Ethyl radicals, from decomposition

Lin and Back have also obtained information about reaction (3), the decomposition of the ethyl radical, from measurements of the rates of formation of ethylene and butane. The scheme of reactions may be written as... 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

In the reaction of 2,3,3-triethyloxazirane (25), three radicals are involved 26, 27, and 28. Radical 26 (Fig. 1) corresponds to the chain reaction propagating radical of the previously mentioned decomposition [Eqs. (20) and (21)]. From 26 hy fragmentation an ethyl radical (27) is formed together with the acid amide. Finally, by radical attack on the oxazirane, 29 can be formed which rearranges to the... 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

The use of PbEt4 as an anti-knock agent in petrol depends in part on the ability of the ethyl radicals, generated on its thermal decomposition, to combine with radicals produced in the over-rapid combustion of petroleum hydrocarbons chain reactions which are building up to explosion (knocking) are thus terminated short of this. The complete details of how PbEt4 operates are not known, but there is some evidence that minute Pb02 particles derived from it can also act as chain-stoppers . 

This experiment showed that some volatile component was formed in the thermal decomposition of tetramethyllead and that this compound consumed a cold lead mirror with formation of a volatile product. If, instead, a zinc mirror was first deposited and allowed to be consumed by the volatile product from decomposition of tetramethyllead, dimethylzinc could be identified as the product. Paneth concluded that free methyl radical was formed in the thermal reaction and could determine its half-life to be 0.006 seconds under the reaction conditions employed. Also, free ethyl radicals could be formed in... 

Paneth22 first demonstrated that the decomposition by heat of certain organic compounds furnished products which removed metallic mirrors of silver, tellurium and other metals from the walls of the tube. For example when vapor of lead tetraethyl was heated a silver coating on the inside of the exit tube was removed for a considerable distance. The results were interpreted to mean that ethyl radicals were liberated in the thermal decomposition and... 

CH3CHCHD and not at all from CH2CHCD3. Ethylene is also formed by disproportionation of ethyl radicals produced in primary processes and perhaps by the decomposition of the excited ethyl radical. 

Owing mainly to its unique properties as a source of free radicals, the decomposition of dtBP has been the subject of intensive investigation by a number of different laboratories. " The products of the gas-phase thermal decomposition arc principally CzHe + acetone, together with small amounts of methyl ethyl ketone, higher boiling ketones, and methane, the latter being assumed to arise from secondary reactions of the product acetone with CH3 radicals. The stoichiometry can be represented by... 

The relative contributions of the three proposed reaction paths remain to be determined. The products from both the retro-ene and the addition reactions can be predicted with some quantitative certainty. For dodecene, the former produces only 1-nonene and propylene. The product distributions from the addition paths should be identical to those from the cracking of the corresponding paraffins. These product distributions can be predicted using the method of Rice and Kossiakoff (16). This approach parallels excellently with experiments (16,17). (From available data we estimate its accuracy as d=10%.) For dodecene, the addition of hydrogen atoms, methyl radicals, and ethyl radicals will produce Ci2H25, Ci3H27, and Ci4H29 parent radicals. The product distributions predicted by the Rice-Kossiakoff method for the decomposition of these radicals at 525°C are shown in Table IV. 

The mode of formation of ethylene is one of the disputed questions of the mechanism. The amount of ethylene rapidly increases with increasing temperature. Boyer and Niclause assumed, in accordance with the direct experimental observations of Sworski and Burton that the decomposition of the ethyl radicals may contribute considerably to the formation of C2H4 at high temperatures. As was pointed out by Laidler and Eusuf ° , the deviation of the reaction order from i at higher temperatures can be explained by taking into consideration the first-order decomposition of the ethyl radicals. These authors found a slight positive curvature in the plot of CaHs/CjH versus [C2H5CHO] and ascribed it to the occurrence of molecular step... 

Halogenation of Alkanes - Reaction Mechanism Section 4.4D The ethyl radicals formed from the decomposition of tetraethyllead can react with methane to form methyl radicals or with chlorine to form chlorine radicals. Both of these are part of the propagation steps. 

The chemical reactivities of ketones follow the order terf-butyl > ethyl > methyl, which is the stability order for the cations or radicals of these groups. This suggests that the mechanisms of ketone decomposition involve a rate-determining migration of an electrophilic alkyl moiety of the ketone, perhaps leading to the production of acyl and alkoxy radicals from some partially oxidized intermediate. 

Kinetics of decomposition at short times (methyl radical from the n-butane [825], 2, 2-dimethylbutane [240] and 2, 2-dimethylpentane [240] ions, loss of ethyl from n-heptane, n-hexane and n-octane ions [522, 825], loss of methane from the neopentane ion [825], and loss of ethane from the 3-ethylpentane ion... 

A number of decompositions of n-butylbenzene and n-pentylbenzene following FI have been elucidated through D- and C-labelling [90, 902]. Methyl and ethyl radicals were lost from the ends of the alkyl chains, but there was evidence of interaction between the chains and the phenyl rings. Hydrogen transfers from the side chains via 5-, 6- emd... 

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