bluuebunny/crossref_metadata_2025_split huggingface dataset:
Catalysis by HBr in the bromination of o‐xylene in acetic acid
Authors: Yesodharan E. P. , Rajaram J. , Kuriacose J. C. 
Published: January 2005

AbstractHydrogen bromide is known to inhibit the bromination of aromatic substrates (ArH), either by fixing up bromine as HBr3 or ArH as ArH · HBr. However, there is catalysis by HBr in the bromination of mesitylene in acetic acid. The bromination of o‐xylene in acetic acid in the dark is found to be autocatalytic, and the reaction is overall third order, first order in o‐xylene with the orders in Br2 and HBr depending on the concentrations. A composite rate expression involving Br2 and HBr as electrophiles has been proposed and verified using iodine bromide as a catalyst where the orders are one in each of the reactants, irrespective of the concentrations used.
Flash photolysis study of the recombination of chlorine atoms in the presence of various inert gases and NO
Authors: Hippler H. , Troe J. 
Published: January 2005

AbstractThe recombination of chlorine atoms has been investigated by flash photolysis in the inert gases He, Ne, Ar, N2, CO2, CF4, SiF4, SF6, and C2F6. The pressure dependence of the reaction has been measured between 0.5 and about 100 atm for He, N2, and CO2. Experiments on the NO‐catalyzed recombination of chlorine in the presence of He (0.5–100 atm) permitted a determination of the falloff curve of the reaction Cl+NO(+He)→ClNO(+He).
Triplet excited states of nitronaphthalenes. II. b‐Nitronaphthalene
Authors: Capellos C. , Suryanarayanan K. 
Published: January 2005

AbstractNanosecond flash photolysis of b‐nitronaphthalene (b‐NO2C10H7) in nonpolar and polar solvents shows a transient species with maximum absorption and lifetime dependent on solvent polarity. In deaerated n‐hexane the absorption maximum and lifetime (1/k) are 425 nm and 530 nsec, while in deaerated ethanol the corresponding values are 470 nm and 1.7 ·sec. This transient absorption is attributed to the triplet excited state of b‐NO2C10H7, and the observed red shift as well as its longer lifetime in polar solvents are indicative of the intramolecular charge transfer character of this state. The change of dipole moment accompanying the transition T1 → Tn, as well as rate constants for electron and proton transfer reactions involving the T1 state of b‐NO2C10H7, were determined. The spectroscopic and kinetic data obtained in this work indicate that the triplet state of b‐NO2C10H7 behaves like a n‐π* state in nonpolar media, while in polar solvents the n‐π* character of the state is reduced with a simultaneous increase in the charge transfer character.
A shock‐tube study of the kinetics of reaction of hydroxyl radicals with H2, CO, CH4, CF3H, C2H4, and C2H6
Authors: Bradley J. N. , Capey W. D. , Fair R. W. , Pritchard D. K. 
Published: January 2005

AbstractConcentration‐time profiles have been measured for hydroxyl radicals generated by the shock‐tube decomposition of hydrogen peroxide in the presence of a variety of additives. At temperatures close to 1300°K the rate constants for the reaction

are found to be in the ratio 0.18:0.19:0.59:1.00:2.33:2.88 for the additives CO:CF3H:H2:CH4:C2H4:C2H6, respectively.
Lyman‐α absorption photometry at high pressure and atom density kinetic results for H recombination
Authors: Lynch K. P. , Schwab T. C. , Michael J. V. 
Published: January 2005

