Alkylperoxy radical rearrangements during the gaseous oxidation of isobutene

1963 ◽  
Vol 273 (1354) ◽  
pp. 427-434 ◽  
Keyword(s):  
Methyl Ethyl Ketone ◽  
Peroxy Radical ◽  
Methyl Ethyl ◽  
Isotopic Tracer ◽  
Cool Flame ◽  
Cool Flames ◽  
Tracer Techniques ◽  
Slow Combustion ◽  
Flame Region ◽  
Subsequent Decomposition

Isotopic tracer techniques have been used to elucidate the mechanism of production of ketones in the gaseous oxidation of isobutane. Both acetone and methyl ethyl ketone are formed from this hydrocarbon, the former predominating in the products of slow combustion and the latter in the products of cool flames. Addition of [1,3- 14 C] acetone to reacting isobutane + oxygen mixtures has established that none of the methyl ethyl ketone formed in the cool-flame region and only 25% of that formed during slow combustion arises from further reactions of acetone. The formation of methyl ethyl ketone probably involves predominantly rearrangement and subsequent decomposition of the tert .-butyl peroxy radical and this indeed appears to be the almost exclusive fate of this radical under cool-flame conditions.

The cool flame of methyl ethyl ketone

1951 ◽  
Vol 205 (1082) ◽  
pp. 375-390 ◽  
Keyword(s):  
General Theory ◽  
Methyl Ethyl Ketone ◽  
Explosive Decomposition ◽  
Methyl Ethyl ◽  
Cool Flame ◽  
Factors Affecting ◽  
Slow Reaction ◽  
Hydrocarbon Combustion ◽  
Cool Flames

The regions of temperature and composition for which slow reaction, explosion, single and multiple cool flames respectively occur in the system gaseous butanone/oxygen have been determined. Factors affecting the frequency of cool flames have also been studied. The concentration of peroxides is shown to increase rapidly before the cool flame passes and to suffer a catastrophic decline as it does so. Aldehyde concentration does not follow a parallel course. The results are related to the general theory of hydrocarbon combustion, and the various phenomena are interpreted in terms of the view that the cool flame represents not the combustion of the primary reactants, but the explosive decomposition of small quantities of accumulated intermediate peroxide.

Isotopic tracer studies of the role of butenes in the combustion of n -butane

1970 ◽  
Vol 316 (1526) ◽  
pp. 377-389 ◽  
Keyword(s):  
Free Radical ◽  
Hydroxyl Radicals ◽  
Reactive Intermediate ◽  
Tracer Studies ◽  
Radical Species ◽  
Isotopic Tracer ◽  
Cool Flame ◽  
Slow Combustion ◽  
Subsequent Decomposition

Studies of the oxidation of n -butane, both in the cool flame and slow combustion regions, show that the principal initial products are butene-1 and butene-2 which are formed sim ultaneously with much smaller quantities of all the possible C 4 O-heterocycles. The analytical results suggest that the same free radical species are responsible for attack on the hydrocarbon over the whole temperature range investigated (315 to 423 °C); since the selectivity of attack is low, these are probably hydroxyl radicals. Experiments in which [1 -14 C]butene-1 and [2 -14 C]butene-2 are added to reacting w-butane plus oxygen mixtures make it possible to assess quantitatively the role of the alkenes in the combustion of the alkane. The results show that tetrahydrofuran and 2-methyloxetan are produced entirely by isomerization and subsequent decomposition of butylperoxy radicals but that at least part of the 2- ethyloxiran and 2,3-dimethyloxiran formed result from a reaction involving the addition of HO 2 radicals to n -butene-1 and butene-2 respectively. The importance of butenes in the oxidation of n-butane is demonstrated by the fact that after 50s reaction at 315°C, at least 35% of the initial alkane has been converted to the two conjugate alkenes and about 60 % of these compounds has reacted further. The results show that in general butene-2 is a more reactive intermediate than butene-1.

