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https://hdl.handle.net/2142/67221
Description
Title
Mechanisms of Chemiluminescence
Author(s)
Horn, Keith Alan
Issue Date
1980
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Language
eng
Abstract
3-Acetyl-4,4-dimethyl-1,2-dioxetane (1) was prepared by the base-catalyzed rearrangement of 4-bromo-3-hydroxy-3,5,5-trimethyl-1,2-dioxolane. Thermal decomposition of this dissymmetric dioxetane to acetone and methylglyoxal proceeds with an activation energy of 26.0 (+OR-) 1 kcal/mol and a log A of 14.2. The enthalpy of activation and entropy of activation were determined to be 25.5 (+OR-) 1.0 kcal/mol and 4.0 (+OR-) 2 eu, respectively. The total yield of excited states produced in the thermal decomposition was determined to be (17 (+OR-) 3) %. Both excited state acetone and excited state methylglyoxal were detected. The excited state multiplicities and yields are: acetone triplet (0.45 (+OR-) 0.20)%, methylglyoxal singlet (1.6 (+OR-) 0.5)%, and methylglyoxal triplet (15 (+OR-) 3)%. No singlet excited state acetone was detected. It is suggested that the observed excited state yields and the low triplet to singlet excited state methylglyoxal ratio can best be rationalized in terms of the energetics of a stepwise bi-radical decomposition of the dioxetane.
The reactions of a diphenoyl peroxide (DPP) and phthaloyl peroxide (PP) with a series of singlet and triplet excited state aromatic hydrocarbon reactants (pyrene singlet (Py('*1)), fluoranthene triplet, anthracene triplet, 9-acetylanthracene triplet and 9,10-dibromoanthracene triplet) were investigated by nanosecond pulsed laser spectrophotometry. It was found that the primary reaction between the excited state and the peroxide is a rate-determining electron transfer to generate a caged radical ion pair. These ions were detected by their characteristic absorption spectra. The bimolecular rate constant for this process was found to depend on the oxidation potential of the excited state involved. The ions formed by this electron transfer can diffuse from the solvent cage or undergo further rapid chemical transformations. Annihilation of those ion pairs which are sufficiently exothermic can generate electronically excited products. The kinetics for the reactions of diphenoyl peroxide with triplet aromatic hydrocarbons were measured and used to verify the generation of radical ion intermediates in the chemically initiated electron exchange luminescence (CIEEL) mechanism for the chemiluminescence of organic peroxides.
The reaction of tetramethyl-1,2-dioxetane with excited singlet pyrene was also investigated.
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