Kinetics of OH radical reactions with a series of ethers

The rate constants for the reactions of OH with dimethyl ether (k₁), diethyl ether (k₂), di-n-propyl ether (k₃), di-isopropyl ether (k₄), and di-n-butyl ether (k₅) have been measured over the temperature range 230–372 K using the pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique. The temperature dependence of k₁,k₄, can be expressed in the Arrhenius plots form: k₁ = (6.30 ± 0.10) × 10^?12 exp[?(234 ± 34)/T] and k₄ = (4.13 ± 0.10) × 10^?12 exp[(274 ± 26)/T]. The Arrhenius plots for k₂,k₃, and k₅, were curved and they were fitted to the three parameter expressions: k₂ = (1.02 ± 0.08) × 10^?17 T² exp[(797 ± 24)/T], k₃ = (1.84 ± 0.23) × 10^?17T² exp[(767 ± 34)/T], and k₅ = (6.29 ± 0.74) × 10^?18T² exp[(1164 ± 34)/T]. The values at 298 K are (2.82 ± 0.21) × 10^?12, (1.36 ± 0.11) × 10^?11,(2.17 ± 0.16) × 10^?11, (1.02 ± 0.10) × 10^?11, and (2.69 ± 0.22) × 10^?11 for k₁, k₂, k₃, k₄, and k₅, respectively, (in cm³ molecule^?1 s^?1). These results are compared to the literature data. © 1995 John Wiley & Sons, Inc.     

Rate constants for the gas-phase reactions of selected dibasic esters with the OH radical

Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with the dibasic esters dimethyl succinate [CH₃OC(O)CH₂CH₂C(O)OCH₃], dimethyl glutarate [CH₃OC(O)CH₂CH₂CH₂C(O)OCH₃], and dimethyl adipate [CH₃OC(O)CH₂CH₂CH₂CH₂C(O)OCH₃] at 298±3 K. The rate constants obtained were (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): dimethyl succinate, 1.4±0.6; dimethyl glutarate, 3.3±1.1; and dimethyl adipate, 8.4±2.5, where the indicated errors include the estimated overall uncertainty of ±25% in the rate constant for cyclohexane, the reference compound. The calculated tropospheric lifetimes of these dibasic esters due to gas-phase reaction with the OH radical range from 1.4 days for dimethyl adipate to 8.3 days for dimethyl succinate for a 24 h average OH radical concentration of 1.0×10⁶ molecule cm⁻³. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 471–474, 1998     

Kinetics and mechanisms of the gas-phase reactions of the NO3 radical with aromatic compounds

The kinetics and nitrated products of the gas-phase reactions of the NO₃ radical with methoxybenzene, 1,2-, 1,3-, and 1,4-dimethoxybenzene, dibenzofuran and dibenzo-p-dioxin have been investigated at 297 ± 2 K and in the presence of one atmosphere of air. A relative rate method was used for the kinetic measurements. No reactions of methoxybenzene or dibenzofuran with the NO₃ radical were observed. The dimethoxybenzenes were observed to react by H-atom abstraction and NO₃ radical addition to the aromatic ring, while dibenzo-p-dioxin reacted by NO₃ radical addition to the aromatic rings. For these compounds, the NO₃ radical addition pathways were observed to be reversible. At the NO₂ concentrations employed, the NO₃-aromatic adducts reacted with NO₂ and the observed rate constants increased with increasing NO₂ concentration. However, for dibenzo-p-dioxin the observed rate constant became independent of the NO₂ concentration for concentrations ≥ 4.8 × 10¹³ molecule cm^?3, and under these conditions the rate constant of 6.8 × 10^?14 cm³ molecule^?1 s^?1 was taken to be that for addition of the NO₃ radical to the aromatic rings. The proposed NO₃ radical reaction mechanisms are discussed. © 1994 John Wiley & Sons, Inc.     

