Con Robert McElroy

Biocatalysis in bio-derived solvents: an improved approach for medium optimisation

An improved multi-parameter approach to the correlation of enzymatic activity and solvent properties is proposed. The development of the correlation facilitated the introduction of renewable solvents in a CALB catalysed synthesis of fatty esters.

Economic Assessment of Supercritical CO2 Extraction of Waxes as Part of a Maize Stover Biorefinery

To date limited work has focused on assessing the economic viability of scCO2 extraction to obtain waxes as part of a biorefinery. This work estimates the economic costs for wax extraction from maize stover. The cost of manufacture (COM) for maize stover wax extraction was found to be €88.89 per kg of wax, with the fixed capital investment (FCI) and utility costs (CUT) contributing significantly to the COM. However, this value is based solely on scCO2 extraction of waxes and does not take into account the downstream processing of the biomass following extraction. The cost of extracting wax from maize stover can be reduced by utilizing pelletized leaves and combusting the residual biomass to generate electricity. This would lead to an overall cost of €10.87 per kg of wax (based on 27% combustion efficiency for electricity generation) and €4.56 per kg of wax (based on 43% combustion efficiency for electricity generation). A sensitivity analysis study showed that utility costs (cost of electricity) had the greatest effect on the COM.

Acid-catalysed carboxymethylation, methylation and dehydration of alcohols and phenols with dimethyl carbonate under mild conditions

Dimethyl carbonate (DMC) chemistry has been extended to include acid-catalysed reactions of different aliphatic alcohols and phenols. For the first time, p-toluenesulfonic acid (PTSA), H2SO4, AlCl3 and FeCl3 have been shown to aid carboxymethylation for primary aliphatic alcohols at catalytic loadings with quantitative conversion and selectivity. For carboxymethylation of secondary alcohols, stoichiometric PTSA and catalytic AlCl3 both gave quantitative conversion and selectivity. Stoichiometric FeCl3 and H2SO4 promoted dehydration of linear aliphatic alcohols. Additionally FeCl3 catalysed methylation of cyclohexanol, whilst AlCl3 resulted in methylation of phenolic compounds. This research expands the range of potential application for DMC in green chemistry.

Towards sustainable kinetic resolution, a combination of bio-catalysis, flow chemistry and bio-based solvents

The esterification of 2-phenylpropionic acid was investigated as a model system for enzyme catalysed (CALB, Novozyme 435) reactions in bio-based solvents. A multi-parameter correlation taking into account solvent parameters was developed to explain experimental observations. A continuous flow process using p-cymene as the solvent was operated over several weeks, thus combining a sustainable solvent and flow chemistry for kinetic resolution.

Development of pharmaceutically relevant bio-based intermediates though aldol condensation and Claisen–Schmidt reactions of dihydrolevoglucosenone (Cyrene®)

Dihydrolevoglucosenone (Cyrene®) has been successfully utilised as a bio-based platform molecule for the synthesis of pharmaceutically relevant intermediates through aldol condensation reactions. Utilising sustainable synthetic methodologies, the self-aldol condensations reaction of Cyrene was achieved in high purity, with isolated yields of 81.3%. Claisen-Schmidt reactions with a range of aromatic and heteroaromatic aldehydes yielded novel cyrene-based compounds, characterised by single-crystal X-ray diffraction, FT-IR, NMR and MS.

Toward Financially Viable Phytoextraction and Production of Plant-Based Palladium Catalysts

Although a promising technique, phytoextraction has yet to see significant commercialization. Major limitations include metal uptake rates and subsequent processing costs. However, it has been shown that liquid-culture-grown Arabidopsis can take up and store palladium as nanoparticles. The processed plant biomass has catalytic activity comparable to that of commercially available catalysts, creating a product of higher value than extracted bulk metal. We demonstrate that the minimum level of palladium in Arabidopsis dried tissues for catalytic activity comparable to commercially available 3% palladium-on-carbon catalysts was achieved from dried plant biomass containing between 12 and 18 g·kg-1 Pd. To advance this technology, species suitable for in-the-field application: mustard, miscanthus, and 16 willow species and cultivars, were tested. These species were able to grow, and take up, palladium from both synthetic and mine-sourced tailings. Although levels of palladium accumulation in field-suitable species are below that required for commercially available 3% palladium-on-carbon catalysts, this study both sets the target, and is a step toward, the development of field-suitable species that concentrate catalytically active levels of palladium. Life cycle assessment on the phytomining approaches described here indicates that the use of plants to accumulate palladium for industrial applications has the potential to decrease the overall environmental impacts associated with extracting palladium using present-day mining processes.

DFT and experimental analysis of aluminium chloride as a Lewis acid proton carrier catalyst for dimethyl carbonate carboxymethylation of alcohols

The Lewis acid catalysed mechanism of dimethyl carbonate (DMC) mediated carboxymethylation of alcohol was investigated experimentally and through computational chemistry methods including density functional theory (DFT). Experimental data showed that catalytic loading of AlCl3 enabled the quantitative carboxymethylation of octanol in less than 20 h, while in the absence of a catalyst only trace product was observed. The geometry of the identified transition states and related energy barriers indicate that the activation energies in AlCl3 catalysed pathways are significantly lower than those in catalyst-free pathways. Theoretical quantum chemistry methods were utilised to explore and analyse the complex of DMC with AlCl3. Natural bond orbital theory analysis and molecular orbital analysis demonstrated that the dipole present in Al–Cl covalent bonding plays a vital role in assisting the proton-transfer process. Most importantly, the reaction mechanism disclosed in this research can aid in the exploration of new Lewis acid catalysed processes in the field of dialkyl carbonate chemistry.