Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

William A. Pryor

Abstract

Allylbenzene ozonide (ABO), a model for poly-unsaturated fatty acid (PUFA) ozonides, is shown to initiate the autoxidation of methyl linoleate (18:2ME) at 37$\sp\circ$C under 760 torr of oxygen. This process is inhibited by d-alpha-tocopherol ($\alpha$-T) and 2,6-di-tert-butyl-4-methylphenol (BHT). Rates of initiated autoxidation were measured by appearance of conjugated diene (C.D.) and oxygen-uptake experiments; rates are proportional to the square root of ABO concentration, implying that the usual free radical autoxidation rate law is obeyed. Activation parameters for the thermal decomposition of ABO were determined under N$\sb2$ in the presence of radical scavengers and found to be E$\sb{\rm a}$ = 28.2 $\pm$ 0.3 kcal mol$\sp{-1}$ and log A = 13.6 $\pm$ 0.2; k$\sb{\rm d}$(37$\sp\circ$C) is calculated to be (5.1 $\pm$ 0.3) $\times$ 10$\sp{-7}$ sec$\sp{-1}$. Preliminary autoxidation data are also reported for ozonides of 18:2ME and methyl oleate (18:1ME). Thermal decomposition of ABO at 98$\sp\circ$C in the liquid phase yields toluene, bibenzyl, phenylacetaldehyde, formic acid, and benzyloxymethyl formate as major products; benzyl chloride is formed when chlorinated solvents are employed. In addition to these products, benzyl formate is formed when ABO is decomposed at 37$\sp\circ$C. When ABO is decomposed at 37$\sp\circ$C in the presence of the spin traps 5,5-dimethyl-1-pyrroline N-oxide (DMPO), $\alpha$-phenyl-N-tert-butyl-nitrone (PBN), or 3,3,5,5-tetramethyl-1-pyrroline N-oxide (TMPO), electron spin resonance (ESR) signals are observed that are consistent with benzyl and other carbon- and oxygen-centered radicals. A mechanism for the thermal decomposition of ABO that involves peroxide bond homolysis and subsequent $\beta$-scission is proposed. Thus, Criegee ozonides decompose to give free radicals at quite modest temperatures.

Pages

213

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