Tetrabutylammonium

Tetrabutylammonium refers to the tetrabutylammonium cation, [N+(C4H9)4], a quaternary ammonium ion. In salts, this cation is paired with various counteranions such as chloride (Cl−), bromide (Br−), tetrafluoroborate (BF4−), hexafluorophosphate (PF6−), or other inorganic or organic anions. The cation is formed by exhaustive alkylation of a tertiary amine with butyl groups, and salts are typically prepared by quaternization of a tertiary amine such as tributylamine with a butyl halide, followed by anion exchange to the desired counteranion.

Structure and properties: The tetrabutylammonium cation consists of a central positively charged nitrogen bound to four butyl groups. Its bulky, hydrophobic character makes the cation lipophilic and largely soluble in nonpolar or moderately polar organic solvents, while the solubility of its salts in water depends on the counteranion. The combination of a lipophilic cation with various anions allows tuning of solubility and reactivity for different applications.

Preparation and availability: Tetrabutylammonium salts are commercially available in several forms, including tetrabutylammonium chloride, bromide, tetrafluoroborate, and hexafluorophosphate. They can be prepared by exhaustive alkylation of tributylamine with butyl halide, followed by counterion exchange to the desired anion.

Applications: The salts are widely used as phase-transfer catalysts to shuttle anions from aqueous to organic phases, facilitating reactions such as substitutions and eliminations in nonpolar media. They also serve as non-coordinating or weakly coordinating counterions and are employed as supporting electrolytes in non-aqueous electrochemistry. In some contexts, they function as reagents or intermediates in organic synthesis and materials science.

Safety: Tetrabutylammonium salts are irritants and should be handled with appropriate PPE. They are typically used in controlled laboratory settings and are not considered highly toxic, but ingestion or inhalation should be avoided.