Chemistry of organic eutectics and 1:1 addition compound: p-phenylenediamine-catechol system

Abstract

The phase diagram of the p-phenylenediamine-catechol system, determined by the thaw-melt method, shows the formation of a 1:1 molecular compound and two eutectics. The linear velocities of crystallization of the pure components, the eutectics and the addition compound, determined by measuring the rate of movement of the growth front in a capillary, suggest that crystallization data obey the Hillig-Turnbull equation v = u(ΔT)n. where u and n are constants and ΔT is the undercooling. Experimental values of the heats of fusion and the entropy of fusion and calculated excess thermodynamic functions were considered and the results were explained on the basis of cluster formation in the eutectic melt. X-ray diffraction data of the pure components, the eutectics and the addition com- pound infer that these eutectics are not simply a mechanical mixture of the two components; preferential ordering of atomic planes occurs during their formation. The IR studies carried out on this system suggest intermolecular hydrogen bonding between the two components which form the molecular compound. © 1989.