Tetraamylammonium iodide is primarily used in organic synthesis as a phase-transfer catalyst. It facilitates the transfer of reactants between immiscible phases, such as aqueous and organic layers, enhancing reaction efficiency. This compound is particularly useful in nucleophilic substitution reactions, where it helps in the smooth transfer of anions to organic substrates. Additionally, it finds application in the preparation of ionic liquids and as a stabilizer in electrochemical processes. Its role in improving reaction rates and yields makes it valuable in various industrial and laboratory settings.