Trifluoromethanesulfonic anhydride, also known as triflic anhydride, is the chemical compound with the formula (CF<sub>3</sub>SO<sub>2</sub>)<sub>2</sub>O. It is the acid anhydride derived from triflic acid. This compound is a strong electrophile, useful for introducing the triflyl group, CF<sub>3</sub>SO<sub>2</sub>. Abbreviated Tf<sub>2</sub>O, triflic anhydride is the acid anhydride of the superacid triflic acid, CF<sub>3</sub>SO<sub>2</sub>OH.
Triflic anhydride is prepared by dehydration of triflic acid using P<sub>4</sub>O<sub>10</sub>.
Triflic anhydride is useful for converting ketones into enol triflates.
In a representative application, is used to convert an imine into a NTf group. It will convert phenols into a triflic ester, which enables cleavage of the C-O bond.
The typical impurity in triflic anhydride is triflic acid, which is also a colorless liquid. Samples of triflic anhydride can be assayed by <sup>19</sup>F NMR spectroscopy: âÂÂ72.6 ppm vs. âÂÂ77.3 for TfOH (std CFCl<sub>3</sub>).
It is an aggressive electrophile and readily hydrolyzes to the strong acid triflic acid. It is very harmful to skin and eyes.