Tributylsulfonium iodide is primarily utilized 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, where it helps in the transfer of anions from the aqueous phase to the organic phase. Additionally, it finds application in the synthesis of various organic compounds, including pharmaceuticals and agrochemicals, due to its ability to stabilize reactive intermediates. Its role in promoting efficient and selective reactions makes it valuable in industrial and laboratory settings.