AbstractAtomic absorption and fluorescence spectrophotometry have been routinely used in kinetic investigations as probes of relative, rather than absolute, atom concentration. The calibration of a Lyman‐α photometer for measurement of absolute hydrogen atom concentrations at levels [H] ι ≤ 1.8 × 1014 atoms/cm2 and total pressure of 1.5 torr He is described. The photometer is characterized in terms of a two‐level emission source and an absorption region in which only Doppler broadening of the transition is considered. The modifications due to pressure broadening by high pressures (500 ≤ P ≤ 1500 torr) in the absorption region are discussed in detail. Application of the technique is reported for the recombination of hydrogen atoms in the presence of six nonreactive heat bath gases. Experiments were performed in a static reaction cell at pressures of 500–1500 torr of heat bath gas, and hydrogen atoms were produced by Hg (3P1) photosensitization of H2. The technique is critically evaluated and the mechanistic implications of the hydrogen atom recombination results are examined. The measured room temperature recombination rate constants in H2, He, Ne, Ar, Kr, and N2 are 8.5 ± 1.2, 6.9 ± 1.5, 5.9 ± 1.5, 8.0 ± 0.8, 10.2 ± 0.9, and 9.6 ± 1.4, respectively, where the units are 1033 cm6/molec2 · sec.
Hydroxyl radical measurements in a photochemical reactor by laser‐induced fluorescence
Authors: Wu C. H. , Wang Charles C. , Japar S. M. , Davis L. I. , Hanabusa M. , Killinger D. , Niki H. , Weinstock B. 
Published: January 2005

AbstractMeasurements of hydroxyl radical (HO) concentrations in ambient air by the technique of laser‐induced fluorescence have been recently reported. The present study was undertaken to provide an independent test of the validity of those measurements. A photochemical reactor was used to provide a source of HO, and the concentration of HO in the reactor was determined by the laser‐induced fluorescence technique. The HO concentration was also deduced from measured hydrocarbon decay rates in the reactor. There was agreement between the HO concentrations obtained by these two different methods, thus providing further validation of the fluorescence method. Some studies of HO fluorescence efficiency as well as of possible interferences with the fluorescence measurements are reported.
The deprotonation of internally hydrogen‐bonded acids. Mechanistic conclusions from the influence of general bases
Authors: Perlmutter‐Hayman Berta , Shinar Ruth 
Published: January 2005

AbstractThe reactions between alizarin yellow G and six different bases B (including OH−) and between tropaeolin 0 and eight different bases have been investigated at 25°C and an ionic strength of 0.5M, using the temperature‐jump method. From the form of the log kB versus ΔpK curves it is concluded that for alizarin yellow G the observed relaxation time is due chiefly to a diffusion‐controlled reaction between the base and that fraction which is present in the “open” non‐hydrogen‐bonded form, whereas for tropaeolin 0 the base attacks the hydrogen bridge.The dissociation constants for the internally bound hydrogen have been measured under the same conditions of temperature and ionic strength, using a spectrophotometric method.
Abstraction of chlorine atoms from polychloroethanes. IV. The kinetics of chlorine abstraction from 1,1,2‐trichloroethane, 1,1‐dichloroethane, and 1,2‐dichloroethane by cyclohexyl radicals
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A. 
Published: January 2005

AbstractThe kinetics of chlorine atom abstraction from the chloroethanes (EClH) 1,1,2‐C2Cl3H3, 1,1‐C2Cl2H4, and 1,2‐C2Cl2H4 by radiolytically generated cyclohexyl radicals was studied in the liquid phase by a competitive method. The chlorine atom abstraction data were put on an absolute basis by comparing the rates of the metathetical reactions with the known rate of addition of cyclohexyl radicals to C2Cl4. The following Arrhenius parameters were obtained:

E(EClH)‐

Temperature

A(ECLH)
E(CCl4)
log A(EClH)
E(EClH)
Range

log

EClH
A(C2Cl4)
(kcal/mol)
(1.mol·sec)
(kcal/mol)
(°C)

