Abstract
A series of novel thiourea and amide liquid crystals containing 5-membered isoxazoline and isoxazole rings were synthetized and the liquid crystal properties studied. Thioureas were obtained using a condensation reaction of benzoyl chlorides, arylamines and ammonium thiocyanate. The amides, on the other hand, were the byproduct of a quantitative reaction which used potassium cyanate as the starting material. Thiourea and amide derivatives were predominantly SmA mesophase inductors. A nematic mesophase was observed only for thioureas and amides containing an isoxazole ring. Additionaly, the liquid crystal behavior was also dependent on the relative position of nitrogen and oxygen atoms on the 5-membered heterocycle.
Highlights
Thioureas are a structurally diversified group of organic compounds, with technological applications in different areas
The amines 3, 8 and 12 containing an isoxazole ring were synthesized in two sequential steps – first a MnO2 oxidation step transforming the isoxazoline ring to an isoxazole ring followed by SnCl2 reduction, according to protocols previously published [19,2124]
The synthetic route used for the synthesis of the hybrid compounds, N-acyl-N'-isoxazolinylthioureas 17a–c and N-acyl-N'isoxazolylthioureas 18a–c is outlined in Scheme 2
Summary
Thioureas are a structurally diversified group of organic compounds, with technological applications in different areas. The structural diversity of the thiourea moiety is linked to possibly one or both nitrogen components, which may be substituted symmetrically or unsymmetrically [1] Applications of this scaffold include complexing agents in anion sensors [2] organocatalysts [3], intermediates in heterocycle synthesis [1] and development of compounds with pharmacological effects [4]. Substituted thioureas can be obtained using a variety of approaches the simplest route involves the heating of ammonium thiocyanate with an amine in an aqueous acid medium [5]. They can be synthesized in the reaction of thiourea with primary amines [6]. Another important synthetic route for substituted thioureas is a two-step approach: (i) the addition/elimination
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