ChemInform Abstract: INTRAMOLECULAR PROPAGATION IN THE OXIDATION OF N‐ALKANES. AUTOXIDATION OF N‐PENTANE AND N‐OCTANE

SICKLE, D. E. VAN; Mill, Theodore; Mayo, Frank R.; Richardson, H. Wayne; Gould, Constance W.

doi:10.1002/chin.197413201

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“…Thus, the liquid-phase oxidation of n-pentane and n-octane at 100" and 125°C give very little intramolecular oxidation [20] despite the fact that in octane each of the six possible sec-octylperoxy radicals can find, on the average, three secondary C-H bonds in the favored geometric positions for internal abstraction. Only when n-alkane concentrations are very low (gas phase) and the temperature is near 300°C does internal hydrogen abstraction appear to compete effectively with external abstraction [1,2].…”

Section: E Competition Between Intra-and Intermolecular Abstractionmentioning

confidence: 90%

The liquid‐phase oxidation of 2,4‐dimethylpentane

Mill

Montorsi

1973

Int J of Chemical Kinetics

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The initiated oxidation of 2,4dimethylpentane in the neat liquid phase at 100°C with 760 torr 0 gives more than 90% of a mixture of 2,4-dihydroperoxy-2,4-dimethylpentane and 2-hydroperoxy-2,4-dimethyIpentane in a ratio of 7 : 1. The rate of oxidation depends closely on the [initiator]"*, consistent with a mechanism in which chain termination occurs mostly by interactions of two 2-hydroperoxy-2,4-dimethyI-4-pentylperoxy radicals. 2,4-Dimethylpentane oxidizes only one sixth as fast as isobutane at the same rate of initiation at 100°C. In cooxidations of the same hydrocarbons? it is 0.71 as reactive as isobutane toward any of the peroxy radicals involved. 2,4-Dimethylpentane oxidizes 7.5 times a s fast at 125°C as at 50°C for the same rate of initiation, but the ratio of dihydroperoxide to monohydroperoxide increases only from 5 to 7, corresponding to a difference in activation energy between intramolecular and intermolecular abstraction of 1 kcal/mole. The overall activation energy (E, -E1,.J is 10.7 kcal/mole, close to the value of 12 kcal/mole found for isobutane.Ring closure of 2-hydroperoxy-2,4-methyl-4-pentyl radicals to oxetane, not detected during oxidation, was observed when this radical was generated at 100°C in the near-absence of oxygen. The rario of rate constants for oxetane formation and addition of oxygen to the 2,4-dimethv1-2-hydroperoxy-4-pentyl radical is about 5.4X 10-5 M at 100°C. Thus, ring closure to oxetane is too slow to compete with addition of oxygen above -200 torr. At 1 OO"C> '2,3-dimethylbutane gave no evidence of any intramolecular abstraction. However, 2.3-dimethylpentane did give at least 1 2yo 2,4-glycol or hydroxvketone.Absolute values for Ep, E,, k,, k,, and k c were derived.

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Section: E Competition Between Intra-and Intermolecular Abstractionmentioning

confidence: 90%