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

1967 ◽  
Vol 20 (6) ◽  
pp. 1155 ◽  
Author(s):  
MFR Mulcahy ◽  
BG Tucker ◽  
DJ Williams ◽  
JR Wilmshurst
Keyword(s):  
Free Radicals ◽  
Gaseous Phase ◽  
Aromatic Compounds ◽  
Phase Iii ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Kinetics Of Reaction ◽  
Kinetics Of

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 free radicals with aromatic compounds in the gaseous phase. II. Kinetics of the reaction of methyl radicals with phenol

1965 ◽  
Vol 18 (1) ◽  
pp. 20 ◽  
Author(s):  
MFR Mulcahy ◽  
DJ Williams
Keyword(s):  
Free Radicals ◽  
Gaseous Phase ◽  
Hydrogen Abstraction ◽  
High Reactivity ◽  
Phenoxy Radical ◽  
Methyl Radicals ◽  
Methyl Radical ◽  
Kinetics Of Formation ◽  
Phenolic Substances ◽  
Kinetics Of

Knowledge of the reactivity of phenols towards simple free radicals is needed to throw light on the behaviour of the phenolic substances involved in the pyrolysis of coal and other organic materials. In the present investigation the reaction between methyl radicals and phenol vapour has been studied a t total pressures from 0.5 to 3 cmHg and temperatures from 445 to 547°K, the concentrations of methyl radicals and phenol being varied from 2 × 10-12 to 4 × 10-11 and 1 × 10-8 to 8 × 10-7 mole cm-3 respectively. The main products identified by gas chromatography were methane and o- and p-cresol, together with a little anisole and 2,4- and 2,6-dimethylphenol. The cresols are produced via hydrogen abstraction Diagram followed by combination of a methyl radical at a ring position of the phenoxy radical either ortho or para to the oxygen atom, e.g. in the case of the para position: Diagram The kinetics can be explained by postulating (a) that the keto forms of the cresols (methylcyclohexadienones) formed initially by reaction (6) have a finite lifetime in the gaseous phase and (b) that these molecules, which contain a tertiary hydrogen atom α to a system of a carbonyl bond and two carbon-carbon double bonds, partly undergo hydrogen abstraction by methyl radicals before they are able to enolize: CH3· + (HCH3 = C6H4 = O → CH4 + CH3C6H4O· The mechanism is consistent with the kinetics of formation of methane, the distribu- tion of the free electron in the phenoxy radical, the formation of o- and p-cresols as major products, the kinetics of formation of the cresols, and the high reactivity of the intermediate product towards methyl radicals.

scholarly journals The mechanism of the catalytic oxidation of ethylene - I. Experiments using a flow system

1946 ◽  
Vol 188 (1012) ◽  
pp. 92-104 ◽  
Keyword(s):  
Carbon Dioxide ◽  
Ethylene Oxide ◽  
Catalytic Oxidation ◽  
Flow System ◽  
Oxidation Reactions ◽  
Direct Oxidation ◽  
Rate Of Reaction ◽  
Reaction Proceeds ◽  
Products Of Reaction ◽  
Kinetics Of

Experiments have been made using a flow system to determine the mechanism of the catalytic oxidation of ethylene on a silver catalyst. The effects of time of contact of the gases with the catalyst, gas concentration, and temperature have been investigated. The products of reaction are ethylene oxide, and carbon dioxide and water. There appear to be two processes whereby the carbon dioxide is formed: (1) by direct oxidation of the ethylene not via ethylene oxide, and (2) by the further oxidation of the ethylene oxide. The isomerization of ethylene oxide to acetaldehyde by the catalyst in the absence of any oxygen has also been examined. By comparison with the oxidation of ethylene oxide, it has been shown that this latter reaction proceeds to a large extent, and possibly entirely, through a preliminary isomerization of the ethylene oxide to acetaldehyde. The rate of oxidation of acetaldehyde is extremely rapid and no trace of acetaldehyde is found during the oxidation of ethylene or of ethylene oxide. Ethylene oxide forms on the catalyst an involatile deposit, which is oxidized away by oxygen, so that during oxidation reactions the quantity of it on the catalyst is kept low. The kinetics of the oxidation of ethylene, i.e. rate of reaction proportional to the oxygen concentration and slightly dependent on the ethylene pressure, are consistent with the view that ethylene reacts with oxygen adsorbed on the catalyst and that the slowest step in the whole series of reactions is the rate of adsorption of the oxygen. An energy of activation of about 27 kcal. was found for the production of ethylene oxide, and slightly less for the production of carbon dioxide and consumption of oxygen.

