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      

The kinetics of thermal dimerization of hexatriene

The thermal isomerization of cis-hexatriene (cHT) to cyclohexadiene (CHD) and the dimerization of CHD and trans-hexatriene (tHT) in the liquid phase in the temperature range 380 K-473 K are reported. The rate coefficients are: for the cHT to CHD isomerization for tHT dimerizationlog and for CHD dimerization; endo form exo form © 1993 John Wiley & Sons, Inc.     

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.     

Kinetics,mechanism, and endo selectivity of Diels–Alder reactions of alkylmonosubstituted ethenes with cyclohexa-1,3-diene in the gas phase

The reactions where Y = CH₃ (M), C₂H₅ (E), i? C₃H₇ (I), and t? C₄H₉ (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.     

Thermal decomposition of cyclopentane and related compounds

Cyclopentane has been decomposed in comparative-rate single-pulse shock-tube experiments. The pyrolytic mechanism involves isomerization to 1-pentene and also a minor pathway leading to cyclopropane and ethylene. This is followed by the decomposition of 1-pentene and cyclopropane. The rate expressions over the temperature range of 1000°–1200° K are Details of the cyclopentane decomposition processes are considered, and it appears that if the trimethylene radical is an intermediate, then ΔH_f(trimethylene) ≤ 280 kJ/mol at 300°K.     

The kinetics of the thermal bromination of CF3I. Determination of the bond dissociation energy D(CF3−I)

The kinetics of the thermal bromination reaction have been studied in the range of 173–321°C. For the step we obtain where θ=2.303RT cal/mole. From the activation energy for reaction (11), we calculate that This is compared with previously published values of D(CF₃?I). The relevance of the result to published work on k_c for a combination of CF₃ radicals is discussed.     

The kinetics of free radical chain reactions in solutions of trichlorofluorethylene in cyclohexane

The kinetics of the gamma-radiation-induced free radical chain reaction in solutions of C₂Cl₃F in cyclohexane (RH) was investigated over a temperature range of 87.5–200°C. The following rate constants and rate constant ratios were determined for the reactions: In competitive experiments in ternary solutions of C₂Cl₄ and C₂Cl₃F in cyclohexane the rate constant ratio k_2c/k_2a was determined By comparing with previous data for the addition of cyclohexyl radicals to other chloroethylenes it is shown that in certain cases the trends in activation energies for cyclohexyl radical addition can be correlated with the C? Cl bond dissociation energies in the adduct radicals.     

Primary steps in the photolysis of cis-1,2-dichloroethylene

The photolysis of cis-1,2-dichloroethylene has been investigated in the presence of I₂ as a function of incident wavelength and as a function of initial cis pressure. The results indicate that at ± > 2200Å the following primary processes occur: The lifetime of the excited state yielding the above products is estimated at about 2.4×10^?9 sec. At shorter wavelengths additional C₂H₂ is produced by decomposition of a vibrationally excited C₂H₂Cl radical. Scavenging of the CHClCH radical by I₂ produced trans and cis-CHClCHl in a ratio of 4 to 1, respectively.     

Basic elimination of HCl from chlorinated ethanes

Chloroethanes react with aqueous caustic to yield either elimination or substitution products. The reaction rates were measured for the dichloroethanes, trichloroethanes, tetrachloroethanes, and pentachloroethane between 283 and 353°K. The constants of HCl eleminations referring to the rate equation are given by all rate constants being in 1./mole·s and R in cal/mole· deg. With ethyl chloride, 1,1-dichloroethane, and 1,1,l-trichloroethane, the elimination is not observed and a slow substitution takes place. The influence of chlorine substituents on both sides of the molecule on mechanism and rate parameters is discussed.     

Thermal stability of primary amines

Tertiary-amyl amine has been decomposed in single-pulse shock-tube experiments. Rate expressions for several of the important primary steps are This leads to D(CH₃? H) – D(NH₂? H) = ?10.5 kJ and D[(CH₃)₃C? H] – D[(CH₃)₂NH₂C? H] = + 6 kJ. The present and earlier comparative rate single-pulse shock-tube data when combined with high-pressure hydrazine decomposition results-(after correcting for fall off effects through RRKM calculations) gives where k_r(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated:      

Hammerstein integral equivalent of Riccati's equation

A transformation exists which allows the general Riccati equation to be written in a simpler form: The transformed equation has the equivalent nonlinear Hammerstein integral equation if the kernel N(r, r′) satisfies three conditions: and and A solution of the nonlinear integral equation is devised by repeatedly integrating the Hammerstein equation. During this procedure the kernel generates an equation that contains only coefficients of β(r)⁰ and β(r)¹. As a result, after truncating at the end of the nth cycle, it is a simple matter to write down a Padé-type approximation: all coefficients in this approximation are capable of being evaluated in terms of simple algebraic formulations of P(r), R(r), and integrals over P(r). The zeroes of the denominator of the Padé-type approximation define the points where singularities occur in β(r).     

