bluuebunny/crossref_metadata_2025 huggingface dataset:
The thermal decomposition of azomethane. III. Kinetics of the noninhibited reaction
Authors: Paquin Y. , Forst W.
Published: January 2005

The thermal decomposition of azomethane (A) has been studied in a static system at temperatures between 250° and 320°C and at pressures between 5 and 402 torr, with particular attention to identification of products. Major products, in decreasing order of importance, were nitrogen, methane, ethane, methylethyldiimide, dimethylhydrazone, propane, tetramethylhydrazine, ethylene, methylpropyldiimide, and methylethylhydrazone. Carbon balance at the lowest pressure and highest temperature was 92%, but decreased with increasing pressure and decreasing temperature owing to the formation of a polymer. A fairly simple mechanism accounts reasonably well for a short chain in the decomposition, propagated by the radical CH3N2CH2 (B), and for the five most abundant products, except ethane. It turns out that there is a second source of ethane, arising by C2H5 + A → C2H6 + B; this explains an anomalously high apparent activation energy for the reaction CH3 + A → CH4 + B. Ethyl radicals are also shown to be responsible for the formation of propane, ethylene, methylethylhydrazone, and methylpropyldiimide. The radical B decomposes to CH3 + CH2 + N2, and the methylene radical (probably both singlet and triplet) is shown to yield C2H5 at low pressure and high temperature, and mostly polymer at high pressure and low temperature.
Reactions in the gas and liquid phases: Comparison of kinetic and thermodynamic data
Authors: Patrick C. R.
Published: January 2005

An analysis is made of relationships to be expected between the enthalpies and entropies of reactions carried out in the gas and liquid phases, assuming ideal thermodynamic behavior of the components. The results of the analysis are compared with experimental results reported in the literature. Some discrepancies are noted. These may be the consequence of experimental error or may be due to substantial deviations from thermodynamic ideality. If the latter is commonplace, there will be difficulties in making useful predictions and correlations of thermodynamic and kinetic parameters in the liquid phase.
The mechanism of cooxidation of isobutyraldehyde and octene‐2
Authors: Montorsi G. , Caprara G. , Pregaglia G. , Messina G.
Published: January 2005

The mechanism of isobutyraldehyde‐octene‐2 cooxidation at 20°C has been investigated. The ratio of cis to trans epoxides in the reaction products shows that, at aldehyde concentrations lower than 1.0M, the epoxide is formed mainly by a radical route. The difference in the ΔH of formation of cis and trans epoxides is around 0.8 kcal/mole at 20°. The isobutyraldehyde involved in the radical epoxidation chain has been found almost quantitatively to be isopropylhydroperoxide, which is formed through the decarboxylation of i‐PrCO2· radicals, addition of oxygen, and abstraction of hydrogen atoms from the aldehyde. A rate constant of about 14 M−1 sec−1 at 20° has been determined for the latter reaction. The chain length for the cooxdination reaction decreases from 75 to 20 as the isobutyraldehyde concentration goes from 1.0 to 0.3M. The termination step seems to involve mainly the interaction of two i‐PrO2 · radicals. The cooxidation of octene‐2 with pivalaldehyde follows a similar mechanism, but the chain length is about ten times higher under the same experimental conditions.
Addition of ethyl radicals to carbon monoxide. Kinetic and thermochemical properties of the propionyl radical
Authors: Watkins K. W. , Thompson William W.
Published: January 2005

Azoethane was irradiated in the presence of carbon monoxide in the temperature range of 238 to 378 K. Kinetic parameters for the addition of ethyl radicals to carbon monoxide and for the decomposition of propionyl radicals were determined. The rate constants were found to be log k(cm3 mol−1 sec−1) = 11.19 ‐ 4.8/θ and log k(sec−1) = 12.77 ‐ 14.4/θ, respectively. Estimated thermochemical properties of the propionyl radical are ΔHf0 = ‐10.6 ± 1.0 kcal mol−1, S0 = 77.3 ± 1.0 cal K−1 mol−1, and D(C2H5COH) = 87.4 kcal mol−1.
Photolysis of alkyl iodides at 147.0 nm. The reaction H + CnH2n + 1I → HI + CnH2n + 1
Authors: Rebbert R. E. , Lias S. G. , Ausloos P.
Published: January 2005

The 147 nm (8.4 eV) photolysis of gaseous C2H5I, n‐C3H7I, and sec‐C3H7I was investigated in the presence of and absence of HI. The main overall processes are:

These dissociative processes occur mainly as a result of initial cleavage of the weak CI bond, followed by decomposition of the internally excited alkyl radicals. In all cases, approximately 5‐10% of the alkyl radicals thus formed do not undergo dissociation at pressures around 3‐7 torr. There is also evidence for the elimination of HI as well as CC cleavage in the primary dissociation. The former is indicated by deuterium labeling experiments and the formation of cyclopropane (Φ = 0.04) as a product in the photolysis of n‐C3H7I. Because the processes listed above provide a constant source of H atoms whose quantum yield can be exactly determined, it was feasible to obtain accurate values for ka/kb: magnified image For thermally equilibrated H atoms (300 K), ka/kb is 0.44 ± 0.04, 0.57 ± 0.06, 0.95 ± 0.1, and 0.024 ± 0.01 for C2H5I, n‐C3H7I, sec‐C3H7I, and C2H5Br, respectively.
Mechanism of oxidation of cyclohexanehexol (inositol) by quinquevalent vanadium
Authors: Kumar Ashok , Mehrotra Raj Narain
Published: January 2005

