Paraffins autoxidation

Examples include high-pressure hydrolysis of a nitrile paraffin autoxidation homogeneous aldehyde hydrogenation olefin hydroformylation to alcohol with paraffin by-product formation, aldehyde condensation to heavy ends, and olefin isomerization cyclo-addition reactions and hydrogen-halide reactions. 

Dichlorine shortens the induction period of autoxidation of paraffin wax [187] and accelerates the oxidation of hydrocarbons [109]. Difluorine is known as very active initiator of gas-phase chain reactions, for example, chlorination [188,189]. 

Contrary to our results, other workers (4, 9, 20, 36) state that in the stabilization of carotene, paraffin wax, and lard the activity of pyrocatechol is favorably affected by substitution at position 4, not only by normal but by tertiary alkyl groups as well. Disparate influences of substitution are not surprising when comparing the activity in different substrates owing to the possibility of directive influences in the process of inhibited oxidation. The participation of phenolic antioxidants in the inhibition of autoxidation can be demonstrated (1, 2, 3) simply as a reaction between the molecule of antioxidant AH and the alkylperoxy radical ROO formed duririg the autoxidation of the substrate RH. During this process, an aryloxy radical (A ) is first generated. 

Primary and secondary alcohols appear to oxidize rapidly to the corresponding carbonyl compounds with good efficiencies [10]. The initial point of attack is predominantly on the hydrogen on the carbinol carbon atom. Tertiary alcohols do not have a hydrogen in this position and are relatively resistant to oxidation. Alcohols, like aldehydes, are usually important intermediates in paraffin oxidations [18]. They undergo subsequent oxidation somewhat less readily than aldehydes, but primary and secondary alcohols oxidize much faster than the starting paraffin(s). Quite unlike aldehydes, however, alcohols do not, in general, autoxidize readily by themselves. Moreover, the deliberate addition of alcohol to an oxidation can slow or even stop the reaction [10, 19-21]. 

Thus, a,a- and /J,/9-dinaphthylamines, and hydroquinone markedly check autoxidation of paraffins at 160° C. but lead tetraethyl and other antiknocks have but little effect.89 Layng and Youker found that in comparison with lead tetraethyl in the gas phase, diphenylamine had a hundred times the effectiveness as an oxidation inhibitor as it possessed as an antiknock dope. Some distinction evidently must be made between inhibitors which act at low or moderate temperatures and antiknock dopes which alter combustion phenomena but do not affect low temperature oxidation. Moureu, Dufraisse and Cliaux explain the ineffectiveness of lead tetraethyl at low temperatures as due to extreme ease of oxidation but this has not been demonstrated. On the contrary it has been shown that the effective antiknock dopes are not readily oxidized by air.01... 

The primary, but unstable products in autoxidation of paraffins are hydroperoxides, which quickly decay to ketones and more slowly to alcohols and acids. Typical selectivities to hydroperoxides and ketones as functions of fractional conversion are shown in Figure 7.4 (first-rank Delplots). The selectivity to hydroperoxides as sole and unstable primary products is 1.0 at zero conversion and decays steeply. The selectivity to ketones as quickly formed secondary products is zero at zero conversion and goes through an early maximum of about 0.35, other products also being formed. However, if no samples were taken during the first 0.5% conversion, the selectivity to ketones would be judged to extrapolate to about 0.4, as though ketones were primary products ... 

Gum formation. Heating of paraffinic hydrocarbon mixtures found in jet fuels, gas oils and similar products may result in the precipitation of gum-like material. A sequence of events has been proposed by Taylor [1967, 1968]. Autoxidation forms a soluble oxidation product, with further oxidation to an insoluble polymer. The polymer may be formed on the wall or transported as particles to the wall. 

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