The Effect of Methyl Group Position in Branched Alkyl Chains on the Thiolic End of 4,4′-Disubstituted Thiophenylbenzoates on Mesomorphic Properties and Some Optically Active Analogs as New Ferroelectric Liquid Crystals

Abstract

The effect of the methyl group position in the branched alkyl chains of the thioesters where X = C₈H₇, RO, and C₉CO₂; m = 1–3 and n = 0–2 on mesomorphic properties is reported. These thioesters were prepared by esterification of the appropriate acid or acid chloride with the branched chain thiol. Synthesis of the thiols was via a Friedel-Crafts acylation of benzene with the branched alkyl chain acid chloride, catalytic reduction, sulfonation in sulfuric acid, conversion to the sulfonyl chloride and reduction to the thiol with zinc and sulfuric acid. Transition temperatures and types of mesophases were determined using hot-stage polarizing microscopy. The same types of meso phases observed in the analogous straight chain thioesters were also found in these compounds, including two unidentified smectic phases like those now believed to be S_G and S₁ phases in the straight chain series. Branching always lowered the clearing temperatures but not always the melting ones. Clearing temperatures do not always increase with increasing distance between the methyl group and the benzene ring as was reported earlier for branched chain phenylbenzoates with a four carbon backbone. Branching