Gas-phase thermolysis of sulfur compounds. Part IV. n-propyl allyl sulfide

The pyrolysis of n-propyl allyl sulfide has been studied in static and stirred-flow systems at temperatures between 270 and 400°C. Propene and 2,4,6-triethyl-1,3,5-trithiane were the only reaction products. The order of the reaction was 0.99 ± 0.05 at 377°C. The first-order rate coefficients followed the Arrhenius equation The rate coefficients and the product distribution remained unchanged when cyclohexene was used as carrier gas. A molecular mechanism involving a six-centered cyclic transition state is proposed to explain the present results. This mechanism is further supported by the pyrolysis of 4-thia-5-dideutero-1-heptene at 377°C, where only 3-deuteropropene is formed. The kinetic deuterium isotope effect had a value of 2.6 ± 0.3 at this temperature. The results are compared with those obtained in the pyrolysis of n-butyl allyl sulfide previously reported.     

Gas phase thermolysis of benzyl t-butyl sulfide,phenyl t-butyl sulfide,and phenyl t-butyl ether

The pyrolysis kinetics of the title compounds has been studied in a stirred-flow reactor over the temperature range 440–530°C and pressures between 5 and 14 torr. Benzyl t-butyl sulfide and phenyl t-butyl ether formed isobutene as product in over 98% yield, together with the corresponding benzyl thiol and phenol. The benzyl thiol decomposes to a large extent into hydrogen sulfide and bibenzyl. In the pyrolysis of phenyl t-butyl sulfide, the hydrocarbon products consisted of 80 ±5% isobutene plus 20% isobutane, while the sulfur containing products were thiophenol and diphenyl disulfide. Order one kinetics was observed for the consumption of the reactants. The first order rate coefficients, based on isobutene production, followed the Arrhenius equations: Benzyl t-butyl sulfide: Phenyl t-butyl sulfide: Phenyl t-butyl ether: For benzyl t-butyl sulfide and phenyl t-butyl ether, the results suggest a unimolecular mechanism involving polar four center cyclic transition states. For phenyl t-butyl sulfide, the t-butyl-sulfur single bond fission mechanism is a parallel, less important process than the complex fission one.     

Gas phase thermolysis of cyanomethyl t-butyl sulfide and cyanomethyl t-butyl ether

The pyrolyses of cyanomethyl t-butyl sulfide and its oxygen homologue have been studied in a stirred-flow system over the temperature range 490–540°C and pressures between 5 and 14 Torr. In both cases, isobutene is formed as product in over 97% yield. Hydrogen sulfide is obtained in about half the amount of isobutene in the pyrolysis of the sulfide. Hydrogen cyanide is formed in the pyrolysis of the ether. The first-order rate coefficients for the consumption of the reactants followed the Arrhenius equations Cyanomethyl t-butyl sulfide: Cyanomethyl t-butyl ether: A molecular mechanism involving polar four-centered cyclic transition states is proposed for both reactions, with the CN group stabilizing the partial negative charge developed at the S and O atoms.     

Gas phase thermolysis of sulfur compounds. II. Ditertiary butyl sulfide

The pyrolysis of di-tert-butyl sulfide has been investigated in static and stirred-flow systems at subambient pressures. The rate of consumption of the sulfide was measured in some experiments, and the rate of pressure increase was followed in others. The results suggest that the reaction is essentially homogeneous in a seasoned reactor and proceeds through a free radical mechanism. In the initial stages, the decomposition rate follows first-order kinetics, and the rate coefficient in the absence of an inhibitor is given by between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately between 360 and 413°C. The stoichiometry of the uninhibited reaction at 380°C and 50% decomposition is approximately.     

The reaction of hydrogen atoms with 1-butanethiol and thiolane the role of chemically activated 1-butanethiol

The reaction of 1-butanethiol with hydrogen atoms has been studied at temperatures of 295° and 576° K under the pressure of 660 Pa, using a conventional discharge-flow apparatus. The reaction products (besides hydrogen sulfide and methane) under the low conversion range (～10%) consisted mainly of n-butane, 1-butene, and propylene-propane, with the relative yields of 70, 25, and 5% at 295° K and 25, 50, and 10% at 576°K. Analysis of kinetic equations by numerical integration indicates that the following initial steps are consistent with the experimental results: where the following expressions have been derived for k₁ and k₂: The subsequent reaction of the butylthio radical with hydrogen atoms leads to the chemically activated 1-butanethiol which either stabilizes to 1-butanethiol or decomposes to 1-butene and hydrogen sulfide, depending on the experimental conditions. A similar analysis of the data on the thiolane-H system has yielded the following rate parameters for the initial step to form the 4-mercapto-1-butyl radical: .     

