Influence of an acetylsalicylic anhydride impurity on the rate of dissolution of acetylsalicylic acid

Disappearing polymorphs revisited

Nearly twenty years ago, Dunitz and Bernstein described a selection of intriguing cases of polymorphs that disappear. The inability to obtain a crystal form that has previously been prepared is indeed a frustrating and potentially serious problem for solid-state scientists. This Review discusses recent occurrences and examples of disappearing polymorphs (as well as the emergence of elusive crystal forms) to demonstrate the enduring relevance of this troublesome, but always captivating, phenomenon in solid-state research. A number of these instances have been central issues in patent litigations. This Review, therefore, also highlights the complex relationship between crystal chemistry and the law.

Decomposition of aspirin in the solid state in the presence of limited amounts of moisture

When limited amounts of moisture are added to aspirin in a closed system, the model for decomposition differs from that experienced in an open system, i.e., a system at constant relative humidity. The composition of the liquid decomposition layer on the surface of the aspirin crystals will constantly change, and a model for accounting for both the change in volume and composition of the decomposition layer as a function of time has been developed. Solid-state decomposition data, when plotted as a function of time, exhibit a profile similar to the one predicted, but the position of the decomposition curve observed differs from that of the predicted. The predicted curve indicates better stability than the observed data.