The oxidation of inositol by quinquevalent vandadium in acid medium is a first‐order reaction both in vanadium (V) and inositol. The stoichiometry of the reaction is consistent with the use of two equivalents of vanadium (V) per mole of inositol with the formation of one mole of inosose. The reaction is catalyzed both by sulfuric and perchloric acid, but the rate is faster in sulfuric acid than in perchloric acid. In 1M–6M perchloric acid solutions the reaction has shown a variable order in H+, but in solutions of 2M–5M sulfuric and perchloric acid of constant ionic strength, the rate has a linear dependence on [H+]2. There is also a linear correlation between the rate and bisulfate ions in sulfuric acid at constant hydrogen ion concentration. The energy of activation is found to be 19 kcal/mole and a negative entropy value of − 14 e.u. A suitable mechanism, consistent with the kinetics in 2M–5M acid solutions, is suggested and the values of various rate constants are evaluated.
The kinetics of the reaction between magnesium and EBT
Authors: Koren Ruth , Perlmutter‐Hayman Berta , Shinar Ruth
Published: January 2005

The kinetics of the reaction between Mg2+ and Eriochrome‐Black‐T (EBT) has been investigated in the pH range between 7.05 and 9.0, in the presence of 12% ethanol. The reaction is found to consist of two parallel paths, one involving the tervalent unprotonated ligand, and one its monoprotonated form. The rate constant for the unprotonated ligand has a “normal” value, whereas that for the protonated form is much lower. The numerical value of the rate constant for the unprotonated ligand obtained from results at a magnesium concentration of 10−3M and a pH up to 9.0 is, however, inconsistent with that obtained from results at [Mg2+] = (1 to 4) × 10−3M and pH up to 8.1. This can be explained, at least partially, if we assume the intermediate MgHD to lose its proton not only to H2O, but also to other bases present in the solution.
Solvation of ligandopentaamminecobalt (III) complexes in dimethyl sulfoxide–water mixtures
Authors: Reynolds Warren L. , Barber Elaine S. , Crandall Robin
Published: January 2005

The rate constants for the replacement of water from the inner‐coordination shell of Co(NH3)5OH23+, I, by dimethyl sulfoxide (DMSO) as DMSO gradually replaced water in the solvation shell of I were found to approach, and finally equal, the water‐exchange rate constant of I in aqueous media in accordance with expectation for a dissociative mechanism. Also the rate constants for the replacement of DMSO from the innercoordination shell of Co(NH3)5DMSO3+, II, by water as water replaced DMSO in the solvation shell of II were found to approach, and approximately equal, the DMSO‐exchange rate constant for II in liquid DMSO in accordance with expectation for a dissociative mechanism.

The DMSO‐exchange rate constant for II in liquid DMSO was determined and found to be equal to (3.6 ± 0.8) × 10−4 sec−1 at 45°C.

The dissociation quotient, [II] [NO3−]/[Co(NH3)5NO32+], was found to be equal to 0.28 ± 0.11 M at 45°C by NMR methods. The pseudo first‐order rate constants for anation of II by NO3− and the solvation of Co(NH3)5NO3 2+ by DMSO were determined at various temperatures.
A study of the collisional quenching of O(21D2) by the noble gases employing time‐resolved attenuation of atomic resonance radiation in the vacuum ultraviolet
Authors: Heidner R. F. , Husain D.
Published: January 2005

Electronically excited oxygen atoms O(21D2) have been generated by the pulsed irradiation of ozone in the Hartley‐band continuum and monitored photoelectrically in absorption by time‐resolved attenuation of atomic resonance radiation at λ = 115.2 nm [O(31D2°) → O(21D2)]. Collisional quenching of the excited atom has been investigated for all the noble gases, and the first absolute values for the second‐order deactivation rate constants are reported. The resulting rate data are discussed in terms of a curve‐crossing mechanism based on existing spectroscopic data for the noble gas oxides. The absolute rate constants are compared with previous relative rate data for the deactivation of O(21D2) by the noble gases.
Evaluated and estimated kinetic data for phase reactions of the hydroperoxyl radical
Authors: Lloyd Alan C.
Published: January 2005

Methods are discussed for the production and detection of the hydroperoxyl radical for use in gas phase kinetic studies. Rate constants for gas phase reactions of the hydroperoxyl radical with itself, H2, H2O, CO, NO, SO2, O3, C2H6, C3H8, i‐and n‐C4H10, C2H4, i‐C4H8, HCHO, C2H5CHO, n‐C3H7CHO, Br, O, OH, and H are critically evaluated. Recommended or estimated rate constant expressions with associated error limits are given applicable over specified temperature ranges (normally 300–1000°K). The reactivity of HO2 compared with OH, O, H, F, Cl, Br, CH3, and CH3O is presented in tabular form and the implications for atmospheric chemistry are discussed.
A kinetic study of the reactions of the hydrogen atom with the cyclohexadiene isomers in the gas phase
Authors: Furukawa Kiyoshi , James D. G. L. , Papic M. M.
Published: January 2005

Absolute values of the rate constants for the reaction of hydrogen atoms with cyclic olefins in the gas phase have been measured in a discharge‐flow system under 3.5, 16, and 22 torr Ar at 23°C. The attenuation of hydrogen atom concentration in the reaction tube in the presence of a large excess of olefin was measured with an ESR spectrometer, and the products were analyzed by gas chromatography. Cyclic C6 hydrocarbons were the only significant products obtained when the hydrogen atom concentration was 2.6 × 10−10 mole/1., the olefin concentration was in the range of 9 to 22 × 10−8 mole/1., and the pressure was 16 torr Ar. The values for the rate constants for reaction with cyclohexadiene‐1,3, cyclohexadiene‐1,4, and cyclohexene are, respectively, (9 ± 2) × 108, (12 ± 1) × 108, and (6 ± 1) × 108 l./mole‐sec, and they are not changed significantly by a sixfold change in total pressure. The fraction of the total interaction that proceeds by addition is 84% in the cyclohexadiene‐1,3 system, but only 18% in the cyclohexadiene‐1,4 system, and the cyclohexadienyl radical is therefore the dominant radical species in the latter system. The pattern of interaction between the hydrogen atom and the cyclohexadienyl radical was determined, and comprises 65% of disproportionation, and 13% and 23% of combination to yield cyclohexadiene‐1,3 and cyclohexadiene‐1,4, respectively. These results are consistent with the general patterns of reactivity emerging from studies of the reactions between free radicals and olefins in related systems.
Thermochemical kinetics of nitrogen compounds. V. The unimolecular thermal decomposition of diallylamine in the gas phase
Authors: Egger Kurt W. , Vitins Peter
Published: January 2005

The kinetics of the thermal decomposition of diallylamine to propylene and prop‐2‐enaldimine have been studied in the gas phase in presence of an excess of methylamine over the temperature range of 532.7 to 615.6°K, using a static reaction system. Methylamine reacted with the unstable primary product prop‐2‐enaldimine, forming the thermally stable N‐methyl prop‐2‐enaldimine.