Kinetics and products of the reactions of selected diols with the OH radical

Using a relative rate method, rate constants have been measured at 296 ± 2 K for the gas‐phase reactions of OH radicals with 1,2‐butanediol, 2,3‐butanediol, 1,3‐butanediol, and 2‐methyl‐2,4‐pentanediol, with rate constants (in units of 10^?12 cm³ molecule^?1 s^?1) of 27.0 ± 5.6, 23.6 ± 6.3, 33.2 ± 6.8, and 27.7 ± 6.1, respectively, where the error limits include the estimated overall uncertainty of ±20% in the rate constant for the reference compound. Gas chromatographic analyses showed the formation of 1‐hydroxy‐2‐butanone from 1,2‐butanediol, 3‐hydroxy‐2‐butanone from 2,3‐butanediol, 1‐hydroxy‐3‐butanone from 1,3‐butanediol, and 4‐hydroxy‐4‐methyl‐2‐pentanone from 2‐methyl‐2,4‐pentanediol, with formation yields of 0.66 ± 0.11, 0.89 ± 0.09, 0.50 ± 0.09, and 0.47 ± 0.09, respectively, where the indicated errors are the estimated overall uncertainties. Pathways for the formation of these products are presented, together with a comparison of the measured and estimated rate constants and product yields. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 310–316, 2001     

Kinetic and mechanistic study of the gas-phase reactions of a series of vinyl ethers with the nitrate radical

NO(3) oxidation of methyl, ethyl, propyl, and butyl vinyl ethers has been studied under tropospheric conditions (atmospheric pressure and T = 293 +/- 3 K) in the LISA indoor simulation chamber. NO(3) was produced inside the reactor by thermal decomposition of N(2)O(5) previously added to the air-VOC mixture, and concentrations were monitored using FTIR spectrometry. All the kinetic experiments were carried out by relative rate technique using isoprene as reference compound, leading to the rate constants k(1) = (7.2 +/- 1.5) x 10(-13), k(2) = (13.1 +/- 2.7) x 10(-13), k(3) = (13.3 +/- 3.0) x 10(-13), and k(4) = (17.0 +/- 3.7) x 10(-13) cm(3) molecule(-1) s(-1) for methyl, ethyl, propyl, and butyl vinyl ethers, respectively. Main oxidation products have been identified like being formaldehyde and respectively methyl, ethyl, propyl, and butyl formates. Production yields of oxidation products were close to 50%. Oxygenated nitrates and peroxynitrates were also detected.     

Kinetic study of the gas-phase reactions of OH and NO3 radicals and O3 with selected vinyl ethers

Kinetic studies on the gas-phase reactions of OH and NO3 radicals and ozone with ethyl vinyl ether (EVE), propyl vinyl ether (PVE) and butyl vinyl ether (BVE) have been performed in a 405 L borosilicate glass chamber at 298 +/- 3 K in synthetic air using in situ FTIR spectroscopy to monitor the reactants. Using a relative kinetic method rate coefficients (in units of cm3 molecule(-1) s(-1)) of (7.79 +/- 1.71) x 10(-11), (9.73 +/- 1.94) x 10(-11) and (1.13 +/- 0.31) x 10(-10) have been obtained for the reaction of OH with EVE, PVE and BVE, respectively, (1.40 +/- 0.35) x 10(-12), (1.85 +/- 0.53) x 10(-12) and (2.10 +/- 0.54) x 10(-12) for the reaction of NO3 with EVE, PVE and BVE, respectively, and (2.06 +/- 0.42) x 10(-16), (2.34 +/- 0.48) x 10(-16) and (2.59 +/- 0.52) x 10(-16) for the ozonolysis of EVE, PVE and BVE, respectively. Tropospheric lifetimes of EVE, PVE and BVE with respect to the reactions with reactive tropospheric species (OH, NO3 and O3) have been estimated for typical OH and NO3 radical and ozone concentrations.     

胺丶醇丶醚类化合物气相碱性的CNDO/2计算

The gas-phase basicities of compounds can be measured by their proton affinities. In this paper we he calculated the gas-phase basicities of about seventy compounds containing N or O by means of the method CNDO/2. For the alkylamines, alcohols, ethers and carbonyl compounds, computational results agree qualitatively with the experimental values. The sequences of gas-phase basicities for the series of these compounds are as follows: Et2NH>Me3N>t-BuNH2>Me2NH>i-PrNH2>n-BuNH2>n-PrNH2>EtNH2>MeNH2>NH3; Et2O>EtOMe>t-BuOH>Me2O>i-PrOH>n-BuOH>n-PrOH>EtOH>MeOH>H2O; n-PrCHO>EtCHO>MeCHO>HCHO; n-BuCO2H>n-PrCO2H>EtCO2H>MeCO2H>HCO2H; HCO2Bu-n>HCO2Pr-N>HCO2Et>HCO2Me>HCO2H Obviously, alkyl substitution plays a role to increase the gas-phase basicities. The squence of increasing effectiveness is t-Bu>i-Pr>n-Bu>n-Pr>Et>Me For the amines containing heteroatoms investigated here, the gas-phase basicities have the following order repectively: CH3NH2>NH2NH2>NH2OH>NH2F>NHF2>NF3 The gas-phase basicities of these compounds change regularly with various substitutents. For the aliphatic compounds, the gas-phase basicity increases with thosizo and the degree of branching of the alkyl groups. For the amines containing heteroatoms, the gas-phase basicity decreases with increasing of the electro-negativity of the substitutent. For the relationship between the gas-phase basksity and the charge distribution and the ionization potentials, the conclusions are as follows: (1) The gas-phase basicities of the homologous compounds are proportional to the electron density of the atom N or O, but those of Rn NH3-n and Rn OH2-n are inversely proportional to the electron denisty of atom N or O. This shows that the base strength of the molecule cannot be determined solely by the electron density of the individual atom. (2) In the protonation reaction the alkyl groups spread the charges from the charged center. This effect enables protonated cations to become more stable because of the charge distribution av     

