Novel Synthetic Route to Liquid Crystalline 4,4'-Bis(n-Alkoxy) Azoxybenzenes: Spectral Characterisation, Mesogenic Behaviour and Crystal Structure of Two New Members

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+1 OPhN(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.