First‐order rate constants, based on the internal standard technique, fit the Arrhenius relationship log k(s−1) = (11.04 ± 0.13) − (37.11 ± 0.33 kcal/mole)/2.303 RT. They were independent on the initial total pressure (46–340 torr), the initial pressure of diallylamine (9.2–65 torr), or methylamine as well as the conversion attained. Despite an apparent surface sensitivity, the reaction is essentially homogeneous in nature as demonstrated by experiments carried out in a packed reaction vessel.

The observed activation parameters for the title reaction together with those observed earlier for triallylamine and allylcyclohexylamine are consistent with the proposed concerted reaction mechanism involving a cyclic 6‐center transition state. The observed substituent effects suggest a nonsynchronous mode of bond breaking and bond formation.
Reaction between ozone and allene in the gas phase
Authors: Toby Frina S. , Toby Sidney
Published: January 2005

The kinetics of the reaction between ozone and allene (A) were studied in the range of 226 to 325°K in the gas phase. Initial O3 pressures varied from 0.01 to 0.7 torr and allene pressures varied from 0.05 to 6 torr. At the higher initial O3 pressures the most important product was O2 followed by CO, H2O, CO2, and C2H4. Oxygen balances averaging about 110% were obtained, which implies that no important oxygenated products were missed. However, carbon balances were only about 50% and hydrogen balances were even less, so that unidentified hydrocarbons were presumably formed. The rate law found was − d[O3]/dt = k1[O3][A] + k2a[O3]2[A]/[O3]0 where log k1(M−1sec−1) = 6.0 ± 0.7 − (5500±1000)/2.30RT and log k2a(M−1sec−1) = 6.9 ± 0.7 − (6200 ± 800/2.30RT). A mechanism is proposed which accounts for the rate law and the observed stoichiometry of O2 formed–O3 used. This involves a heterogeneous catalyzed decomposition of O3. The rate constant k1 is identified with the primary addition reaction A + O3 → AO3, and this rate constant is compared with those from other O3 addition reactions.
The kinetics of nucleophilic substitution processes in the alkyl halides. Part B—analysis of experimental data
Authors: German E. D. , Dogonadze R. R.
Published: January 2005

Nucleophilic substitution reactions in the alkyl halides, RX + Y− → RY + X−, proceeding in polar media are considered on the basis of the theory presented in Part A. It is shown that the solvent reorganization energy is the main part of the activation energy for this processes. According to calculations performed, the values of the solvent reorganization energy equal ∼2.5–3 eV for H2O and ∼ 1.8–2.3 eV for acetone. From experimental data on the kinetic isotope effect, an estimate for the splitting of nonadiabatic terms and for the slope of the potential curve v′ of the intermolecular interaction between halide ion and methyl halide near transition configuration is made. Further, the parameter v′ is used for calculating the activation entropy of substitution reactions in the methyl halides. Theoretical activation energies and activation entropies agree with experimental values. In the framework of theory presented an interpretation of change of Ea and the preexponential factor with the type of alkyl halide is given.
The reaction of cyclohexyl radicals with carbon tetrachloride
Authors: Currie Jim , Sidebottom Howard , Tedder John
Published: January 2005

The photolysis of azocyclohexane, carbon tetrachloride, and cyclohexane at 360 nm has been investigated over a wide temperature range. At moderate temperatures a chain reaction ensues from which the following approximate rate constants could be determined assuming 2CCl3. → C2Cl6, k5 = 109.7 (303–673K):

equation image

The really striking feature of the results is that they show that termination in bicyclohexyl [reaction (7)] is extremely slow:

equation image

The root‐mean‐square rule for estimating the cross‐combination rate

equation image

is also followed.

The photolysis of carbon tetrachloride and cyclohexane at 250 nm has also been investigated. The reaction is complicated by the occurrence of two concurrent photolytic processes, the main one yielding trichloromethyl radicals and chlorine atoms, and the subsidiary one yielding dichlorocarbene and molecular chlorine. Nonetheless the results from this reaction can be interpreted in the medium temperature range 360–430K, where long chains are present, in terms of the rate constants derived from the azocyclohexane system.
The decomposition of acetylenedicarboxylic acid in acetophenone
Authors: Hsu A. M. , Huang Thomas T.‐S.
Published: January 2005

The decomposition of acetylenedicarboxylic acid in acetophenone was studied in the temperature range of 100–130°C. The rate constants and activation parameters for the consecutive pair of first‐order steps (each yielding carbon dioxide) were calculated. Hydrogen kinetic isotope effects were also studied. Comparisons were made with the decompositions of oxalic acid and malonic acid. An intramolecular HC transfer is believed to be the main part of the reaction coordinate in addition to the CC bond breaking.
The unimolecular decomposition of vibrationally excited 1‐deuterio‐1,1,2‐trifluoroethane
Authors: Follmer D. W. , Pritchard G. O.
Published: January 2005

A study has been made of the unimolecular decomposition of the vibrationally excited molecule CF2DCFH2*, formed from the combination of CF2D and CFH2 radicals. The α,β‐elimination channels lead to the products cis‐ and trans‐CFDCFH and CF2CH2 and H(D)F. The α,α‐elimination channel produces cis and trans‐CFHCFH and DF. The pressure dependencies of the various isomer ratios have been examined. For the α,α elimination the energy partitioning pattern is such that subsequent isomerization of the olefin product can occur. This, and previous work on CDCl2CH2Cl*, clearly show that the energy partitioning in α,α and α,β eliminations is very different. It is tentatively concluded that HF (from the CFH2 group) and HD eliminations also take place.
Photochemically induced reaction between perfluoroacetone and ethane
Authors: Gordon Alvin S. , Norris William P. , Knipe R. H. , Johnson Joseph H.
Published: January 2005

