bluuebunny/crossref_metadata_2025 huggingface dataset:
A biphasic role of nuclear transcription factor (NF)‐κB in the islet β‐cell apoptosis induced by interleukin (IL)‐1β
Authors: Papaccio Gianpaolo , Graziano Antonio , d'Aquino Riccardo , Valiante Salvatore , Naro Fabio
Published: December 2004

IL‐1β is an important mediator in the pathogenesis of type 1 diabetes both in vivo and in vitro and it has been shown to induce islet β‐cell apoptosis. Most of the IL‐1β effects seem to be mediated by NF‐κB transcription factor activation, but its role in the induction of islet β‐cell apoptosis has not yet been clarified. Taking advantage of the protease inhibitor TPCK (N‐tosyl‐L‐phenylalanine chloromethyl ketone), which specifically inhibits the nuclear transcription factor NF‐κB activation, we studied the role of NF‐κB in the rIL‐1β treated rat pancreatic islets. Our results show that TPCK blocked rIL‐1β‐mediated early increase of MnSOD activity and β‐cell defence/repair protein expression, suggesting a protective role for NF‐κB at the beginning of IL‐1β treatment; but, in a second phase, NF‐κB induces a sustained decrease of specific β‐cell proteins like insulin, GLUT‐2 and PDX‐1 with a concomitant increase of aspecific proteins and iNOS transcription. The appearance of iNOS expression correlates with increased levels of nitrite + nitrate levels and appearance of mitochondrial damage detected either at morphological and biochemical level. After 36 h of IL‐1β treatment islet β‐cells begin to undergo apoptosis. Since IL‐1β induction of apoptosis is completely prevented by TCPK treatment, this finding underscores the central role of NF‐κB in this process. Thus, our results clearly indicate that NF‐κB regulates MnSOD genes expression and MnSOD activity, which protects islet β‐cells by IL‐1β damage. Furthemore, when the IL‐1β stress impairs islet β‐cell function, NF‐κB activation regulates the entrance of islet β‐cell into the cell death program. © 2004 Wiley‐Liss, Inc.
Neuronal modulation of schwann cell glial fibrillary acidic protein (GFAP)
Authors: Mokuno K. , Kamholz J. , Behrman T. , Black C. , Sessa M. , Feinstein D. , Lee V. , Pleasure D.
Published: December 2004

Adult rat sciatic nerves contain cytoskeletal peptides that resemble CNS glial fibrillary acidic protein (GFAP) in immunoreactivity and molecular weight. Immunohistological examination of teased nerve fascicles indicated that these peptides are expressed selectively by Schwann cells related to small axons. Radiolabelled mouse and rat CNS GFAP cDNA probes hybridized with a single, 2.7 kb RNA band in Northern blots prepared from total RNA from both rat sciatic nerve and rat brain. Sciatic nerve GFAP mRNA was detectable by this means in adult, 2 month, or 21 day postnatal rats, but not in 3, 6, or 10 day postnatal rats. Sciatic nerve transection caused a marked reduction in the level of GFAP mRNA in the axotomized distal stump. We conclude that Schwann cell synthesis of GFAP is developmentally regulated and that Schwann cells, unlike astroglia, require continued trophic input from small axons in order to express GFAP.
Gangliosides stimulate synthesis of prostaglandin E2 and prostacyclin in fetal rat brain hemispheres after episodes of global intrauterine ischemia
Authors: Yavin E. , Gil S. , Kunievsky B. , Harel S.
Published: December 2004

The ability of brain preparations from 20‐day‐old rat fetuses to synthesize prostanoids in vitro before and after interruption of the maternal‐fetal blood flow was examined using a radioimmunoassay technique. Synthesis of thromboxane B2(TxB; the stable thromboxane A2 metabolite) decreased with increasing restriction time; conversely, it was elevated with reperfusion. Synthesis of 6‐keto prostaglandin F1α(PGF; the stable prostacyclin metabolite) and prostaglandin E2 (PGE) prostanoids remained unchanged after 20 min restriction and through a 2 hr reperfusion period. Intraperitoneal administration of GM1 (45 mg/kg) into the pregnant rat, 3 hr before restriction, stimulated synthesis of PGE and reduced synthesis of TxB. A prostanoid vasoactive index (PVI), which reflects the relative proportion of the three prostanoids synthesized and asserts the vasoactive potential of the brain tissue, was established. A rise in this value was attained after intrafetal administration into the peritoneal cavity of either GM1, GM3, or isopropyl‐GM1 (AGF44) gangliosides, each given at 40μg dose in 5 μl volume, and N‐dichloroacetyl‐sphingosine (LIGA20; 15μg/5μl) ganglioside analog, 1 hr before restriction. The effect was primarily due to an increase in the capacity of fetal brain tissue to synthesize PGE and, to a lesser extent PGF, vasodilating prostanoids. The N‐methyl‐D‐aspartate (NMDA) receptor blocker MK801 (6.6 μg/μl) and the platelet activating factor (PAF) receptor antagonist BN52021 (0.1μmol/2μl), given by the same route, effectively raised by 60–80% the vasodilating potential of the brain tissue following ischemia. Based on the commonality seen with these chemically diverse anti‐ischemic agents, it is hypothesized that PGE and PGF elevation by gangliosides may be benefical rather than detrimental for the fetal ischemic brain. © 1993 Wiley‐Liss, Inc.
Interaction between CO and O
Authors: Kondratiev V. N. , Intezarova E. I.
Published: January 2005

The reaction between carbon monoxide and atomic oxygen was studied in a gas flow over a temperature range of 136 to 230°C at atmospheric pressure. The rate constant of this reaction, considered to be one for a second‐order reaction, was found to decrease with increasing temperature and to depend on the ratio of O2 to CO that was varied from 0.11 to 2.69. A conclusion was made that under the experimental conditions the reaction was third order
equation image

