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1.
Yu. Skurlatov 《国际化学动力学杂志》1980,12(5):347-370
The kinetics and mechanism of ascorbic acid (DH2) oxidation have been studied under anaerobic conditions in the presence of Cu2+ ions. At 10?4 ≤ [Cu2+]0 < 10?3M, 10?3 ≤ [DH2]0 < 10?2M, 10?2 ≤ [H2O2] ≤ 0.1M, 3 ≤ pH < 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ2 (25°C) = (6.5 ± 0.6) × 10?3 sec?1. The effective activation energy is E2 = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu+ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu+ initiation in the Cu2+ reaction with ascorbic acid by the expression where C is a function of pH and of H2O2 concentration. The rate equation where k1(25°C) = (5.3 ± 1) × 103M?1 sec?1 is true for the steady-state catalytic reaction. The Cu+ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu2+–DH2–H2O2 system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu+ with H2O2, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme. Initiation: Propagation: Termination: 相似文献
2.
According to our experiments the bromide ion concentration exhibits in the bromate–ascorbic acid–malonic acid–perchloric acid system three extrema as a function of time. To describe this peculiar phenomenon, the kinetics of four component reactions have been studied separately. The following rate equations were obtained: Bromate–ascorbic acid reaction: Bromate–bromide ion reaction: Bromide–ascorbic acid reaction: Bromine–malonic acid reaction: k4 = 6 × 10?3 s?1, k-4 ≥ 1.7 × 103 s?1, k5 ≥ 1 × 107M?1 · s?1 Taking into account the stoichiometry of the component reactions and using these rate equations, the concentration versus time curves of the composite system were calculated. Although the agreement is not as good as in the case of the component reactions, it is remarkable that this kinetic structure exhibits the three extrema found. 相似文献
3.
The kinetics and mechanism of the reaction between iodine and dimethyl ether (DME) have been studied spectrophotometrically from 515–630°K over the pressure ranges, I2 3.8–18.9 torr and DME 39.6–592 torr in a static system. The rate-determining step is, where k1 is given by log (k1/M?1 sec?1) = 11.5 ± 0.3 – 23.2 ± 0.7/θ, with θ = 2.303RT in kcal/mole. The ratio k2/k?1, is given by log (k2/k?1) = ?0.05 ± 0.19 + (0.9 ± 0.45)/θ, whence the carbon-hydrogen bond dissociation energy, DH° (H? CH2OCH3) = 93.3 ± 1 kcal/mole. From this, ΔH°f(CH2OCH3) = ?2.8 kcal and DH°(CH3? OCH2) = 9.1 kcal/mole. Some nmr and uv spectral features of iodomethyl ether are reported. 相似文献
4.
The decomposition of dimethyl peroxide (DMP) was studied in the presence and absence of added NO2 to determine rate constants k1 and k2 in the temperature range of 391–432°K: The results reconcile the studies by Takezaki and Takeuchi, Hanst and Calvert, and Batt and McCulloch, giving log k1(sec?1) = (15.7 ± 0.5) - (37.1 ± 0.9)/2.3 RT and k2 ≈ 5 × 104M?1· sec?1. The disproportionation/recombination ratio k7b/k7a = 0.30 ± 0.05 was also determined: When O2 was added to DMP mixtures containing NO2, relative rate constants k12/k7a were obtained over the temperature range of 396–442°K: A review of literature data produced k7a = 109.8±0.5M?1·sec?1, giving log k12(M?1·sec?1) = (8.5 ± 1.5) - (4.0 ± 2.8)/2.3 RT, where most of the uncertainty is due to the limited temperature range of the experiments. 相似文献
5.
Using published data on the kinetics of pyrolysis of C2Cl6 and estimated rate parameters for all the involved radical reactions, a mechanism is proposed which accounts quantitatively for all the observations: The steady-state rate law valid for after about 0.1% reaction is and the reaction is verified to proceed through the two parallel stages suggested earlier whose net reaction is A reported induction period obtained from pressure measurements used to follow the rate is shown to be compatible with the endothermicity of reaction A, giving rise to a self-cooling of the gaseous mixture and thus an overall pressure decrease. From the analysis, the bond dissociation energy DH0(C2Cl5? Cl) is found to be 70.3 ± 1 kcal/mol and ΔHf3000(·C2Cl5) = 7.7 ± 1 kcal/mol. The resulting π? bond energy in C2Cl4 is 52.5 ± 1 kcal/mol. 相似文献
6.
