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TY - THES AU - Dylong, Dominik TI - Waste2Menthol: development of new synthesis route for (−)-menthol from pulp and paper industrial waste PB - RWTH Aachen University VL - Dissertation CY - Aachen M1 - RWTH-2026-01131 SP - 1 Online-Ressource : Illustrationen PY - 2026 N1 - Veröffentlicht auf dem Publikationsserver der RWTH Aachen University N1 - Dissertation, RWTH Aachen University, 2026 AB - Because of its fresh aroma and cooling effect, (−)-menthol is widely used in the food, cosmetic and pharmaceutical industries as a flavouring and fragrance agent. With its rising popularity, natural menthol extracted from mint can no longer meet the global demand and is increasingly replaced by synthetic menthol. As the established synthesis methods struggle with modern requirements for sustainability, new approaches to synthetic “green” menthol will be needed in the future. This work presents a novel synthesis route for the production of menthol, designed based on the principles of green chemistry. The bicyclic monoterpene 3-carene was chosen as the starting material due to its abundance in crude sulphate turpentine (CST), which is a by-product of the pulp and paper industry. The high reactivity of the strained bicyclic structure of the starting material allows for a transformation to menthol in four steps: (1) saturation of the alkene 3-carene to carane by hydrogenation, (2) transformation of carane to a mixture of isomeric alkenes (menthenes) via scission of a C-C bond, (3) epoxidation of menthenes and (4) hydrogenation of epoxymenthanes to the corresponding alcohols (menthols). For the individual steps, catalyst screening and optimisation of reaction conditions were conducted. For the initial step, various commercially available heterogeneous supported platinum group metal catalysts and Raney nickel were identified as suitable catalysts for the saturation of 3-carene, while significant differences in activity and stereoselectivity were observed. The following isomerisation of carane was conducted over solid acid catalysts and homogeneous acids. As the stereoselectivity of this step is crucial for the overall yield of the route, the focus was on the possible shape selective properties of microporous zeolitic catalysts. However, no significant improvement regarding stereoselectivity was achieved in comparison to homogeneous acids and acidic ion exchange resin. For the epoxidation of menthenes, a suitable biphasic phase transfer catalytic system with hydrogen peroxide as the oxidant and a polyoxometalate as catalyst, was successfully optimised to reduce the formation of by-products by hydrogenolysis. Finally, the reduction of the epoxides via hydrogenation over Raney nickel to a mixture of menthols, from which (−)-menthol can be obtained with suitable methods through isomerisation, was established. Additionally, the isomerisation of the epoxide to the corresponding ketone (menthone) was proposed as an alternative, circumventing the possible epoxide decomposition under hydrogenation conditions. This comparatively short synthesis route combines sustainable raw materials and reagents, heterogeneous catalysis, solvent free conditions and minimal waste generation into an attractive new approach to menthol production. The feasibility of the route was successfully demonstrated, including kinetic and mechanistic investigations, catalyst screening and optimisation of reaction conditions for the individual steps. The remaining challenges for this synthesis are the medium stereoselectivity of the carane isomerisation step and the separation of undesired isomeric by-products. LB - PUB:(DE-HGF)11 DO - DOI:10.18154/RWTH-2026-01131 UR - https://publications.rwth-aachen.de/record/1027007 ER -