Arrhenius Parameters For Reaction Research Articles

The reaction of phenoxy radicals with mono-chlorobenzene and its meaning for gas-phase dioxin formation in incineration

The reaction of (chlorinated) phenoxy radicals with chlorophenols recently has been discussed as a source of gas-phase dioxin formation in incineration. As a surrogate for this reaction, we studied the analogous reaction (1) of phenoxy ( Φ O) with chlorobenzene ( Φ Cl) in a well-stirred reactor between 728 and 984 K. The slow combustion of phenol served as a continuous Φ O source, and chlorobenzene was used as cofuel. Stable end products and reactants were analyzed by gas chromatography (GC), in particular Φ Cl, dibenzofuran (DF), and diphenylether ( Φ O Φ ), the direct product of reaction 1. This made it possible to measure k 1 in competition with Φ O recombination, reaction (2) for which an overall rate coefficient had earlier been established in our laboratory. The Arrhenius parameters for reaction (1) are A 1 =4.8×10 8 L/mol s, E a1 =24.5 kcal/mol When these parameters are adopted for the reaction of chlorinated phenoxy radicals with chlorophenol, an agreement with an earlier kinetic analysis of Shaub and Tsang is achieved that has a meaning for dioxin formation. The given parameters render this reaction at temperatures below 1000 K too slow to contribute significantly as a gas-phase dioxin source. However, since gas-phase dioxin formation recently has been detected in a flow reactor during trichlorophenol combustion with maximum yields of dioxin around 900 K. another dioxin source must be found consequently, we suggest the gas-phase recombination of chlorinated phenoxy radicals.

ChemInform Abstract: Arrhenius Parameters for the Addition of HO2 Radicals to (E)‐But‐2‐ene Over the Range 400‐520 °C.

Studies have been made of the addition of HO2 radicals to (E)-but-2-ene in the temperature range 400–520°C, by use of the co-oxidation of (E)-but-2-ene and propene in the presence of tetramethylbutane as a source of HO2 radicals. From measurements of the relative yields of 2,3-dimethyloxirane and methyloxirane and the known Arrhenius parameters for reaction (6), values of A7= 108.61 ± 0.30 dm3 mol–1 s–1 and E7= 50.0 ± 4 kJ mol–1 have been obtained. HO2+ C3H6→ C3H6O + OH (6), HO2+(E)-C4H8-2 → C4H8O + OH (7)The values are compared with data for HO2 addition to other alkenes. The excellent correlation between the activation energy for addition and the ionisation energy of the alkene is used to provide a kinetic data base for HO2 addition to alkenes over the range 600–1000 K, where the reactions are of major importance.From studies of the relative yields of 2,3-dimethyloxirane and (Z)-but-2-ene from (E)-but-2-ene + H2+ O2 mixtures, further evidence is presented to show that the decomposition of hydroperoxyalkyl radicals, such as CH3CH(OOH)CHCH3, into alkene + HO2 is at most a minor process compared with formation of an oxirane + OH radical.

Arrhenius parameters for the addition of HO2radicals to (E)-but-2-ene over the range 400–520°C

Studies have been made of the addition of HO2 radicals to (E)-but-2-ene in the temperature range 400–520°C, by use of the co-oxidation of (E)-but-2-ene and propene in the presence of tetramethylbutane as a source of HO2 radicals. From measurements of the relative yields of 2,3-dimethyloxirane and methyloxirane and the known Arrhenius parameters for reaction (6), values of A7= 108.61 ± 0.30 dm3 mol–1 s–1 and E7= 50.0 ± 4 kJ mol–1 have been obtained. HO2+ C3H6→ C3H6O + OH (6), HO2+(E)-C4H8-2 → C4H8O + OH (7)The values are compared with data for HO2 addition to other alkenes. The excellent correlation between the activation energy for addition and the ionisation energy of the alkene is used to provide a kinetic data base for HO2 addition to alkenes over the range 600–1000 K, where the reactions are of major importance.From studies of the relative yields of 2,3-dimethyloxirane and (Z)-but-2-ene from (E)-but-2-ene + H2+ O2 mixtures, further evidence is presented to show that the decomposition of hydroperoxyalkyl radicals, such as CH3CH(OOH)CHCH3, into alkene + HO2 is at most a minor process compared with formation of an oxirane + OH radical.