Pulsed laser photolysis of O3 in a large excess of N2 has been used to generate O(3P) atoms in the presence of OCS. By observing chemiluminescence from the small fraction of electronically excited SO2 formed in the reaction of SO with O3, rate constants of (1.7 ± 0.2) × 10?14 and (8.7 ± 1.6) × 10?14 cm3/molecule sec have been determined at 296 ± 4 K for the reactions and In addition, it has been shown that any reaction between SO and OCS has a rate constant 10?14 cm3/molecule sec. 相似文献
7.
Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of linear aliphatic ethers using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for dimethylether (k1), diethylether (k2), and dipropylether (k3) were used to derive the Arrhenius expressions and At 296 K, the measured rate constants (in units of 10?13 cm3 molecule?1 s?1) were: k1 = (24.9 ± 2.2), k2 = (136 ± 9), and k3 = (180 ± 22). Room temperature rate constants for the OH reactions with several other aliphatic ethers were also measured. These were (in the above units): di-n-butylether, (278 ± 36); di-n-pentylether, (347 ± 20); ethyleneoxide, (0.95 ± 0.05); propyleneoxide, (4.95 ± 0.52); and tetrahydrofuran, (178 ± 16). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data. 相似文献
8.
Absolute rate constants were determined for the gas phase reactions of OH radicals with a series of aliphatic alcohols using the flash photolysis resonance fluorescence technique. Experiments were performed over the temperature range 240–440 K at total pressures (using Ar diluent gas) between 25–50 Torr. The kinetic data for methanol (k1), ethanol (k2), and 2-propanol (k3) were used to derive the Arrhenius expressions and At 296 K, the measured rate constants (in units of 10?13 cm3 molecule?1 s?1) were: k1 = (8.61 ± 0.47), k2 = (33.3 ± 2.3), and k3 = (58.1 ± 3.4). Room temperature rate constants for the OH reactions with several other aliphatic alcohols were also measured. These were (in the above units): 1-propanol, (53.4 ± 2.9); 1-butanol, (83.1 ± 6.3) and 1-pentanol, (108 ± 11). The results are discussed in terms of the mechanisms for these reactions and are compared to previous literature data. 相似文献
9.
The ligands (L) bis (2-pyridyl) methane (BPM) and 6-methyl-bis (2-pyridyl)methane (MBPM) form the three complexes CuL2+, CuL, and Cu2L2H with Cu2+. Stability constants are log K1 = 6.23 ± 0.06, log K2 = 4.83 ± 0.01, and log K (Cu2L2H + 2H2+ ? 2 CuL2+) = ?10.99 ± 0.03 for BPM and 4.56 ± 0.02, 2.64 ± 0.02, and ?11.17 ± 0.03 for MBPM, respectively. In the presence of catalytic amounts of Cu2+, the ligands are oxygenated to the corresponding ketones at room temperature and neutral pH. With BPM and 2,4,6-trimethylpyridine (TMP) as the substrate and the buffer base, respectively, the kinetics of the oxygenation can be described by the rate law with k1 = (5.9 ± 0.2) · 10?13 mol l?1 s?1, k2 = (4.0 ± 0.6) · 10?4 mol?1 ls?1, k3 = (1.1 ± 0.1) · 10?12 mol l?1 s?1, and k4 = (9 ± 2) · 10?14 mol l?1 s?1. 相似文献
10.
The kinetics of the reversible reaction have been studied spectrophotometrically in acid solution under conditions in which both the forward and reverse reactions go to virtual completionand in which the reaction comes to a practical equlibrium. The rates of theforward (Rf) and reverse (Rr) reactions are given by where f, g, h, u, and v have the values (4 ± 1) × 10?5 mole/1.·s, (4.2 ± 0.2) × 10?5 mole2/1.2·s, (5.0 · 0.3) × 10?7 mole3/1.3·s, (1.1 ± 0.1) × 10?3 1.2/mole2·s, and (3.7 ± 0.2) × 10?3 1.3/mole3·s at 298.2°K and at an ionic strength of 2.00M maintained by adding sodium chloride. The stoichiometric equilibrium constant under similar conditions is 0.022 ± 0.003. Differentvalues of these parameters were obtained when sodium perchlorate and sodiumnitrate were used to control ionic strength. The results are compared with those from previous reports and a mechanism is proposed based upon an initial rapid equilibrium followed by a rate-determining attack of water upon H3AsO3I+, H2AsO3I, and HAsO3I?. 相似文献
11.
