An efficient synthetic procedure for the preparation of a full series of mesogenic 4-alkoxybenzoic acid and their copper(II) complexes

Abstract

A full series of 4-alkoxybenzoic acid (alkoxy: (OC_nH_2n+1), n = 1–18, 20) (1a–s) was synthesized using a new, efficient, and practical synthetic procedure. These compounds were reacted with copper(II) acetate to produce a new series of copper(II) complexes: bis(4-alkoxybenzoate) copper(II) complexes (alkoxy: (OC_nH_2n+1), n = 1–18, 20) (2a–s). The prepared compounds were described using different technology methods, including ¹H NMR, ¹³C NMR, FTIR, UV-Vis, and microelemental analysis, molar conductivity measurements. Liquid crystal behaviour of the two series of substances employing polarized optical microscopy (POM). In general, the study showed that the series of 4-alkoxybenzoic acid (alkoxy: OC_nH_2n+1, n = 3–18, 20) (1a–s) are mesomorphic materials and exhibit enantiotropic liquid crystal characteristics. (1a, 1b, and 1s show no liquid crystal properties). Compounds 1c–f showed only nematic mesophase when heated and cooled; this was explained by the texture's characteristic thread- or droplet-like appearance.  The rest of the compounds 1g to 1r showed both of smectic and nematic mesophases during the heating and cooling process. Furthermore, the mesomorphic properties of these compounds are fully disappeared upon coordination with the copper(II) ion. Therefore, bis(4-alkoxybenzoate) copper(II) complexes (alkoxy: (OC_nH_2n+1), n=1–18, 20) (2a–s) displays no mesomorphic properties (simply melted to isotropic liquid).

KEY WORDS: 4-Alkoxybenzoic acid, Bis(4-alkoxybenzoate) copper(II) complexes, Liquid crystal properties, Enantiotropic liquid crystal, Mesomorphic materials

Bull. Chem. Soc. Ethiop. 2025, 39(5), 877-895.                                                     

DOI: https://dx.doi.org/10.4314/bcse.v39i5.6