CNDO/2 calculation on gas-phase basicity of amines,alcohols and ethers

The gas-phase basicity of about seventy compounds containing N or O have been calculated by means of the CNDO/2 method. For alkylamines, alcohols, ethers and carbonyl compounds, computational results agree qualitatively with the experimental values. We have also discussed the relationships between gas-phase basicities and charge distributions and ionization potentials of these molecules.     

Rate constants for the gas-phase reactions of ozone with unsaturated alcohols,esters, and carbonyls

The kinetics of the gas-phase reaction of ozone with unsaturated alcohols, carbonyls, and esters in air have been investigated at atmospheric pressure, ambient temperature (285–295 K), and in the presence of sufficient cyclohexane to scavenge the hydroxyl radical which forms as a product of the ozone-unsaturated compound reaction. The reaction rate constants, in units of 10^?18 cm³ molecule^?1 s^?1, are 0.26 ± 0.05 for acrolein, 1.07 ± 0.05 for 2-ethyl acrolein, 6.0 ± 0.4 for ethyl vinyl ketone, 4.9 ± 0.4 for 3-buten-1-ol, 14.4 ± 2.0 for allyl alcohol, 105 ± 7 for cis-3-hexen-1-ol, 7.5 ± 0.9 for methyl methacrylate, 2.9 ± 0.3 for vinyl acetate, 4.4 ± 0.3 for methyl crotonate, and 8.1 ± 0.3 for the 1,1-disubstituted alkene 2-ethyl-1-butene. Substituent effects on reactivity are discussed by comparison with alkenes and indicate that the reactivity of unsaturated alcohols is the same as that of alkene structural homologues and that the —C(O)OR, —C(O)R, and —CHO groups decrease the reactivity towards ozone as compared to alkyl groups. Estimates are made of the atmospheric persistence of these unsaturated compounds using the kinetic data obtained in this study as input to structure-reactivity and linear free-energy relationships. © 1993 John Wiley & Sons, Inc.     

Time-resolved gas-phase kinetic, quantum chemical, and RRKM studies of reactions of silylene with alcohols

Time-resolved kinetic studies of silylene, SiH(2), generated by laser flash photolysis of 1-silacyclopent-3-ene and phenylsilane, have been carried out to obtain rate constants for its bimolecular reactions with methanol, ethanol, 1-propanol, 1-butanol, and 2-methyl-1-butanol. The reactions were studied in the gas phase over the pressure range 1-100 Torr in SF(6) bath gas, at room temperature. In the study with methanol several buffer gases were used. All five reactions showed pressure dependences characteristic of third body assisted association reactions. The rate constant pressure dependences were modeled using RRKM theory, based on E(0) values of the association complexes obtained by ab initio calculation (G3 level). Transition state models were adjusted to fit experimental fall-off curves and extrapolated to obtain k(∞) values in the range (1.9-4.5) × 10(-10) cm(3) molecule(-1) s(-1). These numbers, corresponding to the true bimolecular rate constants, indicate efficiencies of between 16% and 67% of the collision rates for these reactions. In the reaction of SiH(2) + MeOH there is a small kinetic component to the rate which is second order in MeOH (at low total pressures). This suggests an additional catalyzed reaction pathway, which is supported by the ab initio calculations. These calculations have been used to define specific MeOH-for-H(2)O substitution effects on this catalytic pathway. Where possible our experimental and theoretical results are compared with those of previous studies.     