The rate constant of this reaction
equation image
was determined for a mixture of O2 and CO and it was found that the efficiency of O2 as particle M is four times that of CO.
Hydrogen‐abstraction reactions from organosilicon compounds. The reactions of methyl, trideuteromethyl, trifluoromethyl, and ethyl radicals with tetramethylsilane
Authors: Kerr J. A. , Stephens A. , Young J. C.
Published: January 2005

The following Arrhenius parameters have been determined for the hydrogen‐abstraction reactions:
R + (CH3)4Si → RH + (CH3)3SiCH3

R
Temp. (°K)
E (kcal/mole)
Log A (mole−1 cc sec−1)
Log k(400°K) (mole−1 cc sec−1)

CF3
330–433
7.23 ± 0.09
11.90 ± 0.05
7.95

CH3
396–476
10.23 ± 0.36
11.55 ± 0.18
5.68

CD3
396–496
10.36 ± 0.12
11.84 ± 0.06
6.20

C2H5
423–522
11.40 ± 0.48
11.88 ± 0.22
5.68

The activation energies are in keeping with the strengths of the bonds formed during the reaction. By comparison with the activation energies for the analogous reactions of neopentane it is estimated that D((CH3)3SiCH2H) ≃ 97 kcal/mole.

The A factors for the above series of reactions fall within the range predicted by transition‐state theory for this type of process and the validity of previous results of Kerr, Slater, and Young is seriously in doubt.
Hydrogen abstraction reactions from organosilicon compounds. The reactions of methyl, trifluoromethyl, and ethyl radicals with trichlorosilane
Authors: Kerr J. A. , Stephens A. , Young J. C.
Published: January 2005

Arrhenius parameters have been determined for the hydrogen‐abstraction reactions:
R + SiHCl3 + RH + SiCl3

R
Temp (°K)
E(kcal/mole)
Log A(mole−1 cc sec−1)
Log k(400°K) (mole−1 cc sec−1)

CF3
323–461
5.98 ± 0.06
11.77 ± 0.03
8.50

CH3
333–443
4.30 ± 0.08
10.83 ± 0.04
4.48

C2H5
314–413
5.32 ± 0.07
11.54 ± 0.04
8.63

The trend in activation energies E < E < E is interpreted as indicating a polar effect in the reaction of CF3 with SiHCl3 and the similar reactivities of all three radicals appear to be due to the high exothermicity of the reactions.

The A Factors for the reactions are normal for hydrogen abstraction reactions of free radicals. The previous results of Kerr, Slater, and Young for CH3 abstracting an H atom from SiHCl3 have been amended.
The kinetics and thermochemistry of S2F10 pyrolysis
Authors: Benson Sidney W. , Bott Jerry
Published: January 2005

Data on the kinetics of S2F10 pyrolysis, which gives SF4 + SF6, have been reinterpreted to give a value for the equilibrium constant of S2F10 ⇆ SF4 + SF6. This, together with statistical estimates of the entropy and heat capacity of S2F10, can be used to give for this reaction values of ΔH = 19.7 ± 1.0 kcal/mole and ΔS = 47.6 ± 2 gibbs/mole. ΔH(S2F10) = –494 kcal/mole. A compatible mechanism is shown to be
S2F10 ⇆ 2SF5 (fast); 2SF5 ⇆ SF6 + SF4 (slow)
with step 2 rate‐determining. The overall, best first order rate constant is proposed as kmeas = 1017.42–43.0/θ sec−1 = K1k2, where θ = 2.303RT in kcal/mole.

Independent measurements of δH and S° for the SF5 radical, permits the evaluation of the equilibrium constant K1 = 108.92–(27.1 ± 6)/θ l./mole‐sec and yields k2 = 108.50–15.9/θ l./mole‐sec. The observed homogeneous catalysis by NO and CHCl  CHCl can be explained in terms of a direct abstraction of F from S2F10 : C + S2F10 → CF + S2F9, followed by S2F9 → SF5 + SF4 and SF5 + CF ⇆ SF6 + C (C  NO or C2H2Cl2).
On the thermal decomposition of COS
Authors: Schecker H. G. , Wagner H. Gg.
Published: January 2005

The thermal dissociation of COS was investigated in shock waves with argon as carrier gas. The concentration was varied between 0.05 and 0.5% COS in argon, the total density from 2.5 × 10−5mole/cm3to 2.5 × 10−3mole/cm3. Temperatures between 1500°K and 3100°K were applied.

For the reactionthe rate constant was found to bein the low pressure range of the unimolecular reaction andin the high pressure range.
Rate and mechanism of thermal decomposition of 4‐methyl‐l‐pentyne in a single‐pulse shock tube
Authors: Tsang Wing
Published: January 2005

Dilute mixtures of 4‐methyl‐l‐pentyne have been pyrolyzed in a single‐pulse shock tube. The decomposition process involves bond breaking:

as well as a molecular reaction:

The rate parameters are:

The heat of formation of propynyl radical is thus ΔHf300 = 338 kJ mol−1 (80.7 kcal mol−1)˙ This leads to a propynyl resonance energy of 40 kJ mol−1 (9.6 kcal mol−1).
Reactions of atomic nitrogen and atomic hydrogen with methylacetylene
Authors: Solomon W. C. , Homann K. H. , Warnatz J. H.
Published: January 2005

The reaction of nitrogen atoms with methylacetylene has been studied using a fast‐flow low‐pressure reactor coupled to a mass spctrometer by a nozzle‐beam sampling system. Hydrogen atom concentrations were measured by ESR analysis. Experimental second‐order rate constants for the consumption of N atoms, of C3H4, and for the formation of N2 were determined in the temperature range of 283° to 485°K. Product profiles of all stable species and of hydrogen atoms and methyl radicals were obtained for different initial concentrations of the reactants. Two different reaction pathways can be distinguished: one provides for recombination of N atoms, and the second leads to the formation of cyano compounds and other hydrocarbons. Only the latter process is influenced by the addition of hydrogen atoms. Mechanisms for the two pathways are discussed.
Chlorine‐photosensitized oxidations of chloroethanes and chloroethylenes in the gas phase
Authors: Bertrand L. , Exsteen‐Meyers L. , Franklin J. A. , Huybrechts G. , Olbregts J.
Published: January 2005