The gas‐phase photolysis of perfluoroacetone in the presence of ethane has been shown to result in the production of significant amounts of 1, 1‐bis(trifluoromethyl)propanol‐1, (CF3)2(C2H5)COH, and 1, 1, 4, 4‐tetrakis(trifluoromethyl)butane‐1, 4‐diol, (CF3)2C(OH)‐CH2CH2C(OH)(CF3)2. A mechanism is presented which accounts for the relative rates of formation of these products at room temperature.
Kinetics and mechanisms of substitution reactions with sulfur‐containing nucleophiles in aqueous acid solutions. I—rates of reactions of some tetrahalopalladate (II) anions with thiourea and selenourea
Authors: Van Z. Bekker P. , Robb W.
Published: January 2005

The activation energy parameters for the reaction of PdX (X=Cl−, Br−) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to kobs=k[L] where L=tu or seu, and only ligand‐dependent rate constants are observed at 25°C. The ligand‐dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 103 M−1 sec−1 and (4.5±0.1) × 104 M−1 sec−1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 104 M−1 sec−1 and (9.0±0.1) × 104 M−1 sec−1 for X=tu and seu, respectively.
Excited state kinetics and stern‐Volmer quenching plots in the photolysis of azoisopropane at 366 nm
Authors: Pritchard G. O. , Servedio F. M.
Published: January 2005

The photochemistry of azoisopropane is reinvestigated at 366 nm over an extended pressure range by using n‐butane as an added bath gas, and over a range of temperature from 277° to 180°C. The Stern‐Volmer type plot of the N2 product quantum yield is interpreted in terms of the decomposition of the vibrationally excited upper singlet and triplet states, with the onset of the dissociation of the vibrationally equilibrated triplet state as the temperature is increased. The energy barrier for the dissociation of the vibrationally equilibrated first triplet state is found to be 8.8 kcal/mole. Triplet sensitization experiments with biacetyl correlate with our observations, and it is suggested that the proposed mechanism is generally applicable to the photodissociation of acyclic azoalkanes at 366 nm, based on a comparison of our data with those of Wu and Rice on hexafluoroazomethane.
Abstraction of chlorine atoms from chloromethanes by the cyclohexyl radical
Authors: Katz M. G. , Horowitz A. , Rajbenbach L. A.
Published: January 2005

The kinetics of chlorine atom abstraction from the chloromethanes (CM)CCl4, CHCl3, and CH2Cl2 by radiolytically generated cyclohexyl radicals has been studied in the liquid phase by a competitive method. The halogen abstraction data have been 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:

CM
log A(CM)/A(C2Cl4)
E(CM)E(C2Cl4)(kcal/mole)
log A(CM)(1./mole·sec)
E(CM) (kcal/mole)
Temperaure Range(°K)

CCl4
0.72±0.02
−1.42±0.05
9.40±0.08
5.88±0.15
333–453

CHCl3
0.77±0.06
2.86±0.01
9.45±0.12
10.16±0.11
392–492

CH2Cl2
0.56±0.12
6.37±0.27
9.42±0.18
13.67 ± 0.37
463–543

The error limits are the standard deviations from least mean square Arrhenius plots.

The possible application of the Evans–Polanyi relationship to chlorine atom abstraction reaction from CM is considered.
Excited state kinetics of the π*←n photochemistry of hexafluoroacetone
Authors: Servedio Frank M. , Pritchard G. O.
Published: January 2005

The π*←n excited state kinetics of hexafluoroacetone are reinvestigated in the presence of a vibrational relaxer and sufficient triplet state quencher so that only the reactions of the electronically excited upper singlet state are examined. From a Stern–Volmer type analysis it is concluded that vibrational relaxation of the initially formed vibrationally and electronically excited upper singlet state is via a multistage collisional mechanism. An activation energy of about 6 kcal/mole is reported for the unimolecular decomposition of the upper singlet state.
Kinetic demonstration of the intramolecular nature of the rearrangement of aromaticN‐nitroso‐amines (Fischer‐Hepp)
Authors: Williams D. L. H.
Published: January 2005

Rate equations have been deduced for two possible mechanisms for the reactions ofN‐methyl‐N‐nitrosoaniline in acid solution, namely, (1) for the generally acceptedintermolecularmechanism which involves denitrosation followed byC‐nitrosation and (2) a mechanism involvingintramolecularrearrangement which takes place concurrently with denitrosation. The observed rate constants obtained under various experimental conditions are consistent only with mechanism (2). In particular the question of halide ion catalysis differentiates clearly between the two mechanisms. Mechanism (1) predicts a first‐order dependence upon chloride (or other halide) ion under all conditions, whereas (2) allows a first‐order chloride ion dependence only in the presence of a large excess of a “nitrite trap” such as sulphamic acid, urea, hydrazoic acid, hydroxylamine, etc., whereas at the other limit of high concentration of addedN‐methylaniline, the rate constants should be independent of the halide ion concentration. The predictions based on mechanism (2) are all borne out by experiment.
Decarbonylation of complex iridium carbonyls in solution: A problem in chemical dynamics
Authors: D'Agostino Riccardo , Gerardi Sergio , Molinari Ettore
Published: January 2005

The kinetics of decarbonylation of [Ir(CO)(dp)2]Cl and [IrCl(CO)2(Ph3P)2] has been studied in different solvents, at temperatures between −25° and +70°C, by means of reactors of defined fluid dynamics which allow a separation to be made between “physical” and “chemical” rate constants. Chemical rate constants have been found to depend markedly on the diffusion coefficients of carbon monoxide in the various solvents. The process of decarbonylation has been described, for both reactions, by the sequence: structural isomerization, characterized by a very low preexponential factor, decomposition of the less stable isomer against the solvent's barrier, and diffusion of carbon monoxide to the gas–liquid interface. The kinetic problems involved in the determination of rate constants and their implications have been emphasized.
Thermal hydrocracking of indan. Effects of the hydrogen pressure on thekinetics and Arrhenius parameters
Authors: Van Boven M. , Roskam G. J. , Penninger J. M. L.
Published: January 2005

