Abstract
The automotive industry is a major consumer of plastics, relying on virgin polymers from dwindling crude oil resources and contributing significantly to climate change. While some biopolymer–fibre composites have been adopted, these are often derived from food crops, raising sustainability concerns. Terpenes, by contrast, are abundant, lightly oxygenated hydrocarbons with simple scaffolds that can be integrated into existing infrastructures and, within a biorefinery framework, provide diverse value-added products.Crude sulfate turpentine (CST), a low-value by-product of the pulp and paper industry, is currently used mainly as a low-grade fuel but represents a renewable, inexpensive source of monoterpenes. Limonene has been studied extensively as a platform chemical, though its availability is limited to citrus waste streams. β-Pinene, one of the main constituents of CST, offers a scalable alternative. This thesis investigates its selective conversion to pseudolimonene, a monoterpene structurally related to limonene but with subtle differences that may alter polymer properties, thereby broadening the toolkit for sustainable, high-value biopolymers.
The initial investigations focused on the synthesis of pseudolimonene from β-pinene via a two-step process, first performed in bulk. However, yield consistency was strongly affected by temperature fluctuations. To overcome this limitation, flow chemistry was employed, enabling multi-gram scale reactions with improved reproducibility. This approach avoided the need for costly chromatographic purification and provided a more streamlined pathway for large-scale pseudolimonene production. In addition, storage studies were carried out to establish conditions that prevent unintended isomerisation, ensuring product stability.
The synthesis of non-isocyanate polyurethane monomers from pseudolimonene was investigated via a two-step process, with limonene as a benchmark. Epoxidation conditions were explored to assess stereochemical effects on polymer tacticity, followed by a tailored carbonation strategy that enabled the isolation of two novel cyclic pseudolimonene carbonate diastereomers. By contrast, literature on limonene is less definitive, as its structural features generally allow access to only a single carbonate diastereomer in low yield. Future work will compare the polymerisation of pseudolimonene- and limonene-derived monomers, focusing on how stereopure pseudolimonene carbonates influence polymer properties.
The versatility of pseudolimonene as a platform chemical was further explored through the synthesis of a diol monomer for polyester production, with additional functionalisation routes enabling access to a polyamide monomer. To benchmark reactivity, hydroboration–oxidation conditions were compared between pseudolimonene and limonene using both the classical Brown method and Rh-catalysed reactions. This allowed evaluation of regioselectivity and potential stereoselective outcomes. Notably, experimental results revealed unexpected reversals in diastereoselectivity depending on the borane reagent, underscoring the influence of scaffold symmetry, borane identity, and competing pathways on stereochemical control. Future work will focus on expanding the hydroboration–oxidation study to elucidate the stereochemical mechanisms in greater detail and to fully characterise the resulting products.
| Date of Award | 10 Dec 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | James Taylor (Supervisor), Chris Chuck (Supervisor) & Steven Bull (Supervisor) |