Tetrabutylammonium hydrogen sulfate is widely used as a phase-transfer catalyst in organic synthesis. It facilitates the transfer of reactants between immiscible phases, enhancing reaction rates and yields in processes such as alkylation, esterification, and nucleophilic substitution. It is also employed in the preparation of ionic liquids and as a stabilizer in polymerization reactions. Additionally, it finds application in analytical chemistry for ion-pair extraction and separation techniques. Its role in improving solubility and reactivity makes it valuable in various industrial and laboratory processes.