Date of Award

1-1-1987

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

The electrochemical cleavages of diaryl ethers were studied. The radical anions or dianions of diphenyl ether, 1-phenoxynaphthalene, and 9-phenoxyanthracene were generated electrochemically. The cleavage reaction rates were measured and mechanisms of each cleavage reaction were postulated.Direct reduction of diphenyl ether was observed to be by one-electron at $-2.98$ V vs. SCE. A homogeneous redox catalysis process with acenaphthene as electron mediator was used to determine the rate of cleavage. Cyclic voltammetry was used to acquire peak current data. The radical anion of diphenyl ether was found to cleave by a unimolecular pathway at a rate of 4 $\times$ 10$\sp5$s$\sp{-1}$. A 2-(3-butenyl) substituent was employed as an intramolecular trap. The addition of a hydrogen atom donor to the solution effectively decreased cyclization of the 2-(3-butenyl)phenyl radical to 1-methylindan. The rate constant for the cyclization was calculated to be 1-2 $\times$ 10$\sp8$s$\sp{-1}$.The 1-phenoxynaphthalene radical anion, E$\sb{\rm p}$ = $-2.42$ V vs. SCE, cleaved slowly to form phenoxide ion and naphthalene as final products. The use of controlled current methods to form the reducing agent tetra-n-butylammonium-amalgam (TBA(Hg)$\sb{\rm n}$) also produced cleavage. It was postulated that the TBA(Hg)$\sb{\rm n}$ caused formation of the dianion, which subsequently cleaved. A 2-(3-butenyl) substituent was also used on 1-phenoxynaphthalene, i.e., 2-(3-butenyl)-1-phenoxynaphthalene, to help distinguish between naphthyl anion and naphthyl radical intermediacy. The amount of cyclization to 1-methylbenz (e) indan and ratio of cyclized to uncyclized products was controlled by addition of D$\sb2$O (a proton source), or isopropylate (a hydrogen atom source) to the reaction solution. These experiments confirmed naphthyl anion and naphthyl radical formation from specific experiments.9-Phenoxyanthracene radical anion (E$\sb{\rm p}$ = $-1.78$ V vs. SCE) and dianion (E$\sb{\rm p}$ = $-2.58$ V) reduction waves were produced by cyclic voltammetry. Chronamperometric experiments on the radical anion indicated it to be extremely stable with a half-life of $>$500 s. Cyclic voltammetric scan rate studies and chronoamperometry were used to conclude that the dianion was protonated by residual water and a rate determining cleavage reaction followed. The protonated dianion cleaved at a rate of 1 s$\sp{-1}$, as determined by comparison of experimental chronoamperometric data with simulation data for an ECE nuance mechanism. Cleavage of 1-phenoxyanthracene was concluded to have proceeded through a reduction-protonation-elimination mechanism. (Abstract shortened with permission of author.)

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