PHASE-DIAGRAMS AND THE METATHETIC REACTIONS OF SCHIFF-BASES

The presence of metathetical reactions alters the phase diagram of multicomponent Schiff base liquid crystals. Instead of a eutectic point, phase diagrams with a minimum are observed. To observe the minimum, the metathetical reaction must lead to products with homologous structure. Shiff bases of the p-n-alkoxybenylidene-p-n-alkylaniline family form homologous systems if either the alkyl or alkoxy chain but not both differ by not more than one methylene unit. Phase diagrams with a minimum obtain when the number of pairs of such homologous molecules is one less than the number of metathetical reactions or three less than the total number of components. In agreement with these considerations four component mixtures having two sets of binary homologous structures exhibit melting curves with a minimum point.