Synthesis and Characterization of Some Azo-Anil Dyes

A number of azo-anil dyes of the type with with Y=CN or NO2 and R,R′=Me, Me; Me,C6H13; Et,Pr and C6H13,C6,H13 were synthesized by reactions of the aminosubstituted nitrosoamine with phenylene diamine followed by condensation of the resulting aniline with the appropriate 4-substituted benzaldehyde. Mesomorphic properties were determined both by hot-stage polarizing microscopy and DSC. A nematic phase was observed only when R=R′=CH3 while smectic A phases occurred in the other homologs. Melting temperatures were greater than 130°. All had colors ranging from red to orange with UV Δmax ranging from 448–459 nm and ε 2.20–3.67 E+4. The ΔH melting values ranged from 16.8 to 30.7 KJ/mole and solubilities in a BDH-E7 liquid crystal mixture were low.