Spectrophotometric methods have been used to obtain rate laws and rate parameters for the following reactions: with ka, kb, Ea, Eb having the values 85±5 l./mole · s, 5.7±0.2 s?1 (both at 298.2°K), and 56±4 and 66±2 kJ/mole, respectively. with kc=0.106±0.004 l./mole ·s at 298.2°K and Ec=67±2 kJ/mole. with kd=(3.06 ±; 0.15) × 10?3 l./mole ·s at 298.2°K and Ed=66±2 kJ/mole. Mechanisms for these reactions are discussed and compared with previous work. 相似文献
12.
D. A. Parkes 《国际化学动力学杂志》1977,9(3):451-469
Using the technique of molecular modulation spectrometry, we have measured directly the rate constants of several reactions involved in the oxidation of methyl radicals at room temperature: k1 is in the fall-off pressure regime at our experimental pressures (20–760 torr) where the order lies between second and third and we obtain an estimate for the second-orderlimit of (1.2 ± 0.6) × 10?12 cm3/molec · sec, together with third-order rate constants of (3.1 ± 0.8) × 10?31 cm6/molec2 · sec with N2 as third body and (1.5 ± 0.8) × 10?30 with neopentane; we cannot differentiate between k2a and k2c and we conclude k2a + (k2c) = (3.05 ± 0.8) × 10?13 cm3/molec · sec and k2b = (1.6 ± 0.4) × 10?13 cm3/molec · sec; k3 = (6.0 ± 1.0) × 10?11 cm3/molec · sec. 相似文献
13.
Crystal Structure and Electric Conductivity of Spinel-Type Li2–2xMn1+xCl4 Solid Solutions The electric conductivity of the fast lithium ion conductors Li2–2xMn1+xCl4 was measured by impedance spectroscopic methods. The conductivities obtained, e.g. ~ 4 × 10?1 Ω?2 cm?1 at 570 K, depend only little on the lithium content. The crystal structure of Li1.6Mn1.2Cl4 was determined by neutron powder and X-ray single crystal diffraction (space group Fd3 m, Z = 8, a = 1 049.39(6) pm, Rw = 1.4% on the basis of 170 reflections). The lithium deficient chloride crystallizes in an inverse spinel structure like the stoichiometric compound Li2MnCl4 according to the formula (Li0,8)[Li0,4Mn0,6]2Cl4 with vacancies ( ) at the tetrahedral sites. The decrease of the Moct? Cl distances with the increase of x reveals that the ionic radius of Mn2+ in chlorides is equal or even smaller than that of Li+ opposite to fluorides and oxides. The ? Cl distances of spinel type chlorides are 237 ( tet) and 274 pm ( oct), respectively. The mechanism of the ionic conductivity is discussed. 相似文献
14.
The redox system of potassium persulfate–thiomalic acid (I1–I2) was used to initiate the polymerization of acrylamide (M) in aqueous medium. For 20–30% conversion the rate equation is where Rp is the rate of polymerization. Activation energy is 8.34 kcal deg?1 mole?1 in the investigated range of temperature 25–45°C. Mn is directly proportional to [M] and inversely to [I1]. The range of concentrations for which these observations hold at 35°C and pH 4.2 are [I1] = (1.0–3.0) × 10?3, [I2] = (3.0–7.5) × 10?3, and [M] = 5.0 × 10?2–3.0 × 10?1 mole/liter. 相似文献
15.
The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br2]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br2[(2.7–13.6) × 10?3M], H+ (0.03–2.0M), and Br? (up to 0.6M). The mechanism with k1 = 20.2 ± 1.2 M?1 sec?1, pK2 = 3.76, pK3 = ?1.20, accounts for all experimental observations. Br3? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species. 相似文献
16.