Long‐chain chlorine‐photosensitized oxidation has been observed in the gas phase at about 355°K for 1,1,2,2‐ and 1,1,1,2‐C2H2Cl4, C2HCl5, and C2Cl4 but not for C2H6, 1,2‐C2H4Cl2, 1,1,1‐C2H3Cl3, C2H4, and 1,2‐C2H2Cl2. This is shown to depend on the exothermicity of the dissociation of the chloroethoxy radicals which must be involved in each reaction system.
Quenching cross sections for the deactivation of metastable mercury 6 (3P0)
Authors: Campbell J. M. , Penzes S. , Sandhu H. S. , Strausz O. P.
Published: January 2005

By monitoring the relative concentrations of mercury 3P0 atoms using absorption photometry, absolute rate constants have been measured for the excimer‐forming reaction Hg (3P0) + Hg + N2 → Hg2* + N2 and for the quenching of Hg (3P0) atoms by ethane, propane, deuterated propanes, and nitrous oxide.
The pyrolysis of neopentane at small extents of reaction
Authors: Baronnet F. , Dzierzynski M. , Côme G. M. , Martin R. , Niclause M.
Published: January 2005

The pyrolysis of neopentane, at small extents of reaction, was studied by gas chromatography, in Pyrex reaction vessels between 450° and 530°C and in the initial pressure range 25–200 mm Hg. At initial time, this thermal decomposition can be essentially represented by a homogeneous long‐chain radical mechanism. The rate constant of the unimolecular initiation process is approximately given by the expression

The initial rate constant of the global reaction (order 3/2) is nearly equal to

This reaction is strongly inhibited by propene or isobutene and self‐inhibited by the isobutene formed; an interpretation of all these inhibition phenomena of the neopentane pyrolysis is proposed. Our observations and conclusions, which have been summarized in communications during 1968 and 1969, are compared to those of other authors, particularly to the recent ones of Purnell and colleagues [13] and of Taylor and colleagues [14], [15].
Very low‐pressure pyrolysis. IV. The decomposition of i‐propyl iodide and n‐propyl iodide
Authors: King Keith D. , Golden David M. , Spokes G. Neil , Benson Sidney W.
Published: January 2005

The decomposition rate constant of i‐PrI under conditions of very low‐pressure pyrolysis (VLPP) is completely consistent with the well‐known high‐pressure Arrhenius parameters and the RRK(M) theory. The decomposition of n‐PrI under the same conditions proceeds via two pathways, the anti‐Markownikoff dehydroiodination and CI bond scission. The data, analyzed by taking into account the mutual interaction of the two pathways, is completely consistent with the known Arrhenius parameters for the bond scission step and, when combined with a reasonable A‐factor, yields an activation energy for HI elimination which is as predicted for these semi‐ion pair transition states.
Kinetics of the gas phase reaction of methyl benzoate with bromine and iodine: The methoxyl CH bond strength of methyl esters
Authors: Solly Richard K. , Benson Sidney W.
Published: January 2005

The gas phase reactions of PhCOOCH3 with I2 and Br2 were studied spectrophotometrically in a static system over the temperature ranges 344–359° and 246–303°, respectively. For each system the initial rate was first order in PhCOOCH3 and half order in halogen as the concentration of PhCOOCH3 was varied from 1.4 to 15.2 torr, that of I2 from 6.2 to 26.4 torr, and that of Br2 from 3.0 to 13.6 torr. The rate‐determining step is the extraction of a methoxyl hydrogen atom: magnified image Empirical assignment of A‐factors for k1 lead to

for the I2 system, and to

for the Br2 system, where ϕ = 2.303RT in kcal/mole. Combined with the assumption that E–1 = 1 ± 1 kcal/mole and 2 ± 1 kcal/mole for HI and HBr, respectively, DH (PhCOOCH2H) calculated from the two systems shows excellent agreement at 100.2 ± 1.3 kcal/mole and 100.1 ± 1.3 kcal/mole. Using a value of δH (PhCOOMe) = –65.6 ± 1.5 kcal/mole obtained from group additivity estimates, δHf,2980 (PhCOOCH2) is calculated to be –16.7 ± 2.0 kcal/mole. Unimolecular decomposition of the Ph(CO)O°CH2 radical was also observed:

with a rate constant equal to

The abnormally high methoxyl CH bond strength is discussed in relation to the bonding in ethers, alkanes, and esters.
A quantitative study of alkyl radical reactions by kinetic spectroscopy. II. Combination of the methyl radical with the oxygen molecule
Authors: Basco N. , James D. G. L. , James F. C.
Published: January 2005

The kinetics of the reaction

have been studied, using the technique of flash photolysis and kinetic spectroscopy to follow the methyl radical concentration. The order of the reaction lies between 2 and 3 throughout the range of pressure from 25 to 380 torr at 22°C, and the results are consistent with a single reaction sequence:

The limiting values of the third‐order rate coefficients at low pressures are (3.6±0.3) × 1011 1.2 mole−2 sec−1 when M is neopentane, and (0.94 ± 0.03) × 1011 1.2 mole−2 sec−1 when M is nitrogen. The limiting value of the second‐order rate coefficient at high pressures is (3.1 ± 0.3) × 108 1. mole−1 sec−1. The rate constant for the independent second‐order reaction

is shown to be not much greater than 2 × 105 1. mole−1 sec−1, so that this reaction does not complete significantly with the combination reaction.