Rate constants for the reactions of OH radicals and Cl atoms with diethyl sulfide,Di-n-propyl sulfide,and Di-n-butyl sulfide

Rate constants for the reactions of OH radicals and Cl atoms with diethyl sulfide (DES), di-n-propyl sulfide (DPS), and di-n-butyl sulfide (DBS) have been determined at 295 ± 3 K and a total pressure of 1 atm. Hydroxyl radical rate data was obtained using the absolute technique of pulse radiolysis combined with kinetic spectroscopy. The chlorine atom rate constants were measured using a conventional photolytic relative rate method. The rate constant for the reaction of Cl atoms with dimethyl sulfide (DMS) was also determined. The following rate constants were obtained:      

Minor products and initiation rate in the chain pyrolysis of propane

With a continuous jet-stirred tank reactor operating at small space time (0.05–1.2 s) the kinetics of the formation of six minor products (ethane, isobutane, butene-1, 2,3-dimethyl-butane, 4-methylpentene-1, and 1,5-hexadiene) are studied during the pyrolysis of propane, at small extents of reaction and over the temperature range of 600–780°C. The experimental results are in agreement with the free radical mechanism proposed by Jezequel, Baronnet, and Niclause for this reaction. They show that the two most important termination processes are The measured rates of formation of the minor products are consistent with the quasi-identical values estimated by Jezequel and co-workers (between 475 and 505°C) and by Allara and Edelson (between 510 and 560°C) for kinetic parameters (A₁ ? 10^16.65 s^?1 and E₁ ? 84.7 kcal/mole) of the chain initiation process      

Effect of pressure on the radiation-induced polymerization of ethylene in tert-butyl alcohol

The effects of pressure of the radiation-induced polymerization of ethylene in tert-butyl alcohol were studied. The reaction was carried out by use of a reactor with a capacity of 100 ml under the following conditions; pressure, 60–400 kg/cm²; temperature, 24 ± 3°C; dose rate, 2.0 × 10⁴?1.6 × 10⁵ rad/hr; amount of medium (tert-butyl alcohol containing 5 vol-% water), 70 ml. The results of polymerization were analyzed by a kinetical treatment based on a reaction mechanism with both first- and second-order terminations for the concentration of propagating, radical. On the basis of the kinetical treatment the rate constants of each elementary reaction at several pressures were determined, and the activation volumes of elementary reactions were obtained and are discussed in connection with the reaction mechanism. Consequently, the rate constants of propagation, first-order termination, and second-order termination at pressure p and at 24°C were expressed by,      

Polymerization of methyl methacrylate with ferric laurate in combination with various substituted amines as initiators

The effect of various substituted amines on the polymerization of methyl methacrylate initiated by ferric laurate—amine as the initiator system has been studied in carbon tetrachloride medium at 60°C. Amines used are n-butyl amine, di-n-butyl amine. The rate of polymerization is found to follow the order: tertiary > secondary > primary amine. From the detailed kinetic studies it was found that the overall polymerization rate can be expressed by the equation: The relative activity of the different amines has been found to be dependent on the relative electron-donating tendency of the substituents present in the amine. The mechanism of the polymerization is discussed on the basis of these results, and various kinetic constants are evaluated.     

The self-inhibited pyrolysis of isobutane

The pyrolysis of isobutane was investigated in the ranges of 770° to 855°K and 20 to 150 Torr at up to 4% decomposition. The reaction is homogeneous and strongly self-inhibited. A simple Rice-Herzfeld chain terminated by the recombination of methyl radicals is proposed for the initial, uninhibited reaction. Self-inhibition is due to abstraction of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in termination reactions. The reaction chains are shown to be long. It is suggested that a previously published rate constant for the initiation reaction (1) is incorrect and the value k₁ = 10^16.8 exp (?81700 cal mol^?1/RT)s^?1 is recommended. The values of the rate constants for the reactions (4i) (4t) (8) are estimated to be and From a recalculation of previously published data on the pyrolysis of isobutane at lower temperatures and higher pressures, the value k_11c, = 10^9.6 cm³ mol^?1 s^?1 is obtained for the rate constant of recombination of t-butyl. A calculation which is independent of any assumed rate constants or thermochemistry shows that the predominant chain termination reaction is the recombination of two methyl radicals in the conditions of the present work and the recombination of two t-butyl radicals in those of our previous study at lower temperatures and higher pressures.     

