Attempts to Green the Synthesis of Liquid Crystals

This study presents several green approaches to the synthesis of liquid crystals. In the research, three types of reactions (esterification, Suzuki cross-coupling and amidation) have been considered. A series of sulfonated Starbons (mesoporous carbonaceous materials derived from polysaccharides) have been tested for esterification as catalysts. As a result, sulfonated Starbon was found to have selectivity for cis- and trans-isomer of 4-pentyl-cyclohexane carboxylic acid. Cis-isomer has priority in the reaction. With water-soluble carbodiimide as coupling agent, cyclopentylmethyl ether (CPME) as solvent, and microwave irradiation, a series of trans-4-n-alkyl-cyclohexane carboxylic acid 4-cyanophenol esters were synthesized and their liquid crystalline phase transition temperature was determined. Green metrics were applied to assess this reaction with respect to the traditional synthesis. A series of Starbon-Pd were tried in two different solvent systems (ethanol/water and CPME/water) as heterogeneous catalyst for Suzuki reaction. All the Starbon-Pd had a high activity in ethanol/water solvent system. In CPME/water solvent system, only Starbon-500-Pd had a good performance. Starbon-Pd catalyst could be reused approximately 3 times in the Suzuki reaction. With comparison, CPME has been proved that it was a better replacement for THF in Suzuki reaction. A mesoporous structured silica catalyst was applied to amidation for the purpose of generating liquid crystalline amides.