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1.
The title reaction was studied in a standard flow system with F atoms produced by RF discharge in F2-He mixture. Analysis was by gas chromatography using electron capture detection. There were two major products, identified as CF2BrCF2H and CF2BrCF2Br, plus presumably HF which was not detectable. The overall rate of disappearance of reactant was found to be of mixed one and one-half order, indicating a complex reaction. A mechanism is proposed comprising six steps and involving two radical species CF2Br?FBr (R1) and CF2Br?F2. The 300 K rate constant for the initial step F + reactant → HF + R1 is evaluated to be 2.2 × 10?13 cm3/molec·s, which fits in with rates of other saturated hydrocarbon reactants containing one hydrogen atom, thus supporting the view that in this class of reactants the rates of reactions of the type F + saturated hydrocarbon depend mainly on the number of hydrogen atoms in the reactant. 相似文献
2.
Tertiary-amyl methyl ether (TAME) is proposed for use as an additive to increase the oxygen content of gasoline as stipulated in the 1990 Clean Air Amendments. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of TAME. The kinetics of the reaction of OH with TAME was examined by using a relative rate technique in which photolysis of methyl nitrite or nitrous acid was used as the source of OH. The OH rate constant for TAME and two major products (t-amyl formate and methyl acetate) were measured and yields for ten products were determined as primary products from the reaction. Values determined for the rate constants for the reaction with OH were 5.48 × 10?12 (TAME), 1.75 × 10?12 (t-amyl formate), and 3.85 × 10?13 cm3 molec?1 s?1 (methyl acetate) at 298 ± 2 K. The primary products (with corrected yields where required) from the OH + TAME that have been observed include (1) t-amyl formate (0.366), methyl acetate (0.349), acetaldehyde (0.43, corrected), acetone (0.036), formaldehyde (0.549), t-amyl alcohol (0.026), 3-methyoxy-3-methyl-butanal (0.044, corrected), t-amyloxy methyl nitrate (0.029), 3-methyoxy-3-methyl-2-butyl nitrate (0.010), and 2-methoxy-2-methyl butyl nitrate (0.004). Mechanisms leading to these products involve OH abstraction from each of the four different hydrogen atoms of TAME. © 1995 John Wiley & Sons, Inc. 相似文献
3.
D. F. Smith T. E. Kleindienst E. E. Hudgens C. D. McIver J. J. Bufalini 《国际化学动力学杂志》1992,24(2):199-215
Ethyl tertiary butyl ether (ETBE) is being proposed as an additive for use in reformulated gasolines. In this study, experiments were performed to examine the kinetics and mechanism of the atmospheric removal of ETBE. The kinetics of the reaction of ETBE with OH radicals were examined by using a relative rate technique with the photolysis of methyl nitrite to generate OH radicals. With n-hexane as the reference compound, a value of (9.73 ± 0.33) × 10?12 cm3 molecule?1 s?1 was obtained for the rate constant. The OH rate constant for t-butyl acetate, a product of the oxidation of ETBE, was (4.4 ± 0.4) × 10?13 cm3 molecule?1 s?1 at 298 K. The primary products and molar yields for the OH reaction with ETBE in the presence of NOx were t-butyl formate (0.64 ± 0.03), t-butyl acetate (0.13 ± 0.01), ethyl acetate (0.043 ± 0.003), acetaldehyde (0.16 ± 0.01), acetone (0.019 ± 0.002), and formaldehyde (0.53 ± 0.04). Under the described reaction conditions, the formation of t-butyl nitrite was also observed. From these molar yields, approximately 98% of the reacted ETBE could be accounted for by paths leading to these products. Chemical mechanisms to explain the formation of these products are presented. 相似文献
4.