The kinetics of the thermal hydrocracking of indan were investigatedin a high‐pressure flow reactor at temperatures from 470 to 530°C, total pressures of up to 300 atm, and molar ratios from 3 to 40. The effect of the hydrogen pressure was reflected especially in a change of the experimental rate equations for the formation of toluene from rT=k [indan]0.5 [hydrogen] to rT=k′ [indan] 0.75[hydrogen]0.75 with hydrogen partial pressureincreasing from 73 to 230 atm. The rate equation of n‐propylbenzene remained constant at rPr=k″ [indan] [hydrogen]1.5. Simultaneously the Arrheniusparameters of toluene changed significantly, while those of n‐propylbenzene remained unchanged.

The observed effect of the hydrogen pressure is explained as a change inthe rates of the intermediate reactions; it provides an excellent agreementbetween the theoretical and experimental data. It was found that the steady‐state concentration of the hydrogen atoms, which act as chain carriers in the thermal hydrocracking, was much smaller than the thermodynamic equilibrium concentrations
Mechanistic details of the Belousov–Zhabotinskii oscillations
Authors: Edelson D. , Field R. J. , Noyes R. M.
Published: January 2005

A detailed chemical mechanism for the cerium catalyzed bromination and oxidation of malonic acid by bromate has been developed, and complete numerical solutions have been obtained for the temporal behavior of the concentrations of the intermediate species. The many points of similarity with the experimentally observed initial decay, long quiescence, and abrupt transition to sustained oscillation establish confidence in the essential validity of the proposed mechanism. Close examination of the time dependence of these species concentrations as well as the magnitude of the several reaction channels permits the clarification of the switching mechanism causing theoscillatory behavior of this system. The results appear to exhibit limit cycle behavior, in accordance with theoretical predictions.
Reaction rates for nucleophiles with cyanogen chloride: Comparison with two other digonal carbon compounds
Authors: Edwards John O. , Erstfeld Thomas E. , Ibne‐Rasa Khairat M. , Levey Gerrit , Moyer Maria
Published: January 2005

The hydrolysis kinetics of CICN have been reinvestigated from pH 0.0–10.5 and from 18–40°C. In the pH range from 1–5, the hydrolysis rate is invariant and the activation parameters (ΔH‡ = 84 kJ mol−1 and ΔS‡ = −84 J mol−1 K−1) are consistent with water attack. In basic solution the rate is first order each in CICN and OH− concentrations with parameters ΔH‡ and ΔS‡ equal to 82 kJ mol−1 and + 54 J mol−1 K−1, respectively. The rate constants with 20 other donors have been measured. Nitrogen nucleophiles are more reactive than oxygen donors, and an alpha‐effect is seen. The constants follow a pattern indicative of attack at carbon. Cyanate in its acid form reacts with nucleophiles. Further points on the cyanate rate–pH profile have been obtained. A chromate‐catalyzed hydrolysis can contribute between pH 5–10. Some studies were made of the reaction of cyanate with hydrogen peroxide. Free energy correlations are presented.
Effects of olefins on the thermal decomposition of propane part III. Some remarks on the kinetics of decomposition
Authors: Dombi A. , Horváth I. , Huhn P.
Published: January 2005

Conditions of applicability of quasi‐steady‐state kinetic treatment have been investigated with respect to the explanation of the decomposition of propane and the influence of ethylene on this.

From the measured rate of accumulation of ethane and from the relations between the kinetic equations describing product formation, the rate parameters of the initiation reactions
equation image
were determined, for which the temperature‐dependences

and

were found.

In the decomposition of propane under the examined conditions, the chain length exceeds 500. In response to ethylene the chain length significantly decreases, but even in this case the decomposition chains are long enough for it to be assumed that the ratios of radical concentrations are governed by the propagation steps.

Calculations demonstrated that the actual radical concentration during a sufficiently short induction period approximates to the stationary concentration, so that it does not seriously affect the accuracy of the kinetic treatment.
Rate constants for the gas‐phase reactions of the OH radical with a series of monoterpenes at 294 ± 1 K
Authors: Atkinson Roger , Aschmann Sara M. , Pitts James N.
Published: January 2005

Using a relative rate technique, rate constants for the gas‐phase reactions of the OH radical with a series of monoterpenes have been determined in one atmosphere of air at 294 ± 1 K. Relative to a rate constant for the reaction of OH radicals with 2,3‐dimethyl‐2‐butene of 1.12 × 10−10 cm3 molecule−1 sec−1, the rate constants obtained were (in units of 10−11 cm3 molecule−1 sec−1): α‐Pinene, 5.45 ± 0.32; β‐pinene, 7.95 ± 0.52; Δ3‐carene, 8.70 ± 0.43; d‐limonene, 16.9 ± 0.5; α‐terpinene, 36.0 ± 4.0; γ‐terpinene, 17.6 ± 1.8; α‐phellandrene, 31.0 ± 7.1; myrcene, 21.3 ± 1.6; and ocimene (acis‐, trans‐mixture), 25.0 ± 1.9. These are the first quantitative kinetic data reported for many of these monoterpenes. The rate constants obtained are compared with the available literature data and with a priori estimates based on the number and configuration of substituents around the double bond(s). The tropospheric lifetimes of these monoterpenes with OH radicals, NO3 radicals and O3 are estimated and compared. Atmospheric lifetimes with respect to reaction with the OH radical are calculated to range from ∼0.75 hr for α‐terpinene to ∼5 hr for α‐pinene.
Effects of Olefins on the Thermal Decomposition of Propane Part IV. Influence of Propylene
Authors: Dombi A. , Huhn P.
Published: January 2005

On the basis of the thermal decomposition of mixtures of propylene and propane with molar ratios of 0.0–0.33 in the temperature range 779–812K, the influencing functions describing the inhibition by propylene of the decomposition of propane were determined. The rate‐reducing effect is explained mainly by the reactions

(in which .R = .H, .CH3 and 2‐Ċ3H7) and also by the addition reactions

It was established that the bulk of the allyl radicals formed

participate in the chain step, but, due to their lower reactivity, they restore the decomposition chain more slowly than the original radicals do.

