A study of the changes during heating of paracetamol

AbstractThe orthorhombic form of paracetamol has been shown to exhibit greater compressibility and faster dissolution than the monoclinic form. The orthorhombic form is produced by melting of monoclinic crystals of paracetamol followed by cooling at specific rates. Cooling rate, although a very important factor, is not the only factor influencing the formation of either of the two morphs. To study the cooling rate required for production of form II, paracetamol samples were melted in a differential scanning calorimeter, cooled at three specific rates, and melted again. In all of the samples, cooling resulted in the glassy form followed by recrystallization and the melting of form II. On the hot-stage microscope both forms were produced in one sample. Standardizing conditions for prediction of the resulting form remains a problem. There seems to be a great deal of overlap of the two forms' transition phases, which would make it difficult to force the crystallization of one form by keeping the solution or m...