Mechanistic studies of electrocatalytic processes : upgrading of lignin monomers to biofuels (probing substrate synergy); alkylation of amines with alcohols via borrowing hydrogen mechanisms; and reduction of the carboxylic acid functionality in amino ...

Electrochemical synthesis of organic compounds provides a means to revolutionize synthetic industrial chemistry by developing green, cost-effective processes that compete with traditional synthetic routes. For instance, bio-oil, the liquid product from biomass pyrolysis, can be reductively stabilized with electrocatalytic hydrogenation (ECH) using RaneyTM Nickel as the cathode under very mild conditions (75 °C, 1 atm, H2O as electrolyte). This process can be achieved via traditional catalytic hydrogenation protocols, but under harsher conditions of pressurized hydrogen gas and elevated temperature. Electrocatalysis also enables amines to be directly alkylated with low cost and readily available alcohols as electrophiles, where water is the solvent and the only byproduct. Classical alkylation of amines employs alkyl halides or their analogues as electrophiles which leads to a side stream of acids or wasteful salt byproducts. In a third application, ECH provides a means to reduce the carboxylic functionality of amino acids to form amino alcohols. Carboxylic acids are conventionally converted to alcohols using strong reducing agents such as LiAlH4 and BH3. Not only are these reagents costly for large scale production, but they are also hazardous and, like the alkylation above, produce substantial waste byproducts. The outstanding nature of these electrocatalytic methods is the ability to use clean electrons from electricity and protons from water to achieve mild organic transformations using easily prepared heterogenous electrocatalysts, which also allows easy separation and catalyst reusability. This dissertation investigates the mechanisms of three processes: (1) Acknowledging the fact that though a complex mixture of lignin monomers may polymerize under catalytic acid or base and high temperature conditions, we envisage that they may also mutually interfere in the catalytic reduction processes, so the understanding of such interactions is essential to success in moving from model systems to real bio-oil. (2) Abstracting hydrogen (H2) from the CHOH moiety of an alcohol generates a carbonyl group, a good electrophile which enables reductive alkylation of an amine to the corresponding alkylamine via the so-called borrowing hydrogen mechanisms. (3) Electrocatalytic in-situ generation of hydrides on an electrode surface can reduce the carboxylic acid functionality, while retaining the stereochemistry on the amino position of the amino acids.