From the characteristic change in the ratio υ/υ, the rate ratios of hydrogenabstraction reaction by radicals from propylene and propane could be determined. In these reactions there was no significant difference between the selectivities of the radicals. For an interpretation of the changes, the decomposition mechanism must be completed with the reaction

Evaluation of the influencing curves revealed that the initiation reactions

must be taken into account.

By parameter estimation we have determined the rate ratios characterizing the above initiation reactions, the unimolecular decomposition of propane, hydrogen abstraction by radicals from propane and propylene, intermolecular isomerization of the 2‐propyl radical via propane and propylene, and abstraction of propane hydrogens by the ethyl and methyl radicals; these are given in Tables II.
Gas phase decomposition and isomerization reactions of 2‐pentoxy radicals
Authors: Dóbé S. , Bérces T. , Márta F.
Published: January 2005

The rate of decomposition of 2‐pentoxy radical to acetaldehyde and n‐propyl radical has been studied in the presence of NO in competition with nitrite formation at and above 200 kPa pressure over the temperature range of 363‐413 K. The rate coefficient for the decomposition is given as log(kla/s−1) = (14.2 ± 0.4) ‐ (13.8 ± 0.8) kcal mol−1/RT ln 10. Isomerization of 2‐pentoxy radical by 1,5‐hydrogen shift has been investigated in the range 279–385 K in competition with the decomposition in a static system, with methyl radicals present in high concentration to ensure trapping of the isomerized free radicals. The rate coefficient for isomerization is given as log(k3/s−1) = (11.1 ± 0.7) ‐ (9.5 ± 1.1) kcal mol−1/RT ln 10. The implications of the results for atmospheric chemistry are discussed.
Competing Channels in Infrared Multiple Photon Decomposition
Authors: Moylan Christopher R. , Brauman John I.
Published: January 2005

Infrared multiple photon decompositions (IRMPD) with more than one reactive pathway can provide significantly more kinetic information than can single‐channel photolyses. The rates of the competing unimolecular reactions and the rate of photon absorption are interrelated, so that knowledge of one yields information about the others. The goals and pitfalls of IRMPD experiments on several well‐studied classes of reactants are reviewed.
Measurement of the reactivity of OH with methyl nitrate: Implications for prediction of alkyl nitrate‐OH reaction rates
Authors: Gaffney J. S. , Fajer R. , Senum G. I. , Lee J. H.
Published: January 2005

The rate of the gas phase reaction of hydroxyl radical with methyl nitrate has been measured to be (3.4 ± 0.4) × 10−14 cm3 molecule−1 s−1 at 298 K using flow discharge/ resonance fluorescence techniques. By means of correlation methods, this rate determination is used to predict a vertical ionization potential of 12.6 eV, a bond dissociation energy for HCH2ONO2 of 101 kcal mol−1, and a rate for O(3P) reaction with methyl nitrate of ca. 9 × 10−17 cm3 molecule−1 s−1. In conjunction with previously derived relative data for reaction of alkyl nitrates with OH radical in the gas phase, a priori estimated reactivities for 1‐, 2‐, and 3‐positionally substituted straight chain alkyl nitrates have been reexamined. Revised reactivities for OH abstraction of specific hydrogens substituted on straight chain alkyl nitrates are presented and discussed, and an atmospheric lifetime of ca. 2 yrs is estimated for methyl nitrate removal due to OH.
Theory of fast multiple bond‐switching reactions: NO + NH2
Authors: Gilbert Robert G. , Whyte Andrew R. , Phillips Leon F.
Published: January 2005

A theoretical treatment is given for fast, multiple bond‐switching reactions, such as NO + NH2 → N2 + H2O. These reactions are characterized by all or most of the bonds being broken. The collision complex involved (whether long or short lived) is shown to be extremely anharmonic. Consideration of the master equation describing the competing processes of complex formation, internal rearrangement and collisional deactivation yields easily applied sufficient conditions for the recombination rate coefficient being independent of pressure.
On the rates of decarbonylation of hydroxyacetyl and other acyl radicals
Authors: Vollenweider J. ‐K. , Paul H.
Published: January 2005

The rate of decarbonylation of the hydroxyacetyl radical in acetonitrile is measured by effect modulated ESR spectroscopy and found to be log (KD/s−1) = (11.0 ± 1.5)–(2.3RT)−1 (37 ± 8)kJ/mol. The result is shown to be reasonably well connected with a variety of decarbonylation data known for other acyl species by asimple Evans‐Polanyi relation.
The chromatographic retention of H and D atoms on quartz
Authors: Blyth Graham , Clifford Anthony A. , Gray Peter , Waddicor John I.
Published: January 2005

The chromatographic retention of H and D atoms has been observed in a quartz tube using argon as a carrier gas for D and six different gases for H. The results give equilibrium constants for the reversible adsorption of H and D on quartz as well as the rates of desorption. Self‐consistent conclusions can be drawn from the data. The adsorption energy appears to be ca. 50 kJ mol−1 indicating weak chemisorption. The observations are consistent with vibration frequencies on the surface of around 700–900 cm−1 for D. and around 1000–1300 cm−1 for H. It appears that only a fraction of the surface atoms (ca. 10−2) act as adsorption sites.
Measurements of the bimolecular rate constants for S + O2→ SO + O and CS2+ O2→ CS + SO2at high temperatures
Authors: Saito Ko , Ueda Yuji , Ito Reiko , Kakumoto Terumitsu , Imamura Akira
Published: January 2005