This new interpretation is contrary to currently accepted views.
The Competitive dehydrohalogenation of 1,1,1‐trifluoro‐2‐chloroethane in reflected shock waves
Authors: Millward G. E. , Tschuikow‐Roux E.
Published: January 2005

The thermal decomposition of 1,1,1‐trifluoro‐2‐chloroethane has been investigated in the single‐pulse shock tube between 1120° and 1300deg;K at total reflected shock pressures from ∼2610 to 3350 torr. Under these conditions, the major reaction is the α,α‐elimination of hydrogen chloride,

with

The decomposition also involves the slower α,β‐elimination of hydrogen fluoride,

with the first‐order rate constant given by

At temperatures above 1270°K, two additional minor products were observed. These were identified as CF2CFCl and CF3CHCl2 and suggest CCl rupture as a third reaction channel leading to complicated kinetics.
The mechanism of thermal dehydrochlorination. Pyrolysis of 1‐Chloro‐1‐fluoroethane and 1‐chloro‐1, 1‐difluoroethane
Authors: Martens G. J. , Godfroid M. , Decelle R. , Verbeyst J.
Published: January 2005

The thermal decompositions of 1‐chloro‐1‐fluoroethane and 1‐chloro‐1,1‐difluorethane at atmospheric pressure have been studied in the temperature range 500–600°C in a flow system. The dehydrochlorinations are homogenous in a carbonaceous reactor and unimolecular. The rate constants are given by

and

The criteria for molecular or chain processes in thermal dehydrochlorinations are discussed.
A study of the bimolecular intersystem crossing reaction induced in the first excited singlet of SO2 by collisions with O2 and other atmospheric gases
Authors: Wampler Fred B. , Calvert Jack G. , Damon Edward K.
Published: January 2005

The relative intensities of phosphorescence of SO2(3B1) molecules have been determined following the optical excitation of SO2(1B1) molecules by a 2662 Å laser pulse. From a kinetic treatment of these measurements, the intersystem crossing ratio, k2b/(k1b + k2b), was determined; SO2(1B1) + M → SO2(3B1) + M (2b); SO2(1B1) + M → SO2 + M (1b). With M = O2, N2, Ar, CO2, and CO, k2b/(k1b + k2b) = 0.030 ± 0.013, 0.034 ± 0.029, 0.025 ± 0.005, 0.052 ± 0.014, and 0.045 ± 0.028, respectively. These data allow a new, more quantitative evaluation of the extent of involvement of the “excess” triplet SO2 in the 3130 Å‐irradiated mixtures of SO2 and CO at high pressures [5, 6]. The new data are also of direct interest in the determination of the theoretical maximum rates of photooxidation of SO2 in the sunlight‐irratiated atmosphere of the earth.
The kinetics reaction of 1‐chloro‐2,3‐epoxypropane with n‐butyl and iso‐butyl alcohols
Authors: Novák Jiří
Published: January 2005

The reactions of 1‐chloro‐2,3‐epoxypropane with n‐butyl and isobutyl alcohols and their 3‐chloro‐2‐hydroxypropyl ethers, respectively, in the presence of boron fluoride diethyl etherate catalyst are of the first order with regard to 1‐chloro‐2,3‐epoxypropane as well as to the catalyst. In the catalyst concentration range of 1.4 to 47.3 mmol/l., the participation of the catalyst in the reaction is incomplete. The mechanism of the reactions resembles SN2 in regard to changes of activation entropy and influence of dielectric constant of the reaction medium upon the reaction rate. The established values of K (the ratio of propagation to initiation rates) are suitable for calculating the compositions of the adducts obtained. The experimentally obtained yields of 3‐chloro‐2‐hydroxypropyl ethers of lower alcohols are compared with those calculated from the kinetically determined values of K.
Analysis of the kinetics of the thermal and chemically activated elimination of HF from 1,1,1‐trifluoroethane: the CC bond dissociation energy and the heat of formation of 1,1,1‐trifluoroethane
Authors: Rodgers Alan S. , Ford W. G. F.
Published: January 2005

The thermal, unimolecular elimination of HF from CH3CF3 was studied by three different groups over the temperature range 1000° to 1800°K. While the reported kinetic parameters varied greatly, it is shown here that these data may be satisfactorily correlated in terms of a four‐center transition state. This correlation results in ΔE = 69.2 kcal/mol, and log (k/s−1) = 14.6 – 72.6/θ. These results may then be combined with the kinetics of the chemically activated elimination of HF from CH3CF3 formed by the recombination of methyl and trifluoromethyl radicals. The data from three different laboratories are shown to be in excellent agreement. These data, combined with extant thermal data, yield as a best value DH(CH3CF3) = 99.6 ± 1.1 kcal/mol. This gives the unexpectedly high value of DH298°(CH3CF3) = 101.2 ± 1.1 kcal/mol. It is suggested that dipoledipole interactions, primarily in CH3CF3, account for this surprisingly strong CC bond dissociation energy. These results also yield δH(CH3CF3; g, 298) = −178.6 ± 1.5 kcal/mol.
The gas‐phase kinetics of the reaction of 1,1,1‐trifluoroethyl iodine with HI: The CI bond dissocation energy in 2,2,2‐trifluoroethyl iodide
Authors: Wu E‐Chung , Rodgers A. S.
Published: January 2005

The kinetics of the gas‐phase reaction of 2,2,2‐trifluoroethyl iodide with hydrogen iodide has been studied over the temperature range of 525°K to 602°K and a tenfold variation in the ratio of CF3CH2I/HI. The experimental results are in good agreement with the expected free radical‐mechanism:

An analysis of the kinetic data yield:

where θ =2.303RT in kcal/mol. If these results are combined with the assumption that E2 = 0 ± 1 kcal/mol, then one obtains DH (CF3CH2I) = 56.3 kcal/mol. This result may be compared with DH(CH3CH2I) = 52.9 kcal/mol and suggests that substitution of three fluorines for hydrogen in the beta position strengthens the CI bond slightly.
Anchimeric assistance in vapor‐phase acetate thermolysis
Authors: Kramer Daniel J. , Smith Grant Gill
Published: January 2005

