Abstract
Current industrial processes, such as plastic production and energy sector, are strongly dependent on fossil-based feedstocks. However, these feedstocks have a limited availability and adverse environmental impact, thus developing new sustainable feedstocks is one of the biggest challenges of modern research.Terpenes are an abundant, but currently underutilised sustainable feedstocks. In terms of availability, the two major terpene feedstocks are limonene and pinene, but industrial biotechnology processes can deliver alternative terpene feedstocks, such as B-elemene or farnesene. In this project limonene and B-elemene were investigated in epoxidation and carbonation reactions.
Epoxides are used in many branches of industry - for example in the polymer industry to produce polyethers, polycarbonates, polyesters and others. Epoxidation of B-elemene was performed using three different catalysts: Venturello polyoxometalate (VENT), Mizuno polyoxometalate (MIZ) and trifluoroacetophenone (TFAP). All these use H2O2 as a green oxidant.
It has been found that the epoxidation of B-elemene is a consecutive reaction in which monoepoxide (BEMO) is formed first, then the bisepoxide (BEBO), and with long reaction times the trisepoxide (BETO). Epoxidation catalysed by VENT can be performed in flow microreactor and it can yield BEMO, BEBO and BETO. However, catalyst deactivation was found to be an issue.
Epoxidation catalysed by MIZ can yield only BEMO and BEBO, but no BETO. The issues with complex catalyst degradation and high reaction dilution have to be addressed to make this reaction industrially viable. Epoxidation catalysed by TFAP is still to be explored with preliminary results showing it can epoxidise BE to BEMO, BEBO and BETO.
Carbonation was first studied with 1,2-limonene oxide and 8,9-limonene oxide in order to achieve cyclic carbonates. The main focus was on using one catalyst for epoxidation and carbonation. The co-operative effect of VENT and Bu4NBr was observed during 1,2-limonene oxide carbonation, but it did not have significant effect on 8,9-limonene carbonation. The influence of temperature, pressure, different catalysts and the starting stereochemistry of epoxide was tested. The resultant carbonates (trans-1,2-limonene cyclic carbonate and 8,9-limonene cyclic carbonate) underwent thiol-ene reaction to create bi-functional carbonate compounds and opened with an excess of amine resulting in novel hydroxyurethanes.
Carbonation of B-elemene bisepoxide and trisepoxide was performed using the quaternary ammonium salt Bu4NBr in order to produce novel cyclic carbonates. The reactivity of each epoxide was dependent on the reaction temperature. Preliminary polymerisation studies were performed on B-elemene biscarbonate (BEBC), but due to the low purity of monomer these were unsuccessful in yielding polymers. However, the experiments confirmed that BEBC can react with an amine resulting in hydroxyurethanes. The purity of BEBC could be improved by a better synthesis method as the main by-product is B-elemene monocarbonate monoalcohol (BEMCMD) which is a result of epoxide rearranging. It might be due to inefficient CO2 mass transfer, high reaction temperature or a complex interaction between both of those.
Carbonation of BETO yielded B-elemene biscarbonate monoepoxide (BEBCMO) and B-elemene triscarbonate (BETC). However, BETC suffered the same issues as BEBC and under reaction conditions a mixture of BETC and B-elemene biscarbonate monoalcohol (BEBCMD) was produced. The most interesting carbonate synthesised was BEBCMO as it is a bi-functional carbonate species suitable for NIPU synthesis which has an additional epoxide group available for postfunctionalisation. BEBCMO can be synthesised selectivity at 100 °C, which is 40 °C reduction in the reaction temperature comparing to the BEBC and BETC synthesis.
In this work, the catalytic approach to BE epoxidation was shown and carbonation reaction was investigated as a way of utilising epoxides and another renewable feedstock – CO2. Carbonation was first investigated using 1,2-limonene oxide and 8,9-limonene oxide. Then the carbonation of BEBO and BETO was investigated.
| Date of Award | 1 Apr 2020 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Uli Hintermair (Supervisor), Matthew Davidson (Supervisor) & Pawel Plucinski (Supervisor) |
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