Reactions of tea polyphenol four constituents with hydroxyl radical: A pulse radiolytic study

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Formation of radicals in the reactions of tetralin, 2-cyanopropane,and ethylbenzene hydroperoxides with styrene

The formation of free radicals in the reactions of structurally different hydroperoxides with styrene is investigated. The free-radical chain oxidation of styrene initiated by hydroperoxides has been studied volumetrically by measuring O₂ consumption during the reaction. The bimolecular rate constants of radical initiation in the reactions of styrene with tetralin, 2-cyanopropane, and ethylbenzene hydroperoxides are 1.5 × 10^?8, 2.6 × 10^?7, and 6.5 × 10^?9 l mol^?1 s^?1) (323 K), respectively. The reactivity of a hydroperoxide increases with increasing electron-acceptor properties of the substituent in its molecule.     

Quenching of biacetyl (3Au) molecules by near-resonant and off-resonant collisional partners

Laser-induced time-resolved phosphorescence has been used to evaluate the quenching of gaseous biacetyl (³A_u) molecules by various molecules at 25°C. The quenching of biacetyl (³A_u) molecules by biacetyl itself was not detectable under our experimental conditions, and a pressure-independent lifetime of 1.70 ± 0.08 msec was found. The bimolecular rate constants (units of l/mol·sec) for quenching of the ³A_u molecules by cis-2-pentene, trans-2-pentene, cis-1,3-pentadiene, trans-1,3-pentadiene, and oxygen were found to be (3.3 ± 1.9) × 10³, (4.0 ± 0.2) × 10⁴, (3.9 ± 0.1) × 10⁸, (1.3 ± 0.1) × 10⁸, and (5.2 ± 0.4) × 10⁸, respectively.     

Photoinduced Degradation of the Herbicide Clomazone Model Reactions for Natural and Technical Systems

The photodegradation of the herbicide clomazone in the presence of S₂O₈^2? or of humic substances of different origin was investigated. A value of (9.4 ± 0.4) × 10⁸ m ^?1 s^?1 was measured for the bimolecular rate constant for the reaction of sulfate radicals with clomazone in flash‐photolysis experiments. Steady state photolysis of peroxydisulfate, leading to the formation of the sulfate radicals, in the presence of clomazone was shown to be an efficient photodegradation method of the herbicide. This is a relevant result regarding the in situ chemical oxidation procedures involving peroxydisulfate as the oxidant. The main reaction products are 2‐chlorobenzylalcohol and 2‐chlorobenzaldehyde. The degradation kinetics of clomazone was also studied under steady state conditions induced by photolysis of Aldrich humic acid or a vermicompost extract (VCE). The results indicate that singlet oxygen is the main species responsible for clomazone degradation. The quantum yield of O₂(a¹Δ_g) generation (λ = 400 nm) for the VCE in D₂O, Φ_Δ = (1.3 ± 0.1) × 10^?3, was determined by measuring the O₂(a¹Δ_g) phosphorescence at 1270 nm. The value of the overall quenching constant of O₂(a¹Δ_g) by clomazone was found to be (5.7 ± 0.3) × 10⁷ m ^?1 s^?1 in D₂O. The bimolecular rate constant for the reaction of clomazone with singlet oxygen was k_r = (5.4 ± 0.1) × 10⁷ m ^?1 s^?1, which means that the quenching process is mainly reactive.     

Rate coefficients for CS reactions with O2, O3 and NO2 AT 298 K

CS radicals have been produced by photodissociation of CS₂ at 193 nm and their disappearance monitored by LIF. The vibrationally excited CS radicals rapidly relax to CS(ν = 0). At 298 K, the rate coefficients for CS(ν = 0) reactions with O₂, O₃ and NO₂ are (2.9 ± 0.4) × 10_?19, (3.0 ± 0.4) × 10^?16 and (7.6 ± 1.1) × 10^?17 cm³ molecule^?1 s^?1 respectively. The quenching of CS(A ¹II)_ν=0 by He has a rate coefficient of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1.     