Anélia N. Gurova Ana P.C. Ribeiro Carlos A. Nieto de Castro Umesh V. Mardolcar 《Fluid Phase Equilibria》2009
The relative permittivity (?r) data of 1,1,1-trifluoroethane (HFC-143a), (CAS N# 420-46-2), a hydrofluorocarbon (HFC) developed as a refrigerant that has zero ozone depletion potential, is reported. The relative permittivity of HFC-143a in the liquid phase was measured using a direct capacitance method at temperatures from T = 218 to 294 K and at pressures up to P = 15 MPa, for a frequency of 10 kHz. The uncertainty of the ?r measurements is estimated to be better than ±1.2 × 10−2. A complete set of tables of experimental data as a function of temperature, pressure and density, is presented that covers the dielectric property needs for most engineering applications. To study the dependence of ?r on density and temperature on a molecular basis, the theory developed by Vedam et al. and adapted by Diguet was applied to analyse the data. The Kirkwood modification of the Onsager equation was used to obtain the value of its dipole moment in the liquid phase (μ*). The apparent dipole moment obtained was μ* = 3.293 D. The effective dipole in the liquid state predicted by the Kirkwood–Frölich theory is 2.530 D. The measured values are compared with density functional and density functional self-consistent calculations (SCIPCM) of the electronic distribution and of the dipole moment of HFC-143a. Finally, the values of the isobaric thermal expansion and isothermal compressibility were estimated from the reported measurements. 相似文献
5.
Summary The pertechnetate ion oxidizes L-cysteine in strong acid to form yellow and violet (max=430 and 550 nm) species. A reaction mechanism has been determined which satisfactorily accounts for all the experimental findings. The results obtained support the postulate that the yellow species is a technetium(V)-cystine complex and the violet a technetium(V)-cysteine complex. The rate constants and Arrhenius parameters are reported. 相似文献
6.
The kinetics and mechanism of chromium(VI) oxidation of L-methionine in acidic medium have been studied spectrophotometrically. The reaction proceeds via the formation of a transient intermediate (max = 410–420 nm) which decomposes by a proton catalyzed pathway. The rate law is:
The activation enthalpy and activation entropy for the reaction have been calculated to be H
* = 43.85 kJ mol–1, S
* = –286.87 JK–1 mol–1. Also values of k
1, k
–1 and k
3 were determined: 27.2 × 10–3 M–1 S–1, 1.97 × 10–3 S–1, 7.2 × 10–3 s–1, respectively. The results are compared with those of related studies for reduction of chromate by amino acids. 相似文献
7.
Vanadium(V) oxidation ofL-arabinose has been found to be first order with respect to oxidant and substrate concentrations. It has been found that the order with respect to [H+] changes from one in 2.5M–4.5M acid concentration range to two in 5.0M–6.5M acid concentration range. The oxidation rate has been found to increase with ionic strength and decrease with dielectric constant of the medium. Thermodynamic parameters E, S
and G
have been evaluated as 22.63±0.19 kcal/mol,–3.00±0.65 e. u. and 23.59±±0.05 kcal/mol respectively. The reaction has been found to be initiated by the formation of free radical in a slow rate determining step.
Kinetik und mechanismus der oxidation von L-arabinose mit vanadium(V)
Zusammenfassung Die Vanadium(V)-Oxidation vonL-Arabinose verläuft bezüglich des Oxidationsmittels und Substrats erster Ordnung. Bezüglich der Änderung von [H+] zeigte sich für den Bereich 2,5M–4,5M eine Abhängigkeit erster, im Bereich 5,0M–6,5M eine von zweiter Ordnung. Die Oxidationsgeschwindigkeit steigt mit der Ionenstärke und fällt mit der Dielektrizitätskonstanten des Mediums. Es wurden die thermodynamischen Parameter E, S und G bestimmt: 22,63±0,19 kcal mol–1. –3,00±0,65 e. u. und 23,59±±0,05 kcal mol–1. Es wurde festgestellt, daß die Reaktion über die Bildung eines freien Radikals in einem langsamen, geschwindigkeitsbestimmenden Schritt initiiert wird.相似文献
8.
The kinetics of the reaction between glycolaldehyde (GA) and tetrachloroaurate(III) in acetic acid-sodium acetate buffer has been studied. The reaction is first-order with respect to [AuIII] as well as [GA]. Both H+ and Cl− ions retard the rate of reaction. AuCl4−, AuCl3(OH2), and AuCl3(OH)− are the reactive species of gold(III) with gradually increasing reactivity. A reaction mechanism involving two-electron transfer rate determining steps has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 613–619, 1998 相似文献
9.