The bimolecular reactions in the title were measured behind shock waves by monitoring the O‐atom production in COSO2Ar and CS2O2Ar mixtures over the temperature range between 1400 and 2200 K. A value of the rate constant for S + O2→ SO + O was evaluated to be (3.8 ± 0.7) × 1012cm3mol−1s−1between 1900 and 2200 K. This was connected with the data at lower temperatures to give an expressionk2= 1010.85T0.52cm3mol−1s−1between 250 and 2200 K. An expression of the rate constant for CS2+ O2→ CS + SO2was obtained to bek21= 1012.0exp(−32 kcal mol−1/RT) cm3mol−1s−1with an error factor of 2 between 1500 and 2100 K.
Light‐emitting copolymers based on fluorene and selenophene—Comparative studies with its sulfur analogue: Poly(fluorene‐co‐thiophene)
Authors: Yang Renqiang , Tian Renyu , Hou Qiong , Zhang Yong , Li Yongfang , Yang Wei , Zhang Chi , Cao Yong
Published: January 2005

A series of soluble conjugated copolymers derived from 9,9‐dioctylfluorene (FO) and selenophene (SeH) was synthesized by a palladium‐catalyzed Suzuki coupling reaction with various feed ratios of SeH to FO less than or equal to 50%. The efficient energy transfer from fluorene segments to narrow band‐gap selenophene sites was observed. In comparison with the very well studied copolymer poly(fluorene‐co‐thiophene), poly(9,9‐dioctylfluorene‐co‐selenophene) (PFO‐SeH) shows redshifted photoluminescence (PL) and electroluminescence (EL) emission. PL spectra of the PFO‐SeH copolymers show a significant redshift along with increasing selenophene content in the copolymers and also with increasing polymer concentration in solution. PL quantum efficiency of the selenophene‐containing PFO copolymer is much lower than that of corresponding PFO‐thiophene (Th) copolymers. All these features of PFO‐SeH copolymers can be explained by the difference in aromaticity of selenophene and thiophene heterocycles and the heavy atom effect of Se in comparison with S‐atoms. The device fabricated with PFO‐SeH15 as the emissive layer exhibited high external quantum efficiency (0.51%) at a luminance of 1570 cd/m2. Device performance is limited by electron injection and the strong quenching effect of Se atoms. Devices with PFO‐SeH copolymers blended into PFO homopolymers show significant improvement in device performance. External quantum efficiency as high as 1.7% can be obtained for PFO‐SeH30/PFO blend devices. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 823–836, 2005
Randomized trial of continuous positive airways pressure to prevent reventilation in preterm infants
Authors: Peake M. , Dillon P. , Shaw N.J.
Published: January 2005

A prospective randomized controlled trial was performed comparing the use of a short period (24 hr) of postextubation nasal continuous positive airways pressure (CPAP) with direct extubation into headbox oxygen on the outcome of the need for reintubation within 7 days of initial extubation. Infants at less than 32 weeks of gestation who had received mechanical ventilation in the first 28 postnatal days and were being extubated for the first time were recruited. Ninety‐seven babies were entered into the study (48 CPAP and 49 headbox oxygen). Twenty‐four (49%) babies in the headbox group were reventilated within a week, compared to 16 (33%) in the CPAP group (P = 0.17). By 14 days after initial extubation, 25 babies (51%) in the headbox group and 23 (48%) in the CPAP group required reventilation (P = 0.9). There was a trend toward babies in the CPAP group requiring fewer reintubations (median, 2; range, 1–6) compared to those in the headbox group (median, 3; range, 1–7) (P = 0.063). There was no significant difference between groups with respect to total number of days of ventilation (headbox median, 4; range, 1–24; CPAP median, 2; range, 1–20). In conclusion, this study showed that a short period of nasal CPAP is not associated with a reduction in reventilation. Pediatr Pulmonol. 2005; 39:247–250. © 2005 Wiley‐Liss, Inc.
Untersuchungen über Silicate. III. Die Hydrolyse der Natriumsilicate
Authors: Hägg Gunnar
Published: January 2005

Durch elektrometrische Messungen der Hydroxylionenkonzentration, sowie Messungen der Gefrierpunktserniedrigung von Natriumsilicatlösungen ist folgendes gezeigt worden:

Die einzigen Natriumsilicate, die in wäßriger Lösung existieren, sind das Metasilicat Na2SiO3 und das Disilicat NaHiO3. Alle anderen Natriumsilicatlösungen enthalten, in der Reihe ihrer Acidität aufgerechnet, Mischungen von x Na2SiO3 + yNaOH, xNa2SiO3 + yNaHSiO3 oder NaHSiO3 + kolloidale Kieselsäure.
Über das bei der Einwirkung von Chlorwasserstoffgas auf Bromkalium entstehende Gleichgewicht: KBr+HCl ⇄ KCl+HBr
Authors: Jellinek K. , Itelsohn R.
Published: January 2005

Die Reaktion:

wird auf ihre Gleichgewichte zwischen 500 und 800° untersucht. Der Bodenkörper besteht aus einer lückenlosen Reihe von Mischkristallen KC1 + KBr oder einer homogenen Schmelze von KBr + KC1. Die Zusammensetzung der Gasphase wird in Abhängigkeit von der Zusammensetzung des Bodenkörpers und von der Temperatur diskutiert. Die Wärmetönung der Reaktion ergibt sich von der nach thermochemischen Daten zu erwartenden Größenordnung.
Über den Nachweis kleiner Mengen Silber und Cadmium
Authors: Geilmann W.
Published: January 2005

1. Den Nachweis von Silber in Erzen kann man ohne besondere Übung sehr sicher und schnell führen, wenn die Methoden der quantitativen Lötrohranalyse zur Silberbestimmung mit mikrochemischen Reaktionen vereinigt werden. Bei Einwagen von 0,1 bie 0,2 g Erz lassen sich noch 0,005% Silber erkennen.
Über der Zersetzung der Ammoniumdoppelfluoride der Elemente der Titangruppe
Authors: Hartmann S.
Published: January 2005

