Tetrabutylammonium borohydride (TBAB) is an organic salt with the chemical formula (C₄H₉)₄N⁺ BH₄⁻. It is a white to off-white crystalline powder that is soluble in polar organic solvents such as tetrahydrofuran (THF), dichloromethane, and acetonitrile, but has limited solubility in water. This solubility profile distinguishes it from alkali metal borohydrides like sodium borohydride. Its primary application is as a versatile and selective reducing agent in organic synthesis. The tetrabutylammonium cation confers excellent solubility in non-aqueous media, allowing reductions to be performed under mild conditions in a wide range of organic solvents. It is particularly effective for the reduction of acid chlorides to aldehydes (the Rosenmund reduction), the reduction of imines to amines, and the selective reduction of aldehydes and ketones in the presence of other functional groups like esters and nitriles. It is also used in dehalogenation reactions and as a source of hydride in various catalytic processes. TBAB is considered a safer and more convenient alternative to pyrophoric reagents like lithium aluminum hydride for many laboratory-scale reductions. It is typically handled under an inert atmosphere (e.g., nitrogen or argon) due to its sensitivity to moisture and potential decomposition.