UC Santa Barbara
Part 1. Investigations of Reaction Pathways for Catalytic Biomass Conversion Part 2. Mechanistic Study of Hydrogen Peroxide Triggered Carbon Monoxide Release from a Manganese Tricarbonyl Complex
- Author(s): Barrett, Jacob Alexander
- Advisor(s): Ford, Peter C
- et al.
Society’s dependence on fossil carbon resources encompasses many aspects of modern life. Humankind depends on fossil carbon for much of the energy we consume, the medicine we take, and the clothes we wear. Combustion of carbon fuels in a typical engine produces primarily carbon dioxide (CO2) and water which are emitted into the atmosphere. The environmental impact of the resulting anthropogenic CO2 emissions from the combustion of fossil fuels has motivated interest in sustainable technologies to meet our growing energy and manufacturing demands. The selective conversion and upgrading of lignocellulosic biomass and bio-derived chemicals is paramount to creating an environmentally sustainable chemical and fuel industry. This thesis is divided into two parts, where the first part of this work describes efforts to understand the reactivity of Cu-doped porous metal oxide in the conversion of biomass and bioalcohols.
Specifically, lignin conversion into aromatic compounds has the potential to serve as a “green” alternative to the production of petrochemical aromatics. Herein, the use of an earth abundant catalyst, Cu-doped porous metal oxides (CuPMO), for the selective conversion of lignin into oxygenated aromatics was demonstrated using model compounds and organosolv lignin. The catalyst generates hydrogen from alcohols which is then used in hydrogenolysis of aromatic ether bonds. It was shown that in the presence of a non-toxic methylating agent, dimethyl carbonate, O-methylation of hydroxyaromatic intermediates occurs which greatly decreases hydrogenation of the aromatic ring.
Establishing alternatives to petrochemical aromatics only addresses a fraction of the products we utilize. The upgrading of bio-derived alcohols has the potential to serve as “green” alternatives to petrochemicals commonly used in fuels, solvents, and plasticizers. Modification of CuPMO by the addition of small amounts of a chloride salt result in increased catalytic activity and selectivity in the Guerbet condensation of ethanol to n-butanol, due to marked changes in the catalyst’s structural properties.
The second part of this work examines the release of carbon monoxide, a small molecule bioregulator, from manganese carbonyls by photochemical labilization or by the chemical reaction with hydrogen peroxide. Carbon monoxide (CO) and CO releasing molecules have been implicated in several biological applications, including antibacterial and anticancer therapeutics. For example, CO has been shown to negatively affect cellular respiration and thus may be the primary cytotoxic action of manganese carbonyl CORMs against bacterial and tumor cells. On the other hand, manganese carbonyl CORMs that have been depleted of CO also exhibit cytotoxicity. Specifically, it has been proposed that hydrogen peroxide plays a role in the observed cytotoxicity of these manganese carbonyls however, research on the mechanisms of this reaction is currently lacking. Understanding the reaction mechanisms of manganese carbonyls is important in establishing their potential applicability as therapeutics. Herein, the mechanisms of these reactions were probed spectroscopically and electrochemically by kinetic evaluation in aqueous conditions.