Trimethylphenylammonium bromide is a quaternary ammonium salt comprised of a positively charged N,N,N-trimethylphenylamine cation and a negatively charged bromide anion. This compound is commonly employed as a phase transfer catalyst in organic reactions, facilitating the movement of reactants between immiscible phases. It also serves as a reagent in the synthesis of various organic compounds and can be used as a surfactant or corrosion inhibitor in certain applications.