The occurrence of anchimeric assistance in the vapor‐phase thermolysis of anti‐ and syn‐7‐acetoxy‐7‐methylnorbornene and 7‐acetoxy‐7‐methylnorborane has been investigated. The relative rates of thermolysis were found to be 1.9, 0.87, and 1.0, respectively. The nature of the transition state for ester thermolysis is discussed in light of the small amount of anchimeric assistance found in the thermolysis of the anti‐isomer.
Decomposition of chemically activated ethyltrimethylgermane the arrhenius A‐factors for rupture of group IVA—methyl bonds
Authors: Scott R. L. , Richardson A. E. , Simons J. W. , Hase W. L.
Published: January 2005

The decomposition rate of chemically activated ethyltrimethylgermane from the reaction 1CH2 + (CH3)4Ge, where 1CH2 was produced from diazomethane photolysis at 3660 Å, is 8.6 × 105 sec−1. This result combined with RRKM theory and critical energy estimates yields an Arrhenius A factor of log[A (sec−1)/methyl] = 14.7 ± 0.8 for methyl rupture from germanium.

Log A values for methyl rupture from carbon, silicon, and germanium linearly correlate with the vibrational‐rotational entropies of the corresponding tetramethyls. Extrapolation predicts log[A (sec−1)/methyl] = 14.4 and 14.3 for methyl rupture from tin and lead, respectively.
Pyrolysis of tetrafluorohydrazine
Authors: Corbin Warren , Levy Joseph B.
Published: January 2005

The pyrolysis of tetrafluorohydrazine has been studied from 578 to 791°K. The stoichiometry has been established as

Reaction rates have been measured and the effects of surface area, inert gas pressure, and nitric oxide have been examined. The rate‐determining step proposed is

and the general rate expression obtained for this is
A kinetic study of the reaction of O(3P) with toluene
Authors: Furuyama Shozo , Ebara Nozomu
Published: January 2005

The absolute rate constant of the reaction of O(3P) with toluene was measured by the microwave discharge‐fast‐flow method to obtain kT = 109.7–2.7/2.303RT l./mole·sec at 100–375°C. This was in good agreement with the rate constant calculated from the combination of the relative rate constant obtained by Jones and Cvetanovic with the recently determined absolute rate constants of the reaction of O(3P) + olefins. The extrapolation of the above Arrhenius plot to 27°C was also in good agreement with the absolute value of kT = 4.5 × 107 l./mole·sec determined recently by Atkinson and Pitts at 27°C. The rate constant of the reaction of chlorobenzene with O(3P), obtained at 238°C as 108.3 l./mole·sec by a competitive method, was smaller than kT by a factor of about two at the same temperature.
The very‐low‐pressure pyrolysis (VLPP) of n‐propyl nitrate, tert‐butyl nitrite, and methyl nitrite. Rate constants for some alkoxy radical reactions
Authors: Mendenhall G. David , Golden David M. , Benson Sidney W.
Published: January 2005

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 ΔS1,−10 and ΔS2,−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.
An absolute measurement of the rate constant for t‐butyl radical combination
Authors: Choo K. Y. , Beadle P. C. , Piszkiewicz L. W. , Golden D. M.
Published: January 2005

The rate constant for tert‐butyl radical recombination has been measured near 700°K by the very‐low‐pressure pyrolysis (VLPP) technique and was found to be 108.8±0.3 M−1·sec−1 with neglibible temperature dependence. The thermochemical parameters for tertbutyl radicals were varied within reasonable limits to bring into agreement the data for the decomposition of 2,2,3,3‐tetramethyl butane and the recombination of tert‐butyl radicals. The revised thermochemistry also makes the gas‐phase results and liquid‐phase results compatible.
A kinetic study of the oxidation of α‐hydroxy acids and α‐hydroxy ketones by potassium bromate
Authors: Natarajan R. , Venkatasubramanian N.
Published: January 2005

The oxidation of α‐hydroxy acids and α‐hydroxy ketones by Br(V) follows the rate‐law

However, the former reaction exhibits a second‐order dependence on hydrogen ion concentration while the latter reaction has a third‐order dependence. A mechanism involving a slow formation of a bromate ester of the α‐hydroxy acid followed by a fast decomposition is proposed. A rate‐determining formation of a bromate ester from the conjugate acid of benzoin, followed by a rapid decomposition of the bromate ester, explains the kinetic data for the oxidation of benzoin.
The reactions of ozone with methyl and ethyl nitrites
Authors: Hastie D. R. , Freeman C. G. , McEwan M. J. , Schiff H. I.
Published: January 2005

The reactions of O3 with CH3ONO and C2H5ONO were studied using infrared absorption spectroscopy in a static reactor at temperatures between 298 and 352K. Both reactions followed simple second‐order kinetics forming the corresponding nitrate:

equation image

The rate coefficients are given by

.
The isomerization of cycloheptatriene at high temperatures
Authors: Gaynor Brendan J. , Gilbert Robert G. , King Keith D. , Mackie John C.
Published: January 2005

The isomerization of cycloheptatriene at high temperatures (800–1250°K) has been studied experimentally using a shock tube at high pressures and by very low‐pressure pyrolysis in the intermediate‐pressure region (the first direct use of the latter technique for an isomerization). Rate coefficients obtained are in accord with previous results at lower temperatures. The results are examined theoretically to account for weak‐collision nonequilibrium effects. These corrections are found to be appreciable at the temperatures studied.
Unimolecular decomposition of chemically activated methylallylether
Authors: Ibuki Toshio , Takezaki Yoshimasa
Published: January 2005

The unimolecular decomposition of chemically activated methylallylether (MAE) formed by the cross combination of methoxymethyl and vinyl radicals was studied in the gas phase. The experimentally determined rate constant was found to be 1.11 × 108 sec−1 at 9.6°C for the decomposition of MAE into propene and formaldehyde. The decomposition of MAE via the six‐center retro‐“ene” type transition state is analyzed by using the RRKM unimolecular reaction theory. For the molecular parameter assignments of energized MAE, a model which contains one internal rotational mode is supported, and MAE decomposition is characterized by a tight complex model. The best agreement between experimental and theoretical results was found when a critical energy of 40.1 kcal/mol was used.
The interpretation of relaxation rate measurements made in flow systems
Authors: Davis C. C. , Lewittes M. E.
Published: January 2005

