Synthesis of thermotropic liquid crystals derived from phenylpiperazine containing an enyne unit

Thermotropic liquid crystals are of great technological importance. Much research is devoted to the development of stable compounds with transition temperatures close to room temperature. The interest of this work is the synthesis of thermotropic liquid crystal precursor units containing phenylpiperazine and/or phenylacetylenic units. Homologues of a Schiff base series and an enyne series have been synthesized, allowing comparisons of their mesomorphic and thermodynamic properties. The Schiff bases showed smectogenic behavior and the enynes a smectic dimorphism and/or a nematic phase. The synthetic methodology was efficient for the synthesis of the desired precursor, 4-[4'-(prop-1-yn-3-al)phenyl]-piperazine-1-carboxylic acid ethyl ester.