Understanding gold nanoparticle catalysis in the oxidative amidation of aldehydes and amines
File(s)
Author(s)
Hands, Kane Christopher
Type
Thesis
Abstract
The amide bond is ubiquitous in nature and frequently encountered in many areas of industrial and pharmaceutical chemistry. However, industrial scale synthesis of amide bonds relies on the activation of carboxylic acids, a process which typically employs hazardous or toxic reagents and results in the formation of a stoichiometric amount of waste. Activation is required due to the prohibitively high energy cost of direct amide bond formation; a feature which can be circumvented by approaching amide synthesis via the oxidative reaction of amines with either alcohols or aldehydes.
This thesis describes work undertaken to understand and optimise the Au-catalysed oxidative amidation of aldehydes utilising O2 as the terminal oxidant, producing water as the only by-product. Oxidative amide synthesis from alcohols and aldehydes employing O2 as the terminal oxidant is almost unique to AuNP catalysis.
Herein, conditions applicable for many potential supported AuNP catalysts are described, with particular attention paid to the role of additives and mass transfer in the reaction outcome. The preparation and characterisation of a suitable Au/γ-Al2O3 catalyst is presented, with further discussion on thermal pre-treatment and the subsequent physical changes to the catalyst surface. Attempts to elucidate the mechanism of AuNP catalysed oxidative amidation from aldehydes are made using additives. An unexpected result was further investigated and evidences the multiple roles of reactive oxygen species on the catalyst surface and subsequently a revised catalytic cycle is proposed.
The results obtained throughout this work are used in a concerted manner to develop a proof-of-concept slurry bubble column reactor. Which is used to perform the first reported example of a continuous catalytic oxidative amidation from aldehydes using O2 as the terminal oxidant.
This thesis describes work undertaken to understand and optimise the Au-catalysed oxidative amidation of aldehydes utilising O2 as the terminal oxidant, producing water as the only by-product. Oxidative amide synthesis from alcohols and aldehydes employing O2 as the terminal oxidant is almost unique to AuNP catalysis.
Herein, conditions applicable for many potential supported AuNP catalysts are described, with particular attention paid to the role of additives and mass transfer in the reaction outcome. The preparation and characterisation of a suitable Au/γ-Al2O3 catalyst is presented, with further discussion on thermal pre-treatment and the subsequent physical changes to the catalyst surface. Attempts to elucidate the mechanism of AuNP catalysed oxidative amidation from aldehydes are made using additives. An unexpected result was further investigated and evidences the multiple roles of reactive oxygen species on the catalyst surface and subsequently a revised catalytic cycle is proposed.
The results obtained throughout this work are used in a concerted manner to develop a proof-of-concept slurry bubble column reactor. Which is used to perform the first reported example of a continuous catalytic oxidative amidation from aldehydes using O2 as the terminal oxidant.
Version
Open Access
Date Issued
2018-12
Date Awarded
2019-07
Copyright Statement
Creative Commons Attribution Non-Commercial No Derivatives Licence
Advisor
Hellgardt, Klaus
Hii, Mimi
Sponsor
Engineering and Physical Sciences Research Council
Publisher Department
Department of Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)