Radical steps in diethyl ether decomposition

The thermal decomposition of diethyl ether was studied in the temperature range 697.2–760.5 K. The rate constant of reaction (1), and the ratio of the rate constant of reaction (2) to that of (12): were calculated from the amounts of products:      

Kinetics of the thermal gas-phase dimerization of hexafluoropropene

The reversible thermal gas-phase dimerization of hexafluoropropene to the four isomeric cyclobutanes has been studied by pressure change and by gas-liquid chromatographic analysis in the temperature range of 645–708 K with initial pressures of olefin from 802 to 4820 mm Hg. The reaction was accurately second order at low conversions of olefin to dimers, and at higher conversions it gave a very good fit to the rate equation for opposing second- and first-order reactions. The rate constants for the dimerization, calculated from initial rates of reaction, yielded the least-mean-squares Arrhenius equation (95% confidence limits): where k₂ is defined by Studies carried out in a packed vessel showed no evidence of heterogeneity. The rate constants found in this work are in excellent agreement with those found at lower pressures by Atkinson and Tsiamis, and the combined results give the Arrhenius equation      

The thermal unimolecular isomerization of cis-hepta-1,3-diene

The reversible isomerization of cis-hepta-1,3-diene to cis-2-trans-4-heptadiene via a 1,5 hydrogen shift has been investigated kinetically at nine temperatures in the range of 475° to 531°K. Equilibrium is reached near 94% reaction. Some cis-2-cis-4-heptadiene is also formed, but at a rate some 60 times slower than the cis,trans isomer. A least-squares analysis of the data yielded the Arrhenius equation for the isomerization of the cis-hepta-1,3-diene: Possible errors in the equilibrium constant measurements are discussed, and employing an equilibrium constant calculated by using group additivity estimates together with the values of k₁, we obtained for the reverse reaction where .     

Induced heterogeneity,a novel technique for the study of gas-phase reactions. 2. Direct study of C?C bond scission in ethane

Deliberate activation of the reaction vessel surface leads to the domination of chain termination in ethane pyrolysis by the reaction As a result, chains are dramatically reduced in length, methane yields are entirely primary and larger in proportion to other products, and values of k₁ can be directly determined from methane yield data without ambiguity. Experiments carried out in the temperature range of 841–913K at initial ethane pressures of 1–20 torr, without and with added nitrogen, yield the infinite pressure Arrhenius equation It is shown that most previously published data can be combined with those of this study to yield Fall-off curves for k₁ as a function of pressure are in good agreement with those from other laboratories. From these the relevant data for k_?1 can be extracted for use in other kinetic studies.     

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.     

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.     

Time-resolved vibrational chemiluminescence: Rate constants for the reactions of F atoms with H2O and HCN,and for the relaxation of HF (v = 1) by H2O and HCN

Rate constants have been determined at (298 ± 4) K for the reactions: and the relaxation processes: Time-resolved HF(1,0) emission was observed following the photolysis of F₂ with pulses from an excimer laser operating on XeCl (λ = 308 nm). Analysis of the emission traces gave first-order constants for reaction and relaxation, and their dependence on [H₂O] and [HCN] yielded:      

Unexpectedly rapid vapor-phase reaction between bromine and methyl iodide

The overall reaction (1) occurs readily in the gas phase, even at room temperature in the dark. The reaction is much faster than the corresponding process and does not involve the normal bromination mechanism for gas phase reactions. Reaction (1) is probably heterogeneous although other mechanisms cannot be excluded. The overall reactions (1) (2) proceed, for all practical purposes, completely to the right-hand side in the vapor phase. The expected mechanism is (3) (4) (5) (6) (7) where reaction (3) is initiated thermally or photochemically. Reaction (4) is of interest because little kinetic data are available on reactions involving abstraction of halogen by halogen and also because an accurate determination of the activation energy E₄ would prmit us to calculate an acccurate value of the bond dissociation energy D(CH₃? I).     

The kinetics and the mechanism of the thermal gas-phase reaction between NO2 and 1,1-dichlorodifluoroethylene,CF2CCl2

The kinetics of the gas phase reaction between NO₂ and CF₂CCl₂ has been investigated in the temperature range from 50 to 80°C. The reaction is homogeneous. Three products are formed: O₂NCF₂CCl₂NO₂ and equimolecular amounts of CINO and of O₂NCF₂C(O)Cl. The rate of consumption of the reactants is independent of the total pressure, the reaction products, and added inert gases and can be represented by a second-order reaction: However, the distribution of the products is influenced by the pressure of the present gases, which favor the formation of the dinitro-compound in a specific way. The effect of CF₂CCl₂ is the greatest. In the absence of added gases, the ratio of O₂NCF₂CCl₂NO₂ to that of O₂NCF₂C(O)Cl is proportional to (CF₂CCl₂ + γ_P products). The experimental results can be explaned by the following mechanism: P and X represent the products and the added gases: