Rate constants for ozone–alkene reactions under atmospheric conditions

By measuring the rates of decay of ozone in a large excess of reactant, second-order rate constants have been obtained for the reactions of ozone with ethene, propene, but-1-ene, trans-but-2-ene, isobutene, hex-1-ene, cyclopentene, cyclohexene, isoprene, vinyl fluoride, 1,1-difluoroethene, cis-1,2-difluoroethene, trans-1,2-difluoroethene, trifluoroethene, tetrafluoroethene, and 2,5? dihydrofuran. The reactions have been studied in synthetic air at atmospheric pressure and at temperatures of 294 and 260 K. The rate constants and Arrhenius parameters are discussed in relation to existing kinetic data on ozone–alkene reactions.     

Measurements and modeling for the density of 2-methoxy-2,4,4-trimethylpentane,HE for (methanol + 2-methoxy-2,4,4-trimethylpentane), LLE for (water + 2-methoxy-2,4,4-trimethylpentane) and LLE for (water + methanol + 2-methoxy-2,4,4-trimethylpentane)

Oxygenates are used in gasoline to increase the octane number and reduce carbon monoxide emission. 2-methoxy-2,4,4-trimethylpentane (TOME) is a tertiary ether which can potentially be used in addition with current oxygenates. This compound can be produced by etherification of diisobutylene with methanol. During the etherification, water is formed due to the dehydration of methanol. The appearance of water can cause (liquid + liquid) phase split in the production process. In this work, several physical properties of systems containing water, methanol and TOME are studied for the first time. The liquid density of 2-methoxy-2,4,4-trimethylpentane is presented from T = (298.15 to 408.16) K. Excess enthalpies are reported for the binary system of (methanol + 2-methoxy-2,4,4-trimethylpentane) at (T = 298.15 K). The (liquid + liquid) equilibrium (LLE) for (water + 2-methoxy-2,4,4-trimethylpentane) from T = (283.15 to 318.15) K is determined. The LLE is also reported for the ternary system of (water + methanol + 2-methoxy-2,4,4-trimethylpentane) at T = (283.15 and 298.15) K. The UNIQUAC parameters were regressed to model VLE, excess enthalpy and LLE for the binary and ternary data with one set of parameters.     

Kinetics of the diels–alder addition of ethene to cyclohexa-1,3-diene and its reverse reaction in the gas phase

The addition of ethene to cyclohexa-1,3-diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa-1,3-diene. The reaction is of the “Diels–Alder” type and leads to the formation of bicyclo[2.2.2]oct-2-ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by The retron-Diels–Alder pyrolysis of bicyclo[2.2.2]oct-2-ene has also been studied. In the ranges of 548–632 K and 4–21 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 bicyclo[2.2.2]oct-2-ene are estimated.     

Aqueous suspension polymerization of isobutene initiated by 1,2-C6F4[B(C6F5)2]2

Lewis acidic, chelating diborane 1 forms stable oxonium acids 2 in the presence of excess MeOH or water. Diborane 1 is shown to be an effective co-initiator for the suspension polymerization of isobutene in aqueous media at sufficiently low temperatures. Poly(isobutene) or butyl rubber is obtained at moderate to high conversion and with Mw < 200 K and PDI approximately 2 under these conditions.     

Kinetics of the reactions of tert-butanol with C2-C5 alcohols on sulfo cation exchangers

The kinetics of etherification of tert-butanol with aliphatic alcohols on gel KU-2×8 and macroporous KU-23 sulfo cation exchangers was studied. The first order of reaction with respect to tert-butanol and the -CSO₃H groups of a catalyst was established. The activation energy of the process observed on KU-2×8 was 60–95 kJ/mol. It was shown that the etherification of tert-butanol on KU-2×8 occurred in a surface layer. The reactivity of primary alcohols introduced into the reaction with tert-butanol increased with their molecular weights (C₂–C₅). The rate of reaction with secondary alcohols was lower than that with primary alcohols.     

Numerical simulation of the solvate structures of acetylsalicylic acid in supercritical carbon dioxide containing polar co-solvents

Hydrogen-bonded complexes of acetylsalicylic acid with polar co-solvents in supercritical carbon dioxide, modified by methanol, ethanol, and acetone of 0.03 mole fraction concentration, are studied by numerical methods of classical molecular dynamics simulation and quantum chemical calculations. The structure, energy of formation, and lifetime of hydrogen-bonded complexes are determined, along with their temperature dependences (from 318 to 388 K at constant density of 0.7 g cm^?3). It is shown that the hydrogen bonds between acetylsalicylic acid and methanol are most stable at 318 K and are characterized by the highest value of absolute energy. At higher supercritical temperatures, however, the longest lifetime is observed for acetylsalicylic acid–ethanol complexes. These results correlate with the known literature experimental data showing that the maximum solubility of acetylsalicylic acid at density values close to those considered in this work and at temperatures of 318 and 328 K is achieved when using methanol and ethanol as co-solvents, respectively.     