The oxidation of hexane in the cool-flame region

1952 ◽  
Vol 212 (1110) ◽  
pp. 311-330 ◽  
Keyword(s):  
Atmospheric Pressure ◽  
Chemical Nature ◽  
Complex Mixture ◽  
Cyclic Ethers ◽  
Reaction Products ◽  
Cool Flame ◽  
Oxidation Of Methane ◽  
Cool Flames ◽  
Flame Region ◽  
Considerable Support

The chemical nature of the cool flame of hexane at 300°C, maintained stationary in a flow system at atmospheric pressure, has been investigated. The relative intensities of cool flames obtained from mixtures of differing composition have been measured, using a photomultiplier cell, and correlated with analyses made of the complex mixture of reaction products. The stationary two-stage flames which may be obtained at either higher oxygen concentrations or higher pressures than the cool flame are also described, and investigated similarly. The results are examined in the light of a theory of combustion of the higher hydrocarbons via aldehydes and hydroxyl radicals, which is an extension of a mechanism derived for the oxidation of methane. This receives considerable support, particularly from the identification of the complete homologous series of saturated aldehydes which can result from the hexane molecule. Associated with these reactions are others due to the greater stability of peroxide radicals at 300°C than at the higher temperatures of methane oxidation. Thus the building up of a partial pressure of hydroperoxide sufficient to ignite in the presence of oxygen may initiate the cool flame, and considerable amounts of cyclic ethers have been found which probably had a peroxidic precursor.

Isotopic tracer studies of the further reactions of pentenes in the combusion of pentane

1978 ◽  
Vol 364 (1718) ◽  
pp. 309-329 ◽  
Keyword(s):  
Molecular Mass ◽  
Peroxy Radical ◽  
Combustion Products ◽  
Secondary Products ◽  
Tracer Studies ◽  
Isotopic Tracer ◽  
Cool Flames ◽  
Hydroperoxy Radical ◽  
Lower Molecular Mass ◽  
Before And After

Detailed studies have been made of the mechanisms by which products other than the conjugate alkenes are formed when pentane undergoes combustion in the presence of small quantities of isotopically labelled pent-1-ene and pent-2-ene. Seven pentenes, specifically labelled with 14 C in different skeletal positions, have been synthesized and the fate of the labelled carbon atoms during combustion has been determined. Special attention has been paid to the formation and destruction of the pentadienes, acrolein and ethylene, as products derived from pent-1-ene. In particular, measurements have been made of the instantaneous fraction of the original pentene converted into each of these compounds and of the percentages have been shown to be derived exclusively from the pentenes, whilst acrolein and ethylene, which are complementary products resulting simultaneously from the same pentene molecule, are formed principally from the alkenes. It has also been possible to determine the distribution of the points of abstractive attack in the pentenes and the reactivity rations of pent-1-ene to secondary products. There are sharply defined changes in the relative rates for the pentadienes and pent-1-ene before and after the passage of cool flames; the results suggest that penta-1, 2-diene is oxidized to acrolein and ethylene. A significant amount of 2, 4-dimethyloxetan is formed from both pent-1-ene and pent-2-ene; this compound appears to be produced by a somewhat unusual route, involving the isomerization of one hydroperoxy radical to another through a peroxy radical. The majority of these compounds result from reactions involving free radial addition to the alkene molecule. However, abstractive modes of attack, although leading almost exclusively to the pentadienes, acrolein and ethylene, are quantitatively very important in terms of the total amount of attack on the pentenes. The principal products formed from the pentenes are only minor constituents of the combustion products of pentane. This shows that the coujugate alkenes do not play nearly as important a part in the combustion of pentane as they do in the case of alkanes of lower molecular mass.