Arrhenius parameters for the hydrogen abstraction from ammonia by CF3 radicals

AbstractThe reaction of CF3 radicals with NH3 has been studied over a wide temperature range 298–673 K, using the photolysis and the thermal decomposition of CF3I as the free radical source.It was found that the reaction could not be explained in terms of a simple mechanism equation image in the whole temperature range because a marked pressure dependence on the rate of products formation and the presence of a dark reaction complicate the system at low temperatures. Thus, Arrhenius parameters for reaction (1) have been calculated relative to the CF3 recombination from data in the range 523–673 K where pure hydrogen transfer occurs. The rate constant expression is given by where kH/k is in units of cm3/2/mol1/2 s1/2 and θ = 2.303 RT/kJ/mol.

The reaction of methyl radicals with neopentane in flow photolysis at 607–823 K

Acetone was photolyzed in the presence of a large excess of neopentane in a flow system at total pressures between 7 and 150 Torr and at 607–823 K. For reactions[Formula: see text]and[Formula: see text]the quotient of rate coefficients, k12/k2, was calculated from CH4 and C2H6 yields and was extrapolated to the high pressure limit, k12/k2,x. Taking k2,x as 2.2 × 1010 L mol−1 s1, Arrhenius parameters for reaction [1] were found to be: log10A (L mol−1 s−1) = 10.0 ± 0.1, EA = 62( ± 2) kJ mol−1. In combination with data from the literature for the temperature range 365–953 K, the Arrhenius plot for k1/k2,x1/2 was strongly curved, with a heat capacity of activation of 71 ± 4 J K−1 mol−1.

Reactions of oxygenated radicals in the gas phase. Part 11. Reaction of isopropylperoxyl radicals with 2,3-dimethylbut-2-ene

The reaction of isopropylperoxyl radicals with 2,3-dimethylbut-2-ene has been studied between 303 and 363 K, using the photo-oxidation of trans-2,2′-azopropane as a source of the radicals. The only product formed from the alkene is 2,3-dimethyl-2,3-epoxybutane. From a detailed study of the products, Arrhenius parameters for reaction (22) of log (A/dm3 mol–1 s–1)= 7.96 ± 0.50 and E/kJ mol–1= 40.87 ± 1.78 have been obtained. (CH3)2CHO2˙+ [grphic omitted] → [grphic omitted] +(CH3)2CHO˙(22)

Reactions of oxygenated radicals in the gas phase. Part 7. Reactions of methylperoxyl radicals and alkenes

The reactions of methylperoxyl radicals with alkenes have been studied between 373 and 403 K. The peroxyl radicals were generated by the oxidation of di-t-butyl peroxide. Arrhenius parameters for reaction (18) have been CH3O2·+CC→ [graphic omitted] + CH3O·(18) determined for 2-methylbut-1-ene, 2-methylbut-2-ene, and 2,3-dimethylbut-2-ene. They are log(A18/dm3 mol–1 s–1)= 8.60 ± 0.72,8.16 ± 0.49, and 8.14 ± 0.32, and E18= 52.8 ± 5.4, 42.4 ± 3.6, and 36.4 ± 2.8 kJ mol–1, respectively.

The kinetics and mechanism of the reaction of ozone with phenol in aqueous solution

1. Ozone reacts with phenol in aqueous solution, attacking the phenol group and opening the aromatic ring. 2. The reaction follows a bimolecular rate law over the entire range of ozone and phenol concentrations. 3. The Arrhenius parameters for reaction in water are anomalously high in comparison with the parameters for this same reaction in nonaqueous solution.

ChemInform Abstract: RADIATION INDUCED DECHLORINATION OF 1,2‐DICHLOROETHANE AND DETERMINATION OF ARRHENIUS PARAMETERS FOR HYDROGEN ATOM ABSTRACTION FROM CHLOROETHANES BY THE CYCLOHEXYL RADICAL

AbstractBei der Radiolyse einer Lösung von 1,2‐Dichlor‐äthan in Cyclohexan werden durch radiolytisch gebildete Cyclohexylradikale unter Abspaltung von C1 bzw. H Chloräthyl‐ und 1,2‐Dichloräthyl‐Radikale erzeugt, die weiter hauptsächlich zu chlorierten Äthanen, Chlorcyclohexan und β‐Chloräthylcyclohexan reagieren.

