₂ + HBr + C₂F₅I was photolyzed in the vapor phase. The reaction forms C₂F₅ radicals which are removed by Competitive studies over the range of 74–146°C gave ratios of k₁₀/k₉, and these were combined with values obtained previously by different methods at higher temperatures upto 515°C to give where θ = 2.303RT J/mol. A value is assigned to the activation energy E₁₀, and this, with other data, leads to at 25°C. This result is in excellent agreement with two previous independent determinations.     

The determination of the arrhenius parameters for the reaction Cl + C2F5I → ICl + C2F5 using a competitive method

The reactions have been studied competitively over the range of 28–182°C by photolysis of mixtures of Cl₂ + C₂F₅I+ CH₄. We obtain where θ = 2.303RT J/mol. The use of published data on reaction (2) leads to log (k₁cm³/mol sec) = (13.96 ± 0.2) ? (11,500 ± 2000)/θ.     

A shock tube study of H + HNCO → NH2 + CO

The reaction of atomic hydrogen with isocyanic acid (HNCO) to produce the amidogen radical (NH₂) and carbon monoxide, has been studied in shock-heated mixtures of HNCO dilute in argon. Time-histories of the ground-state NH₂ radical were measured behind reflected shock waves using cw, narrowlinewidth laser absorption at 597 nm, and HNCO time-histories were measured using infrared emission from the fundamental v₂-band of HNCO near 5 μm. The second-order rate coefficient of reaction (2(a)) was determined to be: cm³ mol^?1 s^?1, where f and F define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be:      

Kinetics and the mechanism of the thermal reaction between trifluoromethylhypofluorite and hexafluoropropene

The kinetics of the thermal reaction between CF₃OF and C₃F₆ have been investigated between 20 and 75°C. It is a homogeneous chain reaction of moderate length where the main product is a mixture of the two isomers 1-C₃F₇OCF₃ (68%) and 2-C₃F₇OCF₃ (32%). Equimolecular amounts of CF₃OOF₃ and C₆F₁₄ are formed in much smaller quantities. Inert gases and the reaction products have no influence on the reaction, whereas only small amounts of oxygen change the course of reaction and larger amounts produce explosions. The rate of reaction can be represented by eq. (I): The following mechanism explains the experimental results: Reaction (5) can be replaced by reactions (5a) and (5b), without changing the result: Reaction (4) is possibly a two-step reaction: For ∣CF₃ = ∣C₃F₆∣, ν_20°C = 36.8, ν_50°C = 24.0, and ν_70°C = 14.2.     

The reactions of C2F5 radicals with benzene in the vapor phase

C₂F₅ radicals were generated in the presence of benzene vapor by the reaction The radicals react with the benzene by addition and pseudo H abstraction The rate constant k_add for the addition reaction (7) is given by where θ = 2.303RT cal/mole and k_c is the rate constant for combination of C₂F₅ radicals. The addition becomes reversible above 110°C. The reactions of CF₃ and C₂F₅ radicals with benzene vapor are compared.     

Thermal stability of alcohols

3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are They lead to D(iC₃H₇? H) – D((CH₃)₂(OH) C? H) = 8.3 kJ and D(C₂H₅? H) – D(CH₃(OH) CH? H) = 24.2 kJ. These data, in conjunction with reasonable assumptions, give and The rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are and      

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. V. Molybdänoxidtetrachlorid und Molybdänoxidtrichlorid

The formation enthalpies were ascertained from the solution enthalpies in 2 n NaOH resp. 2 n NaOH + 1% H₂O₂. The results of equilibrium measurements in the systems give the formation enthalpies and standard entropies: . The value of the standard entropy of the gaseous MoOCl₄ was estimated to be 91 (±3) cl. From the enthalpies and entropies of sublimation the values were obtained.     