Methods for analyzing reaction rate data obtained from fluorescent decays distorted by flow effects are discussed, with particular reference to the measurement of relaxation rates in flowing mixtures containing reactive species by the laser‐induced fluorescence technique.
Kinetics and mechanisms of the oxidation of sulfur dioxide over titanium dioxide and nickel oxide
Authors: Choi Jae Shi , Kim Keu Hong , Choi Sung Rack
Published: January 2005

The reactions between SO2 and O2 were carried out in the presence of TiO2 and NiO under various partial pressures of SO2 and O2 at temperatures from 240 to 330°C. TiO2 and NiO were pretreated by applying an annealing effect from which the catalysts would have the different activity. The rates are the highest for TiO2 pretreated at high temperature in the region of 400 to 600deg;C in vacuum, 1.21 × 10−4 mmHg. In contrast, the rates are the lowest for NiO pretreated at high temperaturefrom 350 to 550°C. The data have been correlated with 1.4 and first‐order kinetics for TiO2 and NiO, respectively. A reaction mechanism to explain the data was suggested.

The quantities of anionic vacancies in TiO2 surfaces and of positive holes in NiO appeared to be paramount in determining the type of kinetics.
Substituent effects in the gas‐phase eliminations of alpha;‐substituted alkyl chlorides the pyrolyses of 2‐chloro‐3‐methylbutane and pinacolyl chloride
Authors: Chuchani Gabriel , Martin Ignacio , Alonso Miguel E.
Published: January 2005

The gas‐phase pyrolyses of 2‐chloro‐3‐methylbutane and pinacolyl chloride in the temperature range of 345‐390°C and pressure range of 60‐220 mm Hg are homogeneous and unimolecular in a seasoned reaction vessel. The temperature dependence of the rate constants is given by the Arrhenius equations

and

respectively. The Wagner‐Meerwein rearrangement was not observed in these eliminations. Some correlations for the pyrolysis of α‐substituted alkyl chlorides are presented and discussed. These facts are consistent with the heterolytic nature of the cyclic transition state mechanisms for these reactions.
Shock‐tube studies of the reactions of NO2 with NO2, SO2, and CO
Authors: Freund H. , Palmer H. B.
Published: January 2005

The thermal decomposition of NO2 and its atom‐transfer reactions with SO2 and CO have been studied behind incident shock waves using photometric detection methods. From the decomposition study it is possible to obtain information on the rate of the reaction 2NO2 → antisymmetric‐NO3 + NO. The results on the reaction, NO2 + SO2 → NO + SO3 extend the earlier work of Armitage and Cullis to about 2000°K. The reaction with CO [NO2 +] [CO NO + CO2] at shock temperatures is somewhat faster than predicted from available low‐temperature data and provides a modification of the rate‐constant expression that is applicable over a wide temperature range.
Very low‐pressure pyrolysis (VLPP) of 3,3‐dimethylbut‐1‐yne (tert‐butyl acetylene). The heat of formation and stabilization energy of the dimethylpropargyl radical
Authors: King Keith D.
Published: January 2005

The unimolecular decomposition of 3,3‐dimethylbut‐1‐yne has been investigated over the temperature range of 933°‐1182°K using the technique of very low‐pressure pyrolysis (VLPP). The primary process is CC bond fission yielding the resonance stabilized dimethylpropargyl radical. Application of RRKM theory shows that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters given by log (k/sec−1) = (15.8 ± 0.3) ‐ (70.8 ± 1.5)/θ where θ = 2.303RT kcal/mol. The activation energy leads to DH0[(CH3)2C(CCH)CH3] = 70.7 ± 1.5, θH0f((CH3)2ċCCH,g) = 61.5 ± 2.0, and DH0[(CH3)2C(CCH)H] = 81.0 ± 2.3, all in kcal/mol at 298°K. The stabilization energy of the dimethylpropargyl radical has been found to be 11.0±2.5 kcal/mol.
The Kinetics of the thermal oxidation of NO in solid oxygen between 13 and 29 K; direct observation of the reaction of (NO)2 and oxygen
Authors: Smith George R. , Guillory William A.
Published: January 2005

The kinetics of the reaction of cis‐(NO)2 with solid oxygen to form iso‐N2O4 have been studied between 13 and 29 K. The overall reaction is pseudo first order in cis‐(NO)2, and solid oxygen serves both as a reactant and the matrix. The pseudo‐first‐order rate constants are calculated to be k(14N) = 4.25 × 10−2 exp(‐103/RT), and k(15N) = 3.00 × 10−2 exp(‐105/RT) sec−1, based on temperature measurements from a thermocouple junction which may be at most three degrees lower than the actual reacting film. Most significantly, however, 14k/15k = 1.55 at∼13 K. The condensed phase reaction has been compared to that observed in the gas phase, and the extremely small pre‐exponential factors and large isotope effects have been discussed in terms of tunneling corrections and orientational constraints. It is suggested that the form of the crystal plays an integral role in the observed process.
A program system for computer integration of multistep reaction rate equations using the gear integration method
Authors: Stabler Robert N. , Chesick John P.
Published: January 2005

A program system is described for the integration of the rate equations resulting from large systems of elementary reactions. The Gear integration method is used for this problem, which frequently may exhibit stiffness instability when other integration methds are employed. No usage of the quasi‐steady‐state approximation is necessary. Ease in varying the reaction mechanism and simplicity of input structure are coupled with efficient execution and minimal demands for program storage as key features. The input–output structure, method of operation, and implementation are summarized, along with core storage requirements and execution times for trials using an IBM 360/44 computer.
The kinetics of the thermal gas‐phase reaction Br2 + C6F5I → BrI + C6F5Br. An attempt to determine the bond dissociation energy D(C6F5‐I)
Authors: Okafo Ernest N. , Whittle Eric
Published: January 2005

