Trifluoromethanesulfonic anhydride

Description

Trifluoromethanesulfonic anhydride, also known as triflic anhydride, has proven to be an extraordinary reagent for a broad range of transformations. As a commercially and readily available reagent, It has been widely used in synthetic chemistry due to its high electrophilicity. Given its high affinity towards O-nucleophiles, reaction with alcohols, carbonyls, sulfur phosphorus- and iodine oxides towards the formation of the corresponding triflates is strongly favored. As one of the premier leaving groups in organic chemistry, the generated triflates then open the door to various downstream transformations, including (but not limited to) substitution reactions, cross-coupling processes, redox reactions, and rearrangements[1-2].

Chemical Properties

clear colorless to light brown liquid

Uses

Trifluoromethanesulfonic Anhydride is a strong electrophile used in chemical synthesis for introducing the triflyl group.

Reactivity Profile

Electrophilic activation of tertiary and secondary amides with triflic anhydride (Tf2O; rifluoromethanesulfonic anhydride) under mild conditions gives rise to iminium and imino triflates, respectively, which could be utilized as versatile reagents to react with various C-, N-, O- and S-nucleophiles for the transformation of an amide function into different products. Other oxygen-containing nucleophiles, such as sulfoxides and phosphorus oxides, could also undergo nucleophilic attack with Tf2O to generate thionium triflate, electrophilic P-species, and phosphonium triflate. These highly active transient species could readily undergo nucleophilic substitution reactions for further diverse transformations. Furthermore, owing to the strong electrophilic property, Tf2O is prone to react with relatively weak nucleophiles such as nitrile groups or some nitrogen-containing heterocyclic compounds. In addition, Tf2O has also been used as an efficient radical trifluoromethylation and trifluorometh ylthiolation reagent through the release of SO2 or deoxygenation process for the synthesis of trifluoromethylated and trifluoromethylthiolated compounds[2].

Hazard

May be corrosive to metals. Harmful if swallowed. Causes severe skin burns and eye damage.

Synthesis

The synthesis of Trifluoromethanesulfonic anhydride is as follows:
A dry, 100-ml., round-bottomed flask is charged with 36.3 g. (0.242 mole) of trifluoromethanesulfonic acid (Note 1) and 27.3 g. (0.192 mole) of phosphorus pentoxide (Note 2). The flask is stoppered and allowed to stand at room temperature for at least 3 hours. During this period the reaction mixture changes from a slurry to a solid mass. The flask is fitted with a short-path distilling head and heated first with a stream of hot air from a heat gun and then with the flame from a small burner.

The flask is heated until no more trifluoromethanesulfonic anhydride distills, b.p. 82–115°, yielding 28.4–31.2 g. (83–91%) of the anhydride, a colorless liquid. Although this product is sufficiently pure for use in the next step, the remaining acid may be removed from the anhydride by the following procedure. A slurry of 3.2 g. of phosphorus pentoxide in 31.2 g. of the crude anhydride is stirred at room temperature in a stoppered flask for 18 hours. After the reaction flask has been fitted with a short-path distilling head, it is heated with an oil bath, yielding 0.7 g. of forerun, b.p. 74–81°, followed by 27.9 g. of the pure trifluoromethanesulfonic acid anhydride, b.p. 81–84° .

storage

Store in a cool, dry, wellventilated area.  Moisture sensitive.

Purification Methods

It can be freshly prepared from the anhydrous acid (11.5g) and P2O5 (11.5g, or half this weight) by setting aside at room temperature for 1hour, distilling off volatile products then distil it through a short Vigreux column. It is readily hydrolysed by H2O and decomposes appreciably after a few days to liberate SO2 and produce a viscous liquid. Store it dry at low temperatures. [Burdon et al. J Chem Soc 2574 1957, Beard et al. J Org Chem 38 373 1973, Beilstein 3 IV 35.]

References

[1] Haoqi Zhang. “Trifluoromethanesulfonic Anhydride in Amide Activation: A Powerful Tool to Forge Heterocyclic Cores.” TCIMAIL (2021).
[2] Dr. Qixue Qin, Prof. Dr. Ning Jiao, Zengrui Cheng. “Recent Applications of Trifluoromethanesulfonic Anhydride in Organic Synthesis.” Angewandte Chemie 135 10 (2022).