Synthesis and liquid crystalline properties of biphenyl esters of monothio- and dithiotrimellitimides

A series of 4'-substituted biphenyl esters of 5-carboxy-2-hexyl-2,3-dihydro-1H-isoindole-1,3-dione (N-hexyltrimellitimide) has been synthesised. The ester imides obtained were treated with Lawesson's reagent, and the resulting monothio- and dithiotrimellitimides were purified by column chromatography. A majority of the products showed interesting thermotropic properties. For instance, 5-(biphenyl-4-yloxycarbonyl)-2-hexyl-2,3-dihydro-1H-isoindole-1,3-dithione showed a monotropic transition at 70 degrees C, whereas its dioxygen analogue 5-(biphenyl-4-yloxycarbonyl)-2-hexyl-2,3-dihydro-1H-isoindole-1,3-dione was not a mesomorphic compound.