Kinetics of the gas-phase reactions of NO3 radicals with a series of alkynes,haloalkenes, and α,β-unsaturated aldehydes

Rate constants for the gas-phase reactions of NO₃ radicals with a series of alkynes, haloalkenes, and α,β-unsaturated aldehydes have been determined at 298 ± 2 K using a relative rate technique. Using rate constants for the reactions of NO₃ radicals with ethene and propene of (1.1 ± 0.5) × 10^?16 cm³ molecule^?1 s^?1 and (7.5 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1, respectively, the following rate constants (in units of 10^?16 cm³ molecule^?1 s^?1) were obtained: acetylene, ≤0.23; propyne, 0.94 ± 0.44; vinyl chloride, 2.3 ± 1.1; 1,1-dichloroethene, 6.6 ± 3.1; cis-1,2-dichloroethene, 0.75 ± 0.35; trans-1,2-dichloroethene, 0.57 ± 0.27; trichloroethene, 1.5 ± 0.7; tetrachloroethene, <0.4; allyl chloride, 2.9 ± 1.3; acrolein, 5.9 ± 2.8; and crotonaldehyde, 41 ± 9. The atmospheric implications of these data are discussed.     

Vibrational relaxation of NH2|X2B1(O,v2, O)| radicals

Energy transfer processes in NH₂ radicals have been studied using the sensitive laser-induced fluorescence (LIF) technique. The NH₂ radicals were generated by infrared multiple-photon dissociation (IR MPD) of monomethylamine (CH₃NH₂), and the state-selected NH₂(v″₂ = 1) decay was observed by the LIF detection of [NH²]. The vibrational relaxation processes studied are NH₂(v″₂ = 1) + M → NH₂(v″₂ = O)+M, with M  He, Ne, Ar, Kr, H₂, D₂, CO, O₂, and total decay rate of NH₂(v″₂ = 1) in the presence of excess of CH₃NH₂. Rate constants of (3.41±0.03)×10⁻¹³, (1.75±0.09)×10⁻¹³, (3.03±0.08)× 10⁻¹³, (3.58±0.06)×10⁻¹³, (13.4±0.5)×10⁻¹³, (4.70±0.19)×10⁻¹³, (4.3±0.3)×10⁻¹³, (5.9±-0.4)×10⁻¹³, (9.2±0.5)×10⁻¹³), and 8.4×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were determined for the vibrational deactivation of NH₂(v″₂ = 1) by He, Ne, Ar, Kr, H², D₂, N₂, CO, O₂, and CH₃NH₂, respectively. The effect of the different collision partners on the relaxation rate is discussed. The results can be qualitatively well understood in terms of strong vibration—rotation coupling, due to the small moment of inertia of the NH₂ radicals.     

Kinetics of the gas‐phase reactions of CHXCFX (X = H,F) with OH (253–328 K) and NO3 (298 K) radicals and O3 (236–308 K)

Rate constants for the reactions of OH and NO₃ radicals with CH₂?CHF (k₁ and k₄), CH₂?CF₂ (k₂ and k₅), and CHF?CF₂ (k₃ and k₆) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k₁ = (1.20 ± 0.37) × 10^?12 exp[(410 ± 90)/T], k₂ = (1.51 ± 0.37) × 10^?12 exp[(190 ± 70)/T], and k₃ = (2.53 ± 0.60) × 10^?12 exp[(340 ± 70)/T] cm³ molecule^?1 s^?1. The rate constants for NO₃ radical reactions at 298 K were k₄ = (1.78 ± 0.12) × 10^?16 (CH₂?CHF), k₅ = (1.23 ± 0.02) × 10^?16 (CH₂?CF₂), and k₆ = (1.86 ± 0.09) × 10^?16 (CHF?CF₂) cm³ molecule^?1 s^?1. The rate constants for O₃ reactions with CH₂?CHF (k₇), CH₂?CF₂ (k₈), and CHF?CF₂ (k₉) were determined by means of an absolute rate method: k₇ = (1.52 ± 0.22) × 10^?15 exp[?(2280 ± 40)/T], k₈ = (4.91 ± 2.30) × 10^?16 exp[?(3360 ± 130)/T], and k₉ = (5.70 ± 4.04) × 10^?16 exp[?(2580 ± 200)/T] cm³ molecule^?1 s^?1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH₂?CHF, CH₂?CF₂, and CHF?CF₂ with respect to reaction with OH radicals, NO₃ radicals, and O₃ were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010     

Kinetics of the gas-phase reactions of indan,indene, fluorene,and 9,10-dihydroanthracene with OH radicals,NO3 radicals,and O3