Eine Untersuchung der Spaltbarkeit der Ammoniumhexafluoride des Titans, Zirkoniums und Hafniums beim Erwärmen im Stickstoffstrom ergab, daß sich die Hafniumverbindung etwas leichter ale die Zirkonverbindung spaltet, während die Spaltbarkeit des Titansalzes zwischen den der zwei zuerst erwähnten Salzen liegt. Beim Titansalz beginnt von 150° an außer dem NH4F auch das TiF4 zu sublimieren. Dieses Verhalten des Titansalzes ermöglicht einen großen Teil des, der Zirkonverbindung beigemengten, Titans durch Sublimation zu entfernen.
Beiträge zur Kenntnis von Hydrogelen. Über Antimonpentoxydhydrate
Authors: Simon A. , Thaler E.
Published: January 2005

Die Ergebnisse der Experimente und ihrer Auswertung lassen sich in folgende Punkte zusammenfassen:

Die Antimonpentoxydhydrate sind ihrem Hauptcharakter nach Kolloide. Die Darstellung von drei sehr reinen Präparaten unter verschiedenen Bedingungen zeigt, daß sich typische a‐ und b‐Säuren und beliebige Zwischenformen gewinnen lassen, deren Wassergehalte mit der Teilchengröße, d. h. den Darstellungsbedingungen weitgehend variabel sind.

Auch bei der isobaren Entwässerung behalten die einzelnen Modifikationen sehr lange die durch die Vorgeschichte bedingten Differenzierungen bei. Definierte Hydrate, die einer Ortho‐ Pyro‐und Metasäure entsprechen, treten dabei auf. Doch läßt die Form der Abbausiobaren, wie auch die Röntgenuntersuchung verschiedener Präparate eine kräftige Neigung zur Ausbildung gittermäßig geordneter Systeme erkennen, die durch Alterung und besonders Temperaturerhöhung begünstigt wird. An einem bei 0° hergestellten Präparat kann bereits bei Zimmertemperatur starke Interferenz festgestellt werden.

Das andeutungsweise Auftreten eines bisher nicht beschriebenen Hydrates 3 Sb2O5 · 5H2O und das Haltmachen der Lufttrocknung knapp oberhalb eines Wassergehaltes von 4 Molen sprechen dafür, daß die definierenden Valenzverhältnisse des genannten Ordnungsprozesses dieselben sind, wie bei den entsprechenden Arsenverbindungen.

Bei einem längere Zeit bei 300° unter hohem Druck erhitzten Präparat läßt sich das Hydrat 3 Sb2O5 · 3H2O eindeutig herausarbeiten, so daß die Abbaukurve eines so behandelten Gels einen treppenförmigen Absatz bei diesem Wassergehalt aufweist.

Bei einer vergleichenden Anwendung des Capillaritäts‐ und Osmosegesetzes auf die untersuchten Gele wird ein Zusammenhang der beiden Gesetze abgeleitet

.
Zur Erkenntnis der Vanadinsäure
Authors: Meyer Julius
Published: January 2005

Nach CAMMERER vermag Wasserstoffperoxyd festes Vanadinpentoxyd zu einer gelben Flüssigkeit aufzulösen, die sich unter Abspaltung von gasförmigem Sauerstoff zersetzt und allmählich wieder festes V2O5 abscheidet. Die Lösungsgeschwindigkeit hängt von der Beschaffenheit des V2O5, von der Konzentration des H2O2 und von der Temperatur ab. Die Beständigkeit der gelben Lösung ist nur gering und ist vor allem eine Funktion der Temperatur und der Vanadinkonzentration.
Über die Mischungslücke in flüssigen Eisen–Kupfer‐Legierungen
Authors: Müller Anton
Published: January 2005

Durch Versuche an einer Legierung aus gleichen Teilen von eisen und Kupfer wird nachgewiesen daß im flüssigen Gebiet eine Mischungslücke mit einem unteren kritischen Punkt bei etwa 1500° besteht.
Physikochemische Erklärung der normalen Knochenbildung, der Bildung kristallinischer Abscheidungen bei Krankheiten und des Einflusses von Alkalien auf den Stoffwechsel
Authors: Dhar N. R.
Published: January 2005

Calciumphosphat und‐carbonat treten im Körper hauptsächlich als Kolloide auf. Diese Kolloide werden von dem festen Calciumphosphat und‐carbonat in den Knorpeln adsorbiert und koaguliert. Der so gebildete Niederschlag von Calciumcarbonat und‐phosphat wirkt als Koagulationsmittel weiterer Mengen der Sole dieser Verbindungen, so daß der Niederschlag verstärkt wird. Dies ist wahrscheinlich der Mechanismus der normalen Knochenbildung.
Über das Gleichgewicht zwischen Jod und Jod in brauner Farbe Lösungsmitteln
Authors: Radvänyi Frau M. , Urbanek L. , Länyi K. , Gróh J.
Published: January 2005

Es konnte spektralphotometrisch und auch durch die Methode der Löslichkeitsvergrößerung festgestellt werden, daß die Jodmoleküle mit je 1 Molekül der sog. „aktiven”︁ (das Jod in brauner Farbe lösenden) Lösungsmittel Additionsverbindungen bilden, durch welche die braune Farbe dieser Lösungen verursacht wird.
Über Die Mischungslücke in flüssigen Eisen–Kupferlegierungen
Authors: Ruer Rudolf
Published: January 2005

Es wird gezeigt, daß sämtliche von Herrn Müller gegen die Arbeit: „Das System Eisen‐Kupfer”︁ von R. Ruer und F. Goerens erhobenen Einwände unbegründet sind. Insbesondere kann in der Löslichkeitskurve geschmolzener Eisen‐Kupferlegierungen kein unterer kritischer Punkt vorhanden sein, weder, wie er annimmt, bei etwa 1500°, noch auch bei einer anderen Temperatur, da nach den Versuchen von Ruer und Goerens auch bei langsamer Abkühlung und kräftigem Rühren noch bei 1445° ein Zusammenfließen einmal gebildeter Schichten nicht stattfindet. Der von Ruer und Goerens hervorgehobene Widerspruch gegen die Phasenregel ist daher durch die Versuche des Herrn Müller der Aufklärung nicht nähergebracht worden.