Homogeneous Cobalt Catalyzed Oxidations

Mechanistic studies of the oxidation of various substituted phenols to benzoquinones by Co(II) bis(salicylidene-(gamma)-iminopropyl)-methylamine, CoSalMDPT are described in Chapter I. The reaction is first order in {O(,2)}, {substrate}, and {Co}. A series of experiments are reported to provide strong support for a mechanistic scheme that involves reaction of coordinated dioxygen in two distinct steps of the mechanism. Coordination of O(,2) to this cobalt(II) complex enhances the ability of the dioxygen to abstract hydrogen atoms from the phenol to produce phenoxy radicals. This proposed hydrogen atom abstraction step is supported by hydrogen bonding and EPR studies. A deuterium isotope study showed this step is not rate determining. Further reaction of the phenoxy radical with a Co-O(,2) species is supported by several pieces of evidence. If the phenoxy radicals are generated simultaneously via some other reaction in the presence of a cobalt complex that does not bind O(,2), no benzoquinone is formed. Also, the EPR spectrum of a cobalt-peroxy-benzoquinone complex which was isolated from the reaction mixture, displayed an overlapping Co-O(,2) and phenoxy radical signal. This suggests an equilibrium between a Co-O(,2) species and a phenoxy radical. Catalyst deactivation studies revealed benzoquinone and water do not inhibit the reaction, but rather acids produced as oxidized side products eventually deactivate the catalyst. Thus, the addition of non-coordinating bases to the reaction medium greatly enhanced the number of turnovers.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Zombeck, Alan

• Chemistry, Inorganic

Identifier

(UMI)AAI8203646

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70178