Methyl trifluoromethanesulfonate explained

Methyl trifluoromethanesulfonate, also commonly called methyl triflate and abbreviated MeOTf, is the organic compound with the formula . It is a colourless liquid which finds use in organic chemistry as a powerful methylating agent.[1] The compound is closely related to methyl fluorosulfonate . 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.[2]

Synthesis

Methyl triflate is commercially available, however it may also be prepared in the laboratory by treating dimethyl sulfate with triflic acid.[3]

Reactivity

Hydrolysis

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

Methylation

One ranking of methylating agents is .[3] 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.[1] Its ability to methylate N-heterocycles is exploited in certain deprotection schemes.

Cationic polymerization

Methyl triflate initiates the living cationic polymerization of lactide[4] and other lactones including β-propiolactone, ε-caprolactone and glycolide.[5]

Cyclic carbonates like trimethylene carbonate and neopentylene carbonate (5,5-dimethyl-1,3-dioxan-2-one) can be polymerized to the corresponding polycarbonates.[6] 2-alkyl-2-oxazolines, for example 2-ethyl-2-oxazoline, are also polymerized to poly(2-alkyloxazoline)s.[7]

Applications

Radiochemistry

Carbon-11 methyl triflate ([11C]MeOTf[8]), 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

Notes and References

  1. Roger W.. Alder. Justin G. E.. Phillips. Huang Lijun. Huang Xuefei. . Methyltrifluoromethanesulfonate. Encyclopedia of Reagents for Organic Synthesis. 2005. 10.1002/047084289X.rm266m.pub2. 0471936235.
  2. Alder. R. W.. M. L.. Sinnott. M. C.. Whiting. D. A.. Evans. David A. Evans. Hazards of powerful methylating agents. Chemistry in Britain. 14. 7. 1978. 324. Miscited as - - - (1976) Chem. Eng. News, vol. 54, no. 36, p. 56 in
  3. Stang. Peter J.. Hanack. Michael. Subramanian. L. R.. Perfluoroalkanesulfonic Esters: Methods of Preparation and Applications in Organic Chemistry. Synthesis. 1982. 2. 1982. 85–126. 0039-7881. 10.1055/s-1982-29711.
  4. Rangel. Irma. Ricard. Michèle. Ricard. Alain. 1994. Polymerization of L-lactide and ε-caprolactone in the presence of methyl trifluoromethanesulfonate. Macromolecular Chemistry and Physics. 195. 9. 3095–3101. 10.1002/macp.1994.021950908.
  5. Jonté. J. Michael. Dunsing. Ruth. Kricheldorf. Hans R.. 1985. Polylactones. 4. Cationic Polymerization of Lactones by Means of Alkylsulfonates. Journal of Macromolecular Science: Part A - Chemistry. en. 22. 4. 495–514. 10.1080/00222338508056616. 0022-233X.
  6. Kricheldorf. Hans R.. Weegen-Schulz. Bettina. Jenssen. Jörg. 1998. Cationic polymerization of aliphatic cyclocarbonates. Macromolecular Symposia. en. 132. 1. 421–430. 10.1002/masy.19981320139.
  7. Glassner. Mathias. D’hooge. Dagmar R.. Young Park. Jin. Van Steenberge. Paul H.M.. Monnery. Bryn D.. Reyniers. Marie-Françoise. Hoogenboom. Richard. 2015. Systematic investigation of alkyl sulfonate initiators for the cationic ring-opening polymerization of 2-oxazolines revealing optimal combinations of monomers and initiators. European Polymer Journal. en. 65. 298–304. 10.1016/j.eurpolymj.2015.01.019. 1854/LU-5924229. free.
  8. Jewett . D. M. . 1992 . A simple synthesis of [11C]methyl triflate ]. International Journal of Radiation Applications and Instrumentation, Part A . 43 . 11 . 1383–1385 . 10.1016/0883-2889(92)90012-4 . 0883-2889 . 1333459. 2027.42/29777 . free .

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