What is a quaternary ammonium salt?
A quaternary ammonium salt is formed when the nitrogen atom in an amine is bonded to four alkyl or aryl groups and carries a positive charge. It has the general formula [NR₄]⁺ X⁻, where X⁻ is a counterion (e.g., Cl⁻, Br⁻). They are salts and therefore are often water soluble.