HNTf2

HNTf2, also known as triflimide or bis(trifluoromethanesulfonyl)imide acid, is the Brønsted conjugate acid of the bis(trifluoromethanesulfonyl)imide anion [N(SO2CF3)2]−. It is a very strong, non-nucleophilic Brønsted superacid used in organic synthesis and catalysis. The accompanying anion Tf2N− (often abbreviated as TFSI−) is highly delocalized and weakly coordinating, which helps stabilize cations and enables exceptionally high acidity in non-aqueous media.

In solution, HNTf2 is typically generated in dry organic solvents by protonating a bis(trifluoromethanesulfonyl)imide salt with a strong proton source or by metathesis with a superacidic medium. Because it is moisture-sensitive and decomposes upon contact with water, it is handled under strictly anhydrous conditions. In practice, HNTf2 is employed as a catalyst or additive to achieve strong acid catalysis for reactions that are sluggish under conventional acids, including challenging alkylations, rearrangements, and electrophilic aromatic substitutions, particularly with weakly basic or deactivated substrates. It is often used in combination with Lewis acids or as part of non-nucleophilic superacid systems.

Safety considerations: HNTf2 is corrosive and moisture sensitive; it is typically stored and used under dry, inert atmosphere. It can react with water to form related species and may emit hazardous fumes if heated or decomposed. The compound is primarily of interest in chemical research and specialized synthesis settings.