Kinetic study of the iodine monobromide-or iodine monochloride-catalyzed alcoholysis of butoxytriethylsilane: n-butoxy group — s-butoxy group exchange reaction

The catalytic activity of iodine monobromide and iodine monochloride were investigated in the reaction, Et₃SiOBuⁿ + Bu^sOH ? Et₃SiOBu^s + BuⁿOH. Pseudo first-order rate constants were measured by gas chromatography, at 10°, 20°, 30°, and 40°C for iodine monobromide and at 10°, 20°, and 30°C for iodine monochloride, on reaction mixtures containing both butanols in excess. The catalytic coefficients of both catalysts were evaluated from the observed rate constants as follows: The activation paramaters were estimated from these data, and were compared with the values for iodine catalysis. These results are consistent with the mechanism previously proposed.     

Very low-pressure pyrolysis of cyclobutyl cyanide. The cyano stabilization energy

A very low-pressure pyrolysis (VLPP) apparatus has been constructed and shown to yield kinetic data consistent with other VLPP systems. The technique has been applied to the pyrolysis of cyclobutyl cyanide over the temperature range of 833–1203°K. The reaction was found to proceed via a single pathway to yield ethylene and vinyl cyanide. If A_∞ is based on previous high-pressure data for this reaction and for cyclobutane pyrolysis, then RRKM theory calculations show that the experimental unimolecular rate constants are consistent with the high-pressure Arrhenius parameters given by where θ=2.303 RT in kcal/mole. If A_∞ is adjusted relative to the more recent parameters for cyclobutane pyrolysis suggested by VLPP studies, then the Arrhenius expression becomes The cyano group reduces the activation energy for cyclobutane pyrolysis by 6±1 kcal/mole, and on the basis of a biradical mechanism this value may be attributed to the cyano stabilization energy.     

The very-low-pressure pyrolysis (VLPP) of n-propyl nitrate,tert-butyl nitrite,and methyl nitrite. Rate constants for some alkoxy radical reactions

The pyrolysis of n-propyl nitrate and tert-butyl nitrite at very low pressures (VLPP technique) is reported. For the reaction the high-pressure rate expression at 300°K, log k₁ (sec^?1) = 16.5 ? 40.0 kcal/mole/2.3 RT, is derived. The reaction was studied and the high-pressure parameters at 300°K are log k₂(sec^?1) = 15.8 ? 39.3 kcal/mole/2.3 RT. From ΔS_1,?1⁰ and ΔS_2,?2⁰ and the assumption E_?1 and E_?2 ? 0, we derive log k_?1(M^?1·sec^?1) (300°K) = 9.5 and log k_?2 (M^?1·sec^?1) (300°K) = 9.8. In contrast, the pyrolysis of methyl nitrite and methyl d₃ nitrite afford NO and HNO and DNO, respectively, in what appears to be a heterogeneous process. The values of k_?1 and k_?2 in conjunction with independent measurements imply a value at 300°K for of 3.5 × 10⁵ M^?1·sec^?1, which is two orders of magnitude greater than currently accepted values. In the high-pressure static pyrolysis of dimethyl peroxide in the presence of NO₂, the yield of methyl nitrate indicates that the combination of methoxy radicals with NO₂ is in the high-pressure limit at atmospheric pressure.     

Ene reactions of olefins. I. The addition of ethylene to 2-butene and the decomposition of 3-methylpentene-1

The pyrolysis of ethylene–butene-2 mixtures has been studied in a static system over the temperature range of 689°-754°k and for initial pressures of each olefin of 20–200 torr. The two main addition products were cyclopentene and 3-methylpentene-1. Kinetic evidence indicated that cyclopentene was formed from radical processes while 3-methylpentene-1 was formed by the molecular “ene¨?” addition of ethylene to butene-2 through a six-center transition state. The following rate constants were obtained: The pyrolysis of 3-methylpentene-1 has been studied over the same temperature range and for initial pressures of 20–100 torr. Kinetic evidence showed that the products ethylene and butenes were formed in both radical and molecular processes. Estimates of the rate constant k_?1t and k_?1c were, however, in reasonable agreement with the measurements of k_1t and k_1c. The mechanism of the ene reaction is discussed, and it is concluded that the transition state does not involve the formation of a biradical.     