C2H5ONO was photolyzed with 366 nm radiation at ?48, ?22, ?2.5, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yield of CH3CHO, Φ{CH3CHO}, was measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1a = 0.29 ± 0.03 independent of temperature. The C2H5O radicals can react with NO by two routes The C2H5O radical can also react with O2 via Values of k6/k2 were determined at each temperature. They fit the Arrhenius expression: Log(k6/k2) = ?2.17 ± 0.14 ? (924 ± 94)/2.303 T. For k2 ? 4.4 × 10?11 cm3/s, k6 becomes (3.0 ± 1.0) × 10?13 exp{?(924 ± 94)/T} cm3/s. The reaction scheme also provides k8a/k8 = 0.43 ± 0.13, where 相似文献
17.
The title reactions have been investigated in a static system. The addition of acetylene to cyclopentadiene (CPD) results in formation of norbornadiene (BCH), cycloheptatriene (CHT), and toluene (T), while BCH decomposition produces CPD, C2H2, CHT, and T. Kinetic studies, comprising both product–time evolution and initial pressure variation, support a mechanism These reactions are almost certainly homogeneous and molecular in nature. Least mean square analysis of the data yield for temperatures of 525–656°K, log k?1 (1./mole·s)=7.51±0.05? (24.19±0.15 kcal/mole)/RT ln 10, and for temperatures of 584–630°K, 相似文献
18.
n-C3H7ONO was photolyzed with 366 nm radiation at ?26, ?3, 23, 55, 88, and 120°C in a static system in the presence of NO, O2, and N2. The quantum yields of C2H5CHO, C2H5ONO, and CH3CHO were measured as a function of reaction conditions. The primary photochemical act is and it proceeds with a quantum yield ?1 = 0.38 ± 0.04 independent of temperature. The n-C3H7O radicals can react with NO by two routes The n-C3H7O radical can decompose via or react with O2 via Values of k4/k2 ? k4b/k2 were determined to be (2.0 ± 0.2) × 1014, (3.1 ± 0.6) × 1014, and (1.4 ± 0.1) × 1015 molec/cm3 at 55, 88, and 120°C, respectively, at 150-torr total pressure of N2. Values of k6/k2 were determined from ?26 to 88°C. They fit the Arrhenius expression: For k2 ? 4.4 × 10?11 cm3/s, k6 becomes (2.9 ± 1.7) × 10?13 exp{?(879 ± 117)/T} cm3/s. The reaction scheme also provides k4b/k6 = 1.58 × 1018 molec/cm3 at 120°C and k8a/k8 = 0.56 ± 0.24 independent of temperature, where 相似文献
19.
The rate constant for the combination of trichloromethyl radicals in the gas phase has been measured by applying the rotating sector technique to the gas phase carbon tetrachloride–cyclohexane photochemical system. A temperature-independent rate constant, k5, of 3.9 ± 1.0 × 1012 cc mole?1 sec?1 was found. Arrhenius parameters for the reaction were found to be given by the expression log k4 = 11.79 – (10,700/2.3 RT). 相似文献
20.
NO2 was photolyzed with 2288 Å radiation at 300° and 423°K in the presence of H2O, CO, and in some cases excess He. The photolysis produces O(1D) atoms which react with H2O to give HO radicals or are deactivated by CO to O(3P) atoms The ratio k5/k3 is temperature dependent, being 0.33 at 300°K and 0.60 at 423°K. From these two points, the Arrhenius expression is estimated to be k5/k3 = 2.6 exp(?1200/RT) where R is in cal/mole – °K. The OH radical is either removed by NO2 or reacts with CO The ratio k2/kα is 0.019 at 300°K and 0.027 at 423°K, and the ratio k2/k0 is 1.65 × 10?5M at 300°K and 2.84 × 10?5M at 423°K, with H2O as the chaperone gas, where kα = k1 in the high-pressure limit and k0[M] = k1 in the low-pressure limit. When combined with the value of k2 = 4.2 × 108 exp(?1100/RT) M?1sec?1, kα = 6.3 × 109 exp (?340/RT)M?1sec?1 and k0 = 4.0 × 1012M?2sec?1, independent of temperature for H2O as the chaperone gas. He is about 1/8 as efficient as H2O. 相似文献