The kinetics of the gas-phase reactions of OH radicals, NO₃ radicals, and O₃ with indan, indene, fluorene, and 9,10-dihydroanthracene have been studied at 297 ± 2 K and atmospheric pressure of air. The rate constants, or upper limits thereof, for the O₃ reactions were (in cm³ molecule⁻¹ s⁻¹ units): indan, < 3 × 10⁻¹⁹; indene, (1.7 ± 0.5) × 10⁻¹⁶, fluorene, < 2 × 10⁻¹⁹; and 9,10-dihydroanthracene, (9.0 ± 2.0) × 10⁻¹⁹. Using a relative rate method, the rate constants for the OH radical and NO₃ radical reactions, respectively, were (in cm³ molecule⁻¹ s⁻¹ units): indan, (1.9 ± 0.5) × 10⁻¹¹ and (6.6 ± 2.0) × 10⁻¹⁵; indene, (7.8 ± 2.0) × 10⁻¹¹ and (4.1 ± 1.5) × 10⁻¹²; fluorene, (1.6 ± 0.5) × 10⁻¹¹ and (3.5 ± 1.2) × 10⁻¹⁴; and 9,10-dihydroanthracene, (2.3 ± 0.6) × 10⁻¹¹ and (1.2 ± 0.4) × 10⁻¹². These kinetic data were used to assess the relative contributions of the various reaction pathways. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 299–309, 1997.     

Kinetics of the gas-phase reactions of the oh radical with selected glycol ethers,glycols, and alcohols

Using a relative rate method, rate constants have been measured for the gas-phase reactions of the OH radical with 1-hexanol, 1-methoxy-2-propanol, 2-butoxyethanol, 1,2-ethanediol, and 1,2-propanediol at 296±2 K, of (in units of 10⁻¹² cm³ molecule⁻¹ s⁻¹): 15.8±3.5; 20.9±3.1; 29.4±4.3; 14.7±2.6; and 21.5±4.0, respectively, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. These OH radical reaction rate constants are higher than certain of the literature values, by up to a factor of 2. Rate constants were also measured for the reactions of 1-methoxy-2-propanol and 2-butoxyethanol with NO₃ radicals and O₃, with respective NO₃ radical and O₃ reaction rate constants (in cm³ molecule⁻¹ s⁻¹ units) of: 1-methoxy-2-propanol, (1.7±0.7)×10⁻¹⁵, and <1.1×10⁻¹⁹; and 2-butoxyethanol, (3.0±1.2)×10⁻¹⁵, and <1.1×10⁻¹⁹. The dominant tropospheric loss process for the alcohols, glycols, and glycol ethers studied here is calculated to be by reaction with the OH radical, with lifetimes of 0.4–0.8 day 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: 533–540, 1998     

Spectroscopic characterization of 2-naphthylcarbene

The 308 nm excimer laser flash photolysis of 2-naphthyldiazomethane produces triplet 2-naphthylcarbene (λ_max = 362 nm) which decays with the observed pseudo-first-order rate constants (k_exptl) of 5.54 ± 0.03 × 10⁶; 3.33 ± 0.4 × 10⁶; 1.64±0.02 × 10⁷; and 3.05±0.4 × 10⁶ s^-1 in n-pentane, 2,2,4-trimethylpentane (2,2,4-TMP), benzene and Freon 113 respectively. In hydrocarbon solvents the observed decay of triplet 2-naphthylcarbene is correlated with the pseudo-first-order growth of the 2-naphthylmethyl radical (λ_max = 378 nm). Direct kinetic measurements of the reaction of triplet 2-naphthylcarbene in 2,2,4-TMP with cyclohexane, styrene, methanol and carbon tetrachloride yielded bimolecular quenching rate constants of 1.48 ± 0.04 × 10⁶;4.33 ± 0.1 × 10⁷;7.25 ± 0.5 × 10⁶; and 3.35 ± 0.07 × 10⁶M^-1S^-1. It is also found that 2-naphthylcarbene reacts with acetonitrile (k_q = 5.28 ± 0.1 × 10⁵ M^-1 s^-1) to form a nitrile ylide intermediate with a λ_max = 372 nm. These results are interpreted in terms of a rapid singlet-triplet 2-naphthylcarbene equilibrium.     

Absolute rate constants for the reaction of O(3P) aroms with n-butane and NO(M  Ar) over the temperature range 298–439 K

Absolute rate constants for the reaction of O(³P) atoms with n-butane (k₂) and NO(M  Ar)(k₃) have been determined over the temperature range 298–439 K using a flash photolysis-NO₂ chemiluminescence technique. The Arrhenius expressions obtained were k₂ = 2.5 × 10^?11exp[-(4170 ± 300)/RT] cm³ molecule^?1 s^?1, k₃ = 1.46 × 10^?32 exp[940 ± 200)/ RT] cm⁶ molecule^?2 s^?1, with rate constants at room temperature of k₂ = (2.2 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 and k₃ = (7.04 ± 0.70)×10^?32 cm⁶ molecule^?2 s^?1. These rate constants are compared and discussed with literature values.     

