The aryloxenium ion 1 has been invoked to explain the products of synthetically useful electrochemical and chemical oxidations of phenols and oxidative phenolic couplings. Until recently mechanistic studies of 1 were limited. Prior to our investigations only a few highly stabilized aryloxenium ions were observed but they have little in common with those proposed reactive intermediates. Focusing on the generation of less stabilized 1, this dissertation consists of three related projects.
Chapter 2, Decomposition of 4-Acetoxy-4-(4'-methylphenyl)-2,5-cyclohexadienone 2b addresses indirect and direct detection of 4'-methyl-4-biphenylyloxenium ion 1b during hydrolysis and photolysis of 2b. Indirect detection is accomplished by kinetic and product studies of the hydrolysis of 2b in the presence and absence of N3-. Attempted direct detection via laser flash photolysis (LFP) leads to the observation of two transient species in aqueous buffer. They have been identified as 1b with λmax 460 nm and aryloxy radical 5b with λmax 360 nm. The identity of 1b is confirmed by its reactivity with N3- and 5b is confirmed by its biphasic decay kinetics caused by reversible dimerization.
Chapter 3, Decomposition of O-(4-(4'-methylphenyl)phenyl)-N-methanesulfonylhydroxylamine 13b addresses kinetic studies, temperature studies, and product analyses of the hydrolysis of 13b over a wide range of pH. 1b is generated during the hydrolysis of 13b, but it us not the only path for the hydrolysis reaction. Other pathways, including concerted rearrangement and base-catalyzed α-elimination, are demonstrated. LFP of 13b does not generate 1b but 5b.
Chapter 4, Decomposition of 4-Acetoxy-4-(benzothiazol-2-yl)-2,5-cyclohexadien-1-one 19 addresses studies of the decomposition of antitumor agent 4-(benzothiazol-2-yl)-4-hydroxy-2,5-cyclohexadien-1-one 20 and its putative metabolite quinol ester 19 in aqueous buffers. This is a preliminary test of our hypothesis that aryloxenium ion 21 is the reactive intermediate involved in the decomposition of 19. Evidences for the intermediacy of 21 for hydrolysis of 19 are obtained in kinetic studies and azide trapping experiments performed on 19 and 20. These kinetic and trapping results are consistent with what we observed for other quinol esters that generate aryloxenium ions.
Key words: Reactive intermediate, Aryloxenium ion, photolysis