Tetrapropylammonium bisulfate is primarily used as a phase transfer catalyst in organic synthesis. It facilitates the transfer of reactants between immiscible phases, enhancing reaction rates and yields. This compound is particularly effective in nucleophilic substitution reactions and the synthesis of fine chemicals. Additionally, it finds application in the preparation of quaternary ammonium compounds, which are essential in various industrial processes, including the production of surfactants and disinfectants. Its role in improving the efficiency of chemical reactions makes it valuable in pharmaceutical and agrochemical manufacturing.