THE PYROLYSIS OF TRIMETHYLTHALLIUM

1965 ◽  
Vol 43 (7) ◽  
pp. 1961-1967 ◽  
Author(s):  
M. G. Jacko ◽  
S. J. W. Price
Keyword(s):  
Activation Energy ◽  
Rate Constant ◽  
Total Pressure ◽  
Flow System ◽  
Total Darkness ◽  
Methyl Radicals ◽  
Kcal Mole ◽  
Homogeneous Process ◽  
Carrier Flow ◽  
Reaction Proceeds

The pyrolysis of trimethylthallium has been studied in a toluene carrier flow system from 458 to 591 °K using total pressures from 5.6 to 33.0 mm. The progress of the reaction was followed by measuring the amount of methane, ethane, ethylene, and ethylbenzene formed and, in 21 runs, by direct thallium analysis. All preparative and kinetic work was carried out in total darkness where possible. A shielded 10 W lamp was used when some illumination was necessary.The decomposition is approximately 80% heterogeneous in an unconditioned vessel and 14–27% heterogeneous in a vessel pretreated with hot 50% HF for 10 min. The reaction proceeds by the simple consecutive release of three methyl radicals. The rate constant depends only slightly on the total pressure in the system so that the activation energy of the homogeneous process, 27.4 kcal/mole, may be equated to D[(CH3)2Tl—CH3].

scholarly journals KINETICS OF THE REACTIONS BETWEEN ISOPROPYL CUMENE AND TERTIARY BUTYL CUMENE HYDROPEROXIDES AND IRON(II) IN DILUTE AQUEOUS SOLUTIONS IN THE ABSENCE OF OXYGEN

1952 ◽  
Vol 30 (12) ◽  
pp. 985-993 ◽  
Author(s):  
R. J. Orr ◽  
H. Leverne Williams
Keyword(s):  
Free Radicals ◽  
Rate Constants ◽  
Arrhenius Equation ◽  
Cumene Hydroperoxide ◽  
Bimolecular Reaction ◽  
Probable Error ◽  
Tertiary Butyl ◽  
Rate Of Reaction ◽  
Dilute Aqueous Solutions ◽  
Kinetics Of

From studies of the rate of reaction at 11°, 15°, 20°, and 26 °C. it was deduced that the bimolecular reaction between iron(II) and isopropyl cumene hydroperoxide is represented by[Formula: see text]At 0 °C. the radical induced oxidation of iron(II) due to inability of the monomer to remove the free radicals became appreciable. Addition of up to 7.5% methanol did not change the rate appreciably. The effect of traces of oxygen was negligible. Rate constants were measured at 15°, 9°, and 0 °C. for the reaction between iron(II) and the tertiary butyl cumene hydroperoxide. The average probable error in the determinations was 5.4%. From the data, the Arrhenius equation was determined as[Formula: see text]Comparison of the equations measured for cumene hydroperoxide, isopropyl cumene hydroperoxide, and tertiary butyl cumene hydroperoxide and iron(II) has been made. Changes in the constants have been explained qualitatively. The iodometric method of analysis when applied to tertiary butyl cumene hydroperoxide must be modified for accurate results. It is believed that the heating necessary in the presence of water decomposes the hydroperoxide.

THE PHOTOCHEMICAL OXIDATION OF ALDEHYDES IN THE GASEOUS PHASE: PART II. THE KINETICS OF THE PHOTOCHEMICAL OXIDATION OF PROPIONALDEHYDE

1958 ◽  
Vol 36 (1) ◽  
pp. 258-267 ◽  
Author(s):  
C. A. McDowell ◽  
L. K. Sharples
Keyword(s):  
Free Radicals ◽  
Excited States ◽  
Gaseous Phase ◽  
Photochemical Oxidation ◽  
Radical Process ◽  
Velocity Constant ◽  
Absorption Of Light ◽  
Oxidation Chain ◽  
Kinetics Of ◽  
Free Radical Process

The photochemical oxidation of propionaldehyde has been studied in the gaseous phase at 23 °C. and a wavelength of 3130 Å. With pressures of oxygen varying from 0.3 mm. to 100 mm. Hg it has been established that the reaction obeys the same kinetic law as that found for the corresponding reaction with acetaldehyde, namely:[Formula: see text]where k3 is the velocity constant for the propagating reaction [3]:[Formula: see text]and k6 is the velocity constant for the terminating reaction [6]:[Formula: see text][Formula: see text]is the rate of initiation and it is regarded as being a composite quantity representing the rate of formation of propionyl radicals, which are thought to be the initiators of the oxidation chain. The propionyl radicals are thought to be formed by two processes: (a) from the subsequent reactions of free radicals produced in the primary free radical process which occurs when propionaldehyde absorbs a quantum of radiation at 3130 Å, and (b) from the subsequent reactions, with oxygen, of excited states of propionaldehyde, which are also thought to be formed by the absorption of light of wavelength 3130 Å.

