TfOH

Trifluoromethanesulfonic acid, commonly known as triflic acid and abbreviated TfOH, is a strong Brønsted acid with the chemical formula CF3SO3H. It is a colorless, highly hygroscopic liquid that is widely used as a catalyst and reagent in organic synthesis. TfOH is typically employed in non aqueous media and can protonate a wide range of substrates, enabling reactions that require very strong acid catalysis.

TfOH is one of the strongest non-oxidizing Brønsted acids available in common solvents. Its conjugate base, the triflate anion CF3SO3−, is exceptionally stable, which gives TfOH a highly non-nucleophilic character. This combination allows TfOH to activate electrophiles and generate carbocationic intermediates without strong competing nucleophilic attack. TfOH is miscible with water and many organic solvents and is known for its intense acidity and corrosivity.

In practice, TfOH is used as a powerful acid catalyst for reactions such as alkylations, dehydrations, rearrangements, and certain cyclizations. It is also employed to form reactive intermediates and to activate otherwise unreactive substrates in combination with other reagents, including various leaving groups that can be stabilized by the triflate anion. Its utility stems from its strength and the stability of the triflate leaving group, which can participate in downstream transformations.

Safety and handling are essential when working with TfOH. It is highly corrosive and reacts vigorously with water, requiring appropriate safety precautions such as use in a fume hood, protective equipment, and suitable containment to avoid moisture exposure. It should be stored and handled under conditions that minimize moisture contact and material degradation.