The cool-flame oxidation of 3-methylpentane

1972 ◽  
Vol 329 (1579) ◽  
pp. 433-452 ◽  
Keyword(s):  
Hydrogen Transfer ◽  
Detailed Comparison ◽  
Combustion Products ◽  
Experimental Conditions ◽  
Cool Flame ◽  
Slow Combustion ◽  
Flame Region ◽  
The Difference ◽  
Increasing Temperature ◽  
Flame Oxidation

Kinetic and analytical studies of the gaseous oxidation of 3-methylpentane have been carried out both under slow combustion conditions and more especially in the cool-flame region. Analysis of the complex mixtures of in termediate products provides strong evidence for the occurrence of 3-methylpentylperoxy radical isomerization, which leads initially to the formation mainly of the corresponding β- and γ-hydroperoxyalkyl radicals. Detailed comparison of the yields of partial combustion products with those obtained from 3-ethylpentane under similar experimental conditions shows that formation of γ-hydro-peroxyalkyl radicals takes place less readily during the oxidation of 3-methylpentane due to the restricted number of modes of 1:6 hydrogen transfer. In consequence, this branched C 6 alkane gives smaller yields of the corresponding O -heterocycles but larger amounts of β-scission products. During the isomerization of 3-methylpentylperoxy radicals there is evidence for the occurrence of some alkyl group shifts. The results show that there is a somewhat greater tendency for m ethyl groups to migrate than there is for ethyl groups, the difference becoming more marked with increasing temperature.

Slow combustion of methyl ethyl ketone

1968 ◽  
Vol 64 ◽  
pp. 3035 ◽  
Author(s):  
M. Akbar ◽  
J. A. Barnard
Keyword(s):  
Methyl Ethyl Ketone ◽  
Methyl Ethyl ◽  
Slow Combustion

The non-isothermal oxidation of 2-methylpentane. II. The chemistry of cool flames

1967 ◽  
Vol 298 (1453) ◽  
pp. 204-237 ◽  
Keyword(s):  
Flame Temperature ◽  
Complex Mixture ◽  
Isothermal Oxidation ◽  
Qualitative Description ◽  
Cool Flame ◽  
Slow Combustion ◽  
Aldehydes And Ketones ◽  
Flame Region ◽  
Alkylperoxy Radicals ◽  
Liquid Chromatographic

The products of all the modes of non-isothermal oxidation of 2-methylpentane by molecu­lar oxygen and of the attendant slow combustion reactions have been analysed by gas-liquid chromatographic and chemical methods. Oxidation in the cool-flame temperature range produces more than forty molecular species, including O -heterocycles, peroxides, alkenes and saturated and unsaturated aldehydes and ketones. A good qualitative description of the mode of formation of this complex mixture and of its variation with temperature is afforded by the alkylperoxy radical isomerization theory. This theory is developed semi-quantitatively and is in reasonable agreement with the quantitative experimental results. It is concluded that chain propagation in the cool-flame region occurs predominantly by attack on the fuel by hydroxyl radicals; the resulting oxidation is rapid and unselective. In contrast, at temperatures too low for cool-flame formation alkylperoxy radicals are the likely chain-propagating species, whereas at temperatures above the upper cool-flame limit hydroperoxy radicals probably propagate the chain. The mechanism of chain branch­ing is not clear but it is established that, in the cool-flame region, peroxidic compounds are involved.

The cool-flame combustion of decane

1982 ◽  
Vol 382 (1783) ◽  
pp. 429-440 ◽  
Keyword(s):  
Carbonyl Compounds ◽  
Hydrogen Bromide ◽  
Combustion Products ◽  
Cool Flame ◽  
Flame Combustion ◽  
Hydroperoxide Formation ◽  
Slow Combustion ◽  
Flame Region ◽  
Increasing Temperature ◽  
Oxidative Attack

Three approaches have been used to elucidate the mechanism of combustion of decane in the cool-flame region. First, measurements have been made of cool-flame and ignition parameters. These show a well defined change in activation energy at about 530 K. Second, analytical studies have been made of the effect of increasing temperature on the combustion products. These indicate that hydroperoxide formation ceases and that C 10 O-heterocycles become the predominant products at 500-530 K; the relative amounts of decanal and decanone do not however change. Finally, small amounts of hydrogen bromide have been added. These cause the complete conversion of hydroperoxides into decanones even at low temperatures; no lower carbonyl compounds are formed above 500 K. This work has led to two principal conclusions. One, which is shown by all three methods of study, is that the cool-flame combustion of decane involves two distinct mechanisms with a transition at 500-530 K. The other is that the selectivity of initial oxidative attack on decane remains low over the whole of the slow combustion and cool-flame regions between 440 and 680 K, suggesting that hydroxyl radicals are the main attacking species throughout.