The kinetics of the gas phase intramolecular elimination of isobutene from 2-d1-triisobutylaluminum and the deuterium isotope effect in reactions involving cyclic transition states

The intramolecular elimination of isobutene from 2-d₁-triisobutylaluminum has been studied in the gas phase for temperatures ranging between 102.4 and 184.6°C. The reaction is apparently homogeneous and obeys the first order rate law, yielding the following Arrhenius relationship: Excess ethylene was added to the starting material in order to avoid complications from the backreaction. The cyclic 4-center nature of the transition state proposed earlier has been unequivocally demonstrated by deuterium labelling. Mass-spectral analyses show that the isobutene formed contains no deuterium. The hydrolyses products of the mixed trialkylaluminum formed during the reaction consist of monodeuteroethane and 2-d₁-isobutane. The observed negative entropy of activation of ～12 cal/°-mole agrees with prediction and implies a reasonably tight transition state structure. Combined with the corresponding data for the non deuterized Al(i-bu)₃ reported earlier, these data result in a primary kinetic deuterium isotope effect of k_H/k_D = 1.3 × 10^0.6/θ corresponding to a ratio of the isotopic rate constants of 3.7 at 25°C. This result is in excellent agreement with a predicted value of 1.4 × 10^0.7/θ and it is in line with literature data on similar reactions involving cyclic transition state complexes.     

The reaction of atomic oxygen O(3P) with isobutane

The reaction of O(³P) atoms with isobutane has been studied by using the discharge-flow system described previously [1]. The rate constant was measured from determinations of the isobutane concentration in the presence of an excess of O atoms and is given by k₁ = (7.9 ± 1.4) × 10⁷ dm³/mol·s at 307 K. In order to explain the observed reaction products, the mechanism requires that the principal process be the successive abstraction of H atoms from isobutane and from the t-butyl radical to give isobutene. A minor part of the reaction between O(³P) and the t-butyl radical gives the t-butoxy radical, which decomposes to acetone. The branching ratios are .     

The pyrolysis of 2-nitrosoisobutane and the bond dissociation energies of nitroso compounds

Study of the reaction by very-low-pressure pyrolysis (VLPP) in the temperature range of 550–850°K yields for the high-pressure Arrhenius parameters where θ = 2.303RT in kcal/mole. These in turn yield for the high-pressure second-order recombination of tBu + NO, k_?1 = (3.5 ± 1.7) × 10⁹ 1./mole·sec at 600°K. For the competing reaction l./mole·sec and E₄ ≥ 4.2 kcal/mole. The bond dissociation energy DH^o (tBu-NO) was determined to be (39.5 ± 1.5) kcal/mole, both from the equilibrium constant and from the activation energy of reaction (1), obtained from RRKM calculations. A ‘free-volume’ model for the transition state for dissociation is consistent with the data. A limited study of the system at 8–200 torr showed an extremely rapid inhibition by products and a very complex set of products.     

Kinetics of the Diels–Alder addition of acrolein to cyclohexa-1,3-diene and its reverse reaction in the gas phase

The Diels–Alder addition of acrolein to cyclohexa-1,3-diene has been studied between 486 and 571°K at pressures ranging from 55 to 240 torr. The products are endo- and exo-5-formylbicyclo[2.2.2]oct-2-ene (endo- and exo-FBO), and their formations are second order. The rate constants (in l./mole · sec) are given by The retro-Diels–Alder pyrolysis of endo-FBO has also been studied. In the ranges of 565–638°K and 6–38 torr, the reaction is first order, and its rate constant (in sec^?1) is given by The reaction mechanism is discussed. The heat of formation and the entropy of endo-FBO are estimated.     

Effect of substituents in the gas-phase elimination kinetics of β-substituted ethyl acetates

The kinetics of gas-phase elimination of 3-methyl-1-butyl acetate and 3,3-dimethyl-1-butyl acetate into acetic acid and the corresponding substituted butenes have been measured over the temperature range of 360–420°C and the pressure range of 63–250 Torr. The reactions are homogeneous in both clean and seasoned vessels, obey first-order law, and are unimolecular. The temperature dependence of the rate constants is given by the Arrhenius equation 3-methyl-1-butyl acetate: 3,3-dimethyl-1-butyl acetate: The points in a plot of log (k/k₀) of β-alkyl and several β-substituted ethyl acetates against E_s values appear aligned in an approximate linear relationship. These results may be interpreted as a consequence of steric effects, namely, steric accelerations.     

Pyrolysis of 1,2-dichloropropane

The thermal decomposition of 1,2-dichloropropane at atmospheric pressure has been studied in the temperature range 227–590°C, in a flow system. Above 450°C, the reaction is homogenous and unimolecular with a rate constant: Below 450°C, a low activation energy, probably heterogenous process competes with the gas phase reaction The primary reaction products are HCl and the monochloropropene isomers; the relative amounts of each isomer depend on the temperature in the low but not in the high temperature region. The direction of the HCl elimination is discussed in terms of substituent effects at the α- and β-carbon positions and compared with literature data on similar reactions Secondary products are formed principally by further pyrolysis of allyl chloride. The first-order rate constant of this reaction is given by: .