Direct optical observation of the formation of some aliphatic alcohol radicals. A pulse radiolysis study

The kinetics of the reactions of hydroxyl radicals and hydrogen atoms with some aliphatic alcohols in aqueous solutions were studied using pulse radiolysis. Based on the increase in optical absorption in the UV region, the rate constants for the reaction of hydroxyl radicals and hydrogen atoms with methanol, ethanol, 2-propanol ort-butyl alcohol were determined to be 9.0 × 10⁸, 2.2 × 10⁹, 2.0 × 10⁹,6.2×l0⁸ and 1.1 × 10⁶, 1.8 × 10⁷, 5.3 × 10⁷, 2.3 × 10⁵ dm³ mol⁻¹ s⁻¹ respectively. The bimolecular decay rate constants for the alcohol radicals produced in methanol and ethanol were evaluated to be 2.4 × 10⁹ and 1.5 × 10⁹ dm³ mol⁻¹s⁻¹. The values observed are in fairly good agreement with those reported earlier.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm³ molecule^?1 s^?1: CH₃F, (3.7 ± 0.8) × 10^?11, CH₃Cl, (3.3 ± 0.7) × 10^?11; CH₃Br, (3.0 ± 0.7) × 10^?11; CF₂H₂, (4.3 ± 0.9) × 10^?12; CO, (5.5 ± 1.0) × 10^?13 (in 700 torr total pressure of N₂ diluent); CF₃H, (1.4 ± 0.4) × 10^?13; CF₃CCl₂H (HCFC-123), (1.2 ± 0.4) × 10^?12; CF₃CFH₂ (HFC-134a), (1.3 ± 0.3) × 10^?12, CHF₂CHF₂ (HFC-134), (1.0 ± 0.3) × 10^?12; CF₂ClCH₃ (HCFC-42b), (3.9 ± 0.9) × 10^?12, CF₂HCH₃ (HFC-152a), (1.7 ± 0.4) × 10^?11; and CF₃CF₂H (HFC-125), (3.5 ± 0.8) × 10^?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.     

Kinetics of CH(X2Π) radical reactions with propane,isobutane and neopentane

Rate constants over the temperature range 298–689 K are reported for the reaction of CH(X²Π) radicals with C₃H₈, i-C₄H₁₀ and neo-C₅H₁₂. The CH radical was generated by multiphoton laser photolysis of CHBr₃ and its disappearance monitored by laser-induced fluorescence (LIF) at 429.8 nm. Absolute rate constants were determined as a function of temperature and total pressure. The following Arrhenius parameters were derived: k = (1.85 ± 0.13) × 10⁻¹⁰ exp[(240±30)/T] cm³/s for CH+propane; k = (2.03±0.19)×10⁻¹⁰ exp[(240±40)/T] cm³/s for CH+isobutane; k = (1.61±0.10)×10⁻¹⁰ exp[(340±30)/T] cm³/s for CH+neopentane, all independent of total pressure. The negative temperature dependences along with the energetics and lack of pressure effects lead to the conclusion that the reactions proceed by CH insertion into the alkane. The activated adduct thus formed rapidly decomposes via many energetically accessible channels. An analysis of CH reactions with C₁ to C₅ alkanes shows an increase in the room temperature rate constants in going from C₁ to C₄ irrespective of the nature of CH bonds. The rate constant then begins to level off near ≈ 5 × 10⁻¹⁰ cm/s for C₄ and C₅ alkanes.     

Temperature dependence of the reaction rate constants for O(3P) atoms with C2H4, C3H6 and NO(M = N2O), determined by a modulation technique

Rate constants for the reaction of O(³P) atoms with C₃H₄, C₃H₆ and NO(M = N₂O) have been measured over the temperature range 300–392°K using a modulation-phase shift technique. The Arrhenius expressions obtained are:C₂H₄, k₂ = 3.37 × 10⁹ exp[?(1270 ± 200)/RT]liter mole^?1 sec^?1,C₃H₆, k₂ = 2.08 × 10⁹ exp[?(0 ± 300)/RT]liter mole^?1 sec^?1,NO(M = N₂O), k₁ = 9.6 × 10⁹ exp[(900 ± 200/RT]liter² mole^?2 sec^?1.These temperature dependencies of k₂ are in good agreement with recent flash photolysis-resonance flourescence measurements, although lower than previous literature values.     