Kinetics and products of the gas-phase reactions of the OH radical and O3 with allyl chloride and benzyl chloride at room temperature

The kinetics of the gas-phase reactions of allyl chloride and benzyl chloride with the OH radical and O₃ were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of ??(O₃ + allyl chloride) = (1.60 ± 0.18) × 10^?18 cm³ molecule^?1 s^?1 and ??(O₃ + benzyl chloride) < 6 × 10^?20 cm³ molecule^?1 s^?1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of ??(OH + allyl chloride) = (1.69 ± 0.07) × 10^?11 cm³ molecule^?1 s^?1 and ??(OH + benzyl chloride) = (2.80 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT-IR absorption spectroscopy indicated that the co-products ClCH₂CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH₂CHO, (ClCH₂)₂CO, and CH₂ ? CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH₂CHO and the CH₂Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ?4%, respectively), with the remainder of the products being unidentified.     

Kinetics and mechanism of peroxyl radical reactions with nitroxides

Cyclic nitroxides (>NO*) are stable radicals of diverse size, charge, lipophilicility, and cell permeability, which provide protection against oxidative stress via various mechanisms including SOD-mimic activity, oxidation of reduced transition metals and detoxification of oxygen- and nitrogen-centered radicals. However, there is no agreement regarding the reaction of nitroxides with peroxyl radicals, and many controversies in the literature exist. The question of whether nitroxides can protect by scavenging peroxyl radicals is important because peroxyl radicals are formed in biological systems. To further elucidate the mechanism(s) underlying the antioxidative effects of nitroxides, we studied by pulse radiolysis the reaction kinetics of piperidine, pyrrolidine, and oxazolidine nitroxides with several alkyl peroxyl radicals. It is demonstrated that nitroxides mainly reduce alkyl peroxyl radicals forming the respective oxoammonium cations (>N+=O). The most efficient scavenger of peroxyl radicals is 2,2,6,6-tetramethylpiperidine-N-oxyl (TPO), which has the lowest oxidation potential among the nitroxides tested in the present study. The rate constants of peroxyl reduction are in the order CH2(OH)OO*>CH3OO*>t-BuOO*, which correlate with the oxidation potential of these peroxyl radicals. The rate constants for TPO vary between 2.8x10(7) and 1.0x10(8) M-1 s-1 and for 3-carbamoylproxyl (3-CP) between 8.1x10(5) and 9.0x10(6) M-1 s-1. The efficacy of protection of nitroxides against inactivation of glucose oxidase caused by peroxyl radicals was studied. The results demonstrate a clear correlation between the kinetic features of the nitroxides and their ability to inhibit biological damage inflicted by peroxyl radicals.     

An investigation of site-selective gas-phase reactions of amino alcohols with dimethyl ether ions

The reactions of dimethyl ether ions with neutral amino alcohols were examined in both a quadrupole ion trap mass spectrometer and a triple quadrupole mass spectrometer. These ion-molecule reactions produced two types of ions: the protonated species [M+l]⁺ and a more complex product at [M+13]⁺. The abundance of the [M+13]⁺ ions relative to that of the [M+1]⁺ ions decreases with increasing formal interfunctional distance. Multistage collision-activated dissociation techniques were used to characterize the [M+13]⁺ product ions, their reactivities, and the mechanisms for their formation and dissociation. In addition, molecular semiempirical calculation methods were used to probe the thermochemistry of these reactions. Reaction at the amino alcohol nitrogen site is favored, and the resulting [M+13]⁺ addition products may cyclize for additional stabilization. Comparisons were made among the behavior of related compounds, such as alcohols, diols, amines, and diamines. The alcohols reacted only to form the protonated species, but the diols, amines, and diamines all formed significant amounts of [M+13]⁺ ions or related dissociation products.     

Kinetics and mechanism of the reactions of diethylzinc with phenols in cyclic ethers

Reactions of diethylzinc and phenols (phenol, 2-ethylphenol, 2-chlorophenol, 3-ethylphenol, 3-chlorophenol, 4-ethylphenol and 4-chlorophenol) have been carried out in tetrahydrofuran and 1,4-dioxane as solvents. Monomeric ethylzinc phenoxide has been found to be a product of the diethylzinc and phenol (1:1) reaction in 1,4-dioxane solution. Kinetic studies on the ethylzinc phenoxides and phenols reaction in tetrahydrofuran solution established the rate constants and the S_Ei mechanism of the reaction.