Decomposition of BrO studied by kinetic spectroscopy

1970 ◽  
Vol 48 (22) ◽  
pp. 3487-3490 ◽  
Author(s):  
J. Brown ◽  
George Burns
Keyword(s):  
Activation Energy ◽  
Total Pressure ◽  
Reaction Rate ◽  
Second Order ◽  
Kcal Mole ◽  
Kinetic Spectroscopy ◽  
Reaction Proceeds ◽  
One Step ◽  
Kinetics Of ◽  
Activated Complex

Kinetics of BrO decomposition was studied between 293 and 673 °K using the technique of kinetic spectroscopy. At 293 °K the reaction rate is second order with respect to BrO and is independent of [Br2], [O2], and total pressure of diluent gas. The activation energy for decomposition obtained from rate measurements between 293 and 450 °K is 0.65 ± 0.05 kcal/mole. Above 450 °K this activation energy appears to increase to 4.5 kcal/mole. It is shown that, although kinetically the ClO and BrO decompositions are similar, the mechanism for BrO decomposition below 450 °K is much simpler than that of ClO. The reaction proceeds, most likely, via one step: 2 BrO → 2 Br + O2, with Br2O2 being an activated complex, which has either linear or staggered configuration. ClO and BrO decomposition is compared with [Formula: see text] reaction.

Kinetics of the reaction of methyl iodide with sulfite and thiosulfate ions in aqueous solution

1969 ◽  
Vol 47 (24) ◽  
pp. 4537-4541 ◽  
Author(s):  
R. A. Hasty ◽  
S. L. Sutter
Keyword(s):  
Activation Energy ◽  
Methyl Iodide ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Order Reaction ◽  
Second Order Reaction ◽  
Kcal Mole ◽  
Rate Of Reaction ◽  
Kinetics Of ◽  
Sulfite Ion

The rate of reaction of methyl iodide with sulfite ion is determined. In addition, the rate of reaction of methyl iodide with thiosulfate ion is reexamined and the rate of reaction of methyl iodide with bisulfite ion is estimated. A pronounced effect of ionic strength on the reaction rate in the methyl iodide – sulfite ion system is observed, this effect does not occur in the methyl iodide – thiosulfate ion system. The second order reaction rate constant and activation energy for the reaction of methyl iodide with the respective nucleophiles are: SO32−, 4.4 × 10−2M−1 s−1, 18.6 kcal mole−1; HSO3−, 1 × 10−3M−1 s−1, 18.4 kcal mole−1; and S2O32− 3.1 × 10−2M−1 s−1, 19.4 kcal mole−1.

scholarly journals The combustion of aromatic and alicyclic hydrocarbons I—The slow combustion of benzene, toluene, ethylbenzene, n -propylbenzene, n -butylbenzene, o -xylene, m -xylene, p -xylene and mesitylene

1937 ◽  
Vol 161 (904) ◽  
pp. 48-67 ◽  
Keyword(s):  
Gaseous Phase ◽  
Aromatic Compounds ◽  
Chain Mechanism ◽  
Induction Periods ◽  
Slow Combustion ◽  
Benzene Toluene ◽  
Chain Theory ◽  
Characteristic Features ◽  
A Chain ◽  
Kinetics Of

Recent work upon the kinetics of the oxidation of aliphatic hydrocarbons has led to the recognition of certain characteristic features that find a ready interpretation in terms of the chain theory of chemical reaction. Thus, for example, both paraffins and olefines exhibit well-defined induction periods, pressure limits of inflammability and a marked sensitivity to the influence of surface, that point directly to the intervention of reaction chains; and although the precise nature of the chain mechanisms is somewhat uncertain a great deal of information is available as to their length, branching characteristics, mutual interactions and stability. Corresponding data for alicyclic and aromatic compounds are, however, very scanty and only in one instance has a comprehensive systematic kinetic study been made. Fort and Hinshelwood (1930) and Amiel (1933 a, b , 1936) have investigated the slow combustion of benzene and find that whilst it shows a general resemblance to ethylene there are certain respects in which significant differences occur. Fort and Hinshelwood concluded that benzene is oxidized by a chain mechanism, the chains initiated predominantly in the gaseous phase being of short continuation.

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