CHCL2CH2Cl
0.03 ± 0.08
3.87 ± 0.17
8.98 ± 0.14
11.17 ± 0.27
150 – 250

CHCL2CH3
0.13 ± 0.13
4.63 ± 0.27
8.18 ± 0.19
11.93 ± 0.37
130 – 250

CHCL2CH2Cl
0.50 ± 0.17
7.57 ± 0.35
9.18 ± 0.23
14.87 ± 0.45
150 – 250

The error limits are the standard deviations from least mean square Arrhenius plots.The α and ß activation effects on the kinetics of Cl atom abstraction from chloroalkanes are discussed. From the linear relation between the relative reactivities of cyclohexyl radicals toward the XCCl3 and XCHCl2 series, ECl(c‐C6H11· + CHCl2CHCl2) = 10.2 ± 1 kcal/mol and ECl(c‐C6H11· + CHCl22CCl3) = 9.7 ± 1 kcal is derived.
Equilibrium, kinetics, and mechanism of the malonic acid–iodine reaction
Authors: Leopold Kenneth R. , Haim Albert 
Published: January 2005

AbstractThe equilibrium constant for the reaction CH2(COOH)2 + I3− ⇆ CHI(COOH)2 + 2I− + H+, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO4), is (2.79 ± 0.48) × 10−4M2. Stopped‐flow kinetic measurements at 25°C and ionic strength 1.00M with [H+] = (2.09‐95.0) × 10−3M and [I−] = (1.23‐26.1) × 10−3M indicate that the rate of the forward reaction is given by (k1[I2] + k3[I3−]) [HOOCCH2COO−] + (k2[I2] + k4[I3−]) [CH(COOH)2] + k5[H+] [I3−] [CH2(COOH)2]. The values of the rate constants k1‐k5 are (1.21 ± 0.31) × 102, (2.41 ± 0.15) × 101, (1.16 ± 0.33) × 101, (8.7 ± 4.5) × 10−1M−1·sec−1, and (3.20 ± 0.56) × 101M−2·sec−1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by ken[CH2(COOH)2], with ken = 2.0 × 10−3 + 1.0 × 10−2 [CH2(COOH)2]. An intramolecular mechanism, featuring a six‐member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.
The production and subsequent relaxation of vibrationally excited OH in the reaction of atomic oxygen with HBr
Authors: Spencer John E. , Glass G. P. 
Published: January 2005

AbstractA fast discharge flow apparatus equipped for EPR detection of radicals has been used to investigate the reaction O + HBr → OH + Br. At 295°K, measurements showed that more than 97% of all OH produced in this reaction was formed initially in its first vibrationally excited state. Rate constants for physical deactivation of OH(v = 1) by O(3P), Br(2P3/2), H2O, and HBr were measured as (1.45 ± 0.25) × 10−10, (6.4 ± 2.4) × 10−11, (1.35 ± 0.50) × 10−11, and < 10−12 cm3/molec·sec, respectively.
The gas‐phase pyrolysis of alkyl nitrites. IV. Ethyl nitrite
Authors: Batt L. , Milne R. T. , McCulloch R. D. 
Published: January 2005

