Tetrabutylammonium hydrogen sulfate is a quaternary ammonium salt with the formula (C_H_)_N(HSO_). It is a white to off-white crystalline solid, highly soluble in polar solvents like water and acetonitrile. The compound serves as a phase-transfer catalyst (PTC), facilitating the transfer of ionic species from an aqueous phase into an organic phase, thereby accelerating reactions between water-soluble and organic-soluble reactants. Its primary application is as a phase-transfer catalyst in organic synthesis, particularly in alkylation, oxidation, and reduction reactions. It is also widely used as an ion-pairing reagent in analytical chemistry, especially in high-performance liquid chromatography (HPLC) for the separation of basic or ionic compounds. Additionally, it functions as a supporting electrolyte in electrochemical studies and as a reagent in the preparation of other tetrabutylammonium salts. The compound is generally stable under normal conditions but should be stored in a dry, cool environment to prevent moisture absorption. It is considered an irritant and should be handled with appropriate personal protective equipment. Its versatility in both synthetic and analytical chemistry makes it a staple in research and industrial laboratories.