tetraalkylammonium

Tetraalkylammonium refers to a class of quaternary ammonium cations in which four alkyl groups are attached to a central nitrogen. The generic cation is [NR4]+, and salts with various counterions (for example chloride, bromide, iodide, sulfate, or hexafluorophosphate) are called tetraalkylammonium salts.

Geometrically the nitrogen is quaternary and the center is permanently positively charged. The properties of tetraalkylammonium salts depend strongly on the alkyl substituents: small alkyl groups yield highly water-soluble salts, while large, especially long-chain alkyl groups, confer hydrophobicity and enable surface activity as cationic surfactants.

Synthesis typically proceeds by exhaustive alkylation of a tertiary amine with an alkyl halide or related alkylating agent, for example R3N + R'X → [R4N]+X−. Mixed tetraalkylammonium cations (with different R groups) are also known.

Applications of tetraalkylammonium salts are broad. They are widely used as phase-transfer catalysts, especially tetrabutylammonium salts, to shuttle anions between aqueous and organic phases. They also serve as electrolytes and supporting ions in electrochemistry, and as precursors or components in ionic liquids. Long-chain tetraalkylammonium salts function as cationic surfactants and in polymer stabilization.

Safety and environmental concerns vary with substituents; many tetraalkylammonium salts are toxic and irritant, and aquatic toxicity must be considered. Handling requires standard chemical hygiene and proper disposal.