AbstractThe rate of decomposition of methyl nitrite (MN) has been studied in the presence of isobutane‐t‐BuH‐(167‐200°C) and NO (170‐200°C). In the presence of t‐BuH (∼0.9 atm), for low concentrations of MN (∼10−4M) and small extents of reaction (4‐10%), the first‐order homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k4(t‐BuH) »k2(NO): . The results indicate that the termination process involves only \documentclass{article}\pagestyle{empty}\begin{document}$ t - {\rm Bu\, and\, NO:\,\,}t - {\rm Bu} + {\rm NO\stackrel{e}{\longrightarrow}} $\end{document} products, such that ke ∼ 1010 M−1 ∼ sec−1.Under these conditions small amounts of CH2O are formed (3‐8% of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence at low pressures of t‐BuH. Addition of large amounts of NO completely suppresses MeOH formation.The rate constant for reaction (1) is given by k1 = 1015.8°0.6‐41.2°1/· sec−1. Since (E1 + RT) and ΔHΔ1 are identical, within experimental error, both may be equated with D(MeO ‐ NO) = 41.8 + 1 kcal/mole and E2 = 0 ± 1 kcal/mol. From ΔS11 and A1, k2 is calculated to be 1010.1°0.6M−1 · sec−1, in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k6/k2 = 0.17 independent of temperature, we conclude that \documentclass{article}\pagestyle{empty}\begin{document}$ E_6 = 0 \pm 1{\rm kcal}/{\rm mol\, and\,}\,k_6 = 10^{9.3} M^{- 1} \cdot {\rm sec}^{- 1} :{\rm MeO} + {\rm NO}\stackrel{6}{\longrightarrow}{\rm CH}_2 {\rm O} + {\rm HNO} $\end{document}. From the independent observations that k2:k2→: k6→ was 1:0.37:0.04, we find that k2→ = 109.7M−1 ċ sec−1 and k6→ = 108.7M−1 ċ sec−1. In addition, the thermodynamics lead to the result
In the presence of NO (∼0.9 atm) the products are CH2O and N2O (and presumably H2O) such that the ratio N2O/CH2O ∼ 0.5. The rate of CH2O formation was affected by the surface‐to‐volume ratio s/v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CH2O arises as the result of an essentially homogeneous first‐order, fourcenter elimination of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HNO}:{\rm MN\stackrel{5}{\longrightarrow}CH}_{\rm 2} {\rm O} + {\rm HNO} $\end{document}. The rate of CH2O formation is given by k5 = 1013.6°0.6‐38.5‐1/ċ sec−1.
Pyrolysis of trifluoroacetaldehyde. The formation of trifluoromethane and hexafluoroethane
Authors: Liu Michael T. H. , Loucks Leon F. , Hooper David G. 
Published: January 2005

AbstractThe thermal decomposition of trifluoroacetaldehyde at temperatures f 471 to 519°C has been studied by measuring the rates of formation of CF3H and C2F6. It is concluded that the high‐pressure reaction mechanism involves a Rice‐Herzfeld reaction scheme with first‐order initiation and second‐order termination via CF3 combination. However, a falloff in reaction rates is observed at pressures below 100 mmHg. The Arrhenius parameters of the three rate constants corresponding to the overall reaction, the initiation reaction, and an abstraction reaction have been evaluated.
Radical equilibrium studies; the thermodynamic parameters of n‐propyl
Authors: Marshall Roger M. , Rahman Lutfor 
Published: January 2005

AbstractA novel method for the investigation of the thermodynamic properties of free radicals is described. It involves the establishment of an equilibrium of the form

where R1 and R2 are free radicals, and the measurement of the recombination products of R1 and R2. The method is applied to the case where R1 is n‐propyl, R2 is methyl, and the olefin is ethene, using the thermal decomposition of azomethane (a source of methyl) in the presence of ethene in the temperature range of 581–649°K. Using the best available thermodynamic parameters for methyl, it is concluded that those for n‐propyl are in need of adjustment. We recommend the values ΔHf°(300°K) = 22.6 ± 1 kcal/mol and S300° = 67.4 ± 3 cal/mol · K together with either the heat capacity data of O'Neal and Benson or the essentially identical data derivable from the results of Purnell and Quinn.
Shock‐tube study of thermal decomposition of propene in the presence of deuterium
Authors: Yano Takayuki 
Published: January 2005

AbstractThe thermal decomposition of propene in the presence of D2 was studied in a single‐pulse shock tube in the temperature range of 1200–1400°K. The main decomposition products were methane, ethylene, allene, and propyne. Furthermore, deuterated species were observed of each product and of propene, with characteristic compositions that were dependent on propene conversion. Geometrical isomers of monodeuterated propene, as the result of H‐D exchange, were analyzed by microwave spectroscopy. From these observations, the reactivities of n‐ and isopropyl radicals at high temperatures were determined. The former was found to be an intermediate of methane and ethylene and the latter was found to be responsible for the formation of the deuterated propene as follows:
equation image
The rate constant ratio kn/ki was estimated to be 0.5–0.8, which was more than ten times greater than that obtained at room temperature. It was also found that allene or propyne was produced from allyl radicals and that acetylene was produced from vinyl radicals. In addition, the rate constant of the hydrogen abstraction by the hydrogen atom from C3H6 was found to be six times greater than that by the hydrogen atom from D2.
Reactions of the iso‐butyl radical during 1,1′‐azoisobutane pyrolysis
Authors: McKay G. , Turner J. M. C. 
Published: January 2005