The azoethane-initiated thermal reaction of isobutene. Heat of formation of the 2-methyl-2-pentyl radical

The azoethane-sensitized thermal reaction of isobutene has been studied at 526–565 K. The initial concentrations of azoethane and isobutene were in the ranges of 1.40–10.5 × 10^?4 and 6.78–26.6 × 10^?4 mol/dm³, respectively. From the initial rates of formation of ethane and 2-methylpentane the heat of formation of the 2-methyl-2-pentyl radical was determined. The result obtained is ±H(2-methyl-2-pentyl) = 0.8 ± 2.0 kcal/mol. The entropy of the radical, obtained from statistical mechanical calculations and experimentally, is S⁰(2-methyl-2 pentyl) = 92.8 ± 1.5 cal/mol°K. The results support the high heat of formation of the t-butyl radical suggested by different authors.     

SYNTHESIS OF SODIUM MONO(2,4,4'-TRIMETHYLPENTYL) PHOSPHINATE. OPTIMIZATION,PURIFICATION, AND SURFACTANT PROPERTIES.

Sodium mono(2,4,4'-trirnethylpentyl)phosphinate has been obtained as a main product with good yield from the reaction between diisobutylene and sodium hypophosphite. The procedure is defined by a set of operating conditions which enable obtaining the product with optimum yield. Empirical relationships between the product quality and the operative conditions have been found. The purity of the mono(2,4,4',trimethylpentyl)phosphinic acid was checked by 1R and ³¹P NMR spectroscopy and determined by potentiometric titration of an ethanol/water solution. Finally the critical micelle concentration of sodium mono(2,4,4'-trunethylpentyl)phosphinate and sodium mono(n-octyl)phospninate has been determined.     

Reactive collisions in quadrupole cells. Part I. Reaction of [CH3NH2]+˙ with the isomeric butenes and pentenes

The reactions of mass-selected [CH₃NH₂]⁺˙ ions with the isomeric butenes and pentenes were studied at low collision energies in the radiofrequency-only quadrupole collision cell of a hybrid BEqQ tandem mass spectrometer. Characteristic iminium ions arising by addition of the methylamine to the olefin followed by fragmentation are observed for but-1-ene pent-1-ene and 3-methylbut-1-ene. However, for but-2-ene pent-2-ene 2-methylpropene 2-methylbut-1-ene and 2-methylbut-2-ene the major reaction channel of [CH₃NH₂]⁺˙ is charge exchange to form the olefinic molecular ion. The isomeric olefins are characterized to a considerable extent by the characteristic ion–molecule reactions that these molecular ions undergo with the neutral olefin.     

Orbital control of stereochemistry in acid-catalysed addition reactions of endo -tricyclo[3.2.1.02,4]0ct-6-ene

The reaction of endo-tricyclo[3.2.1.0^2,4]oct-6-ene 1 with methanol in the presence of catalytic amounts of toluene-p-sulphonic acid has been shown to give 2-exo- and endo-methoxybicyclo[3.2.1]oct-3-ene (2c) and (2d) and 2-endo-methoxybicyclo[3.2.1]oct-6-ene (13). The formation of 2-exo- methoxybicyclo[3.2.1]oct-3-ene (2c), the major product of reaction, has been probed by deuterium labelling experiments and a series of 6-exo-7-exo- dideuterobicyclo[3.2.1]oct-3-enes synthesised for ²H, ¹H and ¹³C NMR spectral analysis in order unambiguously to determine the stereochemistry of proton attack on endo-tricyclo[3.2.1 0^2,4]oct-6-ene (1). The formation of 2-exo-methoxybicyclo[3.2.1]oct-3-ene (2c) has been determined to involve corner protonation of the cyclopropyl moiety and skeletal rearrangement to an allylic cation with a small but measurable memory effect     

Double bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene to 5-ethylidenebicyclo[2.2.1]hept-2-ene over alkaline earth oxides

All the alkaline earth oxides exhibit activities for double, bond isomerization of 5-vinylbicyclo[2.2.1]hept-2-ene (VBH) to 5-ethylidenebicyclo[2.2.1]hept-2-ene (EBH) at a reaction temperature of 273 K. The order of the activity on the basis of unit weight of catalyst was CaO>MgO>SrO>BaO when compared under optimum pretreatment conditions. The E/Z ratio in the products is determined by the reaction temperature regardless of the type of catalyst; the ratios were 82/18 and 88/12 for the reaction temperatures of 323 and 273 K, respectively.     

