Catalytic upgrading and valorization of biorenewable monoterpenoid feedstocks

Abstract

This thesis describes research carried out into the development of sustainable catalytic upgrading and valorization of biorenewable monoterpenoid feedstocks. Following a review of the state-of-the-art catalytic technology regarding the upgrading of monoterpenoid feedstocks, the research is presented in four sections. The first and second of these are the development of a biorefinery model to transform an industrial waste by-product, crude sulfate turpentine, to terephthalic acid initially, followed by other useful chemical products. The third describes the development of synthetic routes to access all eight stereoisomers of the non-toxic insect repellent, p-menthane-3,8-diol from cheap and abundant renewable monoterpene feedstocks. Finally, the development of scalable batch and flow epoxidation catalytic protocols using a preformed polyoxometalate system was applied to a wide variety of terpene substrates, to enable their use in flavour/fragrance industries and other applications.
The need to transform existing petrochemical-based industries and chemical technologies towards a biobased chemical economy is becoming increasingly urgent due to dwindling supplies of fossil fuels and their impact on the environment. Among the many potential replacements, terpenes and terpenoids have shown great promise due to their lightly oxygenated, monomeric structures which would be compatible with many existing chemical processing technologies, as well as containing useful chemical properties such as chirality.
A sustainable route from crude sulfate turpentine (current largest source of terpenes commercially), to terephthalic acid was developed. This route adopted the principles of green chemistry where possible, using catalytic, atom economical and solvent free protocols to produce high yields of this monomer which is frequently reported in the top 10 commodity chemicals produced globally. As well as this, a biorefinery concept was adopted throughout the development of this route, with intermediates being exploited through different catalytic upgrading methodologies to produce a wide range of potential fuel additives, monomers, solvents, biologically active compounds and chemical intermediates.
The mosquito repellent p-menthane-3,8-diol (PMD) is a much needed non-toxic and pleasant smelling alternative to the most commonly used repellent, N,N-diethyl-m-toluamide (DEET). PMD is currently sold as a mixture of its eight stereoisomers but the individual efficacy of each is relatively unknown. Stereoselective synthetic routes to all eight of these were devised on multi-gram scales, with extensive structural analysis and characterisation carried out, allowing for future work to focus on studying their repellency properties and potential use in commercial/pharmaceutical applications.
Finally, epoxidation protocols were developed for the batch and continuous production of terpene epoxides. Previous work within the group examining a preformed polyoxometalate catalyst was developed to allow for a wider substrate scope, as well as catalyst recycling. The application of these catalysts for terpene epoxidations in flow is reported for the first time to allow the production of large quantities of these industrially relevant and valuable epoxides.

Date of Award	13 May 2020
Original language	English
Awarding Institution	University of Bath
Supervisor	Steven Bull (Supervisor) & Pawel Plucinski (Supervisor)