Phosphorus pentabromide is primarily used as a brominating agent in organic synthesis. It facilitates the conversion of alcohols to alkyl bromides, which are valuable intermediates in the production of pharmaceuticals, agrochemicals, and other organic compounds. Additionally, it is employed in the bromination of carboxylic acids to form acyl bromides, which are crucial in peptide synthesis and other organic transformations. Its strong reactivity makes it a useful reagent in laboratories for introducing bromine atoms into various organic molecules, enabling the creation of complex chemical structures.