ChemInform Abstract: PHOTOLYSIS OF BROMOTRICHLOROMETHANE IN THE PRESENCE OF DICHLOROMETHANE, DIFLUOROMETHANE, CHLOROFLUOROMETHANE AND DICHLOROFLUOROMETHANE

The photolysis of bromotrichloromethane using light of λ= 365 mµ, in the presence of CH2Cl2, CH2FCl, CF2H2 and CHFCl2 has been investigated. The primary process (1) was found to be temperature dependent with an apparent activation CCl3Br +hv→ CCl3·+ Br·(1) energy of 6 330 ± 300 cal mol–1, in good agreement with earlier work.1 The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the halomethane and the only chain termination products are hexachlorethane and molecular bromine. Nonetheless the reaction do not show the expected light dependancy and also show a partial order in the halomethane. Four complicating factors are shown to be important; reversibility of the hydrogen abstraction by trichloromethyl radicals, reversibility of the initiation step, hydrogen abstraction by bromine atoms leading to an alternative chain mechanism and termination involving the halomethyl radicals. Notwithstanding these complications reasonable estimates of the Arrhenius parameters for reaction (2), the hydrogen abstraction by trichloromethyl radicals can be made. CCl3·+ RH → CCl3H + R·(2)[graphic omitted]

Reactions of trifluoromethyl radicals with iodine and nitric oxide

The reactions 2 and 3 have been studied by competitive methods. Use of previous Arrhenius[Formula: see text][Formula: see text]parameters for reaction 2 leads to k3 = 1.3 × 1010 exp −[(700 ± 100J)/RT]. Arrhenius parameters of reactions 2 and 3 are compared with those for reactions of other radicals with I2 and NO.

Reactions of iso-propyl radicals with oxygen, hydrogen and deuterium

i-C3H7 radicals have been produced by the oxidation of i-C3H7CHO at 440°C. From measurements of the relative yields of C3H6 and C3H8 over a wide range of mixture composition, a value for the ratio k4/k1= 0.003 2 ± 0.000 3 has been obtained. From measurements of the increased yield of C3H8(or C3H7D) in the presence of H2(or D2), the ratios k1/k2s= 3 060 ± 250, k1/k3s= 7 680 ± 300 at 440°C are obtained. i-C3H7·+ O2= C3H6+ HO2(1),i-C3H7·+ H2= C3H8+ H (2s), i-C3H7·+ D2= C3H7D + D (3s), + i-C3H7CHO = C3H8+ i-C3H7ĊO or i-Ċ3H6CHO.(4), The value for k2s/k3s= 2.51 ± 0.20 suggests that E3s–E2s= 800 cal mol–1, which indicates a lowering of the zero-point energy in the transition state of about 1 000 cal mol–1 when H2 is replaced by D2. Absolute rate constants for reactions (1), (2s), (3s) and (4) and Arrhenius parameters for reactions (2s) and (3s), are discussed.

Radiation induced dechlorination of 1,2-dichloroethane and determination of arrhenius parameters for hydrogen atom abstraction from chloroethanes by the cyclohexyl radical

The kinetics of the radiation induced free radical chain reactions in solutions of CH2ClCH2Cl in cyclohexane (RH) was studied in the temperature range 150–250°C. Chloroethyl and 1,2-dichloroethyl radicals were produced by the reaction of radiolytically generated cyclohexyl (R) radicals with the solute. The reactions studied were R + CH2ClCH2Cl → RCl + CH2CH2Cl (2), R + CH2ClCH2Cl → RH + CHClCH2Cl (3), CH2CH2Cl + RH → CH3CH2Cl + R (4), CH2CH2Cl → CH2CH2+ Cl. (5), The Arrhenius parameters for reactions (2) and (3) are log10(k3/k2)=(0.39 ± 0.09)+(11.40 ± 0.79) kJ mol–1/2.303 RT. The difference in activation energies for reactions (4) and (5), E5–E4= 35.5 ± 6.0 kJ mol–1, was obtained by assigning the value log(A5/A4)= 5.4 ± 0.4 based on previously published works.The Arrhenius parameters for chlorine atom elimination from chloroethyl radicals in the liquid and gas phases are compared. In addition activation parameters for hydrogen atom abstraction from CCl3CHCl2, CHCl2CHCl2, CH2ClCHCl2, CCl3CH2Cl and CH2ClCH2Cl by cyclohexyl radicals are evaluated based on the present and previously published results. The effect of α and β chlorine atoms on EH values is discussed in terms of polar and enthalpic factors.

