Tetrabutyl ammonium iodide is used primarily when you need both a phase-transfer catalyst AND a co-catalyst to activate an alkyl chloride or bromide alkylating agent. An example is shown in the PTC Reaction of the month above.

Application

Tetrabutyl ammonium iodide is used primarily when you need both a phase-transfer catalyst AND a co-catalyst to activate an alkyl chloride or bromide alkylating agent. ... Many process chemists use tetrabutyl ammonium bromide together with 1 mole% KI, since KI is more likely to be bought at current market price.