Densities and volumetric properties of (N-(2-hydroxyethyl)morpholine + ethanol, + 1-propanol, + 2-propanol, + 1-butanol,and + 2-butanol) at (293.15, 298.15, 303.15, 313.15, and 323.15) K

Densities of binary mixtures of N-(2-hydroxyethyl)morpholine with ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol were measured over the entire composition range at temperatures from (293.15 to 323.15) K and atmospheric pressure using a vibrating-tube densimeter. The excess molar volumes, V^E were calculated from density data and fitted to the Redlich–Kister polynomial equation. Apparent molar volumes, partial molar volume at infinite dilution and the thermal expansion coefficient of the mixtures were also calculated. The V^E values were found to be negative over the entire composition range and at all temperatures studied and become less negative with increasing carbon chain length of the alkanols.     

The effect of temperature and oxygen partial pressure on the reduction mechanism in the Pr2CuO4/Ce0.9Gd0.1O1.95 system

The electrochemical behavior of a porous electrode based on Pr₂CuO₄ (PCO) screen printed on the surface of Ce_0.9Gd_0.1O_1.95 (CGO) solid electrolyte is studied by impedance spectroscopy. The rate-determining stages of the oxygen reduction reaction at the PCO/CGO interface are found for the oxygen partial pressure interval of 30–10₅ Pa and temperatures of 773–1173 K. Changeover of the rate-determining stage of electrode reaction is shown to occur depending on the temperature and the oxygen partial pressure. The PCO electrode polarization resistance is 1.7 Ω cm² at 973 K in air and remains constant at thermocycling of the electrochemical cell in the temperature range of 773–1173 K. Based on the found data, PCO can be considered as the promising cathodic material for solid-oxide fuel cells operating at moderate temperatures (773–973 K).     

Infinite dilution activity coefficient and vapour liquid equilibrium measurements for dimethylsulphide and tetrahydrothiophene with hydrocarbons

The activity coefficients at infinite dilution (γ^∞) of dimethylsulphide (DMS) in four hydrocarbon solvents were measured using the dilutor technique at temperatures between 288 K and 303 K. The four hydrocarbons were hexane, 1-hexene, 2,2,4-trimethylpentane and 2,4,4-trimethyl-1-pentene. The dilutor technique is based on the stripping of the highly diluted solute, i.e. DMS, by a constant flow of inert gas. The gas composition was analysed by gas chromatography and the rate of solute removal was calculated from the area of the peaks.     

Theoretical study of the reaction of ethynyl radical with acetonitrile

A detailed computational study has been performed on the mechanism and kinetics of the C₂H + CH₃CN reaction. The geometries were optimized at the BHandHLYP/6–311G(d, p) level. The single-point energies were calculated using the BMC-CCSD, MC-QCISD and QCISD(T)/6–311+G(2df, 2pd) methods. Five mechanisms were investigated, namely, direct hydrogen abstraction, C-addition/elimination, N-addition/elimination, C₂H–to–CN substitution and H-migration. The kinetics of the title reaction were studied using TST and multichannel RRKM methodologies over a wide range of temperatures (150–3,000 K) and pressures (10^?4–10⁴ torr). The total rate constants show positive temperature dependence and pressure independence. At lower temperatures, the C-addition step is the most feasible channel to produce CH₃ and HCCCN. At higher temperatures, the direct hydrogen abstraction path is the dominant channel leading to C₂H₂ and CH₂CN. The calculated overall rate constants are in good agreement with the experimental data.     

Cyclization and rearrangements of diterpenoids. IX. Isomerization of (1R,2S,7S,10S,11R,12S,13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.01,10.02,7.011,13]pentadecane by fluorosulfonic acid

It has been shown that the opening of the cyclopropane ring in (1R, 2S, 7S, 10S, 11R, 12S, 13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.0^1,10.0^2,7.0^11,13]pentadecane takes place under the action of fluorosulfonic acid at all three carbon-carbon bonds, but at low temperatures the main isomerization product is (1R, 2S, 7S, 10S, 12S, 13S)-2,6,6,10,12-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadecan-13-ol, and at the ordinary temperature the main products are (1R, 2S, 7S, 11S, 12R, 13R)-2,6,6,11,13-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadeca-9-ene and (1S, 2R, 11S, 12R, 15R)-2,7,7,11,15-pentamethyltetracyclo[10.2.1.0^2,11.0^3,8]pentadeca-3(8)-ene.     