Photolysis of bromotrichloromethane in the presence of dichloromethane, difluoromethane, chlorofluoromethane and dichlorofluoromethane

The photolysis of bromotrichloromethane using light of λ= 365 mµ, in the presence of CH2Cl2, CH2FCl, CF2H2 and CHFCl2 has been investigated. The primary process (1) was found to be temperature dependent with an apparent activation CCl3Br +hv→ CCl3·+ Br·(1) energy of 6 330 ± 300 cal mol–1, in good agreement with earlier work.1 The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the halomethane and the only chain termination products are hexachlorethane and molecular bromine. Nonetheless the reaction do not show the expected light dependancy and also show a partial order in the halomethane. Four complicating factors are shown to be important; reversibility of the hydrogen abstraction by trichloromethyl radicals, reversibility of the initiation step, hydrogen abstraction by bromine atoms leading to an alternative chain mechanism and termination involving the halomethyl radicals. Notwithstanding these complications reasonable estimates of the Arrhenius parameters for reaction (2), the hydrogen abstraction by trichloromethyl radicals can be made. CCl3·+ RH → CCl3H + R·(2)[graphic omitted]

ChemInform Abstract: PHOTOLYSIS OF AZOCYCLOHEXANE ALONE AND IN AN OXYGEN ATMOSPHERE

The photolysis of azocyclohexane involves excited molecules which can be deactivated by collision or decompose into cyclohexyl radicals and nitrogen. Arrhenius parameters for reaction (11) have been estimated, cyclo-C6H11·+(cyclo-C6H11)N2 [graphic omitted] cyclo-C6 H12+ cyclo-C6H11N2-cyclo-C6H10˙k11= 105.6±0.1 exp(–6600 ± 1000 cal mol–1/RT) dm3 mol–1 s–1 and a disproportionation/combination rate constant ratio of 0.99 ± 0.10 for cyclohexyl radicals has been determined.The photolysis of azocyclohexane in an oxygen atmosphere and in the presence of cyclohexane yields cyclohexyl hydroperoxide and cyclohexanone as principal products. The results show that these are formed through a radical/radical reaction and no chain process is involved. Evidence is presented to show that the minor products, cyclohexene and water, are formed via a cyclohexyl-trioxyl radical cyclo-C6H11O3˙.

The reaction of trichloromethyl radicals with hydrogen chlorid and a new estimation of the rate of combination of trichloromethyl radicals

AbstractThe effect of the addition of hydrogen chloride on the photolysis of carbon tetrachloride in the presence of cyclohexane has been investigated in a companion paper. The data enable the rate constant ratio k8/(k5)1/2 to be determined. Since k−8 is well established, k5 can be estimated from known thermochemical data. The validity of the thermochemical derivation is checked by applying it to trifluoromethyl radicals. The photolysis of bromotrichloromethane and carbon tetrachloride in the presence of hydrogen chloride has been investigated over a range of temperatures. From these results and assuming reaction (5) has no activation energy, Arrhenius parameters for reaction (8) have been determined: equation image The activation energies for the reaction of methyl, trichloromethyl, and trifluoromethyl radicals with hydrogen chloride are compared, and at first sight surprising results are rationalized in terms of relative electronegativity.

Photolysis of azocyclohexane alone and in an oxygen atmosphere

The photolysis of azocyclohexane involves excited molecules which can be deactivated by collision or decompose into cyclohexyl radicals and nitrogen. Arrhenius parameters for reaction (11) have been estimated, cyclo-C6H11·+(cyclo-C6H11)N2 [graphic omitted] cyclo-C6 H12+ cyclo-C6H11N2-cyclo-C6H10˙k11= 105.6±0.1 exp(–6600 ± 1000 cal mol–1/RT) dm3 mol–1 s–1 and a disproportionation/combination rate constant ratio of 0.99 ± 0.10 for cyclohexyl radicals has been determined.The photolysis of azocyclohexane in an oxygen atmosphere and in the presence of cyclohexane yields cyclohexyl hydroperoxide and cyclohexanone as principal products. The results show that these are formed through a radical/radical reaction and no chain process is involved. Evidence is presented to show that the minor products, cyclohexene and water, are formed via a cyclohexyl-trioxyl radical cyclo-C6H11O3˙.