Summary Rate constants for the oxidation of thiosulphate by hexachloroplatinate(IV) have been measured. The kinetics of the oxidation of thiosulphate follow a second-order rate law, first order with respect to thiosulphate and first order with respect to platinum(IV). The influence of pH is small. The rates are found to depend on the nature and concentration of the cations and follow the order: Cs+>Rb+>K+>Na+>Li+. The activation parameters calculated from the temperature studies are: H=42.9 k J mol–1 and S=–102 JK–1 mol–1. A mechanism of the reaction in terms of intermediate formation of free radicals followed by the formation of tetrathionate is postulated to explain the kinetic behaviour. 相似文献
10.
Sridevi Nadimpalli Rambabu Rallabandi L. S. A. Dikshitulu 《Transition Metal Chemistry》1993,18(5):510-514
Summary The oxidation of selenium(IV) by permanganate has been studied kinetically in acid, neutral and alkaline media. The reaction exhibits unit-order dependence on selenium(IV) and permanganate in all the three media. Manganese(VI) retards the reaction in alkaline medium. The rate-limiting step is the same in all the three media, but the stoichiometry is different, being 2:1 in alkaline medium, 2:3 in neutral medium and 2:5 in acid medium. Evidence has been obtained for a one electron-transfer in the rate-determining step. 相似文献
11.
The oxidation ofd-xylose by Mn(III) pyrophosphate in sulphuric acid has been found to be first order with respect to [Mn(III)]. Variation of rate with [d-xylose] suggests the rapid formation of reversible cyclic complex between Mn(III) and id-xylose, which further disproportionates in a slow rate determining step. Oxidation rate has been found to increase with [H+]. Retardation of rate due to [pyrophosphate] and increase due to [Mn(II)] have been also observed. The value of thermodynamic parameters E, S, and G have been found to be 17.6±0.1 kcal/mole, –10.1±0.1 e.u. and 20.6±0.1 kcal/ mole respectively. A mechanism involving a free radical has been proposed for the reaction under study. 相似文献
12.
13.
Linda Nelson Imelda Shanahan Howard W. Sidebottom Jack Treacy Ole J. Nielsen 《国际化学动力学杂志》1990,22(6):577-590
The reaction mechanisms for oxidation of CH3CCl2 and CCl3CH2 radicals, formed in the atmospheric degradation of CH3CCl3 have been elucidated. The primary oxidation products from these radicals are CH3CClO and CCl3CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH3CCl3 have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH3CCl3) = (5.4 ± 3) 10?12 exp(?3570 ± 890/RT) cm3 molecule?1 s?1. A value of this rate constant of 1.3 × 10?14 cm3 molecule?1 s?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH3 CCl3 reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH3CCl3) = (1.09 ± 0.35) × 10?14, ??(OH + CH3CClO) = (0.91 ± 0.32) × 10?14, ??(OH + CCl3CHO) = (178 ± 31) × 10?14, ??(OH + CCl2O) < 0.1 × 10?14; all in units of cm3 molecule?1 s?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed. 相似文献
14.
Vilasrao A. Kalantre Sanjeev P. Maradur Gavisiddappa S. Gokavi 《Transition Metal Chemistry》2007,32(2):214-218
The reaction between tetrabutylammonium tribromide(TBATB) and vanadium(IV) has been studied in 50% (v/v) acetic acid under
second order conditions. The overall order of reaction is found to be two, unity in each reactant. The reaction involves two
single-electron transfer steps generating bromine free radical in the first rate determining step. The test for the formation
of free radicals in presence of added acrylonitrile was negative while added toluene increases the rate of the reaction considerably
due to its conversion into benzyl bromide. The reaction is retarded by hydrogen ions as a result of protonation prior equilibria
of the active reductant, vanadyl acetate. The oxidation of the vanadylsalen complex by TBATB proceeds more rapidly than that
of vanadyl acetate but follows the similar kinetic behaviour. Considerable decrease in the entropy of activation of the reaction
indicates formation of an ordered transition state between the two reactants and since the kinetic behaviour remains unaltered,
even after the change in the ligand attached to the reductant, indicates an interaction between the reactants through the
oxygen atom on the vanadyl ion. 相似文献
15.