The non-isothermal oxidation of 2-methylpentane I. The properties of cool flames

1966 ◽  
Vol 293 (1434) ◽  
pp. 378-394 ◽  
Keyword(s):  
High Pressure ◽  
Pressure Rise ◽  
Isothermal Oxidation ◽  
Temperature Sensitive ◽  
Gaseous Mixtures ◽  
Cool Flame ◽  
Cool Flames ◽  
Slow Combustion ◽  
Subsequent Passage ◽  
Limiting Pressure

The conditions of pressure and temperature under which gaseous mixtures of 2-methylpentane with oxygen react non-iso thermally have been established. At temperatures greater than 307 °C, 1:2 fuel-oxygen mixtures of sufficiently high pressure ignite by a one-stage mechanism. At lower temperatures, the limiting pressure for ignition decreases and the resulting ignition is a two stage phenomenon, the passage of a cool flame preceding that of the hot flame. At similar temperatures but lower pressures, multiple and single cool flames propagate but do not lead to ignition. Correlation of the intensities of and rates of pressure rise due to cool flames with the limiting conditions for low temperature ignition has shown that cool flames affect profoundly the subsequent passage of a hot flame and that this effect is not purely thermal. The complexity of the limiting pressure/temperature relationship for cool flame propagation shows that the transition from slow combustion to cool flame is dependent upon several temperature-sensitive branching reactions. Moreover, the formation of periodic cool flames would appear to necessitate the participation, even under given conditions of pressure and temperature, of more than one branching agent.

Spectra of cool flames and pre-ignition glows

1955 ◽  
Vol 233 (1193) ◽  
pp. 184-194 ◽  
Keyword(s):  
Formaldehyde Emission ◽  
Cool Flame ◽  
Cool Flames ◽  
Auto Ignition ◽  
Weak Limits ◽  
Flame Region ◽  
The Rich ◽  
Reaction Processes ◽  
Rich Mixtures ◽  
Simple Flow

Cool flames and pre-ignition glows of rich and weak mixtures of propane with air and oxygen have been studied in a simple flow system at atmospheric pressure. In the cool-flame region the spectrum shows the usual formaldehyde emission bands, but in the pre-ignition glow near the high-temperature ignition limit the spectrum is quite different, consisting mainly of hydrocarbon flame bands, due to HCO. With weak mixtures the HCO bands are accompanied by strong OH and some CH and CO-flame bands and the spectrum is rather similar to that of the hot flame. With rich mixtures, the HCO bands are accompanied by some CH and formaldehyde bands and weak OH but no C 2 , so that the spectrum is quite different from that of the rich hot flame, which is dominated by C 2 and CH emission and shows little HCO. The unusual observation of strong HCO with rich mixtures is discussed. It is suggested that the C 2 and CH emission occurs under conditions when free atoms and radicals diffuse back from the burnt mixture, while the HCO emission is associated with chain termination or thermal initiation processes. This supports the view that radical diffusion is important in flame propagation. No pre-ignition glow was observed with methane or formaldehyde. The pre-ignition glow of CO occurs readily at both rich and weak limits at atmospheric and low pressure and shows CO-flame bands (attributed to CO 2 ). Addition of methane or formaldehyde to the CO modifies the ignition limits and reduces the glow region, but with a little methane added to rich CO + O 2 , clear spectra were obtained which showed the cool flame bands of formaldehyde superposed on the CO-flame bands. Addition of formaldehyde instead of methane did not produce the formaldehyde bands. The reaction processes are discussed, and it is suggested that during oxidation of CO, free O atoms or O 3 are produced which may react with methane to result in cool flame processes. The relation of these observations to previous work on the auto-ignition of methane is discussed.

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