Mechanism of pyrolysis of C2Cl6

Using published data on the kinetics of pyrolysis of C₂Cl₆ and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations: The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease. From the analysis, the bond dissociation energy DH⁰(C₂Cl₅? Cl) is found to be 70.3 ± 1 kcal/mol and ΔH_f300⁰(·C₂Cl₅) = 7.7 ± 1 kcal/mol. The resulting π? bond energy in C₂Cl₄ is 52.5 ± 1 kcal/mol.     

H2S-promoted thermal isomerization of cis-2-pentene to 1-pentene and trans-2-pentene around 800 K

H₂S accelerates the thermal isomerization of cis-2-pentene (P2c) to 1-pentene (P1) and trans-2-pentene (P2t) to around 800 K. This effect is interpreted on the basis of a free radical mechanism in which 2-pentenyl and thiyl radicals are the main chain carriers. P1 formation is essentially explained by the competing processes: P2t formation is due to addition-elimination processes: the importance of which has been evaluated against process (?4μ): The following ratios of rate constants have been measured and are discussed: (RT in cal mol^?1).     

Lösungsthermodynamik von FeCl2 in Mischschmelzen aus Alkalichloriden und LaCl3 bzw. CeCl3

Solution Thermodynamics of FeCl₂ in Molten Mixtures of Alkaline Chlorides and LaCl₃ or CeCl₃ Activity coefficients and the chemical excess potential of FeCl₂ dissolved in molten chloride mixtures were determined by EMF measurements with galvanic cells of the type in the concentration range from 0.01–5 mole-% at 720 and 820°C. An average cationic potential is defined and used to calculate a distance parameter () for the different solvent melt mixtures. may be estimated by equations of the type      

The kinetics of the reaction: Br + C3H6 ⇌ HBr + C3H5

Studies of the reaction of Br + propylene to produce HBr and allyl radical were made using VLPR (Very Low Pressure Reactor) over the range 263–363 K. Apparent bimolecular rate constants k were found to vary in an inverse manner with the initial concentration of bromine atoms introduced into the reactor. Plots of k against [Br] give straight lines whose intercepts were taken to be the true bimolecular, metathesis rate constant k₁. The reaction scheme is where k₂ ? k₁ and k_?1 [HBr] is negligibly small under our conditions. Arrhenius parameters for k₁ were assigned for linear and bent transition states and shown to give excellent fits to the observed intercepts. where θ = 2.303 RT (kcal mol^?1). The dependence of k on [Br] is accounted for in terms of the reactivity of Br* (²P_1/2) produced in the microwave discharge. The activation energy for the metathesis reaction of Br* with propylene is shown to be very small.     

Chlorine-photosensitized reactions in the Cl2 + O2 + 1,1,1,2-C2H2Cl4 system

The gas-phase photochlorination (λ = 436 nm) of the 1,1,1,2-C₂H₂Cl₄ has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps: The dissociation energy D(CCl₃CHCl? O₂) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes.     

Über Chalkogenolate. 126. Untersuchungen über N-Cyanformamidinodithiocarbimidsäure 2. Thermisches Verhalten von Kalium-N-cyanformamidinodithiocarbimat in Lösung

On Chalcogenolates. 126. Studies on N-Cyanformamidino Dithiocarbimic Acid. 2. Thermal Behaviour of Potassium N-Cyanformamidino Dithiocarbimate in Solution The thermal treatment of K₂[S₂C?N? C(NH₂)?N? CN] in methanolic solution yields . The semi-hydrate has been isolated. It reacts with acid to form The reaction with H₃CI gives The compounds have been characterized by means of electron absorption, ¹H- and ¹³C-N.M.R., infrared, and mass spectra.     

Thermal decomposition of ammonia in shock waves

The thermal decomposition of ammonia was studied by means of the shock-tube and vacuum ultraviolet absorption spectroscopy monitoring the concentration of atomic hydrogen. The rate constants of both the initiation reaction and the consecutive reaction were determined directly as and respectively.     