The kinetics of the thermal bromination reaction
equation image
have been studied in the range of 261°–391°C. The observed rate law is compatible with initiation by the step
equation image
for which we obtain

where Θ = 2.303RT cal/mol. Using the above value of E6, we have

This result disagrees with values of D(C6F5‐I) obtained in other ways and we conclude that reaction (3) probably does not involve initiation by reaction (6). Instead, initiation may involve an addition of Br to the ring in C6F5I followed by decomposition of the adduct to give C6F5Br. If correct, this implies that the Arrhenius parameters above refer to the addition reaction rather than to reaction (6).
Thermal decomposition of cyclopentane and related compounds
Authors: Tsang Wing
Published: January 2005

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 ΔHf(trimethylene) ≤ 280 kJ/mol at 300°K.
Radiation‐induced dechlorination of carbon tetrachloride in cyclohexane and n‐hexane mixtures. III. The kinetics of liquid‐phase reactions of trichloromethyl radicals
Authors: Katz M. G. , Baruch G. , Rajbenbach L. A.
Published: January 2005

The kinetics of gamma‐radiation‐induced free‐radical chain reactions in solutions of carbon tetrachloride in mixtures of varying composition of cyclohexane and n‐hexane was investigated in the temperature range of 296°–413°K. Trichloromethyl radicals were produced by the reaction of radiolytically generated alkyl radicals with the solute. The kinetics of the following reactions were studied:
equation image

The following rate expression was obtained:

The error limits are the standard deviation from the least mean‐square Arrhenius plots. The present results, combined with previously measured activation parameters for hydrogen‐atom abstraction from c‐C6H12 and n‐C6H14 by CCl3 radicals relative to CCl3 combination, afford experimental evidence that the decay of trichloromethyl species in alkane solutions is a diffusion‐limited process. The thesis that activation energies of reactions (4) and (5) in the liquid phase are equal to their respective values in the gas phase is confirmed.
Correlation of activation energies of radical–molecule metathesis reactions with enthalpic, polar, and steric parameters
Authors: Katz M. G. , Rajbenbach L. A.
Published: January 2005

It is shown that the activation energies E oF chlorine atom abstraction by cyclohexyl radicals and hydrogen atom abstraction by Cl atoms from polychloroalkanes can be correlated with the bond dissociation energies D and the Taft polar and steric substituent constants σ* and Es by the expression:

where ΔE and ΔD represent the differences between the E and D values of a given substrate and those of a reference compound (CH3 substituted substrate) and α, ρ, and δ are the corresponding correlation coefficients. The use of this expression allows quantitative evaluation of the relative contribution of the various factors affecting the activation energies of these reactions and estimation of related thermochemical data.
Very‐low‐pressure pyrolysis of N‐methyl aniline and N,N‐dimethyl aniline. Enthalpy of formation of the anilino and N‐methyl anilino radicals
Authors: Colussi A. J. , Benson S. W.
Published: January 2005

The kinetics of the thermal unimolecular decompositions of N‐methyl aniline and N,N‐dimethyl aniline into anilino and N‐methyl anilino radicals, respectively, have been studied under very low‐pressure conditions. The enthalpies of formation of both radicals, ΔH°f,298°K(PhṄH,g) = 55.1 and ΔH°f,298°K(PhṄMe,g) = 53.2 kcal/mol, which have been derived from the experimental data, lead to BDE(PhNH‐H) = 86.4 ± 2, BDE[PhN(Me)‐H] = 84.9 ± 2 kcal/mol and to a value of 16.4 kcal/mol for the stabilization energy of the PhNH radical (relative to MeNH). These results are discussed in connection with earlier work. At high temperatures, the anilino radical loses HNC and forms the very stable cyclopentadienyl radical, a decomposition comparable to that of the phenoxy radical.
Chemical actinometry at 147.0 nm
Authors: Powell Gerard R. , Sethi Dhanwant S.
Published: January 2005

Hexafluoroacetone (HFA) and O2 were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O3 in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ϕ and ϕCO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O2 flow rate of 200 ml/min at 1 atm pressure for a 20‐minute photolysis period. For light intensity variations between 1.09 × 1014 and 2.10 × 1015 photons absorbed/sec, the ratio I/IHFA was found to be unity. Calibration with the commonly used N2O actinometer for a ϕ value of 1.41 showed that I/IHFA and I/I are unity. Both HFA and O2 are suitable chemical actinometers at 147.0 nm with ϕCO and ϕ of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O3, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N2O actiometry, wherein N2 separation from other noncondensibles at 77°K is required.
Autooxidation of diethyl hydroxylamine
Authors: Cáceres T. , Lissi E. A. , Sanhueza E.
Published: January 2005

The autooxidation of diethyl hydroxylamine (DEHA) has been studied both in solution and in the gas phase between 0° and 60°C. The results obtained are interpreted in terms of a nonchain free radical mechanism in which reaction (1)
equation image
is the rate‐determining step. This reaction is followed by the reaction of HO2 radicals with DEHA to give hydrogen peroxide. The initial stoichiometry is given by

which implies that the hydrogen peroxide reacts with DEHA to give water and diethyl nitroxide radicals.

The activation energy of reaction (1) is 16.5 ± 2 kcal/mol, leading to a dissociation energy of 69.5 ± 2 kcal for the OH bond in DEHA.

