Novel synthetic route to liquid crystalline 4,4′‐bis(n‐alkoxy)azoxybenzenes: spectral characterisation, mesogenic behaviour and crystal structure of two new members

Abstract

A simple synthetic method has been developed for the preparation of long‐chain 4,4′‐bis(n‐alkoxy)azoxybenzenes by reductive coupling of 4‐n‐alkoxynitrobenzenes using zinc powder and ammonium chloride in aqueous ethanol medium at ambient temperature. The new method was employed to synthesise known members (n = 1–12) of the 4,4′‐bis(n‐alkoxy)azoxybenzene (C _n H_2n+1OPhN(O) = NPhOC _n H_2n+1) series and also two hitherto unknown members (n = 13–14) of the series. The new compounds were characterised using spectral (IR, UV–visible, ¹H NMR and FAB‐MS) data. The mesogenic behaviour of both compounds was studied by polarising optical microscopy, differential scanning calorimetry and small‐angle X‐ray diffraction techniques. The crystal structure of 4,4′‐bis(n‐tetradecyloxy)azoxybenzene was determined using single‐crystal X‐ray diffraction data. The packing of the molecules in the crystalline state is found to be a precursor to the smectic C phase structure.

Keywords:

• smectic phase precursor
• crystal structure
• 4,4′‐bis(n‐alkoxy)azoxybenzenes

Acknowledgements

Financial support (SR/S1/IC‐08/2007) from DST, Government of India, is gratefully acknowledged. We thank CSIR (India) for the award of a fellowship (PD) and UGC (New Delhi) for Special Assistance Programme to our Department. We also thank Professor A. Ramanan, IIT Delhi, for X‐ray data collection.