Arrhenius parameters for the alkaline hydrolysis of esters in aqueous solution. Part III. Methyl betaine methyl ester

The kinetics of the alkaline hydrolysis of methyl betaine methyl ester have been studied using a pH-stat in aqueous solution, over a range of hydroxide ion concentrations at 0, 25, and 42°, and at an ionic strength of 0·1M. The results show the presence of a very small but detectable water rate at 25 and 42° but not at 0°. The effect of ionic strength has been studied. Rate constants and the energy and entropy of activation all show the expected dependence on ionic strength. Methyl betaine methyl ester has been shown to hydrolyse approximately three times faster at 25° than ethyl betaine ethyl ester. The Arrhenius parameters for both reactions are discussed. A comparison of ethyl betaine ethyl ester with glycine ethyl ester shows the effect of introducing both charge and substituent, while a comparison with the reaction of the protonated glycine ethyl ester shows the effect of substitution only. Such comparisons indicate that, though the introduction of a charge on the N atom has a major effect on the rate, substitution at this centre has little effect. This is also discussed with reference to the Arrhenius parameters for the relevant reactions.

Reactions of free radicals with aromatic compounds in the gaseous phase. III. Kinetics of the reaction of methyl radicals with anisole (methoxybenzene)

The kinetics of the reaction between methyl radicals and anisole have been studied at temperatures between 453 and 539�K and total pressures between 10 and 30 torr. The concentrations of methyl radicals ranged from 2 x 10-12 to 5 x 10-11 mole and those of anisole from 10-7 to mole cm-3. The reaction proceeds mainly by the mechanism ������������������ C6H5OCH3+CH3· → C6H5OCH2·+CH4���������������� (1)����������������� C6H5OCH2·+CH3· → C6H5OC2H5�������������������� (2)���������������� ���������C6H5OCH2· → C6H5CHO+H·������������������ (3) At 487�K attack on the aromatic ring to yield methyl anisoles is about twelve times slower than reaction (1). The Arrhenius parameters for reactions (1) and (8) are: log10(A1 cm3 mole-1 sec-1) = 11.7 � 0.3, and E1 = 10.5 � 0.8 kcal mole-1; log10(A8 sec-1) = 12.5, and E8 = 21 kcal mole-1. The last two values are based on the assumption that the kinetics of reaction (2) are similar to those of the recombination of methyl radicals. The rate of reaction (1) is about half that of the corre- sponding reaction with toluene and about five times that of the reaction with ethane in the above temperature range.

Reactions of trifluoromethyl radicals with iodine and hydrogen iodide

The reactions CF3+I2→CF3I+I (2) CF3+HI→ CF3H+I (3) have been studied by competitive methods. Use of our previous Arrhenius parameters for reaction (2) leads to, k3= 5.4 × 1011 exp –500/RT, cm3 mole–1 sec–1. Arrhenius parameters are summarized for the reactions CF3+X2→CF3X+X and CF3+HX→CF3H+X, where X = Cl, Br or I and also for CF3+H2→CF3H+H and CF3+H2S→CF3H+SH. These Arrhenius parameters are combined with thermodynamic data to give Cl+CF3Cl→Cl2+CF3, k= 1.9 × 1014 exp –31,300/RT, cm3 mole–1 sec–1. Br+CF3Br→Br2+CF3, k= 6.5 × 1013 exp –24,300/RT, cm3 mole–1 sec–1. I+CF3I→I2+CF3, k= 7.4 × 1013 exp –17,800/RT, cm3 mole–1 sec–1. H+CF3H→H2+CF3, k= 3.2 × 1012 exp –11,200/RT, cm3 mole–1 sec–1. SH+CF3H→H2S+CF3, k= 1.1 × 1012 exp –19,100/RT, cm3 mole–1 sec–1.