The oxidation of DEHA in the gas phase is nearly ten times slower than that observed in chlorobenzene solution under similar experimental conditions. This result is related to the stabilization of the free radicals produced by the solvent.
Gas‐phase pyrolysis of 2,2,3,3‐tetramethylbutane using a wall‐less reactor
Authors: Taylor Jay E. , Milazzo Thomas S.
Published: January 2005

The pyrolysis of 2,2,3,3‐tetramethylbutane (TMB) has been studied using the wall‐less reactor. Under homogeneous conditions up to 670°C, the activation energy is 43.2 kcal/mol and log A is 10.70. The products are 2‐methylpropene, hydrogen, propene, 2‐methyl‐2‐butene, ethane, ethene, methane, neopentane, and 2,3‐dimethyl‐2‐butene in order of abundance. Addition of toluene, cyclopentadiene, or nitrous oxide to the system increases both the activation energy and the A factor; whereas oxygen decreases both the activation energy and the A factor. Incorporation of stainless‐steel rods to provide surface has only a modest effect upon the rate. In view of this evidence, it appears that the homogeneous pyrolysis of TMB at higher pressures is a chain reaction under the described conditions.
Quenching of *UF6 (A state) by alkanes
Authors: Wampler Fred B. , Rice Walter W. , Oldenborg Richard C.
Published: January 2005

The removal of *UF6 (A state) molecules by selected alkanes has been investigated at 25°C. The following rate constants (units of 1011 l/mol·sec) were evaluated: iso‐C4F10, 0.0432 ± 0.0115; n‐C4F10, 0.0764 ± 0.020; C2F6, 0.0192 ± 0.0052; CH4, 0.0612 ± 0.0061; C2H6, 3.78 ± 0.60; C3H8, 5.08 ± 0.60; n‐C4H10, 5.05 ± 0.78; iso‐C4H10, 4.17 ± 1.15; neo‐C5H12, 6.59 ± 0.93; CF3CH3, 0.0385 ± 0.0056; CF2HCF2H, 0.0729 ± 0.0074; and CF2HCFH2, 0.149 ± 0.015. The perfluoro‐alkane quenching of *UF6 proceeds via a physical mechanism. The other alkane quenching reactions are consistent with a chemical mechanism also contributing in varying degrees which may involve removal of two hydrogens from the alkane.
Shock‐tube study of thermal decomposition of nitric oxide between 2700 and 3500 K
Authors: Koshi Mitsuo , Asaba Tetsuro
Published: January 2005

The decomposition of nitric oxide at temperatures ranging from 2700 to 3500 K was studied by means of the shock tube. The experimental data were reduced by the method described in a preceding paper and explained consistently by a set of the elementary reactions. The rate constant of the initiation reaction 2NO → N2O + O, which was not well known in this temperature range, was deduced precisely. k1 was one order of magnitude lower than that reported previously in similar shock‐tube experiments, and was consistent with results obtained below 2000 K and from the reverse reaction.
The interpretation of pressure‐dependent very‐low‐pressure pyrolysis experiments
Authors: Gilbert Robert G. , Gaynor Brendan J. , King Keith D.
Published: January 2005

Unimolecular rate data from systems such as very‐low‐pressure pyrolysis (steady‐state flow) and static experiments where gas‐gas collisions compete with gas‐wall collisions must be interpreted in terms of reactant inhomogeneity arising from finite diffusion rates, rather than using the usual assumption of a well‐stirred reactor. An integrodifferential equation describing this process is derived, and a numerical variational solution applicable to weak gas‐gas collisions is presented. This gives a powerful method for obtaining collisional energy transfer probabilities from such experiments. Previously reported data (on cyclobutane and cycloheptatriene reactions) are reinterpreted to give conventional values for average energy transfer, replacing the anomalously low collisional efficiencies proposed previously.
Mechanism of catalytic ascorbic acid oxidation system Cu2+–ascorbic acid–O2
Authors: Shtamm E. V. , Purmal A. P. , Skurlatov Yu. I.
Published: January 2005

Analysis is made of reported results on the kinetics and mechanism of ascorbic acid oxidation with oxygen in the presence of cupric ions. The diversities due to methodological reasons are cleared up. A kinetic study of the mechanism of Cu2+ anaerobic reaction with ascorbic acid (DH2) is carried out. The true kinetic regularities of catalytic ascorbic acid oxidation with oxygen are established at 2.7 ≤ pH < 4, 5 × 10−4 ≤ [DH2] ≤ 10−2M, 10−4 ≤ [Cu2+] ≤ 10−3M, and 10−4 ≤ [O2] ≤ 10−3M:

where𝔨1 (25°C) = 0.13 ± 0.01 M−0.5˙sec−1. The activation energy for this reaction is E1 = 22 ± 1 kcal/mol. It is found by means of adding Cu+ acceptors (acetonitrile and allyl alcohol) that the catalytic process is of a chain nature. The Cu+ ion generation at the interaction of the Cu2+ ion with ascorbic acid is the initiation step. The rate of the chain initiation at [Cu2+] ± 10−4M, [DH2] ± 10−2M, 2.5 < pH < 4, is

where𝔨i,1 (25°C) = (1.8 ± 0.3)M−1˙sec−1, Ei,1 = 31 ± 2 kcal/mol. The reaction of the Cu+ ion with O2 is involved in a chain propagation, so that the rate of catalytic ascorbic acid oxidation for the system Cu2+DH2O2 is

where𝔨1 (25°C) = (5 ± 0.5) × 104 M−1˙sec−1. The Cu+ ion and a species interacting with ascorbate are involved to quadratic chain termination. By means of photochemical and flow electron spin resonance methods we obtained data characteristic of the reactivities of ascorbic acid radicals and ruled out their importance for the catalytic chain process. A new type of chain mechanism of catalytic ascorbic acid oxidation with oxygen is proposed:
equation image
.
The kinetics of dimerization of chlorotrifluoroethene
Authors: Atkinson Bernard , Tsiamis Christos
Published: January 2005

Rate constants determined for the thermal dimerization of chlorotrifluoroethene to dichlorohexafluorocyclobutane at 404–672 K have been correlated with previously published results. For the temperature range of 404–800 K,

The dependence of the preexponential factor on temperature corresponds to a value of 17 J/K·mol for the difference in heat capacity (ΔCp±) between the activation complex and the reactant.