Keywords: Azo, azomethine, alkylation, condensation, mesophase

Abstract

Six new azo-azomethine derivatives were successfully synthesized and characterized. These derivatives, 5a-f were differentiated by a variety of different terminal lengths such as pentyl, heptyl, nonyl and dodecyl chains. The experiment started with the reaction of p-nitroaniline with phenol, forming 4-(4-nitrophenylazo)-phenol, 1. Alkylation of 1 with pentyl, nonyl and dodecylbromide gave (4-nitrophenyl)-4(4-alkoxyphenyl)-diazene, 2a-c. These nitro intermediates, 2a-c were reduced to afford intermediates 3a-c, 4-(4-alkoxy-phenylazo)-phenylamine. Alkylation reaction of p-hydroxybenzaldehyde with heptyl and dodecylbromide gave intermediates 4a-b, 4-alkoxybenzaldehyde. Cross condensation reactions of 3a-c and 4a-b gave six compounds, 5a-f, with azo and Schiff base linking units but with different chain lengths at both terminal positions. All the compounds were characterized using Fourier Transform Infrared spectroscopy (FT-IR), 1H and 13C Nuclear Magnetic Resonance spectroscopy (NMR) and CHN elemental analysis. The mesophase transitions of these compounds were determined using Polarized Optical Microscope (POM). It was observed that compounds 5b, 5c, 5d, 5e and 5f were mesogenic while compound 5a was not mesogenic. The transition temperature of the compounds having mesophase behaviour were further confirmed using DSC. All the DSC thermograms showed good agreement with the phase transition observed under POM. The study on the structure-properties relationship was conducted in order to determine the effect of the terminal group, length of the chains and linking units to the mesophase behaviour of the compounds.