Kinetics of the reactions of acenaphthene and acenaphthylene and structurally-related aromatic compounds with OH and NO3 radicals,N2O5 and O3 at 296 ± 2 K

The kinetics of the atmospherically important gas-phase reactions of acenaphthene and acenaphthylene with OH and NO₃ radicals, O₃ and N₂O₅ have been investigated at 296 ± 2 K. In addition, rate constants have been determined for the reactions of OH and NO₃ radicals with tetralin and styrene, and for the reactions of NO₃ radicals and/or N₂O₅ with naphthalene, 1- and 2-methylnaphthalene, 2,3-dimethylnaphthalene, toluene, toluene-α,α,α-d₃ and toluene-d₈. The rate constants obtained (in cm³ molecule^?1 s^?1 units) at 296 ± 2 K were: for the reactions of O₃; acenaphthene, <5 × 10^?19 and acenaphthylene, ca. 5.5 × 10^?16; for the OH radical reactions (determined using a relative rate method); acenaphthene, (1.03 ± 0.13) × 10^?10; acenaphthylene, (1.10 ± 0.11) × 10^?10; tetralin, (3.43 ± 0.06) × 10^?11 and styrene, (5.87 ± 0.15) × 10^?11; for the reactions of NO₃ (also determined using a relative rate method); acenaphthene, (4.6 ± 2.6) × 10^?13; acenaphthylene, (5.4 ± 0.8) × 10^?12; tetralin, (8.6 ± 1.3) × 10^?15; styrene, (1.51 ± 0.20) × 10^?13; toluene, (7.8 ± 1.5) × 10^?17; toluene-α,α,α-d₃, (3.8 ± 0.9) × 10^?17 and toluene-d₈, (3.4 ± 1.9) × 10^?17. The aromatic compounds which were observed to react with N₂O₅ and the rate constants derived were (in cm³ molecule^?1 s^?1 units): acenaphthene, 5.5 × 10^?17; naphthalene, 1.1 × 10^?17; 1-methylnaphthalene, 2.3 × 10^?17; 2-methylnaphthalene, 3.6 × 10^?17 and 2,3-dimethylnaphthalene, 5.3 × 10^?17. These data for naphthylene and the alkylnaphthalenes are in good agreement with our previous absolute and relative N₂O₅ reaction rate constants, and show that the NO₃ radical reactions with aromatic compounds proceed by overall H-atom abstraction from substituent-XH bonds (where X = C or O), or by NO₃ radical addition to unsaturated substituent groups while the N₂O₅ reactions only occur for aromatic compounds containing two or more fused six-membered aromatic rings.     

Electron transfer from α-aminoalkyl radicals to methyl viologen

The reactions of tert-butoxyl radicals with amines, leading to the formation of α-aminoalkyl radicals, and the reactions of these with the electron acceptor methyl viologen have been examined using laser flash photolysis techniques. For example, the radicals CH₃?HNEt₂ and HOCH₂?H N(CH₂CH₂OH)₂ react with methyl viologen with rate constants equal to (1.3 ± 0.1) × 10⁹ and (2.1 ± 0.4) × 10⁹M^?1 · s^?1, respectively, in wet acetonitrile at 300 K.     

Gas‐phase reaction of dichlorvos,carbaryl, chlordimeform,and 2,4‐D butyl ester with OH radicals

Widespread use of pesticides has caused serious environmental concern. In order to evaluate the fate of organic pesticides in the atmosphere, rate constants for gas phase reactions of OH radicals with dichlorvos, carbaryl, chlordimeform, and 2,4‐D butyl ester were measured using the relative rate method at ambient temperature and 101 kPa total pressure. On‐line FTIR spectroscopy was used to monitor the concentrations of pesticides as a function of time. The reaction rate constants with OH radicals (in units of cm³ molecule⁻¹ s⁻¹) have been determined as (2.0 ± 0.4) × 10⁻¹¹ for dichlorvos, (3.3 ± 0.5) × 10⁻¹¹ for carbaryl, (3.0 ± 0.7) × 10⁻¹⁰ for chlordimeform, and (1.5 ± 0.2) × 10⁻¹¹ for 2,4‐D butyl ester. These rate constants agree well with those estimated based on the structure–activity relationship. The group rate constant for NC group (k_(NC)) was estimated as 2.7 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Dimethyl phosphite has been tentatively identified as a product of the reaction of dichlorvos with OH radicals. Atmospheric lifetimes due to the reactions with OH radicals were also estimated (in units of h): 14 ± 3 for dichlorvos, 8 ± 1 for carbaryl, 1.0 ± 0.3 for chlordimeform, and 19 ± 3 for 2,4‐D butyl ester. These short atmospheric lifetimes indicate that the four organic pesticides degrade rapidly in the atmosphere, and they themselves are unlikely to cause persistent pollution. Further studies are needed to identify the potential hazard of their degradation products. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 755–762, 2005