Kinetics and mechanism of oxidation of (ethylenediaminediacetato)chromium(III) by N-bromosuccinimide
The kinetics of oxidation of (ethylenediaminediacetato)-chromium(III), [Cr(EDDA)(OH2)2]+, by N-bromosuccinimide (NBS) in aqueous solution to yield CrVI have been studied spectrophotometrically over the 20–40°C range. The reaction rate is first order with respect to both [NBS] and [CrIII], and increases with pH over the range 4.8–5.8. The activation parameters were calculated. A mechanism in which deprotonated [CrIII(EDDA)(OH2)(OH)] is the reactive species is suggested. The electron transfer may proceed via an inner sphere mechanism through bridging of the two reactants by the hydroxo ligand. 相似文献
16.
The oxidation of halotoluenes by hexacyanoferrate(III) in aqueous acetic acid containing perchloric acid (0.5M) at 50°C gave the corresponding aldehyde as the major product, and a small amount of polymeric material. The order with respect to each of the reactants—substrate, oxidant, and acid—was found to be unity. Increasing proportions of acetic acid increased the rate of the reaction. The reaction was influenced by changes in temperature, and the activation parameters have been evaluated. The Hammett plot yielded a ρ+ value of ?1.8. A kinetic isotope effect kH/kD = 6.0 has been observed. The pathway for the conversion of the halotoluenes to the products has been mechanistically visualized as proceeding through the benzylic radical intermediate, formed in the rate-determining step of the reaction. The radical undergoes rapid conversion to the products. 相似文献
17.
The kinetics of oxidation of nitrilotris(methylenephosphonato)chromium(III), CrIIINTMP, by periodate to yield CrVI have been studied spectrophotometrically over the 5.80–6.85 pH range at 22–33 °C. The reaction rate, which is first-order with respect to [CrIIINTMP] and [IO–
4] and inversely dependent on [H+], obeys the rate law:-d[CrIIINTMP/dt=kKKh[IO-
4] [CrIII]T/Kh+ [H+] +KKh[IO-
4] The values of the intramolecular electron transfer, k, and the formation constant of the intermediate complex, K, were determined at various temperatures. The hydrolysis constant for CrIIINTMP, K
h
, was determined spectrophotometrically and is in agreement with the value estimated from the kinetic data. The activation parameters were calculated from the temperature dependence of the specific rate constants. A mechanism is proposed in which the hydroxo complex, [CrHNTMP(OH)]3–, is the reactive species. The results support a mechanism where intramolecular electron transfer is the rate-determining step. 相似文献
18.
Summary The kinetics of the RuIII-catalyzed oxidation of the hydroxy acids; lactic, tartaric, malic and citric acids byN-bromosuccinimide in HClO4 and in the presence of Hg(OAc)2 have been studied. The reactions exhibit a first order rate dependence with respect to the oxidant and zeroth order rate dependence with respect to substrate. The rate is retarded by [H+], accelerated at law RuIII concentrations but independent of [RuIII] at higher RuIII concentrations. A mechanism consistent with the observed kinetic data is proposed. 相似文献
19.
20.
Rajagopala Gurumurthy Mannathusamy Gopalakhrishnan Kulathu Iyer Sathiyanarayanan 《Tetrahedron》1994,50(48):13731-13738
The kinetics of oxidation of several S-phenylthioacetic acids by ceric ammonium nitrate (CAN) in presence of perchloric acid has been studied spectrophoto- metrically in 50 %(v/v) aqueous acetic acid. The order with respect to Ce(IV) is one and the order with respect to S-phenylthioacetic acid is found to be 0.8. A linear plot of kobs−1 vs [substrate]−1 with an intercept on the rate of axis suggests the formation of an equilibrium complex between the reactants prior to the rate determining step. The added acrylonitrile retards the reaction rate considerably suggesting that the oxidation process may involve a free radical mechanism. Electron-releasing substituents generally accelerate the rate, while electron-withdrawing groups retard the rate. A good correlation is found to exist between log k1.8 and Hammett σ constants. 相似文献