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CRYSTAL ENGINEERING TO CONTROL THE REGIOSELECTIVITY IN THE DIMERISATION OF TRANS-CINNAMIC ACID DERIVATIVES

Gubbels, Lisa
(2022)

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Gubbels_25111500_2022.pdf
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Details

Supervisors
Leyssens, Tom
Faculty
Faculté des sciences
Degree label
Master [120] en sciences chimiques, à finalité approfondie
Abstract
This project is focusing on controlling the regioselectivity of a photochemical [2+2] cycloaddition without solvent. It was chosen to focus on trans-cinnamic acid as this compound can dimerise under UV-light in the solid state. The purpose is to use crystal engineering to orient trans-cinnamic acid in a direction that could lead, after reaction, to a desired regioisomer. The final aim is to be able to do this reaction selectively since cyclobutane rings are widely used. It is therefore of interest to broaden this research on cinnamic acid derivatives or molecules that have a similar structure. Cinnamic acid is an acid that has two isomers, trans or cis-cinnamic acid. Trans-cinnamic acid is the predominant form in nature (>99%) because it is more stable than the cis isomer. The cis isomer transforms in the trans-isomer under sunlight. Furthermore, the preparation and isolation of cis-cinnamic acid with high purity is not easy. Trans-cinnamic acid and derivatives of cinnamic acid (four trans and one cis) are the subject of this study. Trans-cinnamic acid has two different polymorphic structures. The alpha polymorph is the most stable solid phase of trans-cinnamic acid, whereas the beta polymorph is metastable, transforming over time into the polymorph. Trans-cinnamic acid reacts under UV-light in the solid state to form a cyclobutane by a [2+2] reaction. The isomer obtained from this reaction depends on the arrangement of molecules in the solid. The alpha polymorph leads to alpha-truxillic acid, whereas the beta polymorph leads to beta-truxinic acid. As the beta polymorph is metastable and transits to the alpha polymorph over time, irradiation of the beta polymorph always leads to a mixture of alpha-truxillic and beta-truxinic acid. Crystal engineering offers a mean to thermodynamically control the formation of the desired regioisomer. In this work, we use cocrystallization as a tool to orient the molecules in the solid state in such a way that a stable structure is obtain that leads to formation of this desired regioisomer.