Understanding urea polymorphism and cocrystallization to develop enhanced fertilizers: A review

Abstract

Polymorphism and cocrystallization are two crucial processes in the development of new urea compounds. These processes primarily involve intermolecular interactions and the molecular arrangement within urea. Understanding polymorphism facilitates modification of the physical and chemical properties of urea compounds. Polymorphism refers to a compound's ability to exist in different forms or crystal structures. Urea exhibits five distinct polymorphic forms under specific temperature and pressure conditions and extensive research has been conducted on the unit cell parameters of different phases of urea. In the realm of urea cocrystal development, polymorphism plays a significant role. Urea cocrystals typically consist of urea molecules and one or more additional molecules, strategically chosen to modify urea's properties for broader applications. The preparation of cocrystals involves mixing pure urea with the chosen coformer under controlled atmospheric conditions. Cocrystal formation can be enhanced through the application of mechanical forces to the reactants, elevated temperatures, and specific relative humidities. The field of cocrystallization provides a powerful toolkit for crafting desirable urea compounds, making them well-suited for applications in agriculture and other industries. In pharmaceuticals, cocrystals with urea allow for the design of more effective and easily administered medications which can enhance drug delivery and absorption. In agriculture, urea cocrystals can optimize the release of nitrogen from urea fertilizers, improving nutrient uptake by plants, and reducing environmental impact. In addition, cocrystals often utilize industrial byproducts or waste materials as coformers to modify the properties of urea. Furthermore, preparing urea cocrystals using solvent-free mechanochemistry eliminates the need for solution handling and evaporation, promoting an environmentally sustainable process.