THE EFFECT OF STRUCTURALLY RELATED SUBSTANCES ON THE NUCLEATION KINETICS OF PARACETAMOL (ACETAMINOPHEN)

A computer controlled and monitored apparatus is described in which supersaturation was induced in paracetamol solutions by cooling. The induction time before nucleation occurred was determined by the attenuation of a laser beam which passed through the solution. Certain additives, particularly p-acetoxyacetanilide (PAA) (2-4 mol%), caused significant inhibition of nucleation. The induction time was expressed as a function of the supersaturation and absolute temperature, leading to estimates of the interfacial tension between the solution and the critical nucleus in the presence and absence of the additives, and to estimates of the number of molecules comprising the critical nucleus.