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.
The mechanism of isobutyraldehyde-octene-2 cooxidation at 20°C has been investigated. The ratio of cis to trans epoxides in the reaction products shows that, at aldehyde concentrations lower than 1 .OM, the epoxide is formed mainly by a radical route. The difference in the A H of formation of cis and trans epoxides is around 0.8 kcal/mole at 20". The isobutyraldehyde involved in the radical epoxidation chain has been found almost quantitatively to be isopropylhydroperoxide, which is formed through the decarboxylation of i-PrCOz. radicals, addition of oxygen, and abstraction of hydrogen atoms from the aldehyde. A rate constant of about 14 M-' sec-l at 20" has been determined for the latter reaction. The chain length for the cooxdination reaction decreases from 75 to 20 as the isobutyraldehyde concentration goes from 1.0 to 0.3M. The termination step seems to involve mainly the interaction of two i-PrO,. radicals. The cooxidation of octene-'2 with pivalaldehyde follows a similar mechanism, but the chain length is about ten times higher under the same experimental conditions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.