Kinetic study and modeling of the hetero-homogeneous pyrolysis and oxidation of isobutane around 800 K. Part I. Pyrolysis in an unpacked pyrex reactor

Isobutane pyrolysis is studied in an unpacked Pyrex reactor at 20–100 torr initial pressures and 750–793 K. Results are interpreted in terms of a long chain radical mechanism and the reaction is modeled. The reaction selectivity or ratio of the initial production rate of isobutene (or hydrogen) to that of propene (or methane) is practically given by the ratio of the rate constant of abstraction of a tertiary hydrogen atom of isobutane to that of a primary one. A sensitivity analysis clearly shows that self-inhibition is essentially due to methylallyl radicals produced by hydrogen abstraction from isobutene. The model has been manually adjusted to experimental results and most of the adjusted rate constants are in agreement with literature data. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 425–437, 1998     

Kinetics studies of 5-methyl-2-hexanol, 2,2-dimethyl-3-hexanol,and 2,4,4-trimethyl-1-pentanol with chlorine atoms: Photooxidation mechanism of 2,4,4-trimethyl-1-pentanol

The rate constants for the reaction between chlorine atoms and either 5-methyl-2-hexanol, 2,2-dimethyl-3-hexanol, or 2,4,4-trimethyl-1-pentanol at 298 K were determined using the relative method with 2-butanol and 1-pentanol as reference compounds. The values obtained for 5-methyl-2-hexanol, 2,2-dimethyl-3-hexanol, and 2,4,4-trimethyl-1-pentanol (k × 10¹⁰ cm³ molec⁻¹ s⁻¹) were, respectively, (2.64 ± 0.5), (2.72 ± 0.5), and (2.50 ± 0.4), in agreement with the values of the rate constants reported in bibliography for similar alcohols and the values estimated by structure activity relationship methods. The photooxidation products of 2,4,4-trimethyl-1-pentanol initiated by chlorine atoms were identified (formaldehyde, 2-propanone, 2,2-dimethyl propanal, 4,4,-dimethyl-2-pentanone, and 3,3-dimethylbutanal), and the reaction mechanism was determined.     

Gas/gas and gas/wall average energy transfer from very low-pressure pyrolysis

It is shown that data obtained using very low-pressure pyrolysis (VLPP) on the pressure and temperature dependence of unimolecular rate coefficients of reactants with several reaction channels yield average energies transferred in gas/gas and gas/wall collisions (the wall being seasoned quartz at 800–1200 K). The downward average energy transferred, «ΔEå, for chlorocyclobutane/ethylene collisions is found to be 1600 cm^?1 at 970 K; «ΔEå for chlorocyclobutane/wall collisions varies from 5000 cm^?1 (wall efficiency β_w = 0.8) at 930 K to 3500 cm^?1 (β_w = 0.4) at 1150 K; similar values are found from published data on cycloheptatriene and cyclopropane-d₂. This indicates that the assumption of unit wall efficiency usually used in fitting VLPP experiments to RRKM theory needs revision.     

Untersuchungen an oxidischen Katalysatoren. XXXIV. Redoxverhalten des Nickels in NiNaY-Zeolithen 1. Reduzierbarkeit und Reoxydierbarkeit von Nickel in NiNaY-Zeolithen

Studies on Oxide Catalysts. XXXIV. Redoxbehaviour of Nickel in Zeolite NiNaY. 1. Reducibility and Reoxidizability of Nickel in Zeolites NiNaY The properties of metallic nickel in reduced (470–870 K) and reoxidized (470, 670 K) samples were studied by chemical analysis (reaction with K₂Cr₂O₇) and spectroscopic methods (FMR, IR after CO adsorption, UV/VIS). The reduction of Ni²⁺ cations from oxidic clusters proceeds in an onestep reaction. Contrary to this, isolated Ni²⁺ cations are reduced stepwise to Ni⁺ cations and subsequently to metallic nickel. The reduction degree depends in characteristic manner on the reduction temperature. Metallic nickel which was reduced at temperatures < 620 K, can be completely reoxidized at 470 K. Higher temperatures result in metallic aggregations which are not completely reoxidized even at 670 K.