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.

THE PHOTOCHEMICAL OXIDATION OF ALDEHYDES IN THE GASEOUS PHASE: PART I. THE KINETICS OF THE PHOTOCHEMICAL OXIDATION OF ACETALDEHYDE

1958 ◽  
Vol 36 (1) ◽  
pp. 251-257 ◽  
Author(s):  
C. A. McDowell ◽  
L. K. Sharples
Keyword(s):  
Gaseous Phase ◽  
Photochemical Oxidation ◽  
Velocity Constant ◽  
Kinetics Of

The photochemical oxidation of acetaldehyde has been studied in the gaseous phase at 20 °C. and a wavelength of 3130 Å. It has been established that when the pressure of oxygen is between 0.5 mm. and 150 mm. the reaction obeys the kinetic law:[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 of the photooxidation, i.e. the rate of formation of acetyl radicals, which are thought to be produced in one or both of the following ways:[Formula: see text]

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.

Oxidation of Hydrocarbons. III. Kinetics and Mechanism of the Oxidation of Arenes by Aqueous Sodium Dichromate

1971 ◽  
Vol 49 (17) ◽  
pp. 2763-2769 ◽  
Author(s):  
Donald G. Lee ◽  
Udo A. Spitzer
Keyword(s):  
Free Radical ◽  
Kinetics And Mechanism ◽  
Sodium Dichromate ◽  
Radical Process ◽  
Aqueous Sodium ◽  
Oxidation Of Hydrocarbons ◽  
Acidic Conditions ◽  
Kinetics Of ◽  
Chromate Ion ◽  
Free Radical Process

The kinetics of the Oxidation of several sodium p-alkylbenzenesulfonates by aqueous dichromate have been studied under slightly acidic conditions (pH = 7.0 to 5.4). The results indicate that the only active oxidant under these conditions is the acid chromate ion, HCrO4−, and that the reaction probably involves a free radical process.

THE PHOTOCHEMICAL OXIDATION OF ALDEHYDES IN THE GASEOUS PHASE: PART III. THE ABSOLUTE VALUES OF THE VELOCITY CONSTANTS FOR THE PROPAGATING AND TERMINATING STEPS IN THE PHOTOCHEMICAL OXIDATION OF ACETALDEHYDE AND PROPIONALDEHYDE

1958 ◽  
Vol 36 (1) ◽  
pp. 268-278 ◽  
Author(s):  
C. A. McDowell ◽  
L. K. Sharples
Keyword(s):  
Gas Phase ◽  
Gaseous Phase ◽  
Mutual Interaction ◽  
Photochemical Oxidation ◽  
Velocity Constant ◽  
Kinetic Expression ◽  
The Absolute ◽  
Recombination Reactions

It has been established (Parts I and II) that the photochemical oxidation of acetaldehyde and propionaldehyde obeys the kinetic expression[Formula: see text]where RCHO represents the aldehyde and RCO3H the corresponding peracid. k3 is the velocity constant for the propagating reaction, and k6 that for the terminating reaction involving the mutual interaction of two RCO3 radicals. [Formula: see text] represents the rate of initiation of the photooxidation.Alcohols have been found to retard the photooxidation and it has been shown that the retarded reaction obeys the kinetic expression:[Formula: see text]It has thus been possible to determine the rates of initiation [Formula: see text] for each of the photooxidations. Application of the rotating sector technique has enabled the lifetime of the oxidation chains to be measured. These data together with the information given in Parts I and II have been used to calculate the absolute values for the velocity constants for the propagating and terminating reactions, k3 and k6:[Formula: see text]in the gas-phase photooxidations of acetaldehyde and propionaldehyde.The values of the respective velocity constants are: acetaldehyde at 20°, k3 = 8.05( ±2.04) × 103 1. mole−1 sec−1, k6 = 8.93( ±4.20) × 1010 1. mole−1 sec−1; propionaldehyde at 22°, k3 = 4.35( ±0.9) × 104 1. mole−1 sec−1, k6 = 2.69( ±1.35) × 1010 1 mole−1 sec−1.These values for the velocity constants for the "recombination" reactions of the peracetic and perpropionic radicals indicate that for these radicals reaction [6] is very efficient.

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.

THE KINETICS OF THE THERMAL REACTIONS OF ETHYLENE OXIDE

1963 ◽  
Vol 41 (12) ◽  
pp. 2956-2961 ◽  
Author(s):  
M. Lynne Neufeld ◽  
Arthur T. Blades
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Ethylene Oxide ◽  
Thermal Reactions ◽  
Kinetics Of

The thermal reactions of ethylene oxide in the presence of an excess of propylene have been studied as a function of pressure and it has been found that there are two sets of products, acetaldehyde and free radicals, presumably methyl and formyl. These products are believed to arise from an excited acetaldehyde intermediate. Some evidence has been obtained for the occurrence of a surface-catalyzed rearrangement to acetaldehyde but the free radical products are uninfluenced by surface.

Mercury in Arctic snow: Quantifying the kinetics of photochemical oxidation and reduction

2015 ◽  
Vol 509-510 ◽  
pp. 115-132 ◽  
Author(s):  
E.A. Mann ◽  
M.L. Mallory ◽  
S.E. Ziegler ◽  
R. Tordon ◽  
N.J. O'Driscoll
Keyword(s):  
Photochemical Oxidation ◽  
Kinetics Of
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