The pyrolysis of dimethyl sulfide,kinetics and mechanism

The kinetics of the gas phase pyrolysis of dimethyl sulfide (DMS) was studied in a static system at 681–723 K by monitoring total pressure-time behavior. Analysis showed the pressure increase to follow DMS loss. The reaction follows two concurrent paths: with a slow, minor, secondary reaction: In a seasoned reactor the reaction follows a 3/2 order rate law with rate coefficient given by with θ = 2.303 RT in kcal/mol. A free radical mechanism is proposed to account for the data and a theoretical rate coefficient is derived from independent data: which agrees well with the experimental one over the range studied. The reaction is initiated by Me₂S → Me + MeS? and propagated by metathetical radical attack on Me₂S. C₂H₄ is formed by an isomerization reaction which may in part be due to a hot radical: Thermochemical data are listed, many from estimations, for both molecular and radical species of interest in the present system.     

Über Chalkogenolate. 121. Untersuchungen über N-Cyanomonothiocarbimidsäure 1. Darstellung und Eigenschaften von Alkalimetall-N-cyanomonothiocarbimaten

On Chalcogenolates. 121. Studies on N-Cyanomonothiocarbimic Acid. 1. Synthesis and Properties of Alkali Metal N-Cyanomonothiocarbimates The hitherto unknown N-cyanomonothiocarbimates M₂[SOC?N? CN] · H₂O, where M = Na, K, Rb, Cs, have been prepared by reaction of the corresponding alkali metal salt of cyanamide with COS. N-Cyanomonothiocarbimates react with sulfur to form the ion, which gives with an acid and with CH₃I the methyl compound . The reaction of the latter compound with H₂O₂ yields . All compounds have been characterized by means of diverse methods.     

Kinetics of the gas-phase reaction of allyl alcohol with iodine. The heat of formation and stabilization energy of the hydroxyallyl radical

The reaction of iodine with allyl alcohol has been studied in a static system, following the absorption of visible light by iodine, in the temperature range 150-190°C and in the pressure range 10-200 torr. The rate-determining step has been found to be and k₃ is consistent with the equation From the activation energy and the assumption E_-3 = 1 ± 1 kcal mol^?1, it has been calculated that kcal mol^?1. The stabilization energy of the hydroxyallyl radical has been found to be 11.4 ± 2.2 kcal mol^?1.     

The kinetics of the reactions of i-C3F7 radicals with BR2 and HBr

The reactions have been studied competitively in the vapor phase over the range of 52–204°C. The i-C₃F₇ radicals were generated by means of the reaction It was found that where θ = 2.303RT J/mol. Absolute Arrhenius parameters are derived for the reactions where R = CF₃, C₂F₅, and i-C₃F₇.     

A shock tube study of reactions of atomic oxygen with isocyanic acid

Reactions of atomic oxygen with isocyanic acid (HNCO) have been studied in incident and reflected shock wave experiments using HNCO/N₂O/Ar mixtures. Quantitative time-histories of the NH(X³Σ^?) and OH(X²Π_i) radicals were measured behind the shock waves using cw, narrow-linewidth laser absorption at 336 nm and 307 nm, respectively. The second-order rate coefficients of the reactions: and were determined from early-time NH and OH formation rates, with least-squares two-parameter fits of the results given by: and cm³ mol^?1 s^?1. The minimum and maximum rate constant factors (?,F) define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be: .     

On the reaction between ethylene and cyclopentene,a radical mechanism

The bimolecular reaction is shown to proceed via a simple, nonchain, radical mechanism: with the net reaction the same as (1). Rate constants are estimated for each step and for each possible competing reaction and shown to yield minor or negligible side reactions in agreement with the observations of Lalonde and Back. Estimated and observed rate constants (1) and (1′) are in excellent agreement with the assumption that k'_-1 is a typical radical disproportionation with zero activation energy. From the reported data a best value for k′₁ is where θ = 2.303RT kcal/mol.