AbstractQuantitative analysis of the products formed in 1,1′‐azoisobutane pyrolyses in the temperature range of 553°–602°K has shown that the major reactions of the iso‐butyl radical are
equation image
Analysis of initial rate data gave log10k4/(kc)1/2(cm−3/2.mol 1/2.sec−1/2) = 7.54±0.44 − (136.5 + 4.8) kJ/mol/2.303RT, the Arrhenius parameters obtained being in good agreement with thermodynamic data for reaction (4). Measured values of ka/(kc)1/2 where ka is the rate constant of the reaction iC4H9 + AIB → iC4H10 +. AIB were consistent with published parameters determined by photolysis of 1,1′‐azoisobutane. Combination of photolysis and pyrolysis data gave log10 ka/(kc)1/2(cm3/2.mol−1/22.sec−1/2) = 3.68 ± 0.15 − (27.2 ± 1.2) kJ/mol/2.303RT. The crosscombination ratio for methyl and iso‐butyl radicals has been found to be 0.25, indicating that the geometric mean rule does not hold for methyl and iso‐butyl radicals.
Kinetics of the gas‐phase reaction between iodine and trifluorosilane and the bond dissociation energy D(F3SiH)
Authors: Doncaster Alan M. , Walsh Robin 
Published: January 2005

AbstractThe title reaction has been investigated in the temperature range 667–715K. The only reaction products were trifluorosilyl iodide and hydrogen iodide. The rate law

was obeyed over a wide range of iodine and trifluorosilane pressures. This expression is consistent with an iodine atom abstraction mechanism and for the step

log k1(dm3/mol·sec) = (11.54 ± 0.17) − (130.5 ± 2.2 kJ/mol)/RT In 10 has been deduced. From this the bond dissociation energy D(F3SiH) = (419 ± 5) kJ/mol (100.1 kcal/mol) is obtained. The kinetic andthermochemical implications of this value are discussed.
Ene reactions of olefins, part II. The addition of ethylene to propylene and to isobutene and the addition of propylene to propylene
Authors: Richard C. , Back M. H. 
Published: January 2005

AbstractThe pyrolysis of ethylene–propylene and ethylene–isobutene mixtures has been studied in a static system over the temperature range of 682°–754° K and for initial pressures of each olefin of 33–300 torr. The following molecular ene reactions were observed and the rate constants measured:
equation image
Using thermodynamic data, rate constants for the corresponding retro‐ene decomposition reactions were calculated and compared to kinetic data reported for similar compounds. Other products were formed by radical chain processes, the main higher molecular weight ones being cyclopentene and 1‐methylcyclopentene. A mechanism involving addition of allyl radicals is suggested for the formation of these products.
Recombination of carbon monoxide and oxygen atoms
Authors: Hardy J. E. , Gardiner W. C. , Burcat A. 
Published: January 2005

AbstractThe recombination of carbon monoxide and oxygen atoms was studied in reflected shock waves in H2:O2:CO:Ar = 0.1:1:24:75 with 1300 < T5 2200 K and 2 < P5 < 4 atm. Reaction progress was monitored by observations of the carbon monoxide flame spectrum near 435 nm and carbon dioxide thermal emission near 4.2 μm. Data analysis was accomplished with the aid of computer modeling using a 27‐reaction mechanism. Computer modeling experiments also showed that these measurements were sensitive primarily to the rate of the reaction CO + O + M = CO2 + M and only slightly sensitive to the rates of other reactions. The best fit to the data was achieved with a rate constant for this reaction of 7.7 × 10−35 exp[19 kJ/RT] cm6 s for the temperature range of these experiments. Correlation of this result and previous data covering the temperature range 250 < T < 11,000 K confirms that this recombination reaction is governed by a nonadiabatic curve crossing with an activation barrier of about 20 kJ and subsequent deactivation of a singlet CO2 molecule.
Rate constant and activation energy for the gaseous reaction between hydroxyl and formaldehyde
Authors: Smith Roland H. 
Published: January 2005

