Addition of metals to control the regioselectivity in the dimerization of TCA at the solid state

Details

Supervisors

Leyssens, Tom

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité spécialisée: chimie de l'industrie

Abstract

Trans-cinnamic acid is an organic compound occurring naturally in a number of plants and crystallize into two known forms: “head-to-tail” (α-polymorph) and “head-to-head” (β-polymorph). Due to the presence of an unsaturated carboxylic acid, this molecule can dimerize through a [2+2] photocycloaddition in solid state to form the α-truxillic acid and β-truxinic acid. Those two differ by the position of the phenyl groups and carboxylic acids in the cycle: they alternate in the α-truxillic acid and are next to each other in the β-truxinic acid. The synthesis of one over the other, called “regioselectivity”, is determined by the arrangement of molecules in the solid, with the α-form leading to the α-truxillic acid, and the β-form to the β-truxinic acid. The stability of the two forms is not identical. While the α-form is stable, and leads automatically to the α-truxillic acid upon irradiation, the β-form is metastable, and with time transforms itself into the α-form, meaning that after irradiation, a mix of truxillic and truxinic acid will be always obtained, without the possibility of obtaining only the truxinic acid. The goal of this work is to develop an approach that can control the regioselectivity of the photoreaction product of the trans-cinnamic acid, and selectively produce a pure β-truxinic acid. This will be achieved using crystal engineering, by trying to form of a coordination bond between the organic molecule and a metal, creating a complex that orients the molecules in the “head-to-head” configuration, while conserving the right characteristics for the dimerization. The right conditions, determined by Schmidt, impose an intermolecular distance of 3.5 Å to 4.2 Å and parallel bonds between the two molecules. In addition, this study is extended to three trans-cinnamic acid derivatives: 4-coumaric acid; 2-methoxy-trans-cinnamic acid; 2-ethoxy-trans-cinnamic acid. New forms of truxinic and truxillic acids, called δ-truxinic and ε-truxillic acids respectively, which was never observed for the studied compounds, could also potentially be synthesized by the approach explained above.