Co-Oxidations of Hydrocarbons

The oxidations of acetaldehyde, heptanal, octanal, cyclohexanecarboxaldehyde, pivaldehyde, and benzaldehyde in chlorobenzene at 0 "C have been studied. These aldehydes oxidize at similar rates under similar conditions because there are compensating changes in the rate constants for chain propagation (k,) and chain termination (2k,). The termination rate constants increase from -7 x lo6 M-I S-I f or pivaldehyde and cyclohexanecarboxaldehyde to -2 x lo9 M-' s-' f or benzaldehyde. The propagation rate constants increase from -1 x lo3 M-'s-' for pivaldehyde to -1 x lo4 M-l s-' f ox benzaldehyde.The rate of oxidation of the aldehydes was decreased by the addition of 1,4-cyclohexadiene, tetralin, tetralin hydroperoxide, cumene, cumene hydroperoxide, t-butyl hydroperoxide, and 2,6-di-t-butyl-4-methylphenol. As a result of product analysis and absolute rate constant measurements, it is concluded that the peroxy radicals derived from aldehydes are considerably more reactive in hydrogen atom abstraction from hydrocarbons than are the peroxy radicals derived from the hydrocarbons. In the abstraction from cyclohexadiene, the acylperoxy radicals appear to be from 15 to 70 times as reactive, and the benzoylperoxy radicals about 8W900 times as reactive, as the hydroperoxy radical. The differences in reactivity are very much less pronounced in the abstraction from 2,6-di-t-butyl-4-methylphenol.The great ease of oxidation of all aldehydes, and particularly benzaldehyde, is due at least in part to the high reactivity of the peroxy radicals formed in these reactions.

Section: Composition Co-oxidationsmentioning

confidence: 99%

Section: Composition Co-oxidationsmentioning

confidence: 99%

Section: /0'mentioning

confidence: 99%

See 1 more Smart Citation

Absolute rate constants for hydrocarbon autoxidation. XIII. Aldehydes: photo-oxidation, co-oxidation, and inhibition

Заиков¹,

Howard²,

Ingold³

1969

“…ref. 34). The present results raise the distinct possibility that the directly measured propagation (kPRR) and termination (2ktRR) rate constants for these styrenes may be too large by a factor of about four because of some unappreciated feature of their copolymerization reactions with oxygen.…”

Section: The Oxidatiolz Of Ring-substituted Cumenesmentioning

confidence: 99%

Absolute rate constants for hydrocarbon oxidation. VIII. The reactions of cumylperoxy radicals

Howard¹,

Ingold²,

Symonds³

1968

104

Absolute rate constants have been measured for the reactions of cumylperoxy radicals with a number of hydrocarbons. The cumylperoxy radicals were produced from cumene hydroperoxide. Sufficient hydroperoxide was present to ensure that only cumylperoxy radicals were involved in the rate-determining propagation reaction.Primary and secondary deuterium isotope effects have been measured for propagation and termination in the oxidation of cumene. The rate of hydrogen atom abstraction from ring-substituted cumenes by cumylperoxy radicals can be correlated by the Hammett equation using o* substituent constants, p = -0.29. Primary and secondary peroxy radicals are about 3-5 times more reactive in hydrogen abstraction than tertiary peroxy radicals.

“…The importance of polar effects on peroxy radical selectivity and relative reactivity has recently been stressed by Mayo et nl. (16). More directly, we have previously shown that the rate constant for hydrogen atom abstraction from 2,6-di-t-butyl-4-metl~ylpl~e1~ol (where the transition state involves a similar separation of charge (20,22)) by ring-substituted polystyrylThe propagation rate constants for the izbutylperoxy radical are larger than the values found for sec-butylperoxy and cyclohexylperoxy but are, nevertheless, within the overall range of values found for the various secondary peroxy radicals.…”

Section: Inhibition Experimelztsmentioning

confidence: 73%

Absolute rate constants for hydrocarbon oxidation. XII. Rate constants for secondary peroxy radicals

Howard¹,

Ingold²

1968

Rate constants have been measured for hydrogen abstraction from four aralkanes and addition to two aralkenes by five secondary and one primary peroxy radical. These rate constants appear to show a slight dependence on the structure of the attacking peroxy radicals which may be due to the inductive effects of the substituents on the radical. The secondary and primary peroxy radicals are generally about 2 4 times more reactive than tertiary peroxy radicals in abstraction and 4-8 times more reactive in addition. The lower reactivity of tertiary peroxy radicals is probably due to steric factors.