AbstractThe rate constant k4 has been measured at 268°, 298°, and 334° K for the reaction CH2O + 2OH → CO + 2H2O relative to that for OH + OH (k2) by competition experiments in a discharge flow tube using mass‐spectrometric analysis. Based on k2 = 2.24 × 10−12cm3/molec·sec at 298°K and E2 = 4 kJ/mol, k4 = (6.5 ± 1.5) × 10−12cm3/molec·sec at 298°K and E4 = (6 ± 2)kJ/mol.
The quantum efficiency of the primary processes in formaldehyde photolysis at 3130 Å and 25°C
Authors: Horowitz Abraham , Calvert Jack G. 
Published: January 2005

AbstractThe mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1–12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH2O +hν → H + HCO (1): CH2O +hν → H2+ CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on ΦCOand Φ. The ratio ΦCO/Φwas found to be 1.01 ± 0.09(2σ) and (Φ+ ΦCO)/2 = 1.10 ± 0.08 over the range of pressures and a 12‐fold change in incident light intensity. Isobutene and nitric oxide additions reduced Φto about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on ΦCO. With isobutene addition ΦCO/Φreached a limiting value of 2.3; with NO addition ΦCOexceeded unity. The addition of small amounts of Me3SiH reduced Φto 1.02 ± 0.08 and lowered ΦCOto 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with ϕ2= 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with ϕ1= 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)–(5): H + CH2O → H2+ HCO (3); 2HCO → CH2O + CO (4); 2HCO → H2+ 2CO (5). The data suggestk4/k5≅ 5.8. Isobutene reduced Φby the reaction H +iso‐C4H8→ C4H9(20), and the results givek20/k3≅ 43 ± 4, in good agreement with the ratio of the reported values of the individual constantsk3andk20.
The decomposition kinetics of chemically activated methyl‐d1‐methylsilane‐d2 and ethylsilane‐d3
Authors: Richardson T. H. , Simons J. W. 
Published: January 2005

AbstractThe decomposition kinetics of chemically activated methyl‐d1‐methylsilane‐d2 (DMS‐d) and ethylsilane‐d3 (ES‐d) from the Si‐D and C‐H insertion reactions of CH2 (1A1) with methylsilane‐d3 have been studied. The total rate constants for decomposition of chemically activated DMS‐d3 and ES‐d3 have been measured. The individual rate constants for molecular elimination of CH3D, CH2D2, and D2 from DMS‐d and for molecular elimination of CH3CH2D and D2 from ES‐d have been measured. All of the above rate constants exhibit the expected kinetic isotope effect when compared to those found previously in the undeuterated system. RRKM theory calculations of the rate constants for the expected C‐Si and Si‐D bond rupture processes, based on energetics and activated comple× models deduced previously for the undeuterated system, were carried out. In the case of DMS‐d the RRKM theory calculations of rate constants for the bond rupture processes combined with experimental rate constants for the molecular elimination processes gave a total rate constant for decomposition in agreement with the measured value. The results of a high‐pressure study of the CH3D/CH2D2 ratio from chemically activated DMS‐d3 decomposition were consistent with complete randomization of internal energy up to a pressure of 4 atmospheres (lifetime of ∼1.7 × 10×11 sec). This is not an unexpected result in light of earlier work.
Molecular beam sampling
Authors: Colussi A. J. , Benson S. W. 
Published: January 2005

AbstractBeam attenuation and mass discrimination in effusive and quasieffusive molecular beams of gaseous mixtures have been studied experimentally in an instrument of conventional design, and have been rationalized in terms of transition flow effects and elastic scattering. Their implication in the quantitative monitoring of reacting chemical systems is examined, with particular emphasis in the case of the very‐low‐pressure pyrolysis technique.