Methyl trifluoromethanesulfonate

Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula CF₃SO₂OCH₃. It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent.^[2] The compound is closely related to methyl fluorosulfonate (FSO₂OCH₃). Although there has yet to be a reported human fatality, several cases were reported for methyl fluorosulfonate (LC₅₀ (rat, 1 h) = 5 ppm), and methyl triflate is expected to have similar toxicity based on available evidence.^{[3][verification needed]}

Methyl trifluoromethanesulfonate

Structural formula of methyl triflate
Ball-and-stick model of methyl triflate
Names
Preferred IUPAC name Methyl trifluoromethanesulfonate
Other names Trifluoromethanesulfonic acid, methyl ester Triflic acid, methyl ester, methyl triflate
Identifiers
CAS Number	333-27-7 Y
3D model (JSmol)	Interactive image
ChemSpider	9153 Y
ECHA InfoCard	100.005.793
EC Number	206-371-7
PubChem CID	9526
UNII	7B25Z22EPV Y
UN number	2924
CompTox Dashboard (EPA)	DTXSID6049272
InChI InChI=1S/C2H3F3O3S/c1-8-9(6,7)2(3,4)5/h1H3 Y Key: OIRDBPQYVWXNSJ-UHFFFAOYSA-N Y InChI=1/C2H3F3O3S/c1-8-9(6,7)2(3,4)5/h1H3 Key: OIRDBPQYVWXNSJ-UHFFFAOYAL
SMILES COS(=O)(=O)C(F)(F)F
Properties
Chemical formula	C2H3F3O3S
Molar mass	164.10 g·mol−1
Appearance	Colourless Liquid
Density	1.496 g/mL
Melting point	−64 °C (−83 °F; 209 K)
Boiling point	100 °C (212 °F; 373 K)
Solubility in water	Hydrolyzes
Hazards[1]
Occupational safety and health (OHS/OSH):
Main hazards	reactive and toxic substance
GHS labelling:
Signal word	Danger
Hazard statements	H226, H301, H311, H314, H330
Precautionary statements	P210, P233, P303+P361+P353, P304+P340+P310, P305+P351+P338, P380
Flash point	38 °C (100 °F; 311 K)
Related compounds
Related compounds	Methyl fluorosulfonate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Synthesis

Methyl triflate is commercially available, however it may also be prepared in the laboratory by using dimethyl sulfate to methylate triflic acid.^[4]

CF₃SO₂OH + (CH₃O)₂SO₂ → CF₃SO₂OCH₃ + CH₃OSO₂OH

Reactivity

Hydrolysis

Upon contact with water, methyl triflate loses its methyl group, forming triflic acid and methanol:

CF₃SO₂OCH₃ + H₂O → CF₃SO₂OH + CH₃OH

Methylation

One ranking of methylating agents is (CH₃)₃O⁺ > CF₃SO₂OCH₃ ≈ FSO₂OCH₃ > (CH₃)₂SO₄ > CH₃I.^[4] Methyl triflate will alkylate many functional groups which are very poor nucleophiles such as aldehydes, amides, and nitriles. It does not methylate benzene or the bulky 2,6-di-tert-butylpyridine.^[2] Its ability to methylate N-heterocycles is exploited in certain deprotection schemes.^[5]

Cationic polymerization

Methyl triflate initiates the living cationic polymerization of lactide^[6] and other lactones including β-propiolactone, ε-caprolactone and glycolide.^[7]

Polymerization of ε-caprolactone initiated by methyl triflate

Cyclic carbonates like trimethylene carbonate and neopentylene carbonate (5,5-dimethyl-1,3-dioxan-2-one) can be polymerized to the corresponding polycarbonates.^[8] 2-alkyl-2-oxazolines, for example 2-ethyl-2-oxazoline, are also polymerized to poly(2-alkyloxazoline)s.^[9]

Applications

Radiochemistry

Carbon-11 methyl triflate ([11C]MeOTf^[10]), or methyl triflate containing the carbon-11 isotope, is commonly used in radiochemistry to synthesize radioactively labeled compounds that can be traced in living organisms using positron emission tomography (PET). For example, [11C]MeOTf has been used extensively in the production of Pittsburgh Compound B, which first allowed β-amyloid plaques to be imaged in a living brain.

See also

• Triflate
• Magic methyl