Phase diagram for the mixtures of ibuprofen and stearic acid

Abstract

The binary mixtures of ibuprofen and stearic acid have been tested on the DSC at a heating rate of 5°C min −1. All temperatures reported here are for endothermic peak temperatures. The heating curves are employed to construct a phase diagram. The resultant phase diagram shows the existence of a compound formed between the two materials and is essentially two simple eutectic systems compressed into one equilibrium diagram. The component in excess melts at a lower temperature than its single entity. There are two eutectic melting points at 42% ibuprofen and 65% ibuprofen. It would seem probable that the “condensed phase compound” has the formula AB 2, where A is stearic acid (C 18H 36O 2) and B is ibuprofen (C 13H 18O 2). A relationship between the enthalpy of melting (Δ H m) and %composition is found. However, the overlapped endothermic peaks pose difficulty in peak integration resulting in a deviation from a typical plot. DSC is a fast, useful, and reliable analytical tool to detect and investigate the eutectic compound in this study.