4'-Bromobenzo-18-crown-6-ether is used primarily in chemical research and industrial processes as a selective complexing agent for alkali metal ions, particularly potassium (K⁺) and rubidium (Rb⁺). Its crown ether structure enables it to trap specific ions, making it valuable in ion separation techniques, such as liquid-liquid extraction, and in the synthesis of complex molecules. It is also employed in the development of sensors, including ion-selective electrodes, and in studies involving ion transport across membranes. Additionally, it finds application in organic synthesis as a phase-transfer catalyst, facilitating reactions between compounds in different phases.